This is gawk.info, produced by makeinfo version 4.6 from gawk.texi.

INFO-DIR-SECTION Text creation and manipulation
START-INFO-DIR-ENTRY
* Gawk: (gawk).                 A text scanning and processing language.
END-INFO-DIR-ENTRY
INFO-DIR-SECTION Individual utilities
START-INFO-DIR-ENTRY
* awk: (gawk)Invoking gawk.                     Text scanning and processing.
END-INFO-DIR-ENTRY

Copyright (C) 1989, 1991, 1992, 1993, 1996, 1997, 1998, 1999, 2000,
2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.


   This is Edition 3 of `GAWK: Effective AWK Programming: A User's
Guide for GNU Awk', for the 3.1.5 (or later) version of the GNU
implementation of AWK.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU General Public License", the Front-Cover
texts being (a) (see below), and with the Back-Cover Texts being (b)
(see below).  A copy of the license is included in the section entitled
"GNU Free Documentation License".

  a. "A GNU Manual"

  b. "You have freedom to copy and modify this GNU Manual, like GNU
     software.  Copies published by the Free Software Foundation raise
     funds for GNU development."


File: gawk.info,  Node: Top,  Next: Foreword,  Up: (dir)

General Introduction
********************

This file documents `awk', a program that you can use to select
particular records in a file and perform operations upon them.

Copyright (C) 1989, 1991, 1992, 1993, 1996, 1997, 1998, 1999, 2000,
2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.


   This is Edition 3 of `GAWK: Effective AWK Programming: A User's
Guide for GNU Awk', for the 3.1.5 (or later) version of the GNU
implementation of AWK.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU General Public License", the Front-Cover
texts being (a) (see below), and with the Back-Cover Texts being (b)
(see below).  A copy of the license is included in the section entitled
"GNU Free Documentation License".

  a. "A GNU Manual"

  b. "You have freedom to copy and modify this GNU Manual, like GNU
     software.  Copies published by the Free Software Foundation raise
     funds for GNU development."

* Menu:

* Foreword::                       Some nice words about this
                                   Info file.
* Preface::                        What this Info file is about; brief
                                   history and acknowledgments.
* Getting Started::                A basic introduction to using
                                   `awk'. How to run an `awk'
                                   program. Command-line syntax.
* Regexp::                         All about matching things using regular
                                   expressions.
* Reading Files::                  How to read files and manipulate fields.
* Printing::                       How to print using `awk'. Describes
                                   the `print' and `printf'
                                   statements. Also describes redirection of
                                   output.
* Expressions::                    Expressions are the basic building blocks
                                   of statements.
* Patterns and Actions::           Overviews of patterns and actions.
* Arrays::                         The description and use of arrays. Also
                                   includes array-oriented control statements.
* Functions::                      Built-in and user-defined functions.
* Internationalization::           Getting `gawk' to speak your
                                   language.
* Advanced Features::              Stuff for advanced users, specific to
                                   `gawk'.
* Invoking Gawk::                  How to run `gawk'.
* Library Functions::              A Library of `awk' Functions.
* Sample Programs::                Many `awk' programs with complete
                                   explanations.
* Language History::               The evolution of the `awk'
                                   language.
* Installation::                   Installing `gawk' under various
                                   operating systems.
* Notes::                          Notes about `gawk' extensions and
                                   possible future work.
* Basic Concepts::                 A very quick intoduction to programming
                                   concepts.
* Glossary::                       An explanation of some unfamiliar terms.
* Copying::                        Your right to copy and distribute
                                   `gawk'.
* GNU Free Documentation License:: The license for this Info file.
* Index::                          Concept and Variable Index.

* History::                        The history of `gawk' and
                                   `awk'.
* Names::                          What name to use to find `awk'.
* This Manual::                    Using this Info file. Includes
                                   sample input files that you can use.
* Conventions::                    Typographical Conventions.
* Manual History::                 Brief history of the GNU project and this
                                   Info file.
* How To Contribute::              Helping to save the world.
* Acknowledgments::                Acknowledgments.
* Running gawk::                   How to run `gawk' programs;
                                   includes command-line syntax.
* One-shot::                       Running a short throwaway `awk'
                                   program.
* Read Terminal::                  Using no input files (input from terminal
                                   instead).
* Long::                           Putting permanent `awk' programs in
                                   files.
* Executable Scripts::             Making self-contained `awk'
                                   programs.
* Comments::                       Adding documentation to `gawk'
                                   programs.
* Quoting::                        More discussion of shell quoting issues.
* Sample Data Files::              Sample data files for use in the
                                   `awk' programs illustrated in this
                                   Info file.
* Very Simple::                    A very simple example.
* Two Rules::                      A less simple one-line example using two
                                   rules.
* More Complex::                   A more complex example.
* Statements/Lines::               Subdividing or combining statements into
                                   lines.
* Other Features::                 Other Features of `awk'.
* When::                           When to use `gawk' and when to use
                                   other things.
* Regexp Usage::                   How to Use Regular Expressions.
* Escape Sequences::               How to write nonprinting characters.
* Regexp Operators::               Regular Expression Operators.
* Character Lists::                What can go between `[...]'.
* GNU Regexp Operators::           Operators specific to GNU software.
* Case-sensitivity::               How to do case-insensitive matching.
* Leftmost Longest::               How much text matches.
* Computed Regexps::               Using Dynamic Regexps.
* Locales::                        How the locale affects things.
* Records::                        Controlling how data is split into records.
* Fields::                         An introduction to fields.
* Nonconstant Fields::             Nonconstant Field Numbers.
* Changing Fields::                Changing the Contents of a Field.
* Field Separators::               The field separator and how to change it.
* Regexp Field Splitting::         Using regexps as the field separator.
* Single Character Fields::        Making each character a separate field.
* Command Line Field Separator::   Setting `FS' from the command-line.
* Field Splitting Summary::        Some final points and a summary table.
* Constant Size::                  Reading constant width data.
* Multiple Line::                  Reading multi-line records.
* Getline::                        Reading files under explicit program
                                   control using the `getline' function.
* Plain Getline::                  Using `getline' with no arguments.
* Getline/Variable::               Using `getline' into a variable.
* Getline/File::                   Using `getline' from a file.
* Getline/Variable/File::          Using `getline' into a variable from a
                                   file.
* Getline/Pipe::                   Using `getline' from a pipe.
* Getline/Variable/Pipe::          Using `getline' into a variable from a
                                   pipe.
* Getline/Coprocess::              Using `getline' from a coprocess.
* Getline/Variable/Coprocess::     Using `getline' into a variable from a
                                   coprocess.
* Getline Notes::                  Important things to know about
                                   `getline'.
* Getline Summary::                Summary of `getline' Variants.
* Print::                          The `print' statement.
* Print Examples::                 Simple examples of `print' statements.
* Output Separators::              The output separators and how to change
                                   them.
* OFMT::                           Controlling Numeric Output With
                                   `print'.
* Printf::                         The `printf' statement.
* Basic Printf::                   Syntax of the `printf' statement.
* Control Letters::                Format-control letters.
* Format Modifiers::               Format-specification modifiers.
* Printf Examples::                Several examples.
* Redirection::                    How to redirect output to multiple files
                                   and pipes.
* Special Files::                  File name interpretation in `gawk'.
                                   `gawk' allows access to inherited
                                   file descriptors.
* Special FD::                     Special files for I/O.
* Special Process::                Special files for process information.
* Special Network::                Special files for network communications.
* Special Caveats::                Things to watch out for.
* Close Files And Pipes::          Closing Input and Output Files and Pipes.
* Constants::                      String, numeric and regexp constants.
* Scalar Constants::               Numeric and string constants.
* Nondecimal-numbers::             What are octal and hex numbers.
* Regexp Constants::               Regular Expression constants.
* Using Constant Regexps::         When and how to use a regexp constant.
* Variables::                      Variables give names to values for later
                                   use.
* Using Variables::                Using variables in your programs.
* Assignment Options::             Setting variables on the command-line and a
                                   summary of command-line syntax. This is an
                                   advanced method of input.
* Conversion::                     The conversion of strings to numbers and
                                   vice versa.
* Arithmetic Ops::                 Arithmetic operations (`+', `-',
                                   etc.)
* Concatenation::                  Concatenating strings.
* Assignment Ops::                 Changing the value of a variable or a
                                   field.
* Increment Ops::                  Incrementing the numeric value of a
                                   variable.
* Truth Values::                   What is ``true'' and what is ``false''.
* Typing and Comparison::          How variables acquire types and how this
                                   affects comparison of numbers and strings
                                   with `<', etc.
* Boolean Ops::                    Combining comparison expressions using
                                   boolean operators `||' (``or''),
                                   `&&' (``and'') and `!' (``not'').
* Conditional Exp::                Conditional expressions select between two
                                   subexpressions under control of a third
                                   subexpression.
* Function Calls::                 A function call is an expression.
* Precedence::                     How various operators nest.
* Pattern Overview::               What goes into a pattern.
* Regexp Patterns::                Using regexps as patterns.
* Expression Patterns::            Any expression can be used as a pattern.
* Ranges::                         Pairs of patterns specify record ranges.
* BEGIN/END::                      Specifying initialization and cleanup
                                   rules.
* Using BEGIN/END::                How and why to use BEGIN/END rules.
* I/O And BEGIN/END::              I/O issues in BEGIN/END rules.
* Empty::                          The empty pattern, which matches every
                                   record.
* Using Shell Variables::          How to use shell variables with
                                   `awk'.
* Action Overview::                What goes into an action.
* Statements::                     Describes the various control statements in
                                   detail.
* If Statement::                   Conditionally execute some `awk'
                                   statements.
* While Statement::                Loop until some condition is satisfied.
* Do Statement::                   Do specified action while looping until
                                   some condition is satisfied.
* For Statement::                  Another looping statement, that provides
                                   initialization and increment clauses.
* Switch Statement::               Switch/case evaluation for conditional
                                   execution of statements based on a value.
* Break Statement::                Immediately exit the innermost enclosing
                                   loop.
* Continue Statement::             Skip to the end of the innermost enclosing
                                   loop.
* Next Statement::                 Stop processing the current input record.
* Nextfile Statement::             Stop processing the current file.
* Exit Statement::                 Stop execution of `awk'.
* Built-in Variables::             Summarizes the built-in variables.
* User-modified::                  Built-in variables that you change to
                                   control `awk'.
* Auto-set::                       Built-in variables where `awk'
                                   gives you information.
* ARGC and ARGV::                  Ways to use `ARGC' and `ARGV'.
* Array Intro::                    Introduction to Arrays
* Reference to Elements::          How to examine one element of an array.
* Assigning Elements::             How to change an element of an array.
* Array Example::                  Basic Example of an Array
* Scanning an Array::              A variation of the `for' statement. It
                                   loops through the indices of an array's
                                   existing elements.
* Delete::                         The `delete' statement removes an
                                   element from an array.
* Numeric Array Subscripts::       How to use numbers as subscripts in
                                   `awk'.
* Uninitialized Subscripts::       Using Uninitialized variables as
                                   subscripts.
* Multi-dimensional::              Emulating multidimensional arrays in
                                   `awk'.
* Multi-scanning::                 Scanning multidimensional arrays.
* Array Sorting::                  Sorting array values and indices.
* Built-in::                       Summarizes the built-in functions.
* Calling Built-in::               How to call built-in functions.
* Numeric Functions::              Functions that work with numbers, including
                                   `int', `sin' and `rand'.
* String Functions::               Functions for string manipulation, such as
                                   `split', `match' and
                                   `sprintf'.
* Gory Details::                   More than you want to know about `\'
                                   and `&' with `sub', `gsub',
                                   and `gensub'.
* I/O Functions::                  Functions for files and shell commands.
* Time Functions::                 Functions for dealing with timestamps.
* Bitwise Functions::              Functions for bitwise operations.
* I18N Functions::                 Functions for string translation.
* User-defined::                   Describes User-defined functions in detail.
* Definition Syntax::              How to write definitions and what they
                                   mean.
* Function Example::               An example function definition and what it
                                   does.
* Function Caveats::               Things to watch out for.
* Return Statement::               Specifying the value a function returns.
* Dynamic Typing::                 How variable types can change at runtime.
* I18N and L10N::                  Internationalization and Localization.
* Explaining gettext::             How GNU `gettext' works.
* Programmer i18n::                Features for the programmer.
* Translator i18n::                Features for the translator.
* String Extraction::              Extracting marked strings.
* Printf Ordering::                Rearranging `printf' arguments.
* I18N Portability::               `awk'-level portability issues.
* I18N Example::                   A simple i18n example.
* Gawk I18N::                      `gawk' is also internationalized.
* Nondecimal Data::                Allowing nondecimal input data.
* Two-way I/O::                    Two-way communications with another
                                   process.
* TCP/IP Networking::              Using `gawk' for network
                                   programming.
* Portal Files::                   Using `gawk' with BSD portals.
* Profiling::                      Profiling your `awk' programs.
* Command Line::                   How to run `awk'.
* Options::                        Command-line options and their meanings.
* Other Arguments::                Input file names and variable assignments.
* AWKPATH Variable::               Searching directories for `awk'
                                   programs.
* Obsolete::                       Obsolete Options and/or features.
* Undocumented::                   Undocumented Options and Features.
* Known Bugs::                     Known Bugs in `gawk'.
* Library Names::                  How to best name private global variables
                                   in library functions.
* General Functions::              Functions that are of general use.
* Nextfile Function::              Two implementations of a `nextfile'
                                   function.
* Assert Function::                A function for assertions in `awk'
                                   programs.
* Round Function::                 A function for rounding if `sprintf'
                                   does not do it correctly.
* Cliff Random Function::          The Cliff Random Number Generator.
* Ordinal Functions::              Functions for using characters as numbers
                                   and vice versa.
* Join Function::                  A function to join an array into a string.
* Gettimeofday Function::          A function to get formatted times.
* Data File Management::           Functions for managing command-line data
                                   files.
* Filetrans Function::             A function for handling data file
                                   transitions.
* Rewind Function::                A function for rereading the current file.
* File Checking::                  Checking that data files are readable.
* Empty Files::                    Checking for zero-length files.
* Ignoring Assigns::               Treating assignments as file names.
* Getopt Function::                A function for processing command-line
                                   arguments.
* Passwd Functions::               Functions for getting user information.
* Group Functions::                Functions for getting group information.
* Running Examples::               How to run these examples.
* Clones::                         Clones of common utilities.
* Cut Program::                    The `cut' utility.
* Egrep Program::                  The `egrep' utility.
* Id Program::                     The `id' utility.
* Split Program::                  The `split' utility.
* Tee Program::                    The `tee' utility.
* Uniq Program::                   The `uniq' utility.
* Wc Program::                     The `wc' utility.
* Miscellaneous Programs::         Some interesting `awk' programs.
* Dupword Program::                Finding duplicated words in a document.
* Alarm Program::                  An alarm clock.
* Translate Program::              A program similar to the `tr'
                                   utility.
* Labels Program::                 Printing mailing labels.
* Word Sorting::                   A program to produce a word usage count.
* History Sorting::                Eliminating duplicate entries from a
                                   history file.
* Extract Program::                Pulling out programs from Texinfo source
                                   files.
* Simple Sed::                     A Simple Stream Editor.
* Igawk Program::                  A wrapper for `awk' that includes
                                   files.
* V7/SVR3.1::                      The major changes between V7 and System V
                                   Release 3.1.
* SVR4::                           Minor changes between System V Releases 3.1
                                   and 4.
* POSIX::                          New features from the POSIX standard.
* BTL::                            New features from the Bell Laboratories
                                   version of `awk'.
* POSIX/GNU::                      The extensions in `gawk' not in
                                   POSIX `awk'.
* Contributors::                   The major contributors to `gawk'.
* Gawk Distribution::              What is in the `gawk' distribution.
* Getting::                        How to get the distribution.
* Extracting::                     How to extract the distribution.
* Distribution contents::          What is in the distribution.
* Unix Installation::              Installing `gawk' under various
                                   versions of Unix.
* Quick Installation::             Compiling `gawk' under Unix.
* Additional Configuration Options:: Other compile-time options.
* Configuration Philosophy::       How it's all supposed to work.
* Non-Unix Installation::          Installation on Other Operating Systems.
* Amiga Installation::             Installing `gawk' on an Amiga.
* BeOS Installation::              Installing `gawk' on BeOS.
* PC Installation::                Installing and Compiling `gawk' on
                                   MS-DOS and OS/2.
* PC Binary Installation::         Installing a prepared distribution.
* PC Compiling::                   Compiling `gawk' for MS-DOS, Windows32,
                                   and OS/2.
* PC Using::                       Running `gawk' on MS-DOS, Windows32 and
                                   OS/2.
* PC Dynamic::                     Compiling `gawk' for dynamic
                                   libraries.
* Cygwin::                         Building and running `gawk' for
                                   Cygwin.
* VMS Installation::               Installing `gawk' on VMS.
* VMS Compilation::                How to compile `gawk' under VMS.
* VMS Installation Details::       How to install `gawk' under VMS.
* VMS Running::                    How to run `gawk' under VMS.
* VMS POSIX::                      Alternate instructions for VMS POSIX.
* Unsupported::                    Systems whose ports are no longer
                                   supported.
* Atari Installation::             Installing `gawk' on the Atari ST.
* Atari Compiling::                Compiling `gawk' on Atari.
* Atari Using::                    Running `gawk' on Atari.
* Tandem Installation::            Installing `gawk' on a Tandem.
* Bugs::                           Reporting Problems and Bugs.
* Other Versions::                 Other freely available `awk'
                                   implementations.
* Compatibility Mode::             How to disable certain `gawk'
                                   extensions.
* Additions::                      Making Additions To `gawk'.
* Adding Code::                    Adding code to the main body of
                                   `gawk'.
* New Ports::                      Porting `gawk' to a new operating
                                   system.
* Dynamic Extensions::             Adding new built-in functions to
                                   `gawk'.
* Internals::                      A brief look at some `gawk'
                                   internals.
* Sample Library::                 A example of new functions.
* Internal File Description::      What the new functions will do.
* Internal File Ops::              The code for internal file operations.
* Using Internal File Ops::        How to use an external extension.
* Future Extensions::              New features that may be implemented one
                                   day.
* Basic High Level::               The high level view.
* Basic Data Typing::              A very quick intro to data types.
* Floating Point Issues::          Stuff to know about floating-point numbers.

                  To Miriam, for making me complete.

                  To Chana, for the joy you bring us.

                To Rivka, for the exponential increase.

                  To Nachum, for the added dimension.

                   To Malka, for the new beginning.
 


File: gawk.info,  Node: Foreword,  Next: Preface,  Prev: Top,  Up: Top

Foreword
********

Arnold Robbins and I are good friends. We were introduced 11 years ago
by circumstances--and our favorite programming language, AWK.  The
circumstances started a couple of years earlier. I was working at a new
job and noticed an unplugged Unix computer sitting in the corner.  No
one knew how to use it, and neither did I.  However, a couple of days
later it was running, and I was `root' and the one-and-only user.  That
day, I began the transition from statistician to Unix programmer.

   On one of many trips to the library or bookstore in search of books
on Unix, I found the gray AWK book, a.k.a. Aho, Kernighan and
Weinberger, `The AWK Programming Language', Addison-Wesley, 1988.
AWK's simple programming paradigm--find a pattern in the input and then
perform an action--often reduced complex or tedious data manipulations
to few lines of code.  I was excited to try my hand at programming in
AWK.

   Alas,  the `awk' on my computer was a limited version of the
language described in the AWK book.  I discovered that my computer had
"old `awk'" and the AWK book described "new `awk'."  I learned that
this was typical; the old version refused to step aside or relinquish
its name.  If a system had a new `awk', it was invariably called
`nawk', and few systems had it.  The best way to get a new `awk' was to
`ftp' the source code for `gawk' from `prep.ai.mit.edu'.  `gawk' was a
version of new `awk' written by David Trueman and Arnold, and available
under the GNU General Public License.

   (Incidentally, it's no longer difficult to find a new `awk'. `gawk'
ships with Linux, and you can download binaries or source code for
almost any system; my wife uses `gawk' on her VMS box.)

   My Unix system started out unplugged from the wall; it certainly was
not plugged into a network.  So, oblivious to the existence of `gawk'
and the Unix community in general, and desiring a new `awk', I wrote my
own, called `mawk'.  Before I was finished I knew about `gawk', but it
was too late to stop, so I eventually posted to a `comp.sources'
newsgroup.

   A few days after my posting, I got a friendly email from Arnold
introducing himself.   He suggested we share design and algorithms and
attached a draft of the POSIX standard so that I could update `mawk' to
support language extensions added after publication of the AWK book.

   Frankly, if our roles had been reversed, I would not have been so
open and we probably would have never met.  I'm glad we did meet.  He
is an AWK expert's AWK expert and a genuinely nice person.  Arnold
contributes significant amounts of his expertise and time to the Free
Software Foundation.

   This book is the `gawk' reference manual, but at its core it is a
book about AWK programming that will appeal to a wide audience.  It is
a definitive reference to the AWK language as defined by the 1987 Bell
Labs release and codified in the 1992 POSIX Utilities standard.

   On the other hand, the novice AWK programmer can study a wealth of
practical programs that emphasize the power of AWK's basic idioms: data
driven control-flow, pattern matching with regular expressions, and
associative arrays.  Those looking for something new can try out
`gawk''s interface to network protocols via special `/inet' files.

   The programs in this book make clear that an AWK program is
typically much smaller and faster to develop than a counterpart written
in C.  Consequently, there is often a payoff to prototype an algorithm
or design in AWK to get it running quickly and expose problems early.
Often, the interpreted performance is adequate and the AWK prototype
becomes the product.

   The new `pgawk' (profiling `gawk'), produces program execution
counts.  I recently experimented with an algorithm that for n lines of
input, exhibited ~ C n^2 performance, while theory predicted ~ C n log n
behavior. A few minutes poring over the `awkprof.out' profile
pinpointed the problem to a single line of code.  `pgawk' is a welcome
addition to my programmer's toolbox.

   Arnold has distilled over a decade of experience writing and using
AWK programs, and developing `gawk', into this book.  If you use AWK or
want to learn how, then read this book.

     Michael Brennan
     Author of `mawk'


File: gawk.info,  Node: Preface,  Next: Getting Started,  Prev: Foreword,  Up: Top

Preface
*******

Several kinds of tasks occur repeatedly when working with text files.
You might want to extract certain lines and discard the rest.  Or you
may need to make changes wherever certain patterns appear, but leave
the rest of the file alone.  Writing single-use programs for these
tasks in languages such as C, C++, or Pascal is time-consuming and
inconvenient.  Such jobs are often easier with `awk'.  The `awk'
utility interprets a special-purpose programming language that makes it
easy to handle simple data-reformatting jobs.

The GNU implementation of `awk' is called `gawk'; it is fully
compatible with the System V Release 4 version of `awk'.  `gawk' is
also compatible with the POSIX specification of the `awk' language.
This means that all properly written `awk' programs should work with
`gawk'.  Thus, we usually don't distinguish between `gawk' and other
`awk' implementations.

Using `awk' allows you to:

   * Manage small, personal databases

   * Generate reports

   * Validate data

   * Produce indexes and perform other document preparation tasks

   * Experiment with algorithms that you can adapt later to other
     computer languages

In addition, `gawk' provides facilities that make it easy to:

   * Extract bits and pieces of data for processing

   * Sort data

   * Perform simple network communications

This Info file teaches you about the `awk' language and how you can use
it effectively.  You should already be familiar with basic system
commands, such as `cat' and `ls',(1) as well as basic shell facilities,
such as input/output (I/O) redirection and pipes.

Implementations of the `awk' language are available for many different
computing environments.  This Info file, while describing the `awk'
language in general, also describes the particular implementation of
`awk' called `gawk' (which stands for "GNU awk").  `gawk' runs on a
broad range of Unix systems, ranging from 80386 PC-based computers up
through large-scale systems, such as Crays. `gawk' has also been ported
to Mac OS X, MS-DOS, Microsoft Windows (all versions) and OS/2 PCs,
Atari and Amiga microcomputers, BeOS, Tandem D20, and VMS.

* Menu:

* History::                     The history of `gawk' and
                                `awk'.
* Names::                       What name to use to find `awk'.
* This Manual::                 Using this Info file. Includes sample
                                input files that you can use.
* Conventions::                 Typographical Conventions.
* Manual History::              Brief history of the GNU project and this
                                Info file.
* How To Contribute::           Helping to save the world.
* Acknowledgments::             Acknowledgments.

---------- Footnotes ----------

(1) These commands are available on POSIX-compliant systems, as well as
on traditional Unix-based systems. If you are using some other
operating system, you still need to be familiar with the ideas of I/O
redirection and pipes.


File: gawk.info,  Node: History,  Next: Names,  Up: Preface

History of `awk' and `gawk'
===========================

                   Recipe For A Programming Language
          1 part  `egrep'   1 part  `snobol'
          2 parts `ed'      3 parts C

     Blend all parts well using `lex' and `yacc'.  Document minimally
     and release.

     After eight years, add another part `egrep' and two more parts C.
     Document very well and release.

The name `awk' comes from the initials of its designers: Alfred V.
Aho, Peter J. Weinberger and Brian W. Kernighan.  The original version
of `awk' was written in 1977 at AT&T Bell Laboratories.  In 1985, a new
version made the programming language more powerful, introducing
user-defined functions, multiple input streams, and computed regular
expressions.  This new version became widely available with Unix System
V Release 3.1 (SVR3.1).  The version in SVR4 added some new features
and cleaned up the behavior in some of the "dark corners" of the
language.  The specification for `awk' in the POSIX Command Language
and Utilities standard further clarified the language.  Both the `gawk'
designers and the original Bell Laboratories `awk' designers provided
feedback for the POSIX specification.

Paul Rubin wrote the GNU implementation, `gawk', in 1986.  Jay Fenlason
completed it, with advice from Richard Stallman.  John Woods
contributed parts of the code as well.  In 1988 and 1989, David
Trueman, with help from me, thoroughly reworked `gawk' for compatibility
with the newer `awk'.  Circa 1995, I became the primary maintainer.
Current development focuses on bug fixes, performance improvements,
standards compliance, and occasionally, new features.

In May of 1997, Ju"rgen Kahrs felt the need for network access from
`awk', and with a little help from me, set about adding features to do
this for `gawk'.  At that time, he also wrote the bulk of `TCP/IP
Internetworking with `gawk'' (a separate document, available as part of
the `gawk' distribution).  His code finally became part of the main
`gawk' distribution with `gawk' version 3.1.

*Note Contributors::, for a complete list of those who made important
contributions to `gawk'.


File: gawk.info,  Node: Names,  Next: This Manual,  Prev: History,  Up: Preface

A Rose by Any Other Name
========================

The `awk' language has evolved over the years. Full details are
provided in *Note Language History::.  The language described in this
Info file is often referred to as "new `awk'" (`nawk').

Because of this, many systems have multiple versions of `awk'.  Some
systems have an `awk' utility that implements the original version of
the `awk' language and a `nawk' utility for the new version.  Others
have an `oawk' version for the "old `awk'" language and plain `awk' for
the new one.  Still others only have one version, which is usually the
new one.(1)

All in all, this makes it difficult for you to know which version of
`awk' you should run when writing your programs.  The best advice I can
give here is to check your local documentation. Look for `awk', `oawk',
and `nawk', as well as for `gawk'.  It is likely that you already have
some version of new `awk' on your system, which is what you should use
when running your programs.  (Of course, if you're reading this Info
file, chances are good that you have `gawk'!)

Throughout this Info file, whenever we refer to a language feature that
should be available in any complete implementation of POSIX `awk', we
simply use the term `awk'.  When referring to a feature that is
specific to the GNU implementation, we use the term `gawk'.

---------- Footnotes ----------

(1) Often, these systems use `gawk' for their `awk' implementation!


File: gawk.info,  Node: This Manual,  Next: Conventions,  Prev: Names,  Up: Preface

Using This Book
===============

The term `awk' refers to a particular program as well as to the
language you use to tell this program what to do.  When we need to be
careful, we call the language "the `awk' language," and the program
"the `awk' utility."  This Info file explains both the `awk' language
and how to run the `awk' utility.  The term "`awk' program" refers to a
program written by you in the `awk' programming language.

Primarily, this Info file explains the features of `awk', as defined in
the POSIX standard.  It does so in the context of the `gawk'
implementation.  While doing so, it also attempts to describe important
differences between `gawk' and other `awk' implementations.(1) Finally,
any `gawk' features that are not in the POSIX standard for `awk' are
noted.

There are subsections labelled as *Advanced Notes* scattered throughout
the Info file.  They add a more complete explanation of points that are
relevant, but not likely to be of interest on first reading.  All
appear in the index, under the heading "advanced features."

Most of the time, the examples use complete `awk' programs.  In some of
the more advanced sections, only the part of the `awk' program that
illustrates the concept currently being described is shown.

While this Info file is aimed principally at people who have not been
exposed to `awk', there is a lot of information here that even the `awk'
expert should find useful.  In particular, the description of POSIX
`awk' and the example programs in *Note Library Functions::, and in
*Note Sample Programs::, should be of interest.

*Note Getting Started::, provides the essentials you need to know to
begin using `awk'.

*Note Regexp::, introduces regular expressions in general, and in
particular the flavors supported by POSIX `awk' and `gawk'.

*Note Reading Files::, describes how `awk' reads your data.  It
introduces the concepts of records and fields, as well as the `getline'
command.  I/O redirection is first described here.

*Note Printing::, describes how `awk' programs can produce output with
`print' and `printf'.

*Note Expressions::, describes expressions, which are the basic
building blocks for getting most things done in a program.

*Note Patterns and Actions::, describes how to write patterns for
matching records, actions for doing something when a record is matched,
and the built-in variables `awk' and `gawk' use.

*Note Arrays::, covers `awk''s one-and-only data structure: associative
arrays.  Deleting array elements and whole arrays is also described, as
well as sorting arrays in `gawk'.

*Note Functions::, describes the built-in functions `awk' and `gawk'
provide, as well as how to define your own functions.

*Note Internationalization::, describes special features in `gawk' for
translating program messages into different languages at runtime.

*Note Advanced Features::, describes a number of `gawk'-specific
advanced features.  Of particular note are the abilities to have
two-way communications with another process, perform TCP/IP networking,
and profile your `awk' programs.

*Note Invoking Gawk::, describes how to run `gawk', the meaning of its
command-line options, and how it finds `awk' program source files.

*Note Library Functions::, and *Note Sample Programs::, provide many
sample `awk' programs.  Reading them allows you to see `awk' solving
real problems.

*Note Language History::, describes how the `awk' language has evolved
since first release to present.  It also describes how `gawk' has
acquired features over time.

*Note Installation::, describes how to get `gawk', how to compile it
under Unix, and how to compile and use it on different non-Unix
systems.  It also describes how to report bugs in `gawk' and where to
get three other freely available implementations of `awk'.

*Note Notes::, describes how to disable `gawk''s extensions, as well as
how to contribute new code to `gawk', how to write extension libraries,
and some possible future directions for `gawk' development.

*Note Basic Concepts::, provides some very cursory background material
for those who are completely unfamiliar with computer programming.
Also centralized there is a discussion of some of the issues
surrounding floating-point numbers.

The *Note Glossary::, defines most, if not all, the significant terms
used throughout the book.  If you find terms that you aren't familiar
with, try looking them up here.

*Note Copying::, and *Note GNU Free Documentation License::, present
the licenses that cover the `gawk' source code and this Info file,
respectively.

---------- Footnotes ----------

(1) All such differences appear in the index under the entry
"differences in `awk' and `gawk'."


File: gawk.info,  Node: Conventions,  Next: Manual History,  Prev: This Manual,  Up: Preface

Typographical Conventions
=========================

This Info file is written using Texinfo, the GNU documentation
formatting language.  A single Texinfo source file is used to produce
both the printed and online versions of the documentation.  This minor
node briefly documents the typographical conventions used in Texinfo.

Examples you would type at the command-line are preceded by the common
shell primary and secondary prompts, `$' and `>'.  Output from the
command is preceded by the glyph "-|".  This typically represents the
command's standard output.  Error messages, and other output on the
command's standard error, are preceded by the glyph "error-->".  For
example:

     $ echo hi on stdout
     -| hi on stdout
     $ echo hello on stderr 1>&2
     error--> hello on stderr

Characters that you type at the keyboard look `like this'.  In
particular, there are special characters called "control characters."
These are characters that you type by holding down both the `CONTROL'
key and another key, at the same time.  For example, a `Ctrl-d' is typed
by first pressing and holding the `CONTROL' key, next pressing the `d'
key and finally releasing both keys.

Dark Corners
............

     Dark corners are basically fractal -- no matter how much you
     illuminate, there's always a smaller but darker one.
     Brian Kernighan

Until the POSIX standard (and `The Gawk Manual'), many features of
`awk' were either poorly documented or not documented at all.
Descriptions of such features (often called "dark corners") are noted
in this Info file with "(d.c.)".  They also appear in the index under
the heading "dark corner."

As noted by the opening quote, though, any coverage of dark corners is,
by definition, something that is incomplete.


File: gawk.info,  Node: Manual History,  Next: How To Contribute,  Prev: Conventions,  Up: Preface

The GNU Project and This Book
=============================

The Free Software Foundation (FSF) is a nonprofit organization dedicated
to the production and distribution of freely distributable software.
It was founded by Richard M. Stallman, the author of the original Emacs
editor.  GNU Emacs is the most widely used version of Emacs today.

The GNU(1) Project is an ongoing effort on the part of the Free Software
Foundation to create a complete, freely distributable, POSIX-compliant
computing environment.  The FSF uses the "GNU General Public License"
(GPL) to ensure that their software's source code is always available
to the end user. A copy of the GPL is included for your reference
(*note Copying::).  The GPL applies to the C language source code for
`gawk'.  To find out more about the FSF and the GNU Project online, see
the GNU Project's home page (http://www.gnu.org).  This Info file may
also be read from their web site (http://www.gnu.org/manual/gawk/).

A shell, an editor (Emacs), highly portable optimizing C, C++, and
Objective-C compilers, a symbolic debugger and dozens of large and
small utilities (such as `gawk'), have all been completed and are
freely available.  The GNU operating system kernel (the HURD), has been
released but is still in an early stage of development.

Until the GNU operating system is more fully developed, you should
consider using GNU/Linux, a freely distributable, Unix-like operating
system for Intel 80386, DEC Alpha, Sun SPARC, IBM S/390, and other
systems.(2) There are many books on GNU/Linux. One that is freely
available is `Linux Installation and Getting Started', by Matt Welsh.
Many GNU/Linux distributions are often available in computer stores or
bundled on CD-ROMs with books about Linux.  (There are three other
freely available, Unix-like operating systems for 80386 and other
systems: NetBSD, FreeBSD, and OpenBSD. All are based on the 4.4-Lite
Berkeley Software Distribution, and they use recent versions of `gawk'
for their versions of `awk'.)

The Info file itself has gone through a number of previous editions.
Paul Rubin wrote the very first draft of `The GAWK Manual'; it was
around 40 pages in size.  Diane Close and Richard Stallman improved it,
yielding a version that was around 90 pages long and barely described
the original, "old" version of `awk'.

I started working with that version in the fall of 1988.  As work on it
progressed, the FSF published several preliminary versions (numbered
0.X).  In 1996, Edition 1.0 was released with `gawk' 3.0.0.  The FSF
published the first two editions under the title `The GNU Awk User's
Guide'.

This edition maintains the basic structure of Edition 1.0, but with
significant additional material, reflecting the host of new features in
`gawk' version 3.1.  Of particular note is *Note Array Sorting::, as
well as *Note Bitwise Functions::, *Note Internationalization::, and
also *Note Advanced Features::, and *Note Dynamic Extensions::.

`GAWK: Effective AWK Programming' will undoubtedly continue to evolve.
An electronic version comes with the `gawk' distribution from the FSF.
If you find an error in this Info file, please report it!  *Note
Bugs::, for information on submitting problem reports electronically,
or write to me in care of the publisher.

---------- Footnotes ----------

(1) GNU stands for "GNU's not Unix."

(2) The terminology "GNU/Linux" is explained in the *Note Glossary::.


File: gawk.info,  Node: How To Contribute,  Next: Acknowledgments,  Prev: Manual History,  Up: Preface

How to Contribute
=================

As the maintainer of GNU `awk', I am starting a collection of publicly
available `awk' programs.  For more information, see
`ftp://ftp.freefriends.org/arnold/Awkstuff'.  If you have written an
interesting `awk' program, or have written a `gawk' extension that you
would like to share with the rest of the world, please contact me
(<arnold@skeeve.com>).  Making things available on the Internet helps
keep the `gawk' distribution down to manageable size.


File: gawk.info,  Node: Acknowledgments,  Prev: How To Contribute,  Up: Preface

Acknowledgments
===============

The initial draft of `The GAWK Manual' had the following
acknowledgments:

     Many people need to be thanked for their assistance in producing
     this manual.  Jay Fenlason contributed many ideas and sample
     programs.  Richard Mlynarik and Robert Chassell gave helpful
     comments on drafts of this manual.  The paper `A Supplemental
     Document for `awk'' by John W.  Pierce of the Chemistry Department
     at UC San Diego, pinpointed several issues relevant both to `awk'
     implementation and to this manual, that would otherwise have
     escaped us.

I would like to acknowledge Richard M. Stallman, for his vision of a
better world and for his courage in founding the FSF and starting the
GNU Project.

The following people (in alphabetical order) provided helpful comments
on various versions of this book, up to and including this edition.
Rick Adams, Nelson H.F. Beebe, Karl Berry, Dr. Michael Brennan, Rich
Burridge, Claire Cloutier, Diane Close, Scott Deifik, Christopher
("Topher") Eliot, Jeffrey Friedl, Dr. Darrel Hankerson, Michal
Jaegermann, Dr. Richard J. LeBlanc, Michael Lijewski, Pat Rankin,
Miriam Robbins, Mary Sheehan, and Chuck Toporek.

Robert J. Chassell provided much valuable advice on the use of Texinfo.
He also deserves special thanks for convincing me _not_ to title this
Info file `How To Gawk Politely'.  Karl Berry helped significantly with
the TeX part of Texinfo.

I would like to thank Marshall and Elaine Hartholz of Seattle and Dr.
Bert and Rita Schreiber of Detroit for large amounts of quiet vacation
time in their homes, which allowed me to make significant progress on
this Info file and on `gawk' itself.

Phil Hughes of SSC contributed in a very important way by loaning me
his laptop GNU/Linux system, not once, but twice, which allowed me to
do a lot of work while away from home.

David Trueman deserves special credit; he has done a yeoman job of
evolving `gawk' so that it performs well and without bugs.  Although he
is no longer involved with `gawk', working with him on this project was
a significant pleasure.

The intrepid members of the GNITS mailing list, and most notably Ulrich
Drepper, provided invaluable help and feedback for the design of the
internationalization features.

Nelson Beebe, Martin Brown, Andreas Buening, Scott Deifik, Darrel
Hankerson, Isamu Hasegawa, Michal Jaegermann, Ju"rgen Kahrs, Pat Rankin,
Kai Uwe Rommel, and Eli Zaretskii (in alphabetical order) make up the
`gawk' "crack portability team."  Without their hard work and help,
`gawk' would not be nearly the fine program it is today.  It has been
and continues to be a pleasure working with this team of fine people.

David and I would like to thank Brian Kernighan of Bell Laboratories for
invaluable assistance during the testing and debugging of `gawk', and
for help in clarifying numerous points about the language.  We could
not have done nearly as good a job on either `gawk' or its
documentation without his help.

Chuck Toporek, Mary Sheehan, and Claire Coutier of O'Reilly &
Associates contributed significant editorial help for this Info file
for the 3.1 release of `gawk'.

I must thank my wonderful wife, Miriam, for her patience through the
many versions of this project, for her proofreading, and for sharing me
with the computer.  I would like to thank my parents for their love,
and for the grace with which they raised and educated me.  Finally, I
also must acknowledge my gratitude to G-d, for the many opportunities
He has sent my way, as well as for the gifts He has given me with which
to take advantage of those opportunities.


Arnold Robbins
Nof Ayalon
ISRAEL
March, 2001


File: gawk.info,  Node: Getting Started,  Next: Regexp,  Prev: Preface,  Up: Top

1 Getting Started with `awk'
****************************

The basic function of `awk' is to search files for lines (or other
units of text) that contain certain patterns.  When a line matches one
of the patterns, `awk' performs specified actions on that line.  `awk'
keeps processing input lines in this way until it reaches the end of
the input files.

Programs in `awk' are different from programs in most other languages,
because `awk' programs are "data-driven"; that is, you describe the
data you want to work with and then what to do when you find it.  Most
other languages are "procedural"; you have to describe, in great
detail, every step the program is to take.  When working with procedural
languages, it is usually much harder to clearly describe the data your
program will process.  For this reason, `awk' programs are often
refreshingly easy to read and write.

When you run `awk', you specify an `awk' "program" that tells `awk'
what to do.  The program consists of a series of "rules".  (It may also
contain "function definitions", an advanced feature that we will ignore
for now.  *Note User-defined::.)  Each rule specifies one pattern to
search for and one action to perform upon finding the pattern.

Syntactically, a rule consists of a pattern followed by an action.  The
action is enclosed in curly braces to separate it from the pattern.
Newlines usually separate rules.  Therefore, an `awk' program looks
like this:

     PATTERN { ACTION }
     PATTERN { ACTION }
     ...

* Menu:

* Running gawk::                How to run `gawk' programs; includes
                                command-line syntax.
* Sample Data Files::           Sample data files for use in the `awk'
                                programs illustrated in this Info file.
* Very Simple::                 A very simple example.
* Two Rules::                   A less simple one-line example using two
                                rules.
* More Complex::                A more complex example.
* Statements/Lines::            Subdividing or combining statements into
                                lines.
* Other Features::              Other Features of `awk'.
* When::                        When to use `gawk' and when to use
                                other things.


File: gawk.info,  Node: Running gawk,  Next: Sample Data Files,  Up: Getting Started

1.1 How to Run `awk' Programs
=============================

There are several ways to run an `awk' program.  If the program is
short, it is easiest to include it in the command that runs `awk', like
this:

     awk 'PROGRAM' INPUT-FILE1 INPUT-FILE2 ...

When the program is long, it is usually more convenient to put it in a
file and run it with a command like this:

     awk -f PROGRAM-FILE INPUT-FILE1 INPUT-FILE2 ...

This minor node discusses both mechanisms, along with several
variations of each.

* Menu:

* One-shot::                    Running a short throwaway `awk'
                                program.
* Read Terminal::               Using no input files (input from terminal
                                instead).
* Long::                        Putting permanent `awk' programs in
                                files.
* Executable Scripts::          Making self-contained `awk' programs.
* Comments::                    Adding documentation to `gawk'
                                programs.
* Quoting::                     More discussion of shell quoting issues.


File: gawk.info,  Node: One-shot,  Next: Read Terminal,  Up: Running gawk

1.1.1 One-Shot Throwaway `awk' Programs
---------------------------------------

Once you are familiar with `awk', you will often type in simple
programs the moment you want to use them.  Then you can write the
program as the first argument of the `awk' command, like this:

     awk 'PROGRAM' INPUT-FILE1 INPUT-FILE2 ...

where PROGRAM consists of a series of PATTERNS and ACTIONS, as
described earlier.

This command format instructs the "shell", or command interpreter, to
start `awk' and use the PROGRAM to process records in the input
file(s).  There are single quotes around PROGRAM so the shell won't
interpret any `awk' characters as special shell characters.  The quotes
also cause the shell to treat all of PROGRAM as a single argument for
`awk', and allow PROGRAM to be more than one line long.

This format is also useful for running short or medium-sized `awk'
programs from shell scripts, because it avoids the need for a separate
file for the `awk' program.  A self-contained shell script is more
reliable because there are no other files to misplace.

*Note Very Simple::, presents several short, self-contained programs.


File: gawk.info,  Node: Read Terminal,  Next: Long,  Prev: One-shot,  Up: Running gawk

1.1.2 Running `awk' Without Input Files
---------------------------------------

You can also run `awk' without any input files.  If you type the
following command line:

     awk 'PROGRAM'

`awk' applies the PROGRAM to the "standard input", which usually means
whatever you type on the terminal.  This continues until you indicate
end-of-file by typing `Ctrl-d'.  (On other operating systems, the
end-of-file character may be different.  For example, on OS/2 and
MS-DOS, it is `Ctrl-z'.)

As an example, the following program prints a friendly piece of advice
(from Douglas Adams's `The Hitchhiker's Guide to the Galaxy'), to keep
you from worrying about the complexities of computer programming
(`BEGIN' is a feature we haven't discussed yet):

     $ awk "BEGIN { print \"Don't Panic!\" }"
     -| Don't Panic!

This program does not read any input.  The `\' before each of the inner
double quotes is necessary because of the shell's quoting rules--in
particular because it mixes both single quotes and double quotes.(1)

This next simple `awk' program emulates the `cat' utility; it copies
whatever you type on the keyboard to its standard output (why this
works is explained shortly).

     $ awk '{ print }'
     Now is the time for all good men
     -| Now is the time for all good men
     to come to the aid of their country.
     -| to come to the aid of their country.
     Four score and seven years ago, ...
     -| Four score and seven years ago, ...
     What, me worry?
     -| What, me worry?
     Ctrl-d

---------- Footnotes ----------

(1) Although we generally recommend the use of single quotes around the
program text, double quotes are needed here in order to put the single
quote into the message.


File: gawk.info,  Node: Long,  Next: Executable Scripts,  Prev: Read Terminal,  Up: Running gawk

1.1.3 Running Long Programs
---------------------------

Sometimes your `awk' programs can be very long.  In this case, it is
more convenient to put the program into a separate file.  In order to
tell `awk' to use that file for its program, you type:

     awk -f SOURCE-FILE INPUT-FILE1 INPUT-FILE2 ...

The `-f' instructs the `awk' utility to get the `awk' program from the
file SOURCE-FILE.  Any file name can be used for SOURCE-FILE.  For
example, you could put the program:

     BEGIN { print "Don't Panic!" }

into the file `advice'.  Then this command:

     awk -f advice

does the same thing as this one:

     awk "BEGIN { print \"Don't Panic!\" }"

This was explained earlier (*note Read Terminal::).  Note that you
don't usually need single quotes around the file name that you specify
with `-f', because most file names don't contain any of the shell's
special characters.  Notice that in `advice', the `awk' program did not
have single quotes around it.  The quotes are only needed for programs
that are provided on the `awk' command line.

If you want to identify your `awk' program files clearly as such, you
can add the extension `.awk' to the file name.  This doesn't affect the
execution of the `awk' program but it does make "housekeeping" easier.


File: gawk.info,  Node: Executable Scripts,  Next: Comments,  Prev: Long,  Up: Running gawk

1.1.4 Executable `awk' Programs
-------------------------------

Once you have learned `awk', you may want to write self-contained `awk'
scripts, using the `#!' script mechanism.  You can do this on many Unix
systems(1) as well as on the GNU system.  For example, you could update
the file `advice' to look like this:

     #! /bin/awk -f

     BEGIN { print "Don't Panic!" }

After making this file executable (with the `chmod' utility), simply
type `advice' at the shell and the system arranges to run `awk'(2) as
if you had typed `awk -f advice':

     $ chmod +x advice
     $ advice
     -| Don't Panic!

(We assume you have the current directory in your shell's search path
variable (typically `$PATH').  If not, you may need to type `./advice'
at the shell.)

Self-contained `awk' scripts are useful when you want to write a
program that users can invoke without their having to know that the
program is written in `awk'.

Advanced Notes: Portability Issues with `#!'
--------------------------------------------

Some systems limit the length of the interpreter name to 32 characters.
Often, this can be dealt with by using a symbolic link.

You should not put more than one argument on the `#!' line after the
path to `awk'. It does not work. The operating system treats the rest
of the line as a single argument and passes it to `awk'.  Doing this
leads to confusing behavior--most likely a usage diagnostic of some
sort from `awk'.

Finally, the value of `ARGV[0]' (*note Built-in Variables::) varies
depending upon your operating system.  Some systems put `awk' there,
some put the full pathname of `awk' (such as `/bin/awk'), and some put
the name of your script (`advice').  Don't rely on the value of
`ARGV[0]' to provide your script name.

---------- Footnotes ----------

(1) The `#!' mechanism works on Linux systems, systems derived from the
4.4-Lite Berkeley Software Distribution, and most commercial Unix
systems.

(2) The line beginning with `#!' lists the full file name of an
interpreter to run and an optional initial command-line argument to
pass to that interpreter.  The operating system then runs the
interpreter with the given argument and the full argument list of the
executed program.  The first argument in the list is the full file name
of the `awk' program.  The rest of the argument list contains either
options to `awk', or data files, or both.


File: gawk.info,  Node: Comments,  Next: Quoting,  Prev: Executable Scripts,  Up: Running gawk

1.1.6 Comments in `awk' Programs
--------------------------------

A "comment" is some text that is included in a program for the sake of
human readers; it is not really an executable part of the program.
Comments can explain what the program does and how it works.  Nearly all
programming languages have provisions for comments, as programs are
typically hard to understand without them.

In the `awk' language, a comment starts with the sharp sign character
(`#') and continues to the end of the line.  The `#' does not have to
be the first character on the line. The `awk' language ignores the rest
of a line following a sharp sign.  For example, we could have put the
following into `advice':

     # This program prints a nice friendly message.  It helps
     # keep novice users from being afraid of the computer.
     BEGIN    { print "Don't Panic!" }

You can put comment lines into keyboard-composed throwaway `awk'
programs, but this usually isn't very useful; the purpose of a comment
is to help you or another person understand the program when reading it
at a later time.

*Caution:* As mentioned in *Note One-shot::, you can enclose small to
medium programs in single quotes, in order to keep your shell scripts
self-contained.  When doing so, _don't_ put an apostrophe (i.e., a
single quote) into a comment (or anywhere else in your program). The
shell interprets the quote as the closing quote for the entire program.
As a result, usually the shell prints a message about mismatched
quotes, and if `awk' actually runs, it will probably print strange
messages about syntax errors.  For example, look at the following:

     $ awk '{ print "hello" } # let's be cute'
     >

The shell sees that the first two quotes match, and that a new quoted
object begins at the end of the command line.  It therefore prompts
with the secondary prompt, waiting for more input.  With Unix `awk',
closing the quoted string produces this result:

     $ awk '{ print "hello" } # let's be cute'
     > '
     error--> awk: can't open file be
     error-->  source line number 1

Putting a backslash before the single quote in `let's' wouldn't help,
since backslashes are not special inside single quotes.  The next
node describes the shell's quoting rules.


File: gawk.info,  Node: Quoting,  Prev: Comments,  Up: Running gawk

1.1.7 Shell-Quoting Issues
--------------------------

For short to medium length `awk' programs, it is most convenient to
enter the program on the `awk' command line.  This is best done by
enclosing the entire program in single quotes.  This is true whether
you are entering the program interactively at the shell prompt, or
writing it as part of a larger shell script:

     awk 'PROGRAM TEXT' INPUT-FILE1 INPUT-FILE2 ...

Once you are working with the shell, it is helpful to have a basic
knowledge of shell quoting rules.  The following rules apply only to
POSIX-compliant, Bourne-style shells (such as `bash', the GNU
Bourne-Again Shell).  If you use `csh', you're on your own.

   * Quoted items can be concatenated with nonquoted items as well as
     with other quoted items.  The shell turns everything into one
     argument for the command.

   * Preceding any single character with a backslash (`\') quotes that
     character.  The shell removes the backslash and passes the quoted
     character on to the command.

   * Single quotes protect everything between the opening and closing
     quotes.  The shell does no interpretation of the quoted text,
     passing it on verbatim to the command.  It is _impossible_ to
     embed a single quote inside single-quoted text.  Refer back to
     *Note Comments::, for an example of what happens if you try.

   * Double quotes protect most things between the opening and closing
     quotes.  The shell does at least variable and command substitution
     on the quoted text.  Different shells may do additional kinds of
     processing on double-quoted text.

     Since certain characters within double-quoted text are processed
     by the shell, they must be "escaped" within the text.  Of note are
     the characters `$', ``', `\', and `"', all of which must be
     preceded by a backslash within double-quoted text if they are to
     be passed on literally to the program.  (The leading backslash is
     stripped first.)  Thus, the example seen in *Note Read Terminal::,
     is applicable:

          $ awk "BEGIN { print \"Don't Panic!\" }"
          -| Don't Panic!

     Note that the single quote is not special within double quotes.

   * Null strings are removed when they occur as part of a non-null
     command-line argument, while explicit non-null objects are kept.
     For example, to specify that the field separator `FS' should be
     set to the null string, use:

          awk -F "" 'PROGRAM' FILES # correct

     Don't use this:

          awk -F"" 'PROGRAM' FILES  # wrong!

     In the second case, `awk' will attempt to use the text of the
     program as the value of `FS', and the first file name as the text
     of the program!  This results in syntax errors at best, and
     confusing behavior at worst.

Mixing single and double quotes is difficult.  You have to resort to
shell quoting tricks, like this:

     $ awk 'BEGIN { print "Here is a single quote <'"'"'>" }'
     -| Here is a single quote <'>

This program consists of three concatenated quoted strings.  The first
and the third are single-quoted, the second is double-quoted.

This can be "simplified" to:

     $ awk 'BEGIN { print "Here is a single quote <'\''>" }'
     -| Here is a single quote <'>

Judge for yourself which of these two is the more readable.

Another option is to use double quotes, escaping the embedded,
`awk'-level double quotes:

     $ awk "BEGIN { print \"Here is a single quote <'>\" }"
     -| Here is a single quote <'>

This option is also painful, because double quotes, backslashes, and
dollar signs are very common in `awk' programs.

A third option is to use the octal escape sequence equivalents for the
single- and double-quote characters, like so:

     $ awk 'BEGIN { print "Here is a single quote <\47>" }'
     -| Here is a single quote <'>
     $ awk 'BEGIN { print "Here is a double quote <\42>" }'
     -| Here is a double quote <">

This works nicely, except that you should comment clearly what the
escapes mean.

A fourth option is to use command-line variable assignment, like this:

     $ awk -v sq="'" 'BEGIN { print "Here is a single quote <" sq ">" }'
     -| Here is a single quote <'>

If you really need both single and double quotes in your `awk' program,
it is probably best to move it into a separate file, where the shell
won't be part of the picture, and you can say what you mean.


File: gawk.info,  Node: Sample Data Files,  Next: Very Simple,  Prev: Running gawk,  Up: Getting Started

1.2 Data Files for the Examples
===============================

Many of the examples in this Info file take their input from two sample
data files.  The first, `BBS-list', represents a list of computer
bulletin board systems together with information about those systems.
The second data file, called `inventory-shipped', contains information
about monthly shipments.  In both files, each line is considered to be
one "record".

In the data file `BBS-list', each record contains the name of a computer
bulletin board, its phone number, the board's baud rate(s), and a code
for the number of hours it is operational.  An `A' in the last column
means the board operates 24 hours a day.  A `B' in the last column
means the board only operates on evening and weekend hours.  A `C'
means the board operates only on weekends:

     aardvark     555-5553     1200/300          B
     alpo-net     555-3412     2400/1200/300     A
     barfly       555-7685     1200/300          A
     bites        555-1675     2400/1200/300     A
     camelot      555-0542     300               C
     core         555-2912     1200/300          C
     fooey        555-1234     2400/1200/300     B
     foot         555-6699     1200/300          B
     macfoo       555-6480     1200/300          A
     sdace        555-3430     2400/1200/300     A
     sabafoo      555-2127     1200/300          C

The data file `inventory-shipped' represents information about
shipments during the year.  Each record contains the month, the number
of green crates shipped, the number of red boxes shipped, the number of
orange bags shipped, and the number of blue packages shipped,
respectively.  There are 16 entries, covering the 12 months of last year
and the first four months of the current year.

     Jan  13  25  15 115
     Feb  15  32  24 226
     Mar  15  24  34 228
     Apr  31  52  63 420
     May  16  34  29 208
     Jun  31  42  75 492
     Jul  24  34  67 436
     Aug  15  34  47 316
     Sep  13  55  37 277
     Oct  29  54  68 525
     Nov  20  87  82 577
     Dec  17  35  61 401

     Jan  21  36  64 620
     Feb  26  58  80 652
     Mar  24  75  70 495
     Apr  21  70  74 514

If you are reading this in GNU Emacs using Info, you can copy the
regions of text showing these sample files into your own test files.
This way you can try out the examples shown in the remainder of this
document.  You do this by using the command `M-x write-region' to copy
text from the Info file into a file for use with `awk' (*Note
Miscellaneous File Operations: (emacs)Misc File Ops, for more
information).  Using this information, create your own `BBS-list' and
`inventory-shipped' files and practice what you learn in this Info file.

If you are using the stand-alone version of Info, see *Note Extract
Program::, for an `awk' program that extracts these data files from
`gawk.texi', the Texinfo source file for this Info file.


File: gawk.info,  Node: Very Simple,  Next: Two Rules,  Prev: Sample Data Files,  Up: Getting Started

1.3 Some Simple Examples
========================

The following command runs a simple `awk' program that searches the
input file `BBS-list' for the character string `foo' (a grouping of
characters is usually called a "string"; the term "string" is based on
similar usage in English, such as "a string of pearls," or "a string of
cars in a train"):

     awk '/foo/ { print $0 }' BBS-list

When lines containing `foo' are found, they are printed because
`print $0' means print the current line.  (Just `print' by itself means
the same thing, so we could have written that instead.)

You will notice that slashes (`/') surround the string `foo' in the
`awk' program.  The slashes indicate that `foo' is the pattern to
search for.  This type of pattern is called a "regular expression",
which is covered in more detail later (*note Regexp::).  The pattern is
allowed to match parts of words.  There are single quotes around the
`awk' program so that the shell won't interpret any of it as special
shell characters.

Here is what this program prints:

     $ awk '/foo/ { print $0 }' BBS-list
     -| fooey        555-1234     2400/1200/300     B
     -| foot         555-6699     1200/300          B
     -| macfoo       555-6480     1200/300          A
     -| sabafoo      555-2127     1200/300          C

In an `awk' rule, either the pattern or the action can be omitted, but
not both.  If the pattern is omitted, then the action is performed for
_every_ input line.  If the action is omitted, the default action is to
print all lines that match the pattern.

Thus, we could leave out the action (the `print' statement and the curly
braces) in the previous example and the result would be the same: all
lines matching the pattern `foo' are printed.  By comparison, omitting
the `print' statement but retaining the curly braces makes an empty
action that does nothing (i.e., no lines are printed).

Many practical `awk' programs are just a line or two.  Following is a
collection of useful, short programs to get you started.  Some of these
programs contain constructs that haven't been covered yet. (The
description of the program will give you a good idea of what is going
on, but please read the rest of the Info file to become an `awk'
expert!)  Most of the examples use a data file named `data'.  This is
just a placeholder; if you use these programs yourself, substitute your
own file names for `data'.  For future reference, note that there is
often more than one way to do things in `awk'.  At some point, you may
want to look back at these examples and see if you can come up with
different ways to do the same things shown here:

   * Print the length of the longest input line:

          awk '{ if (length($0) > max) max = length($0) }
               END { print max }' data

   * Print every line that is longer than 80 characters:

          awk 'length($0) > 80' data

     The sole rule has a relational expression as its pattern and it
     has no action--so the default action, printing the record, is used.

   * Print the length of the longest line in `data':

          expand data | awk '{ if (x < length()) x = length() }
                        END { print "maximum line length is " x }'

     The input is processed by the `expand' utility to change tabs into
     spaces, so the widths compared are actually the right-margin
     columns.

   * Print every line that has at least one field:

          awk 'NF > 0' data

     This is an easy way to delete blank lines from a file (or rather,
     to create a new file similar to the old file but from which the
     blank lines have been removed).

   * Print seven random numbers from 0 to 100, inclusive:

          awk 'BEGIN { for (i = 1; i <= 7; i++)
                           print int(101 * rand()) }'

   * Print the total number of bytes used by FILES:

          ls -l FILES | awk '{ x += $5 }
                            END { print "total bytes: " x }'

   * Print the total number of kilobytes used by FILES:

          ls -l FILES | awk '{ x += $5 }
             END { print "total K-bytes: " (x + 1023)/1024 }'

   * Print a sorted list of the login names of all users:

          awk -F: '{ print $1 }' /etc/passwd | sort

   * Count the lines in a file:

          awk 'END { print NR }' data

   * Print the even-numbered lines in the data file:

          awk 'NR % 2 == 0' data

     If you use the expression `NR % 2 == 1' instead, the program would
     print the odd-numbered lines.


File: gawk.info,  Node: Two Rules,  Next: More Complex,  Prev: Very Simple,  Up: Getting Started

1.4 An Example with Two Rules
=============================

The `awk' utility reads the input files one line at a time.  For each
line, `awk' tries the patterns of each of the rules.  If several
patterns match, then several actions are run in the order in which they
appear in the `awk' program.  If no patterns match, then no actions are
run.

After processing all the rules that match the line (and perhaps there
are none), `awk' reads the next line.  (However, *note Next Statement::,
and also *note Nextfile Statement::).  This continues until the program
reaches the end of the file.  For example, the following `awk' program
contains two rules:

     /12/  { print $0 }
     /21/  { print $0 }

The first rule has the string `12' as the pattern and `print $0' as the
action.  The second rule has the string `21' as the pattern and also
has `print $0' as the action.  Each rule's action is enclosed in its
own pair of braces.

This program prints every line that contains the string `12' _or_ the
string `21'.  If a line contains both strings, it is printed twice,
once by each rule.

This is what happens if we run this program on our two sample data
files, `BBS-list' and `inventory-shipped':

     $ awk '/12/ { print $0 }
     >      /21/ { print $0 }' BBS-list inventory-shipped
     -| aardvark     555-5553     1200/300          B
     -| alpo-net     555-3412     2400/1200/300     A
     -| barfly       555-7685     1200/300          A
     -| bites        555-1675     2400/1200/300     A
     -| core         555-2912     1200/300          C
     -| fooey        555-1234     2400/1200/300     B
     -| foot         555-6699     1200/300          B
     -| macfoo       555-6480     1200/300          A
     -| sdace        555-3430     2400/1200/300     A
     -| sabafoo      555-2127     1200/300          C
     -| sabafoo      555-2127     1200/300          C
     -| Jan  21  36  64 620
     -| Apr  21  70  74 514

Note how the line beginning with `sabafoo' in `BBS-list' was printed
twice, once for each rule.


File: gawk.info,  Node: More Complex,  Next: Statements/Lines,  Prev: Two Rules,  Up: Getting Started

1.5 A More Complex Example
==========================

Now that we've mastered some simple tasks, let's look at what typical
`awk' programs do.  This example shows how `awk' can be used to
summarize, select, and rearrange the output of another utility.  It uses
features that haven't been covered yet, so don't worry if you don't
understand all the details:

     ls -l | awk '$6 == "Nov" { sum += $5 }
                  END { print sum }'

This command prints the total number of bytes in all the files in the
current directory that were last modified in November (of any year).
(1) The `ls -l' part of this example is a system command that gives you
a listing of the files in a directory, including each file's size and
the date the file was last modified. Its output looks like this:

     -rw-r--r--  1 arnold   user   1933 Nov  7 13:05 Makefile
     -rw-r--r--  1 arnold   user  10809 Nov  7 13:03 awk.h
     -rw-r--r--  1 arnold   user    983 Apr 13 12:14 awk.tab.h
     -rw-r--r--  1 arnold   user  31869 Jun 15 12:20 awkgram.y
     -rw-r--r--  1 arnold   user  22414 Nov  7 13:03 awk1.c
     -rw-r--r--  1 arnold   user  37455 Nov  7 13:03 awk2.c
     -rw-r--r--  1 arnold   user  27511 Dec  9 13:07 awk3.c
     -rw-r--r--  1 arnold   user   7989 Nov  7 13:03 awk4.c

The first field contains read-write permissions, the second field
contains the number of links to the file, and the third field
identifies the owner of the file. The fourth field identifies the group
of the file.  The fifth field contains the size of the file in bytes.
The sixth, seventh, and eighth fields contain the month, day, and time,
respectively, that the file was last modified.  Finally, the ninth field
contains the name of the file.(2)

The `$6 == "Nov"' in our `awk' program is an expression that tests
whether the sixth field of the output from `ls -l' matches the string
`Nov'.  Each time a line has the string `Nov' for its sixth field, the
action `sum += $5' is performed.  This adds the fifth field (the file's
size) to the variable `sum'.  As a result, when `awk' has finished
reading all the input lines, `sum' is the total of the sizes of the
files whose lines matched the pattern.  (This works because `awk'
variables are automatically initialized to zero.)

After the last line of output from `ls' has been processed, the `END'
rule executes and prints the value of `sum'.  In this example, the
value of `sum' is 80600.

These more advanced `awk' techniques are covered in later sections
(*note Action Overview::).  Before you can move on to more advanced
`awk' programming, you have to know how `awk' interprets your input and
displays your output.  By manipulating fields and using `print'
statements, you can produce some very useful and impressive-looking
reports.

---------- Footnotes ----------

(1) In the C shell (`csh'), you need to type a semicolon and then a
backslash at the end of the first line; see *Note Statements/Lines::,
for an explanation.  In a POSIX-compliant shell, such as the Bourne
shell or `bash', you can type the example as shown.  If the command
`echo $path' produces an empty output line, you are most likely using a
POSIX-compliant shell.  Otherwise, you are probably using the C shell
or a shell derived from it.

(2) On some very old systems, you may need to use `ls -lg' to get this
output.


File: gawk.info,  Node: Statements/Lines,  Next: Other Features,  Prev: More Complex,  Up: Getting Started

1.6 `awk' Statements Versus Lines
=================================

Most often, each line in an `awk' program is a separate statement or
separate rule, like this:

     awk '/12/  { print $0 }
          /21/  { print $0 }' BBS-list inventory-shipped

However, `gawk' ignores newlines after any of the following symbols and
keywords:

     ,    {    ?    :    ||    &&    do    else

A newline at any other point is considered the end of the statement.(1)

If you would like to split a single statement into two lines at a point
where a newline would terminate it, you can "continue" it by ending the
first line with a backslash character (`\').  The backslash must be the
final character on the line in order to be recognized as a continuation
character.  A backslash is allowed anywhere in the statement, even in
the middle of a string or regular expression.  For example:

     awk '/This regular expression is too long, so continue it\
      on the next line/ { print $1 }'

We have generally not used backslash continuation in the sample programs
in this Info file.  In `gawk', there is no limit on the length of a
line, so backslash continuation is never strictly necessary; it just
makes programs more readable.  For this same reason, as well as for
clarity, we have kept most statements short in the sample programs
presented throughout the Info file.  Backslash continuation is most
useful when your `awk' program is in a separate source file instead of
entered from the command line.  You should also note that many `awk'
implementations are more particular about where you may use backslash
continuation. For example, they may not allow you to split a string
constant using backslash continuation.  Thus, for maximum portability
of your `awk' programs, it is best not to split your lines in the
middle of a regular expression or a string.

*Caution:* _Backslash continuation does not work as described with the
C shell._  It works for `awk' programs in files and for one-shot
programs, _provided_ you are using a POSIX-compliant shell, such as the
Unix Bourne shell or `bash'.  But the C shell behaves differently!
There, you must use two backslashes in a row, followed by a newline.
Note also that when using the C shell, _every_ newline in your awk
program must be escaped with a backslash. To illustrate:

     % awk 'BEGIN { \
     ?   print \\
     ?       "hello, world" \
     ? }'
     -| hello, world

Here, the `%' and `?' are the C shell's primary and secondary prompts,
analogous to the standard shell's `$' and `>'.

Compare the previous example to how it is done with a POSIX-compliant
shell:

     $ awk 'BEGIN {
     >   print \
     >       "hello, world"
     > }'
     -| hello, world

`awk' is a line-oriented language.  Each rule's action has to begin on
the same line as the pattern.  To have the pattern and action on
separate lines, you _must_ use backslash continuation; there is no
other option.

Another thing to keep in mind is that backslash continuation and
comments do not mix. As soon as `awk' sees the `#' that starts a
comment, it ignores _everything_ on the rest of the line. For example:

     $ gawk 'BEGIN { print "dont panic" # a friendly \
     >                                    BEGIN rule
     > }'
     error--> gawk: cmd. line:2:                BEGIN rule
     error--> gawk: cmd. line:2:                ^ parse error

In this case, it looks like the backslash would continue the comment
onto the next line. However, the backslash-newline combination is never
even noticed because it is "hidden" inside the comment. Thus, the
`BEGIN' is noted as a syntax error.

When `awk' statements within one rule are short, you might want to put
more than one of them on a line.  This is accomplished by separating
the statements with a semicolon (`;').  This also applies to the rules
themselves.  Thus, the program shown at the start of this minor node
could also be written this way:

     /12/ { print $0 } ; /21/ { print $0 }

     NOTE: The requirement that states that rules on the same line must
     be separated with a semicolon was not in the original `awk'
     language; it was added for consistency with the treatment of
     statements within an action.

---------- Footnotes ----------

(1) The `?' and `:' referred to here is the three-operand conditional
expression described in *Note Conditional Exp::.  Splitting lines after
`?' and `:' is a minor `gawk' extension; if `--posix' is specified
(*note Options::), then this extension is disabled.


File: gawk.info,  Node: Other Features,  Next: When,  Prev: Statements/Lines,  Up: Getting Started

1.7 Other Features of `awk'
===========================

The `awk' language provides a number of predefined, or "built-in",
variables that your programs can use to get information from `awk'.
There are other variables your program can set as well to control how
`awk' processes your data.

In addition, `awk' provides a number of built-in functions for doing
common computational and string-related operations.  `gawk' provides
built-in functions for working with timestamps, performing bit
manipulation, and for runtime string translation.

As we develop our presentation of the `awk' language, we introduce most
of the variables and many of the functions. They are defined
systematically in *Note Built-in Variables::, and *Note Built-in::.


File: gawk.info,  Node: When,  Prev: Other Features,  Up: Getting Started

1.8 When to Use `awk'
=====================

Now that you've seen some of what `awk' can do, you might wonder how
`awk' could be useful for you.  By using utility programs, advanced
patterns, field separators, arithmetic statements, and other selection
criteria, you can produce much more complex output.  The `awk' language
is very useful for producing reports from large amounts of raw data,
such as summarizing information from the output of other utility
programs like `ls'.  (*Note More Complex::.)

Programs written with `awk' are usually much smaller than they would be
in other languages.  This makes `awk' programs easy to compose and use.
Often, `awk' programs can be quickly composed at your terminal, used
once, and thrown away.  Because `awk' programs are interpreted, you can
avoid the (usually lengthy) compilation part of the typical
edit-compile-test-debug cycle of software development.

Complex programs have been written in `awk', including a complete
retargetable assembler for eight-bit microprocessors (*note Glossary::,
for more information), and a microcode assembler for a special-purpose
Prolog computer.  More recently, `gawk' was used for writing a Wiki
clone.(1) While the original `awk''s capabilities were strained by tasks
of such complexity, modern versions are more capable.  Even the Bell
Labs version of `awk' has fewer predefined limits, and those that it
has are much larger than they used to be.

If you find yourself writing `awk' scripts of more than, say, a few
hundred lines, you might consider using a different programming
language.  Emacs Lisp is a good choice if you need sophisticated string
or pattern matching capabilities.  The shell is also good at string and
pattern matching; in addition, it allows powerful use of the system
utilities.  More conventional languages, such as C, C++, and Java, offer
better facilities for system programming and for managing the complexity
of large programs.  Programs in these languages may require more lines
of source code than the equivalent `awk' programs, but they are easier
to maintain and usually run more efficiently.

---------- Footnotes ----------

(1) Yet Another Wiki Clone
(http://www.awk-scripting.de/cgi/wiki.cgi/yawk/).


File: gawk.info,  Node: Regexp,  Next: Reading Files,  Prev: Getting Started,  Up: Top

2 Regular Expressions
*********************

A "regular expression", or "regexp", is a way of describing a set of
strings.  Because regular expressions are such a fundamental part of
`awk' programming, their format and use deserve a separate major node.

A regular expression enclosed in slashes (`/') is an `awk' pattern that
matches every input record whose text belongs to that set.  The
simplest regular expression is a sequence of letters, numbers, or both.
Such a regexp matches any string that contains that sequence.  Thus,
the regexp `foo' matches any string containing `foo'.  Therefore, the
pattern `/foo/' matches any input record containing the three
characters `foo' _anywhere_ in the record.  Other kinds of regexps let
you specify more complicated classes of strings.

* Menu:

* Regexp Usage::                How to Use Regular Expressions.
* Escape Sequences::            How to write nonprinting characters.
* Regexp Operators::            Regular Expression Operators.
* Character Lists::             What can go between `[...]'.
* GNU Regexp Operators::        Operators specific to GNU software.
* Case-sensitivity::            How to do case-insensitive matching.
* Leftmost Longest::            How much text matches.
* Computed Regexps::            Using Dynamic Regexps.
* Locales::                     How the locale affects things.


File: gawk.info,  Node: Regexp Usage,  Next: Escape Sequences,  Up: Regexp

2.1 How to Use Regular Expressions
==================================

A regular expression can be used as a pattern by enclosing it in
slashes.  Then the regular expression is tested against the entire text
of each record.  (Normally, it only needs to match some part of the
text in order to succeed.)  For example, the following prints the
second field of each record that contains the string `foo' anywhere in
it:

     $ awk '/foo/ { print $2 }' BBS-list
     -| 555-1234
     -| 555-6699
     -| 555-6480
     -| 555-2127

`~' (tilde), `~' operator Regular expressions can also be used in
matching expressions.  These expressions allow you to specify the
string to match against; it need not be the entire current input
record.  The two operators `~' and `!~' perform regular expression
comparisons.  Expressions using these operators can be used as
patterns, or in `if', `while', `for', and `do' statements.  (*Note
Statements::.)  For example:

     EXP ~ /REGEXP/

is true if the expression EXP (taken as a string) matches REGEXP.  The
following example matches, or selects, all input records with the
uppercase letter `J' somewhere in the first field:

     $ awk '$1 ~ /J/' inventory-shipped
     -| Jan  13  25  15 115
     -| Jun  31  42  75 492
     -| Jul  24  34  67 436
     -| Jan  21  36  64 620

So does this:

     awk '{ if ($1 ~ /J/) print }' inventory-shipped

This next example is true if the expression EXP (taken as a character
string) does _not_ match REGEXP:

     EXP !~ /REGEXP/

The following example matches, or selects, all input records whose
first field _does not_ contain the uppercase letter `J':

     $ awk '$1 !~ /J/' inventory-shipped
     -| Feb  15  32  24 226
     -| Mar  15  24  34 228
     -| Apr  31  52  63 420
     -| May  16  34  29 208
     ...

When a regexp is enclosed in slashes, such as `/foo/', we call it a
"regexp constant", much like `5.27' is a numeric constant and `"foo"'
is a string constant.


File: gawk.info,  Node: Escape Sequences,  Next: Regexp Operators,  Prev: Regexp Usage,  Up: Regexp

2.2 Escape Sequences
====================

Some characters cannot be included literally in string constants
(`"foo"') or regexp constants (`/foo/').  Instead, they should be
represented with "escape sequences", which are character sequences
beginning with a backslash (`\').  One use of an escape sequence is to
include a double-quote character in a string constant.  Because a plain
double quote ends the string, you must use `\"' to represent an actual
double-quote character as a part of the string.  For example:

     $ awk 'BEGIN { print "He said \"hi!\" to her." }'
     -| He said "hi!" to her.

The  backslash character itself is another character that cannot be
included normally; you must write `\\' to put one backslash in the
string or regexp.  Thus, the string whose contents are the two
characters `"' and `\' must be written `"\"\\"'.

Backslash also represents unprintable characters such as TAB or
newline.  While there is nothing to stop you from entering most
unprintable characters directly in a string constant or regexp constant,
they may look ugly.

The following table lists all the escape sequences used in `awk' and
what they represent. Unless noted otherwise, all these escape sequences
apply to both string constants and regexp constants:

`\\'
     A literal backslash, `\'.

`\a'
     The "alert" character, `Ctrl-g', ASCII code 7 (BEL).  (This
     usually makes some sort of audible noise.)

`\b'
     Backspace, `Ctrl-h', ASCII code 8 (BS).

`\f'
     Formfeed, `Ctrl-l', ASCII code 12 (FF).

`\n'
     Newline, `Ctrl-j', ASCII code 10 (LF).

`\r'
     Carriage return, `Ctrl-m', ASCII code 13 (CR).

`\t'
     Horizontal TAB, `Ctrl-i', ASCII code 9 (HT).

`\v'
     Vertical tab, `Ctrl-k', ASCII code 11 (VT).

`\NNN'
     The octal value NNN, where NNN stands for 1 to 3 digits between
     `0' and `7'.  For example, the code for the ASCII ESC (escape)
     character is `\033'.

`\xHH...'
     The hexadecimal value HH, where HH stands for a sequence of
     hexadecimal digits (`0'-`9', and either `A'-`F' or `a'-`f').  Like
     the same construct in ISO C, the escape sequence continues until
     the first nonhexadecimal digit is seen.  However, using more than
     two hexadecimal digits produces undefined results. (The `\x'
     escape sequence is not allowed in POSIX `awk'.)

`\/'
     A literal slash (necessary for regexp constants only).  This
     expression is used when you want to write a regexp constant that
     contains a slash. Because the regexp is delimited by slashes, you
     need to escape the slash that is part of the pattern, in order to
     tell `awk' to keep processing the rest of the regexp.

`\"'
     A literal double quote (necessary for string constants only).
     This expression is used when you want to write a string constant
     that contains a double quote. Because the string is delimited by
     double quotes, you need to escape the quote that is part of the
     string, in order to tell `awk' to keep processing the rest of the
     string.

In `gawk', a number of additional two-character sequences that begin
with a backslash have special meaning in regexps.  *Note GNU Regexp
Operators::.

In a regexp, a backslash before any character that is not in the
previous list and not listed in *Note GNU Regexp Operators::, means
that the next character should be taken literally, even if it would
normally be a regexp operator.  For example, `/a\+b/' matches the three
characters `a+b'.

For complete portability, do not use a backslash before any character
not shown in the previous list.

To summarize:

   * The escape sequences in the table above are always processed first,
     for both string constants and regexp constants. This happens very
     early, as soon as `awk' reads your program.

   * `gawk' processes both regexp constants and dynamic regexps (*note
     Computed Regexps::), for the special operators listed in *Note GNU
     Regexp Operators::.

   * A backslash before any other character means to treat that
     character literally.

Advanced Notes: Backslash Before Regular Characters
---------------------------------------------------

If you place a backslash in a string constant before something that is
not one of the characters previously listed, POSIX `awk' purposely
leaves what happens as undefined.  There are two choices:

Strip the backslash out
     This is what Unix `awk' and `gawk' both do.  For example, `"a\qc"'
     is the same as `"aqc"'.  (Because this is such an easy bug both to
     introduce and to miss, `gawk' warns you about it.)  Consider `FS =
     "[ \t]+\|[ \t]+"' to use vertical bars surrounded by whitespace as
     the field separator. There should be two backslashes in the string
     `FS = "[ \t]+\\|[ \t]+"'.)

Leave the backslash alone
     Some other `awk' implementations do this.  In such
     implementations, typing `"a\qc"' is the same as typing `"a\\qc"'.

Advanced Notes: Escape Sequences for Metacharacters
---------------------------------------------------

Suppose you use an octal or hexadecimal escape to represent a regexp
metacharacter.  (See *Note Regexp Operators::.)  Does `awk' treat the
character as a literal character or as a regexp operator?

Historically, such characters were taken literally.  (d.c.)  However,
the POSIX standard indicates that they should be treated as real
metacharacters, which is what `gawk' does.  In compatibility mode
(*note Options::), `gawk' treats the characters represented by octal
and hexadecimal escape sequences literally when used in regexp
constants. Thus, `/a\52b/' is equivalent to `/a\*b/'.


File: gawk.info,  Node: Regexp Operators,  Next: Character Lists,  Prev: Escape Sequences,  Up: Regexp

2.3 Regular Expression Operators
================================

You can combine regular expressions with special characters, called
"regular expression operators" or "metacharacters", to increase the
power and versatility of regular expressions.

The escape sequences described in *Note Escape Sequences::, are valid
inside a regexp.  They are introduced by a `\' and are recognized and
converted into corresponding real characters as the very first step in
processing regexps.

Here is a list of metacharacters.  All characters that are not escape
sequences and that are not listed in the table stand for themselves:

`\'
     This is used to suppress the special meaning of a character when
     matching.  For example, `\$' matches the character `$'.

`^'
     This matches the beginning of a string.  For example, `^@chapter'
     matches `@chapter' at the beginning of a string and can be used to
     identify chapter beginnings in Texinfo source files.  The `^' is
     known as an "anchor", because it anchors the pattern to match only
     at the beginning of the string.

     It is important to realize that `^' does not match the beginning of
     a line embedded in a string.  The condition is not true in the
     following example:

          if ("line1\nLINE 2" ~ /^L/) ...

`$'
     This is similar to `^', but it matches only at the end of a string.
     For example, `p$' matches a record that ends with a `p'.  The `$'
     is an anchor and does not match the end of a line embedded in a
     string.  The condition in the following example is not true:

          if ("line1\nLINE 2" ~ /1$/) ...

`.'
     This matches any single character, _including_ the newline
     character.  For example, `.P' matches any single character
     followed by a `P' in a string.  Using concatenation, we can make a
     regular expression such as `U.A', which matches any
     three-character sequence that begins with `U' and ends with `A'.

     In strict POSIX mode (*note Options::), `.' does not match the NUL
     character, which is a character with all bits equal to zero.
     Otherwise, NUL is just another character. Other versions of `awk'
     may not be able to match the NUL character.

`[...]'
     This is called a "character list".(1) It matches any _one_ of the
     characters that are enclosed in the square brackets.  For example,
     `[MVX]' matches any one of the characters `M', `V', or `X' in a
     string.  A full discussion of what can be inside the square
     brackets of a character list is given in *Note Character Lists::.

`[^ ...]'
     This is a "complemented character list".  The first character after
     the `[' _must_ be a `^'.  It matches any characters _except_ those
     in the square brackets.  For example, `[^awk]' matches any
     character that is not an `a', `w', or `k'.

`|'
     This is the "alternation operator" and it is used to specify
     alternatives.  The `|' has the lowest precedence of all the regular
     expression operators.  For example, `^P|[[:digit:]]' matches any
     string that matches either `^P' or `[[:digit:]]'.  This means it
     matches any string that starts with `P' or contains a digit.

     The alternation applies to the largest possible regexps on either
     side.

`(...)'
     Parentheses are used for grouping in regular expressions, as in
     arithmetic.  They can be used to concatenate regular expressions
     containing the alternation operator, `|'.  For example,
     `@(samp|code)\{[^}]+\}' matches both `@code{foo}' and `@samp{bar}'.
     (These are Texinfo formatting control sequences. The `+' is
     explained further on in this list.)

`*'
     This symbol means that the preceding regular expression should be
     repeated as many times as necessary to find a match.  For example,
     `ph*' applies the `*' symbol to the preceding `h' and looks for
     matches of one `p' followed by any number of `h's.  This also
     matches just `p' if no `h's are present.

     The `*' repeats the _smallest_ possible preceding expression.
     (Use parentheses if you want to repeat a larger expression.)  It
     finds as many repetitions as possible.  For example, `awk
     '/\(c[ad][ad]*r x\)/ { print }' sample' prints every record in
     `sample' containing a string of the form `(car x)', `(cdr x)',
     `(cadr x)', and so on.  Notice the escaping of the parentheses by
     preceding them with backslashes.

`+'
     This symbol is similar to `*', except that the preceding
     expression must be matched at least once.  This means that `wh+y'
     would match `why' and `whhy', but not `wy', whereas `wh*y' would
     match all three of these strings.  The following is a simpler way
     of writing the last `*' example:

          awk '/\(c[ad]+r x\)/ { print }' sample

`?'
     This symbol is similar to `*', except that the preceding
     expression can be matched either once or not at all.  For example,
     `fe?d' matches `fed' and `fd', but nothing else.

`{N}'
`{N,}'
`{N,M}'
     One or two numbers inside braces denote an "interval expression".
     If there is one number in the braces, the preceding regexp is
     repeated N times.  If there are two numbers separated by a comma,
     the preceding regexp is repeated N to M times.  If there is one
     number followed by a comma, then the preceding regexp is repeated
     at least N times:

    `wh{3}y'
          Matches `whhhy', but not `why' or `whhhhy'.

    `wh{3,5}y'
          Matches `whhhy', `whhhhy', or `whhhhhy', only.

    `wh{2,}y'
          Matches `whhy' or `whhhy', and so on.

     Interval expressions were not traditionally available in `awk'.
     They were added as part of the POSIX standard to make `awk' and
     `egrep' consistent with each other.

     However, because old programs may use `{' and `}' in regexp
     constants, by default `gawk' does _not_ match interval expressions
     in regexps.  If either `--posix' or `--re-interval' are specified
     (*note Options::), then interval expressions are allowed in
     regexps.

     For new programs that use `{' and `}' in regexp constants, it is
     good practice to always escape them with a backslash.  Then the
     regexp constants are valid and work the way you want them to, using
     any version of `awk'.(2)

In regular expressions, the `*', `+', and `?' operators, as well as the
braces `{' and `}', have the highest precedence, followed by
concatenation, and finally by `|'.  As in arithmetic, parentheses can
change how operators are grouped.

In POSIX `awk' and `gawk', the `*', `+', and `?' operators stand for
themselves when there is nothing in the regexp that precedes them.  For
example, `/+/' matches a literal plus sign.  However, many other
versions of `awk' treat such a usage as a syntax error.

If `gawk' is in compatibility mode (*note Options::), POSIX character
classes and interval expressions are not available in regular
expressions.

---------- Footnotes ----------

(1) In other literature, you may see a character list referred to as
either a "character set", a "character class", or a "bracket
expression".

(2) Use two backslashes if you're using a string constant with a regexp
operator or function.


File: gawk.info,  Node: Character Lists,  Next: GNU Regexp Operators,  Prev: Regexp Operators,  Up: Regexp

2.4 Using Character Lists
=========================

Within a character list, a "range expression" consists of two
characters separated by a hyphen.  It matches any single character that
sorts between the two characters, using the locale's collating sequence
and character set.  For example, in the default C locale, `[a-dx-z]' is
equivalent to `[abcdxyz]'.  Many locales sort characters in dictionary
order, and in these locales, `[a-dx-z]' is typically not equivalent to
`[abcdxyz]'; instead it might be equivalent to `[aBbCcDdxXyYz]', for
example.  To obtain the traditional interpretation of bracket
expressions, you can use the C locale by setting the `LC_ALL'
environment variable to the value `C'.

To include one of the characters `\', `]', `-', or `^' in a character
list, put a `\' in front of it.  For example:

     [d\]]

matches either `d' or `]'.

This treatment of `\' in character lists is compatible with other `awk'
implementations and is also mandated by POSIX.  The regular expressions
in `awk' are a superset of the POSIX specification for Extended Regular
Expressions (EREs).  POSIX EREs are based on the regular expressions
accepted by the traditional `egrep' utility.

"Character classes" are a new feature introduced in the POSIX standard.
A character class is a special notation for describing lists of
characters that have a specific attribute, but the actual characters
can vary from country to country and/or from character set to character
set.  For example, the notion of what is an alphabetic character
differs between the United States and France.

A character class is only valid in a regexp _inside_ the brackets of a
character list.  Character classes consist of `[:', a keyword denoting
the class, and `:]'.  *Note table-char-classes:: lists the character
classes defined by the POSIX standard.

Class       Meaning
--------------------------------------------------------------------------
`[:alnum:]' Alphanumeric characters.
--------------------------------------------------------------------------
`[:alpha:]' Alphabetic characters.
--------------------------------------------------------------------------
`[:blank:]' Space and TAB characters.
--------------------------------------------------------------------------
`[:cntrl:]' Control characters.
--------------------------------------------------------------------------
`[:digit:]' Numeric characters.
--------------------------------------------------------------------------
`[:graph:]' Characters that are both printable and visible.  (A space is
            printable but not visible, whereas an `a' is both.)
--------------------------------------------------------------------------
`[:lower:]' Lowercase alphabetic characters.
--------------------------------------------------------------------------
`[:print:]' Printable characters (characters that are not control
            characters).
--------------------------------------------------------------------------
`[:punct:]' Punctuation characters (characters that are not letters,
            digits, control characters, or space characters).
--------------------------------------------------------------------------
`[:space:]' Space characters (such as space, TAB, and formfeed, to name
            a few).
--------------------------------------------------------------------------
`[:upper:]' Uppercase alphabetic characters.
--------------------------------------------------------------------------
`[:xdigit:]'Characters that are hexadecimal digits.
--------------------------------------------------------------------------

Table 2.1: POSIX Character Classes

   For example, before the POSIX standard, you had to write
`/[A-Za-z0-9]/' to match alphanumeric characters.  If your character
set had other alphabetic characters in it, this would not match them,
and if your character set collated differently from ASCII, this might
not even match the ASCII alphanumeric characters.  With the POSIX
character classes, you can write `/[[:alnum:]]/' to match the alphabetic
and numeric characters in your character set.

   Two additional special sequences can appear in character lists.
These apply to non-ASCII character sets, which can have single symbols
(called "collating elements") that are represented with more than one
character. They can also have several characters that are equivalent for
"collating", or sorting, purposes.  (For example, in French, a plain "e"
and a grave-accented "e`" are equivalent.)  These sequences are:

Collating symbols
     Multicharacter collating elements enclosed between `[.' and `.]'.
     For example, if `ch' is a collating element, then `[[.ch.]]' is a
     regexp that matches this collating element, whereas `[ch]' is a
     regexp that matches either `c' or `h'.

Equivalence classes
     Locale-specific names for a list of characters that are equal. The
     name is enclosed between `[=' and `=]'.  For example, the name `e'
     might be used to represent all of "e," "e`," and "e'." In this
     case, `[[=e=]]' is a regexp that matches any of `e', `e'', or `e`'.

   These features are very valuable in non-English-speaking locales.

   *Caution:* The library functions that `gawk' uses for regular
expression matching currently recognize only POSIX character classes;
they do not recognize collating symbols or equivalence classes.


File: gawk.info,  Node: GNU Regexp Operators,  Next: Case-sensitivity,  Prev: Character Lists,  Up: Regexp

2.5 `gawk'-Specific Regexp Operators
====================================

GNU software that deals with regular expressions provides a number of
additional regexp operators.  These operators are described in this
minor node and are specific to `gawk'; they are not available in other
`awk' implementations.  Most of the additional operators deal with word
matching.  For our purposes, a "word" is a sequence of one or more
letters, digits, or underscores (`_'):

`\w'
     Matches any word-constituent character--that is, it matches any
     letter, digit, or underscore. Think of it as shorthand for
     `[[:alnum:]_]'.

`\W'
     Matches any character that is not word-constituent.  Think of it
     as shorthand for `[^[:alnum:]_]'.

`\<'
     Matches the empty string at the beginning of a word.  For example,
     `/\<away/' matches `away' but not `stowaway'.

`\>'
     Matches the empty string at the end of a word.  For example,
     `/stow\>/' matches `stow' but not `stowaway'.

`\y'
     Matches the empty string at either the beginning or the end of a
     word (i.e., the word boundar*y*).  For example, `\yballs?\y'
     matches either `ball' or `balls', as a separate word.

`\B'
     Matches the empty string that occurs between two word-constituent
     characters. For example, `/\Brat\B/' matches `crate' but it does
     not match `dirty rat'.  `\B' is essentially the opposite of `\y'.

   There are two other operators that work on buffers.  In Emacs, a
"buffer" is, naturally, an Emacs buffer.  For other programs, `gawk''s
regexp library routines consider the entire string to match as the
buffer.  The operators are:

`\`'
     Matches the empty string at the beginning of a buffer (string).

`\''
     Matches the empty string at the end of a buffer (string).

   Because `^' and `$' always work in terms of the beginning and end of
strings, these operators don't add any new capabilities for `awk'.
They are provided for compatibility with other GNU software.

   In other GNU software, the word-boundary operator is `\b'. However,
that conflicts with the `awk' language's definition of `\b' as
backspace, so `gawk' uses a different letter.  An alternative method
would have been to require two backslashes in the GNU operators, but
this was deemed too confusing. The current method of using `\y' for the
GNU `\b' appears to be the lesser of two evils.

   The various command-line options (*note Options::) control how
`gawk' interprets characters in regexps:

No options
     In the default case, `gawk' provides all the facilities of POSIX
     regexps and the GNU regexp operators described in *Note Regexp
     Operators::.  However, interval expressions are not supported.

`--posix'
     Only POSIX regexps are supported; the GNU operators are not special
     (e.g., `\w' matches a literal `w').  Interval expressions are
     allowed.

`--traditional'
     Traditional Unix `awk' regexps are matched. The GNU operators are
     not special, interval expressions are not available, nor are the
     POSIX character classes (`[[:alnum:]]', etc.).  Characters
     described by octal and hexadecimal escape sequences are treated
     literally, even if they represent regexp metacharacters.

`--re-interval'
     Allow interval expressions in regexps, even if `--traditional' has
     been provided.  (`--posix' automatically enables interval
     expressions, so `--re-interval' is redundant when `--posix' is is
     used.)


File: gawk.info,  Node: Case-sensitivity,  Next: Leftmost Longest,  Prev: GNU Regexp Operators,  Up: Regexp

2.6 Case Sensitivity in Matching
================================

Case is normally significant in regular expressions, both when matching
ordinary characters (i.e., not metacharacters) and inside character
sets.  Thus, a `w' in a regular expression matches only a lowercase `w'
and not an uppercase `W'.

   The simplest way to do a case-independent match is to use a character
list--for example, `[Ww]'.  However, this can be cumbersome if you need
to use it often, and it can make the regular expressions harder to
read.  There are two alternatives that you might prefer.

   One way to perform a case-insensitive match at a particular point in
the program is to convert the data to a single case, using the
`tolower' or `toupper' built-in string functions (which we haven't
discussed yet; *note String Functions::).  For example:

     tolower($1) ~ /foo/  { ... }

converts the first field to lowercase before matching against it.  This
works in any POSIX-compliant `awk'.

Another method, specific to `gawk', is to set the variable `IGNORECASE'
to a nonzero value (*note Built-in Variables::).  When `IGNORECASE' is
not zero, _all_ regexp and string operations ignore case.  Changing the
value of `IGNORECASE' dynamically controls the case-sensitivity of the
program as it runs.  Case is significant by default because
`IGNORECASE' (like most variables) is initialized to zero:

     x = "aB"
     if (x ~ /ab/) ...   # this test will fail

     IGNORECASE = 1
     if (x ~ /ab/) ...   # now it will succeed

In general, you cannot use `IGNORECASE' to make certain rules
case-insensitive and other rules case-sensitive, because there is no
straightforward way to set `IGNORECASE' just for the pattern of a
particular rule.(1) To do this, use either character lists or
`tolower'.  However, one thing you can do with `IGNORECASE' only is
dynamically turn case-sensitivity on or off for all the rules at once.

`IGNORECASE' can be set on the command line or in a `BEGIN' rule (*note
Other Arguments::; also *note Using BEGIN/END::).  Setting `IGNORECASE'
from the command line is a way to make a program case-insensitive
without having to edit it.

Prior to `gawk' 3.0, the value of `IGNORECASE' affected regexp
operations only. It did not affect string comparison with `==', `!=',
and so on.  Beginning with version 3.0, both regexp and string
comparison operations are also affected by `IGNORECASE'.

Beginning with `gawk' 3.0, the equivalences between upper- and
lowercase characters are based on the ISO-8859-1 (ISO Latin-1)
character set. This character set is a superset of the traditional 128
ASCII characters, which also provides a number of characters suitable
for use with European languages.

As of `gawk' 3.1.4, the case equivalencies are fully locale-aware.
They are based on the C `<ctype.h>' facilities, such as `isalpha()' and
`toupper()'.

The value of `IGNORECASE' has no effect if `gawk' is in compatibility
mode (*note Options::).  Case is always significant in compatibility
mode.

---------- Footnotes ----------

(1) Experienced C and C++ programmers will note that it is possible,
using something like `IGNORECASE = 1 && /foObAr/ { ... }' and
`IGNORECASE = 0 || /foobar/ { ... }'.  However, this is somewhat
obscure and we don't recommend it.


File: gawk.info,  Node: Leftmost Longest,  Next: Computed Regexps,  Prev: Case-sensitivity,  Up: Regexp

2.7 How Much Text Matches?
==========================

Consider the following:

     echo aaaabcd | awk '{ sub(/a+/, "<A>"); print }'

This example uses the `sub' function (which we haven't discussed yet;
*note String Functions::) to make a change to the input record. Here,
the regexp `/a+/' indicates "one or more `a' characters," and the
replacement text is `<A>'.

The input contains four `a' characters.  `awk' (and POSIX) regular
expressions always match the leftmost, _longest_ sequence of input
characters that can match.  Thus, all four `a' characters are replaced
with `<A>' in this example:

     $ echo aaaabcd | awk '{ sub(/a+/, "<A>"); print }'
     -| <A>bcd

For simple match/no-match tests, this is not so important. But when
doing text matching and substitutions with the `match', `sub', `gsub',
and `gensub' functions, it is very important.  *Note String Functions::,
for more information on these functions.  Understanding this principle
is also important for regexp-based record and field splitting (*note
Records::, and also *note Field Separators::).


File: gawk.info,  Node: Computed Regexps,  Next: Locales,  Prev: Leftmost Longest,  Up: Regexp

2.8 Using Dynamic Regexps
=========================

The righthand side of a `~' or `!~' operator need not be a regexp
constant (i.e., a string of characters between slashes).  It may be any
expression.  The expression is evaluated and converted to a string if
necessary; the contents of the string are used as the regexp.  A regexp
that is computed in this way is called a "dynamic regexp":

     BEGIN { digits_regexp = "[[:digit:]]+" }
     $0 ~ digits_regexp    { print }

This sets `digits_regexp' to a regexp that describes one or more digits,
and tests whether the input record matches this regexp.

*Caution:* When using the `~' and `!~' operators, there is a difference
between a regexp constant enclosed in slashes and a string constant
enclosed in double quotes.  If you are going to use a string constant,
you have to understand that the string is, in essence, scanned _twice_:
the first time when `awk' reads your program, and the second time when
it goes to match the string on the lefthand side of the operator with
the pattern on the right.  This is true of any string-valued expression
(such as `digits_regexp', shown previously), not just string constants.

What difference does it make if the string is scanned twice? The answer
has to do with escape sequences, and particularly with backslashes.  To
get a backslash into a regular expression inside a string, you have to
type two backslashes.

For example, `/\*/' is a regexp constant for a literal `*'.  Only one
backslash is needed.  To do the same thing with a string, you have to
type `"\\*"'.  The first backslash escapes the second one so that the
string actually contains the two characters `\' and `*'.

Given that you can use both regexp and string constants to describe
regular expressions, which should you use?  The answer is "regexp
constants," for several reasons:

   * String constants are more complicated to write and more difficult
     to read. Using regexp constants makes your programs less
     error-prone.  Not understanding the difference between the two
     kinds of constants is a common source of errors.

   * It is more efficient to use regexp constants. `awk' can note that
     you have supplied a regexp and store it internally in a form that
     makes pattern matching more efficient.  When using a string
     constant, `awk' must first convert the string into this internal
     form and then perform the pattern matching.

   * Using regexp constants is better form; it shows clearly that you
     intend a regexp match.

Advanced Notes: Using `\n' in Character Lists of Dynamic Regexps
----------------------------------------------------------------

Some commercial versions of `awk' do not allow the newline character to
be used inside a character list for a dynamic regexp:

     $ awk '$0 ~ "[ \t\n]"'
     error--> awk: newline in character class [
     error--> ]...
     error-->  source line number 1
     error-->  context is
     error-->          >>>  <<<

But a newline in a regexp constant works with no problem:

     $ awk '$0 ~ /[ \t\n]/'
     here is a sample line
     -| here is a sample line
     Ctrl-d

`gawk' does not have this problem, and it isn't likely to occur often
in practice, but it's worth noting for future reference.


File: gawk.info,  Node: Locales,  Prev: Computed Regexps,  Up: Regexp

2.9 Where You Are Makes A Difference
====================================

Modern systems support the notion of "locales": a way to tell the
system about the local character set and language.  The current locale
setting can affect the way regexp matching works, often in surprising
ways.  In particular, many locales do case-insensitive matching, even
when you may have specified characters of only one particular case.

The following example uses the `sub' function, which does text
replacement (*note String Functions::).  Here, the intent is to remove
trailing uppercase characters:

     $ echo something1234abc | gawk '{ sub("[A-Z]*$", ""); print }'
     -| something1234

This output is unexpected, since the `abc' at the end of
`something1234abc' should not normally match `[A-Z]*'.  This result is
due to the locale setting (and thus you may not see it on your system).
There are two fixes.  The first is to use the POSIX character class
`[[:upper:]]', instead of `[A-Z]'.  The second is to change the locale
setting in the environment, before running `gawk', by using the shell
statements:

     LANG=C LC_ALL=C
     export LANG LC_ALL

The setting `C' forces `gawk' to behave in the traditional Unix manner,
where case distinctions do matter.  You may wish to put these
statements into your shell startup file, e.g., `$HOME/.profile'.

Similar considerations apply to other ranges.  For example, `["-/]' is
perfectly valid in ASCII, but is not valid in many Unicode locales,
such as `en_US.UTF-8'.  (In general, such ranges should be avoided;
either list the characters individually, or use a POSIX character class
such as `[[:punct:]]'.)

For the normal case of `RS = "\n"', the locale is largely irrelevant.
For other single byte record separators, using `LC_ALL=C' will give you
much better performance when reading records.  Otherwise, `gawk' has to
make several function calls, _per input character_ to find the record
terminator.


File: gawk.info,  Node: Reading Files,  Next: Printing,  Prev: Regexp,  Up: Top

3 Reading Input Files
*********************

In the typical `awk' program, all input is read either from the
standard input (by default, this is the keyboard, but often it is a
pipe from another command) or from files whose names you specify on the
`awk' command line.  If you specify input files, `awk' reads them in
order, processing all the data from one before going on to the next.
The name of the current input file can be found in the built-in variable
`FILENAME' (*note Built-in Variables::).

The input is read in units called "records", and is processed by the
rules of your program one record at a time.  By default, each record is
one line.  Each record is automatically split into chunks called
"fields".  This makes it more convenient for programs to work on the
parts of a record.

On rare occasions, you may need to use the `getline' command.  The
`getline' command is valuable, both because it can do explicit input
from any number of files, and because the files used with it do not
have to be named on the `awk' command line (*note Getline::).

* Menu:

* Records::                     Controlling how data is split into records.
* Fields::                      An introduction to fields.
* Nonconstant Fields::          Nonconstant Field Numbers.
* Changing Fields::             Changing the Contents of a Field.
* Field Separators::            The field separator and how to change it.
* Constant Size::               Reading constant width data.
* Multiple Line::               Reading multi-line records.
* Getline::                     Reading files under explicit program control
                                using the `getline' function.


File: gawk.info,  Node: Records,  Next: Fields,  Up: Reading Files

3.1 How Input Is Split into Records
===================================

The `awk' utility divides the input for your `awk' program into records
and fields.  `awk' keeps track of the number of records that have been
read so far from the current input file.  This value is stored in a
built-in variable called `FNR'.  It is reset to zero when a new file is
started.  Another built-in variable, `NR', is the total number of input
records read so far from all data files.  It starts at zero, but is
never automatically reset to zero.

Records are separated by a character called the "record separator".  By
default, the record separator is the newline character.  This is why
records are, by default, single lines.  A different character can be
used for the record separator by assigning the character to the
built-in variable `RS'.

Like any other variable, the value of `RS' can be changed in the `awk'
program with the assignment operator, `=' (*note Assignment Ops::).
The new record-separator character should be enclosed in quotation
marks, which indicate a string constant.  Often the right time to do
this is at the beginning of execution, before any input is processed,
so that the very first record is read with the proper separator.  To do
this, use the special `BEGIN' pattern (*note BEGIN/END::).  For example:

     awk 'BEGIN { RS = "/" }
          { print $0 }' BBS-list

changes the value of `RS' to `"/"', before reading any input.  This is
a string whose first character is a slash; as a result, records are
separated by slashes.  Then the input file is read, and the second rule
in the `awk' program (the action with no pattern) prints each record.
Because each `print' statement adds a newline at the end of its output,
this `awk' program copies the input with each slash changed to a
newline.  Here are the results of running the program on `BBS-list':

     $ awk 'BEGIN { RS = "/" }
     >      { print $0 }' BBS-list
     -| aardvark     555-5553     1200
     -| 300          B
     -| alpo-net     555-3412     2400
     -| 1200
     -| 300     A
     -| barfly       555-7685     1200
     -| 300          A
     -| bites        555-1675     2400
     -| 1200
     -| 300     A
     -| camelot      555-0542     300               C
     -| core         555-2912     1200
     -| 300          C
     -| fooey        555-1234     2400
     -| 1200
     -| 300     B
     -| foot         555-6699     1200
     -| 300          B
     -| macfoo       555-6480     1200
     -| 300          A
     -| sdace        555-3430     2400
     -| 1200
     -| 300     A
     -| sabafoo      555-2127     1200
     -| 300          C
     -|

Note that the entry for the `camelot' BBS is not split.  In the
original data file (*note Sample Data Files::), the line looks like
this:

     camelot      555-0542     300               C

It has one baud rate only, so there are no slashes in the record,
unlike the others which have two or more baud rates.  In fact, this
record is treated as part of the record for the `core' BBS; the newline
separating them in the output is the original newline in the data file,
not the one added by `awk' when it printed the record!

Another way to change the record separator is on the command line,
using the variable-assignment feature (*note Other Arguments::):

     awk '{ print $0 }' RS="/" BBS-list

This sets `RS' to `/' before processing `BBS-list'.

Using an unusual character such as `/' for the record separator
produces correct behavior in the vast majority of cases.  However, the
following (extreme) pipeline prints a surprising `1':

     $ echo | awk 'BEGIN { RS = "a" } ; { print NF }'
     -| 1

There is one field, consisting of a newline.  The value of the built-in
variable `NF' is the number of fields in the current record.

Reaching the end of an input file terminates the current input record,
even if the last character in the file is not the character in `RS'.
(d.c.)

The empty string `""' (a string without any characters) has a special
meaning as the value of `RS'. It means that records are separated by
one or more blank lines and nothing else.  *Note Multiple Line::, for
more details.

If you change the value of `RS' in the middle of an `awk' run, the new
value is used to delimit subsequent records, but the record currently
being processed, as well as records already processed, are not affected.

After the end of the record has been determined, `gawk' sets the
variable `RT' to the text in the input that matched `RS'.  When using
`gawk', the value of `RS' is not limited to a one-character string.  It
can be any regular expression (*note Regexp::).  In general, each record
ends at the next string that matches the regular expression; the next
record starts at the end of the matching string.  This general rule is
actually at work in the usual case, where `RS' contains just a newline:
a record ends at the beginning of the next matching string (the next
newline in the input), and the following record starts just after the
end of this string (at the first character of the following line).  The
newline, because it matches `RS', is not part of either record.

When `RS' is a single character, `RT' contains the same single
character. However, when `RS' is a regular expression, `RT' contains
the actual input text that matched the regular expression.

The following example illustrates both of these features.  It sets `RS'
equal to a regular expression that matches either a newline or a series
of one or more uppercase letters with optional leading and/or trailing
whitespace:

     $ echo record 1 AAAA record 2 BBBB record 3 |
     > gawk 'BEGIN { RS = "\n|( *[[:upper:]]+ *)" }
     >             { print "Record =", $0, "and RT =", RT }'
     -| Record = record 1 and RT =  AAAA
     -| Record = record 2 and RT =  BBBB
     -| Record = record 3 and RT =
     -|

The final line of output has an extra blank line. This is because the
value of `RT' is a newline, and the `print' statement supplies its own
terminating newline.  *Note Simple Sed::, for a more useful example of
`RS' as a regexp and `RT'.

If you set `RS' to a regular expression that allows optional trailing
text, such as `RS = "abc(XYZ)?"' it is possible, due to implementation
constraints, that `gawk' may match the leading part of the regular
expression, but not the trailing part, particularly if the input text
that could match the trailing part is fairly long.  `gawk' attempts to
avoid this problem, but currently, there's no guarantee that this will
never happen.

     NOTE: Remember that in `awk', the `^' and `$' anchor
     metacharacters match the beginning and end of a _string_, and not
     the beginning and end of a _line_.  As a result, something like
     `RS = "^[[:upper:]]"' can only match at the beginning of a file.
     This is because `gawk' views the input file as one long string
     that happens to contain newline characters in it.  It is thus best
     to avoid anchor characters in the value of `RS'.

The use of `RS' as a regular expression and the `RT' variable are
`gawk' extensions; they are not available in compatibility mode (*note
Options::).  In compatibility mode, only the first character of the
value of `RS' is used to determine the end of the record.

Advanced Notes: `RS = "\0"' Is Not Portable
-------------------------------------------

There are times when you might want to treat an entire data file as a
single record.  The only way to make this happen is to give `RS' a
value that you know doesn't occur in the input file.  This is hard to
do in a general way, such that a program always works for arbitrary
input files.

You might think that for text files, the NUL character, which consists
of a character with all bits equal to zero, is a good value to use for
`RS' in this case:

     BEGIN { RS = "\0" }  # whole file becomes one record?

`gawk' in fact accepts this, and uses the NUL character for the record
separator.  However, this usage is _not_ portable to other `awk'
implementations.

All other `awk' implementations(1) store strings internally as C-style
strings.  C strings use the NUL character as the string terminator.  In
effect, this means that `RS = "\0"' is the same as `RS = ""'.
(d.c.)

The best way to treat a whole file as a single record is to simply read
the file in, one record at a time, concatenating each record onto the
end of the previous ones.

---------- Footnotes ----------

(1) At least that we know about.


File: gawk.info,  Node: Fields,  Next: Nonconstant Fields,  Prev: Records,  Up: Reading Files

3.2 Examining Fields
====================

When `awk' reads an input record, the record is automatically "parsed"
or separated by the interpreter into chunks called "fields".  By
default, fields are separated by "whitespace", like words in a line.
Whitespace in `awk' means any string of one or more spaces, tabs, or
newlines;(1) other characters, such as formfeed, vertical tab, etc.
that are considered whitespace by other languages, are _not_ considered
whitespace by `awk'.

The purpose of fields is to make it more convenient for you to refer to
these pieces of the record.  You don't have to use them--you can
operate on the whole record if you want--but fields are what make
simple `awk' programs so powerful.

A dollar-sign (`$') is used to refer to a field in an `awk' program,
followed by the number of the field you want.  Thus, `$1' refers to the
first field, `$2' to the second, and so on.  (Unlike the Unix shells,
the field numbers are not limited to single digits.  `$127' is the one
hundred twenty-seventh field in the record.)  For example, suppose the
following is a line of input:

     This seems like a pretty nice example.

Here the first field, or `$1', is `This', the second field, or `$2', is
`seems', and so on.  Note that the last field, `$7', is `example.'.
Because there is no space between the `e' and the `.', the period is
considered part of the seventh field.

`NF' is a built-in variable whose value is the number of fields in the
current record.  `awk' automatically updates the value of `NF' each
time it reads a record.  No matter how many fields there are, the last
field in a record can be represented by `$NF'.  So, `$NF' is the same
as `$7', which is `example.'.  If you try to reference a field beyond
the last one (such as `$8' when the record has only seven fields), you
get the empty string.  (If used in a numeric operation, you get zero.)

The use of `$0', which looks like a reference to the "zero-th" field, is
a special case: it represents the whole input record when you are not
interested in specific fields.  Here are some more examples:

     $ awk '$1 ~ /foo/ { print $0 }' BBS-list
     -| fooey        555-1234     2400/1200/300     B
     -| foot         555-6699     1200/300          B
     -| macfoo       555-6480     1200/300          A
     -| sabafoo      555-2127     1200/300          C

This example prints each record in the file `BBS-list' whose first
field contains the string `foo'.  The operator `~' is called a
"matching operator" (*note Regexp Usage::); it tests whether a string
(here, the field `$1') matches a given regular expression.

By contrast, the following example looks for `foo' in _the entire
record_ and prints the first field and the last field for each matching
input record:

     $ awk '/foo/ { print $1, $NF }' BBS-list
     -| fooey B
     -| foot B
     -| macfoo A
     -| sabafoo C

---------- Footnotes ----------

(1) In POSIX `awk', newlines are not considered whitespace for
separating fields.


File: gawk.info,  Node: Nonconstant Fields,  Next: Changing Fields,  Prev: Fields,  Up: Reading Files

3.3 Nonconstant Field Numbers
=============================

The number of a field does not need to be a constant.  Any expression in
the `awk' language can be used after a `$' to refer to a field.  The
value of the expression specifies the field number.  If the value is a
string, rather than a number, it is converted to a number.  Consider
this example:

     awk '{ print $NR }'

Recall that `NR' is the number of records read so far: one in the first
record, two in the second, etc.  So this example prints the first field
of the first record, the second field of the second record, and so on.
For the twentieth record, field number 20 is printed; most likely, the
record has fewer than 20 fields, so this prints a blank line.  Here is
another example of using expressions as field numbers:

     awk '{ print $(2*2) }' BBS-list

`awk' evaluates the expression `(2*2)' and uses its value as the number
of the field to print.  The `*' sign represents multiplication, so the
expression `2*2' evaluates to four.  The parentheses are used so that
the multiplication is done before the `$' operation; they are necessary
whenever there is a binary operator in the field-number expression.
This example, then, prints the hours of operation (the fourth field)
for every line of the file `BBS-list'.  (All of the `awk' operators are
listed, in order of decreasing precedence, in *Note Precedence::.)

If the field number you compute is zero, you get the entire record.
Thus, `$(2-2)' has the same value as `$0'.  Negative field numbers are
not allowed; trying to reference one usually terminates the program.
(The POSIX standard does not define what happens when you reference a
negative field number.  `gawk' notices this and terminates your
program.  Other `awk' implementations may behave differently.)

As mentioned in *Note Fields::, `awk' stores the current record's
number of fields in the built-in variable `NF' (also *note Built-in
Variables::).  The expression `$NF' is not a special feature--it is the
direct consequence of evaluating `NF' and using its value as a field
number.


File: gawk.info,  Node: Changing Fields,  Next: Field Separators,  Prev: Nonconstant Fields,  Up: Reading Files

3.4 Changing the Contents of a Field
====================================

The contents of a field, as seen by `awk', can be changed within an
`awk' program; this changes what `awk' perceives as the current input
record.  (The actual input is untouched; `awk' _never_ modifies the
input file.)  Consider the following example and its output:

     $ awk '{ nboxes = $3 ; $3 = $3 - 10
     >        print nboxes, $3 }' inventory-shipped
     -| 25 15
     -| 32 22
     -| 24 14
     ...

The program first saves the original value of field three in the
variable `nboxes'.  The `-' sign represents subtraction, so this
program reassigns field three, `$3', as the original value of field
three minus ten: `$3 - 10'.  (*Note Arithmetic Ops::.)  Then it prints
the original and new values for field three.  (Someone in the warehouse
made a consistent mistake while inventorying the red boxes.)

For this to work, the text in field `$3' must make sense as a number;
the string of characters must be converted to a number for the computer
to do arithmetic on it.  The number resulting from the subtraction is
converted back to a string of characters that then becomes field three.
*Note Conversion::.

When the value of a field is changed (as perceived by `awk'), the text
of the input record is recalculated to contain the new field where the
old one was.  In other words, `$0' changes to reflect the altered
field.  Thus, this program prints a copy of the input file, with 10
subtracted from the second field of each line:

     $ awk '{ $2 = $2 - 10; print $0 }' inventory-shipped
     -| Jan 3 25 15 115
     -| Feb 5 32 24 226
     -| Mar 5 24 34 228
     ...

It is also possible to also assign contents to fields that are out of
range.  For example:

     $ awk '{ $6 = ($5 + $4 + $3 + $2)
     >        print $6 }' inventory-shipped
     -| 168
     -| 297
     -| 301
     ...

We've just created `$6', whose value is the sum of fields `$2', `$3',
`$4', and `$5'.  The `+' sign represents addition.  For the file
`inventory-shipped', `$6' represents the total number of parcels
shipped for a particular month.

Creating a new field changes `awk''s internal copy of the current input
record, which is the value of `$0'.  Thus, if you do `print $0' after
adding a field, the record printed includes the new field, with the
appropriate number of field separators between it and the previously
existing fields.

This recomputation affects and is affected by `NF' (the number of
fields; *note Fields::).  For example, the value of `NF' is set to the
number of the highest field you create.  The exact format of `$0' is
also affected by a feature that has not been discussed yet: the "output
field separator", `OFS', used to separate the fields (*note Output
Separators::).

Note, however, that merely _referencing_ an out-of-range field does
_not_ change the value of either `$0' or `NF'.  Referencing an
out-of-range field only produces an empty string.  For example:

     if ($(NF+1) != "")
         print "can't happen"
     else
         print "everything is normal"

should print `everything is normal', because `NF+1' is certain to be
out of range.  (*Note If Statement::, for more information about
`awk''s `if-else' statements.  *Note Typing and Comparison::, for more
information about the `!=' operator.)

It is important to note that making an assignment to an existing field
changes the value of `$0' but does not change the value of `NF', even
when you assign the empty string to a field.  For example:

     $ echo a b c d | awk '{ OFS = ":"; $2 = ""
     >                       print $0; print NF }'
     -| a::c:d
     -| 4

The field is still there; it just has an empty value, denoted by the
two colons between `a' and `c'.  This example shows what happens if you
create a new field:

     $ echo a b c d | awk '{ OFS = ":"; $2 = ""; $6 = "new"
     >                       print $0; print NF }'
     -| a::c:d::new
     -| 6

The intervening field, `$5', is created with an empty value (indicated
by the second pair of adjacent colons), and `NF' is updated with the
value six.

Decrementing `NF' throws away the values of the fields after the new
value of `NF' and recomputes `$0'.  (d.c.)  Here is an example:

     $ echo a b c d e f | awk '{ print "NF =", NF;
     >                            NF = 3; print $0 }'
     -| NF = 6
     -| a b c

*Caution:* Some versions of `awk' don't rebuild `$0' when `NF' is
decremented. Caveat emptor.

Finally, there are times when it is convenient to force `awk' to
rebuild the entire record, using the current value of the fields and
`OFS'.  To do this, use the seemingly innocuous assignment:

     $1 = $1   # force record to be reconstituted
     print $0  # or whatever else with $0

This forces `awk' rebuild the record.  It does help to add a comment,
as we've shown here.

There is a flip side to the relationship between `$0' and the fields.
Any assignment to `$0' causes the record to be reparsed into fields
using the _current_ value of `FS'.  This also applies to any built-in
function that updates `$0', such as `sub' and `gsub' (*note String
Functions::).


File: gawk.info,  Node: Field Separators,  Next: Constant Size,  Prev: Changing Fields,  Up: Reading Files

3.5 Specifying How Fields Are Separated
=======================================

* Menu:

* Regexp Field Splitting::       Using regexps as the field separator.
* Single Character Fields::      Making each character a separate field.
* Command Line Field Separator:: Setting `FS' from the command-line.
* Field Splitting Summary::      Some final points and a summary table.

The "field separator", which is either a single character or a regular
expression, controls the way `awk' splits an input record into fields.
`awk' scans the input record for character sequences that match the
separator; the fields themselves are the text between the matches.

In the examples that follow, we use the bullet symbol (*) to represent
spaces in the output.  If the field separator is `oo', then the
following line:

     moo goo gai pan

is split into three fields: `m', `*g', and `*gai*pan'.  Note the
leading spaces in the values of the second and third fields.

The field separator is represented by the built-in variable `FS'.
Shell programmers take note:  `awk' does _not_ use the name `IFS' that
is used by the POSIX-compliant shells (such as the Unix Bourne shell,
`sh', or `bash').

The value of `FS' can be changed in the `awk' program with the
assignment operator, `=' (*note Assignment Ops::).  Often the right
time to do this is at the beginning of execution before any input has
been processed, so that the very first record is read with the proper
separator.  To do this, use the special `BEGIN' pattern (*note
BEGIN/END::).  For example, here we set the value of `FS' to the string
`","':

     awk 'BEGIN { FS = "," } ; { print $2 }'

Given the input line:

     John Q. Smith, 29 Oak St., Walamazoo, MI 42139

this `awk' program extracts and prints the string `*29*Oak*St.'.

Sometimes the input data contains separator characters that don't
separate fields the way you thought they would.  For instance, the
person's name in the example we just used might have a title or suffix
attached, such as:

     John Q. Smith, LXIX, 29 Oak St., Walamazoo, MI 42139

The same program would extract `*LXIX', instead of `*29*Oak*St.'.  If
you were expecting the program to print the address, you would be
surprised.  The moral is to choose your data layout and separator
characters carefully to prevent such problems.  (If the data is not in
a form that is easy to process, perhaps you can massage it first with a
separate `awk' program.)

Fields are normally separated by whitespace sequences (spaces, tabs,
and newlines), not by single spaces.  Two spaces in a row do not
delimit an empty field.  The default value of the field separator `FS'
is a string containing a single space, `" "'.  If `awk' interpreted
this value in the usual way, each space character would separate
fields, so two spaces in a row would make an empty field between them.
The reason this does not happen is that a single space as the value of
`FS' is a special case--it is taken to specify the default manner of
delimiting fields.

If `FS' is any other single character, such as `","', then each
occurrence of that character separates two fields.  Two consecutive
occurrences delimit an empty field.  If the character occurs at the
beginning or the end of the line, that too delimits an empty field.  The
space character is the only single character that does not follow these
rules.


File: gawk.info,  Node: Regexp Field Splitting,  Next: Single Character Fields,  Up: Field Separators

3.5.1 Using Regular Expressions to Separate Fields
--------------------------------------------------

The previous node discussed the use of single characters or simple
strings as the value of `FS'.  More generally, the value of `FS' may be
a string containing any regular expression.  In this case, each match
in the record for the regular expression separates fields.  For
example, the assignment:

     FS = ", \t"

makes every area of an input line that consists of a comma followed by a
space and a TAB into a field separator.  (`\t' is an "escape sequence"
that stands for a TAB; *note Escape Sequences::, for the complete list
of similar escape sequences.)

For a less trivial example of a regular expression, try using single
spaces to separate fields the way single commas are used.  `FS' can be
set to `"[ ]"' (left bracket, space, right bracket).  This regular
expression matches a single space and nothing else (*note Regexp::).

There is an important difference between the two cases of `FS = " "' (a
single space) and `FS = "[ \t\n]+"' (a regular expression matching one
or more spaces, tabs, or newlines).  For both values of `FS', fields
are separated by "runs" (multiple adjacent occurrences) of spaces, tabs,
and/or newlines.  However, when the value of `FS' is `" "', `awk' first
strips leading and trailing whitespace from the record and then decides
where the fields are.  For example, the following pipeline prints `b':

     $ echo ' a b c d ' | awk '{ print $2 }'
     -| b

However, this pipeline prints `a' (note the extra spaces around each
letter):

     $ echo ' a  b  c  d ' | awk 'BEGIN { FS = "[ \t\n]+" }
     >                                  { print $2 }'
     -| a

In this case, the first field is "null" or empty.

The stripping of leading and trailing whitespace also comes into play
whenever `$0' is recomputed.  For instance, study this pipeline:

     $ echo '   a b c d' | awk '{ print; $2 = $2; print }'
     -|    a b c d
     -| a b c d

The first `print' statement prints the record as it was read, with
leading whitespace intact.  The assignment to `$2' rebuilds `$0' by
concatenating `$1' through `$NF' together, separated by the value of
`OFS'.  Because the leading whitespace was ignored when finding `$1',
it is not part of the new `$0'.  Finally, the last `print' statement
prints the new `$0'.


File: gawk.info,  Node: Single Character Fields,  Next: Command Line Field Separator,  Prev: Regexp Field Splitting,  Up: Field Separators

3.5.2 Making Each Character a Separate Field
--------------------------------------------

There are times when you may want to examine each character of a record
separately.  This can be done in `gawk' by simply assigning the null
string (`""') to `FS'. In this case, each individual character in the
record becomes a separate field.  For example:

     $ echo a b | gawk 'BEGIN { FS = "" }
     >                  {
     >                      for (i = 1; i <= NF; i = i + 1)
     >                          print "Field", i, "is", $i
     >                  }'
     -| Field 1 is a
     -| Field 2 is
     -| Field 3 is b

Traditionally, the behavior of `FS' equal to `""' was not defined.  In
this case, most versions of Unix `awk' simply treat the entire record
as only having one field.  (d.c.)  In compatibility mode (*note
Options::), if `FS' is the null string, then `gawk' also behaves this
way.


File: gawk.info,  Node: Command Line Field Separator,  Next: Field Splitting Summary,  Prev: Single Character Fields,  Up: Field Separators

3.5.3 Setting `FS' from the Command Line
----------------------------------------

`FS' can be set on the command line.  Use the `-F' option to do so.
For example:

     awk -F, 'PROGRAM' INPUT-FILES

sets `FS' to the `,' character.  Notice that the option uses an
uppercase `F' instead of a lowercase `f'. The latter option (`-f')
specifies a file containing an `awk' program.  Case is significant in
command-line options: the `-F' and `-f' options have nothing to do with
each other.  You can use both options at the same time to set the `FS'
variable _and_ get an `awk' program from a file.

The value used for the argument to `-F' is processed in exactly the
same way as assignments to the built-in variable `FS'.  Any special
characters in the field separator must be escaped appropriately.  For
example, to use a `\' as the field separator on the command line, you
would have to type:

     # same as FS = "\\"
     awk -F\\\\ '...' files ...

Because `\' is used for quoting in the shell, `awk' sees `-F\\'.  Then
`awk' processes the `\\' for escape characters (*note Escape
Sequences::), finally yielding a single `\' to use for the field
separator.

As a special case, in compatibility mode (*note Options::), if the
argument to `-F' is `t', then `FS' is set to the TAB character.  If you
type `-F\t' at the shell, without any quotes, the `\' gets deleted, so
`awk' figures that you really want your fields to be separated with
tabs and not `t's.  Use `-v FS="t"' or `-F"[t]"' on the command line if
you really do want to separate your fields with `t's.

For example, let's use an `awk' program file called `baud.awk' that
contains the pattern `/300/' and the action `print $1':

     /300/   { print $1 }

Let's also set `FS' to be the `-' character and run the program on the
file `BBS-list'.  The following command prints a list of the names of
the bulletin boards that operate at 300 baud and the first three digits
of their phone numbers:

     $ awk -F- -f baud.awk BBS-list
     -| aardvark     555
     -| alpo
     -| barfly       555
     -| bites        555
     -| camelot      555
     -| core         555
     -| fooey        555
     -| foot         555
     -| macfoo       555
     -| sdace        555
     -| sabafoo      555

Note the second line of output.  The second line in the original file
looked like this:

     alpo-net     555-3412     2400/1200/300     A

The `-' as part of the system's name was used as the field separator,
instead of the `-' in the phone number that was originally intended.
This demonstrates why you have to be careful in choosing your field and
record separators.

Perhaps the most common use of a single character as the field
separator occurs when processing the Unix system password file.  On
many Unix systems, each user has a separate entry in the system password
file, one line per user.  The information in these lines is separated
by colons.  The first field is the user's logon name and the second is
the user's (encrypted or shadow) password.  A password file entry might
look like this:

     arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/bash

The following program searches the system password file and prints the
entries for users who have no password:

     awk -F: '$2 == ""' /etc/passwd


File: gawk.info,  Node: Field Splitting Summary,  Prev: Command Line Field Separator,  Up: Field Separators

3.5.4 Field-Splitting Summary
-----------------------------

It is important to remember that when you assign a string constant as
the value of `FS', it undergoes normal `awk' string processing.  For
example, with Unix `awk' and `gawk', the assignment `FS = "\.."'
assigns the character string `".."' to `FS' (the backslash is
stripped).  This creates a regexp meaning "fields are separated by
occurrences of any two characters."  If instead you want fields to be
separated by a literal period followed by any single character, use `FS
= "\\.."'.

The following table summarizes how fields are split, based on the value
of `FS' (`==' means "is equal to"):

`FS == " "'
     Fields are separated by runs of whitespace.  Leading and trailing
     whitespace are ignored.  This is the default.

`FS == ANY OTHER SINGLE CHARACTER'
     Fields are separated by each occurrence of the character.  Multiple
     successive occurrences delimit empty fields, as do leading and
     trailing occurrences.  The character can even be a regexp
     metacharacter; it does not need to be escaped.

`FS == REGEXP'
     Fields are separated by occurrences of characters that match
     REGEXP.  Leading and trailing matches of REGEXP delimit empty
     fields.

`FS == ""'
     Each individual character in the record becomes a separate field.
     (This is a `gawk' extension; it is not specified by the POSIX
     standard.)

Advanced Notes: Changing `FS' Does Not Affect the Fields
--------------------------------------------------------

According to the POSIX standard, `awk' is supposed to behave as if each
record is split into fields at the time it is read.  In particular,
this means that if you change the value of `FS' after a record is read,
the value of the fields (i.e., how they were split) should reflect the
old value of `FS', not the new one.

However, many implementations of `awk' do not work this way.  Instead,
they defer splitting the fields until a field is actually referenced.
The fields are split using the _current_ value of `FS'!  (d.c.)  This
behavior can be difficult to diagnose. The following example
illustrates the difference between the two methods.  (The `sed'(1)
command prints just the first line of `/etc/passwd'.)

     sed 1q /etc/passwd | awk '{ FS = ":" ; print $1 }'

which usually prints:

     root

on an incorrect implementation of `awk', while `gawk' prints something
like:

     root:nSijPlPhZZwgE:0:0:Root:/:

Advanced Notes: `FS' and `IGNORECASE'
-------------------------------------

The `IGNORECASE' variable (*note User-modified::) affects field
splitting _only_ when the value of `FS' is a regexp.  It has no effect
when `FS' is a single character, even if that character is a letter.
Thus, in the following code:

     FS = "c"
     IGNORECASE = 1
     $0 = "aCa"
     print $1

The output is `aCa'.  If you really want to split fields on an
alphabetic character while ignoring case, use a regexp that will do it
for you.  E.g., `FS = "[c]"'.  In this case, `IGNORECASE' will take
effect.

---------- Footnotes ----------

(1) The `sed' utility is a "stream editor."  Its behavior is also
defined by the POSIX standard.


File: gawk.info,  Node: Constant Size,  Next: Multiple Line,  Prev: Field Separators,  Up: Reading Files

3.6 Reading Fixed-Width Data
============================

(This minor node discusses an advanced feature of `awk'.  If you are a
novice `awk' user, you might want to skip it on the first reading.)

`gawk' version 2.13 introduced a facility for dealing with fixed-width
fields with no distinctive field separator.  For example, data of this
nature arises in the input for old Fortran programs where numbers are
run together, or in the output of programs that did not anticipate the
use of their output as input for other programs.

An example of the latter is a table where all the columns are lined up
by the use of a variable number of spaces and _empty fields are just
spaces_.  Clearly, `awk''s normal field splitting based on `FS' does
not work well in this case.  Although a portable `awk' program can use
a series of `substr' calls on `$0' (*note String Functions::), this is
awkward and inefficient for a large number of fields.

The splitting of an input record into fixed-width fields is specified by
assigning a string containing space-separated numbers to the built-in
variable `FIELDWIDTHS'.  Each number specifies the width of the field,
_including_ columns between fields.  If you want to ignore the columns
between fields, you can specify the width as a separate field that is
subsequently ignored.  It is a fatal error to supply a field width that
is not a positive number.  The following data is the output of the Unix
`w' utility.  It is useful to illustrate the use of `FIELDWIDTHS':

      10:06pm  up 21 days, 14:04,  23 users
     User     tty       login  idle   JCPU   PCPU  what
     hzuo     ttyV0     8:58pm            9      5  vi p24.tex
     hzang    ttyV3     6:37pm    50                -csh
     eklye    ttyV5     9:53pm            7      1  em thes.tex
     dportein ttyV6     8:17pm  1:47                -csh
     gierd    ttyD3    10:00pm     1                elm
     dave     ttyD4     9:47pm            4      4  w
     brent    ttyp0    26Jun91  4:46  26:46   4:41  bash
     dave     ttyq4    26Jun9115days     46     46  wnewmail

The following program takes the above input, converts the idle time to
number of seconds, and prints out the first two fields and the
calculated idle time:

     NOTE: This program uses a number of `awk' features that haven't
     been introduced yet.

     BEGIN  { FIELDWIDTHS = "9 6 10 6 7 7 35" }
     NR > 2 {
         idle = $4
         sub(/^  */, "", idle)   # strip leading spaces
         if (idle == "")
             idle = 0
         if (idle ~ /:/) {
             split(idle, t, ":")
             idle = t[1] * 60 + t[2]
         }
         if (idle ~ /days/)
             idle *= 24 * 60 * 60

         print $1, $2, idle
     }

Running the program on the data produces the following results:

     hzuo      ttyV0  0
     hzang     ttyV3  50
     eklye     ttyV5  0
     dportein  ttyV6  107
     gierd     ttyD3  1
     dave      ttyD4  0
     brent     ttyp0  286
     dave      ttyq4  1296000

Another (possibly more practical) example of fixed-width input data is
the input from a deck of balloting cards.  In some parts of the United
States, voters mark their choices by punching holes in computer cards.
These cards are then processed to count the votes for any particular
candidate or on any particular issue.  Because a voter may choose not to
vote on some issue, any column on the card may be empty.  An `awk'
program for processing such data could use the `FIELDWIDTHS' feature to
simplify reading the data.  (Of course, getting `gawk' to run on a
system with card readers is another story!)

Assigning a value to `FS' causes `gawk' to use `FS' for field splitting
again.  Use `FS = FS' to make this happen, without having to know the
current value of `FS'.  In order to tell which kind of field splitting
is in effect, use `PROCINFO["FS"]' (*note Auto-set::).  The value is
`"FS"' if regular field splitting is being used, or it is
`"FIELDWIDTHS"' if fixed-width field splitting is being used:

     if (PROCINFO["FS"] == "FS")
         REGULAR FIELD SPLITTING ...
     else
         FIXED-WIDTH FIELD SPLITTING ...

This information is useful when writing a function that needs to
temporarily change `FS' or `FIELDWIDTHS', read some records, and then
restore the original settings (*note Passwd Functions::, for an example
of such a function).


File: gawk.info,  Node: Multiple Line,  Next: Getline,  Prev: Constant Size,  Up: Reading Files

3.7 Multiple-Line Records
=========================

In some databases, a single line cannot conveniently hold all the
information in one entry.  In such cases, you can use multiline
records.  The first step in doing this is to choose your data format.

One technique is to use an unusual character or string to separate
records.  For example, you could use the formfeed character (written
`\f' in `awk', as in C) to separate them, making each record a page of
the file.  To do this, just set the variable `RS' to `"\f"' (a string
containing the formfeed character).  Any other character could equally
well be used, as long as it won't be part of the data in a record.

Another technique is to have blank lines separate records.  By a special
dispensation, an empty string as the value of `RS' indicates that
records are separated by one or more blank lines.  When `RS' is set to
the empty string, each record always ends at the first blank line
encountered.  The next record doesn't start until the first nonblank
line that follows.  No matter how many blank lines appear in a row, they
all act as one record separator.  (Blank lines must be completely
empty; lines that contain only whitespace do not count.)

You can achieve the same effect as `RS = ""' by assigning the string
`"\n\n+"' to `RS'. This regexp matches the newline at the end of the
record and one or more blank lines after the record.  In addition, a
regular expression always matches the longest possible sequence when
there is a choice (*note Leftmost Longest::).  So the next record
doesn't start until the first nonblank line that follows--no matter how
many blank lines appear in a row, they are considered one record
separator.

There is an important difference between `RS = ""' and `RS = "\n\n+"'.
In the first case, leading newlines in the input data file are ignored,
and if a file ends without extra blank lines after the last record, the
final newline is removed from the record.  In the second case, this
special processing is not done.  (d.c.)

Now that the input is separated into records, the second step is to
separate the fields in the record.  One way to do this is to divide each
of the lines into fields in the normal manner.  This happens by default
as the result of a special feature.  When `RS' is set to the empty
string, _and_ `FS' is a set to a single character, the newline
character _always_ acts as a field separator.  This is in addition to
whatever field separations result from `FS'.(1)

The original motivation for this special exception was probably to
provide useful behavior in the default case (i.e., `FS' is equal to
`" "').  This feature can be a problem if you really don't want the
newline character to separate fields, because there is no way to
prevent it.  However, you can work around this by using the `split'
function to break up the record manually (*note String Functions::).
If you have a single character field separator, you can work around the
special feature in a different way, by making `FS' into a regexp for
that single character.  For example, if the field separator is a
percent character, instead of `FS = "%"', use `FS = "[%]"'.

Another way to separate fields is to put each field on a separate line:
to do this, just set the variable `FS' to the string `"\n"'.  (This
single character seperator matches a single newline.)  A practical
example of a data file organized this way might be a mailing list,
where each entry is separated by blank lines.  Consider a mailing list
in a file named `addresses', which looks like this:

     Jane Doe
     123 Main Street
     Anywhere, SE 12345-6789

     John Smith
     456 Tree-lined Avenue
     Smallville, MW 98765-4321
     ...

A simple program to process this file is as follows:

     # addrs.awk --- simple mailing list program

     # Records are separated by blank lines.
     # Each line is one field.
     BEGIN { RS = "" ; FS = "\n" }

     {
           print "Name is:", $1
           print "Address is:", $2
           print "City and State are:", $3
           print ""
     }

Running the program produces the following output:

     $ awk -f addrs.awk addresses
     -| Name is: Jane Doe
     -| Address is: 123 Main Street
     -| City and State are: Anywhere, SE 12345-6789
     -|
     -| Name is: John Smith
     -| Address is: 456 Tree-lined Avenue
     -| City and State are: Smallville, MW 98765-4321
     -|
     ...

*Note Labels Program::, for a more realistic program that deals with
address lists.  The following table summarizes how records are split,
based on the value of `RS'.  (`==' means "is equal to.")

`RS == "\n"'
     Records are separated by the newline character (`\n').  In effect,
     every line in the data file is a separate record, including blank
     lines.  This is the default.

`RS == ANY SINGLE CHARACTER'
     Records are separated by each occurrence of the character.
     Multiple successive occurrences delimit empty records.

`RS == ""'
     Records are separated by runs of blank lines.  The newline
     character always serves as a field separator, in addition to
     whatever value `FS' may have. Leading and trailing newlines in a
     file are ignored.

`RS == REGEXP'
     Records are separated by occurrences of characters that match
     REGEXP.  Leading and trailing matches of REGEXP delimit empty
     records.  (This is a `gawk' extension; it is not specified by the
     POSIX standard.)

In all cases, `gawk' sets `RT' to the input text that matched the value
specified by `RS'.

---------- Footnotes ----------

(1) When `FS' is the null string (`""') or a regexp, this special
feature of `RS' does not apply.  It does apply to the default field
separator of a single space: `FS = " "'.


File: gawk.info,  Node: Getline,  Prev: Multiple Line,  Up: Reading Files

3.8 Explicit Input with `getline'
=================================

So far we have been getting our input data from `awk''s main input
stream--either the standard input (usually your terminal, sometimes the
output from another program) or from the files specified on the command
line.  The `awk' language has a special built-in command called
`getline' that can be used to read input under your explicit control.

The `getline' command is used in several different ways and should
_not_ be used by beginners.  The examples that follow the explanation
of the `getline' command include material that has not been covered
yet.  Therefore, come back and study the `getline' command _after_ you
have reviewed the rest of this Info file and have a good knowledge of
how `awk' works.

The `getline' command returns one if it finds a record and zero if it
encounters the end of the file.  If there is some error in getting a
record, such as a file that cannot be opened, then `getline' returns
-1.  In this case, `gawk' sets the variable `ERRNO' to a string
describing the error that occurred.

In the following examples, COMMAND stands for a string value that
represents a shell command.

* Menu:

* Plain Getline::               Using `getline' with no arguments.
* Getline/Variable::            Using `getline' into a variable.
* Getline/File::                Using `getline' from a file.
* Getline/Variable/File::       Using `getline' into a variable from a
                                file.
* Getline/Pipe::                Using `getline' from a pipe.
* Getline/Variable/Pipe::       Using `getline' into a variable from a
                                pipe.
* Getline/Coprocess::           Using `getline' from a coprocess.
* Getline/Variable/Coprocess::  Using `getline' into a variable from a
                                coprocess.
* Getline Notes::               Important things to know about `getline'.
* Getline Summary::             Summary of `getline' Variants.


File: gawk.info,  Node: Plain Getline,  Next: Getline/Variable,  Up: Getline

3.8.1 Using `getline' with No Arguments
---------------------------------------

The `getline' command can be used without arguments to read input from
the current input file.  All it does in this case is read the next
input record and split it up into fields.  This is useful if you've
finished processing the current record, but want to do some special
processing on the next record _right now_.  For example:

     {
          if ((t = index($0, "/*")) != 0) {
               # value of `tmp' will be "" if t is 1
               tmp = substr($0, 1, t - 1)
               u = index(substr($0, t + 2), "*/")
               while (u == 0) {
                    if (getline <= 0) {
                         m = "unexpected EOF or error"
                         m = (m ": " ERRNO)
                         print m > "/dev/stderr"
                         exit
                    }
                    t = -1
                    u = index($0, "*/")
               }
               # substr expression will be "" if */
               # occurred at end of line
               $0 = tmp substr($0, u + 2)
          }
          print $0
     }

This `awk' program deletes all C-style comments (`/* ...  */') from the
input.  By replacing the `print $0' with other statements, you could
perform more complicated processing on the decommented input, such as
searching for matches of a regular expression.  (This program has a
subtle problem--it does not work if one comment ends and another begins
on the same line.)

This form of the `getline' command sets `NF', `NR', `FNR', and the
value of `$0'.

     NOTE: The new value of `$0' is used to test the patterns of any
     subsequent rules.  The original value of `$0' that triggered the
     rule that executed `getline' is lost.  By contrast, the `next'
     statement reads a new record but immediately begins processing it
     normally, starting with the first rule in the program.  *Note Next
     Statement::.


File: gawk.info,  Node: Getline/Variable,  Next: Getline/File,  Prev: Plain Getline,  Up: Getline

3.8.2 Using `getline' into a Variable
-------------------------------------

You can use `getline VAR' to read the next record from `awk''s input
into the variable VAR.  No other processing is done.  For example,
suppose the next line is a comment or a special string, and you want to
read it without triggering any rules.  This form of `getline' allows
you to read that line and store it in a variable so that the main
read-a-line-and-check-each-rule loop of `awk' never sees it.  The
following example swaps every two lines of input:

     {
          if ((getline tmp) > 0) {
               print tmp
               print $0
          } else
               print $0
     }

It takes the following list:

     wan
     tew
     free
     phore

and produces these results:

     tew
     wan
     phore
     free

The `getline' command used in this way sets only the variables `NR' and
`FNR' (and of course, VAR).  The record is not split into fields, so
the values of the fields (including `$0') and the value of `NF' do not
change.


File: gawk.info,  Node: Getline/File,  Next: Getline/Variable/File,  Prev: Getline/Variable,  Up: Getline

3.8.3 Using `getline' from a File
---------------------------------

Use `getline < FILE' to read the next record from FILE.  Here FILE is a
string-valued expression that specifies the file name.  `< FILE' is
called a "redirection" because it directs input to come from a
different place.  For example, the following program reads its input
record from the file `secondary.input' when it encounters a first field
with a value equal to 10 in the current input file:

     {
         if ($1 == 10) {
              getline < "secondary.input"
              print
         } else
              print
     }

Because the main input stream is not used, the values of `NR' and `FNR'
are not changed. However, the record it reads is split into fields in
the normal manner, so the values of `$0' and the other fields are
changed, resulting in a new value of `NF'.

According to POSIX, `getline < EXPRESSION' is ambiguous if EXPRESSION
contains unparenthesized operators other than `$'; for example,
`getline < dir "/" file' is ambiguous because the concatenation
operator is not parenthesized.  You should write it as `getline < (dir
"/" file)' if you want your program to be portable to other `awk'
implementations.


File: gawk.info,  Node: Getline/Variable/File,  Next: Getline/Pipe,  Prev: Getline/File,  Up: Getline

3.8.4 Using `getline' into a Variable from a File
-------------------------------------------------

Use `getline VAR < FILE' to read input from the file FILE, and put it
in the variable VAR.  As above, FILE is a string-valued expression that
specifies the file from which to read.

In this version of `getline', none of the built-in variables are
changed and the record is not split into fields.  The only variable
changed is VAR.  For example, the following program copies all the
input files to the output, except for records that say
`@include FILENAME'.  Such a record is replaced by the contents of the
file FILENAME:

     {
          if (NF == 2 && $1 == "@include") {
               while ((getline line < $2) > 0)
                    print line
               close($2)
          } else
               print
     }

Note here how the name of the extra input file is not built into the
program; it is taken directly from the data, specifically from the
second field on the `@include' line.

The `close' function is called to ensure that if two identical
`@include' lines appear in the input, the entire specified file is
included twice.  *Note Close Files And Pipes::.

One deficiency of this program is that it does not process nested
`@include' statements (i.e., `@include' statements in included files)
the way a true macro preprocessor would.  *Note Igawk Program::, for a
program that does handle nested `@include' statements.


File: gawk.info,  Node: Getline/Pipe,  Next: Getline/Variable/Pipe,  Prev: Getline/Variable/File,  Up: Getline

3.8.5 Using `getline' from a Pipe
---------------------------------

The output of a command can also be piped into `getline', using
`COMMAND | getline'.  In this case, the string COMMAND is run as a
shell command and its output is piped into `awk' to be used as input.
This form of `getline' reads one record at a time from the pipe.  For
example, the following program copies its input to its output, except
for lines that begin with `@execute', which are replaced by the output
produced by running the rest of the line as a shell command:

     {
          if ($1 == "@execute") {
               tmp = substr($0, 10)
               while ((tmp | getline) > 0)
                    print
               close(tmp)
          } else
               print
     }

The `close' function is called to ensure that if two identical
`@execute' lines appear in the input, the command is run for each one.
*Note Close Files And Pipes::.  Given the input:

     foo
     bar
     baz
     @execute who
     bletch

the program might produce:

     foo
     bar
     baz
     arnold     ttyv0   Jul 13 14:22
     miriam     ttyp0   Jul 13 14:23     (murphy:0)
     bill       ttyp1   Jul 13 14:23     (murphy:0)
     bletch

Notice that this program ran the command `who' and printed the previous
result.  (If you try this program yourself, you will of course get
different results, depending upon who is logged in on your system.)

This variation of `getline' splits the record into fields, sets the
value of `NF', and recomputes the value of `$0'.  The values of `NR'
and `FNR' are not changed.

According to POSIX, `EXPRESSION | getline' is ambiguous if EXPRESSION
contains unparenthesized operators other than `$'--for example,
`"echo " "date" | getline' is ambiguous because the concatenation
operator is not parenthesized.  You should write it as `("echo "
"date") | getline' if you want your program to be portable to other
`awk' implementations.


File: gawk.info,  Node: Getline/Variable/Pipe,  Next: Getline/Coprocess,  Prev: Getline/Pipe,  Up: Getline

3.8.6 Using `getline' into a Variable from a Pipe
-------------------------------------------------

When you use `COMMAND | getline VAR', the output of COMMAND is sent
through a pipe to `getline' and into the variable VAR.  For example, the
following program reads the current date and time into the variable
`current_time', using the `date' utility, and then prints it:

     BEGIN {
          "date" | getline current_time
          close("date")
          print "Report printed on " current_time
     }

In this version of `getline', none of the built-in variables are
changed and the record is not split into fields.

According to POSIX, `EXPRESSION | getline VAR' is ambiguous if
EXPRESSION contains unparenthesized operators other than `$'; for
example, `"echo " "date" | getline VAR' is ambiguous because the
concatenation operator is not parenthesized. You should write it as
`("echo " "date") | getline VAR' if you want your program to be
portable to other `awk' implementations.


File: gawk.info,  Node: Getline/Coprocess,  Next: Getline/Variable/Coprocess,  Prev: Getline/Variable/Pipe,  Up: Getline

3.8.7 Using `getline' from a Coprocess
--------------------------------------

Input into `getline' from a pipe is a one-way operation.  The command
that is started with `COMMAND | getline' only sends data _to_ your
`awk' program.

On occasion, you might want to send data to another program for
processing and then read the results back.  `gawk' allows you start a
"coprocess", with which two-way communications are possible.  This is
done with the `|&' operator.  Typically, you write data to the
coprocess first and then read results back, as shown in the following:

     print "SOME QUERY" |& "db_server"
     "db_server" |& getline

which sends a query to `db_server' and then reads the results.

The values of `NR' and `FNR' are not changed, because the main input
stream is not used.  However, the record is split into fields in the
normal manner, thus changing the values of `$0', of the other fields,
and of `NF'.

Coprocesses are an advanced feature. They are discussed here only
because this is the minor node on `getline'.  *Note Two-way I/O::,
where coprocesses are discussed in more detail.


File: gawk.info,  Node: Getline/Variable/Coprocess,  Next: Getline Notes,  Prev: Getline/Coprocess,  Up: Getline

3.8.8 Using `getline' into a Variable from a Coprocess
------------------------------------------------------

When you use `COMMAND |& getline VAR', the output from the coprocess
COMMAND is sent through a two-way pipe to `getline' and into the
variable VAR.

In this version of `getline', none of the built-in variables are
changed and the record is not split into fields.  The only variable
changed is VAR.

Coprocesses are an advanced feature. They are discussed here only
because this is the minor node on `getline'.  *Note Two-way I/O::,
where coprocesses are discussed in more detail.


File: gawk.info,  Node: Getline Notes,  Next: Getline Summary,  Prev: Getline/Variable/Coprocess,  Up: Getline

3.8.9 Points to Remember About `getline'
----------------------------------------

Here are some miscellaneous points about `getline' that you should bear
in mind:

   * When `getline' changes the value of `$0' and `NF', `awk' does
     _not_ automatically jump to the start of the program and start
     testing the new record against every pattern.  However, the new
     record is tested against any subsequent rules.

   * Many `awk' implementations limit the number of pipelines that an
     `awk' program may have open to just one.  In `gawk', there is no
     such limit.  You can open as many pipelines (and coprocesses) as
     the underlying operating system permits.

   * An interesting side effect occurs if you use `getline' without a
     redirection inside a `BEGIN' rule. Because an unredirected
     `getline' reads from the command-line data files, the first
     `getline' command causes `awk' to set the value of `FILENAME'.
     Normally, `FILENAME' does not have a value inside `BEGIN' rules,
     because you have not yet started to process the command-line data
     files.  (d.c.)  (*Note BEGIN/END::, also *note Auto-set::.)

   * Using `FILENAME' with `getline' (`getline < FILENAME') is likely
     to be a source for confusion.  `awk' opens a separate input stream
     from the current input file.  However, by not using a variable,
     `$0' and `NR' are still updated.  If you're doing this, it's
     probably by accident, and you should reconsider what it is you're
     trying to accomplish.


File: gawk.info,  Node: Getline Summary,  Prev: Getline Notes,  Up: Getline

3.8.10 Summary of `getline' Variants
------------------------------------

*Note table-getline-variants:: summarizes the eight variants of
`getline', listing which built-in variables are set by each one.

Variant                   Effect
--------------------------------------------------------------------------
`getline'                 Sets `$0', `NF', `FNR', and `NR'
--------------------------------------------------------------------------
`getline' VAR             Sets VAR, `FNR', and `NR'
--------------------------------------------------------------------------
`getline <' FILE          Sets `$0' and `NF'
--------------------------------------------------------------------------
`getline VAR < FILE'      Sets VAR
--------------------------------------------------------------------------
COMMAND `| getline'       Sets `$0' and `NF'
--------------------------------------------------------------------------
COMMAND `| getline' VAR   Sets VAR
--------------------------------------------------------------------------
COMMAND `|& getline'      Sets `$0' and `NF'.  This is a `gawk' extension
--------------------------------------------------------------------------
COMMAND `|& getline' VAR  Sets VAR.  This is a `gawk' extension
--------------------------------------------------------------------------

Table 3.1: getline Variants and What They Set


File: gawk.info,  Node: Printing,  Next: Expressions,  Prev: Reading Files,  Up: Top

4 Printing Output
*****************

One of the most common programming actions is to "print", or output,
some or all of the input.  Use the `print' statement for simple output,
and the `printf' statement for fancier formatting.  The `print'
statement is not limited when computing _which_ values to print.
However, with two exceptions, you cannot specify _how_ to print
them--how many columns, whether to use exponential notation or not, and
so on.  (For the exceptions, *note Output Separators::, and *Note
OFMT::.)  For printing with specifications, you need the `printf'
statement (*note Printf::).

   Besides basic and formatted printing, this major node also covers
I/O redirections to files and pipes, introduces the special file names
that `gawk' processes internally, and discusses the `close' built-in
function.

* Menu:

* Print::                       The `print' statement.
* Print Examples::              Simple examples of `print' statements.
* Output Separators::           The output separators and how to change them.
* OFMT::                        Controlling Numeric Output With `print'.
* Printf::                      The `printf' statement.
* Redirection::                 How to redirect output to multiple files and
                                pipes.
* Special Files::               File name interpretation in `gawk'.
                                `gawk' allows access to inherited file
                                descriptors.
* Close Files And Pipes::       Closing Input and Output Files and Pipes.


File: gawk.info,  Node: Print,  Next: Print Examples,  Up: Printing

4.1 The `print' Statement
=========================

The `print' statement is used to produce output with simple,
standardized formatting.  Specify only the strings or numbers to print,
in a list separated by commas.  They are output, separated by single
spaces, followed by a newline.  The statement looks like this:

     print ITEM1, ITEM2, ...

The entire list of items may be optionally enclosed in parentheses.  The
parentheses are necessary if any of the item expressions uses the `>'
relational operator; otherwise it could be confused with a redirection
(*note Redirection::).

The items to print can be constant strings or numbers, fields of the
current record (such as `$1'), variables, or any `awk' expression.
Numeric values are converted to strings and then printed.

The simple statement `print' with no items is equivalent to `print $0':
it prints the entire current record.  To print a blank line, use `print
""', where `""' is the empty string.  To print a fixed piece of text,
use a string constant, such as `"Don't Panic"', as one item.  If you
forget to use the double-quote characters, your text is taken as an
`awk' expression, and you will probably get an error.  Keep in mind
that a space is printed between any two items.


File: gawk.info,  Node: Print Examples,  Next: Output Separators,  Prev: Print,  Up: Printing

4.2 Examples of `print' Statements
==================================

Each `print' statement makes at least one line of output.  However, it
isn't limited to only one line.  If an item value is a string that
contains a newline, the newline is output along with the rest of the
string.  A single `print' statement can make any number of lines this
way.

The following is an example of printing a string that contains embedded
newlines (the `\n' is an escape sequence, used to represent the newline
character; *note Escape Sequences::):

     $ awk 'BEGIN { print "line one\nline two\nline three" }'
     -| line one
     -| line two
     -| line three

The next example, which is run on the `inventory-shipped' file, prints
the first two fields of each input record, with a space between them:

     $ awk '{ print $1, $2 }' inventory-shipped
     -| Jan 13
     -| Feb 15
     -| Mar 15
     ...

A common mistake in using the `print' statement is to omit the comma
between two items.  This often has the effect of making the items run
together in the output, with no space.  The reason for this is that
juxtaposing two string expressions in `awk' means to concatenate them.
Here is the same program, without the comma:

     $ awk '{ print $1 $2 }' inventory-shipped
     -| Jan13
     -| Feb15
     -| Mar15
     ...

To someone unfamiliar with the `inventory-shipped' file, neither
example's output makes much sense.  A heading line at the beginning
would make it clearer.  Let's add some headings to our table of months
(`$1') and green crates shipped (`$2').  We do this using the `BEGIN'
pattern (*note BEGIN/END::) so that the headings are only printed once:

     awk 'BEGIN {  print "Month Crates"
                   print "----- ------" }
                {  print $1, $2 }' inventory-shipped

When run, the program prints the following:

     Month Crates
     ----- ------
     Jan 13
     Feb 15
     Mar 15
     ...

The only problem, however, is that the headings and the table data
don't line up!  We can fix this by printing some spaces between the two
fields:

     awk 'BEGIN { print "Month Crates"
                  print "----- ------" }
                { print $1, "     ", $2 }' inventory-shipped

Lining up columns this way can get pretty complicated when there are
many columns to fix.  Counting spaces for two or three columns is
simple, but any more than this can take up a lot of time. This is why
the `printf' statement was created (*note Printf::); one of its
specialties is lining up columns of data.

     NOTE: You can continue either a `print' or `printf' statement
     simply by putting a newline after any comma (*note
     Statements/Lines::).


File: gawk.info,  Node: Output Separators,  Next: OFMT,  Prev: Print Examples,  Up: Printing

4.3 Output Separators
=====================

As mentioned previously, a `print' statement contains a list of items
separated by commas.  In the output, the items are normally separated
by single spaces.  However, this doesn't need to be the case; a single
space is only the default.  Any string of characters may be used as the
"output field separator" by setting the built-in variable `OFS'.  The
initial value of this variable is the string `" "'--that is, a single
space.

The output from an entire `print' statement is called an "output
record".  Each `print' statement outputs one output record, and then
outputs a string called the "output record separator" (or `ORS').  The
initial value of `ORS' is the string `"\n"'; i.e., a newline character.
Thus, each `print' statement normally makes a separate line.

In order to change how output fields and records are separated, assign
new values to the variables `OFS' and `ORS'.  The usual place to do
this is in the `BEGIN' rule (*note BEGIN/END::), so that it happens
before any input is processed.  It can also be done with assignments on
the command line, before the names of the input files, or using the
`-v' command-line option (*note Options::).  The following example
prints the first and second fields of each input record, separated by a
semicolon, with a blank line added after each newline:

     $ awk 'BEGIN { OFS = ";"; ORS = "\n\n" }
     >            { print $1, $2 }' BBS-list
     -| aardvark;555-5553
     -|
     -| alpo-net;555-3412
     -|
     -| barfly;555-7685
     ...

If the value of `ORS' does not contain a newline, the program's output
is run together on a single line.


File: gawk.info,  Node: OFMT,  Next: Printf,  Prev: Output Separators,  Up: Printing

4.4 Controlling Numeric Output with `print'
===========================================

When the `print' statement is used to print numeric values, `awk'
internally converts the number to a string of characters and prints
that string.  `awk' uses the `sprintf' function to do this conversion
(*note String Functions::).  For now, it suffices to say that the
`sprintf' function accepts a "format specification" that tells it how
to format numbers (or strings), and that there are a number of
different ways in which numbers can be formatted.  The different format
specifications are discussed more fully in *Note Control Letters::.

The built-in variable `OFMT' contains the default format specification
that `print' uses with `sprintf' when it wants to convert a number to a
string for printing.  The default value of `OFMT' is `"%.6g"'.  The way
`print' prints numbers can be changed by supplying different format
specifications as the value of `OFMT', as shown in the following
example:

     $ awk 'BEGIN {
     >   OFMT = "%.0f"  # print numbers as integers (rounds)
     >   print 17.23, 17.54 }'
     -| 17 18

According to the POSIX standard, `awk''s behavior is undefined if
`OFMT' contains anything but a floating-point conversion specification.
(d.c.)


File: gawk.info,  Node: Printf,  Next: Redirection,  Prev: OFMT,  Up: Printing

4.5 Using `printf' Statements for Fancier Printing
==================================================

For more precise control over the output format than what is normally
provided by `print', use `printf'.  `printf' can be used to specify the
width to use for each item, as well as various formatting choices for
numbers (such as what output base to use, whether to print an exponent,
whether to print a sign, and how many digits to print after the decimal
point).  This is done by supplying a string, called the "format
string", that controls how and where to print the other arguments.

* Menu:

* Basic Printf::                Syntax of the `printf' statement.
* Control Letters::             Format-control letters.
* Format Modifiers::            Format-specification modifiers.
* Printf Examples::             Several examples.


File: gawk.info,  Node: Basic Printf,  Next: Control Letters,  Up: Printf

4.5.1 Introduction to the `printf' Statement
--------------------------------------------

A simple `printf' statement looks like this:

     printf FORMAT, ITEM1, ITEM2, ...

The entire list of arguments may optionally be enclosed in parentheses.
The parentheses are necessary if any of the item expressions use the
`>' relational operator; otherwise, it can be confused with a
redirection (*note Redirection::).

The difference between `printf' and `print' is the FORMAT argument.
This is an expression whose value is taken as a string; it specifies
how to output each of the other arguments.  It is called the "format
string".

The format string is very similar to that in the ISO C library function
`printf'.  Most of FORMAT is text to output verbatim.  Scattered among
this text are "format specifiers"--one per item.  Each format specifier
says to output the next item in the argument list at that place in the
format.

The `printf' statement does not automatically append a newline to its
output.  It outputs only what the format string specifies.  So if a
newline is needed, you must include one in the format string.  The
output separator variables `OFS' and `ORS' have no effect on `printf'
statements. For example:

     $ awk 'BEGIN {
     >    ORS = "\nOUCH!\n"; OFS = "+"
     >    msg = "Dont Panic!"
     >    printf "%s\n", msg
     > }'
     -| Dont Panic!

Here, neither the `+' nor the `OUCH' appear when the message is printed.


File: gawk.info,  Node: Control Letters,  Next: Format Modifiers,  Prev: Basic Printf,  Up: Printf

4.5.2 Format-Control Letters
----------------------------

A format specifier starts with the character `%' and ends with a
"format-control letter"--it tells the `printf' statement how to output
one item.  The format-control letter specifies what _kind_ of value to
print.  The rest of the format specifier is made up of optional
"modifiers" that control _how_ to print the value, such as the field
width.  Here is a list of the format-control letters:

`%c'
     This prints a number as an ASCII character; thus, `printf "%c",
     65' outputs the letter `A'. (The output for a string value is the
     first character of the string.)

`%d, %i'
     These are equivalent; they both print a decimal integer.  (The
     `%i' specification is for compatibility with ISO C.)

`%e, %E'
     These print a number in scientific (exponential) notation; for
     example:

          printf "%4.3e\n", 1950

     prints `1.950e+03', with a total of four significant figures,
     three of which follow the decimal point.  (The `4.3' represents
     two modifiers, discussed in the next node.)  `%E' uses `E' instead
     of `e' in the output.

`%f'
     This prints a number in floating-point notation.  For example:

          printf "%4.3f", 1950

     prints `1950.000', with a total of four significant figures, three
     of which follow the decimal point.  (The `4.3' represents two
     modifiers, discussed in the next node.)

     On systems supporting IEEE 754 floating point format, values
     representing negative infinity are formatted as `-inf' or
     `-infinity', and positive infinity as `inf' and `-infinity'.  The
     special "not a number" value formats as `-nan' or `nan'.

`%F'
     Like `%f' but the infinity and "not a number" values are spelled
     using uppercase letters.

     The `%F' format is a POSIX extension to ISO C; not all systems
     support.  On those that don't, `gawk' uses `%f' instead.

`%g, %G'
     These print a number in either scientific notation or in
     floating-point notation, whichever uses fewer characters; if the
     result is printed in scientific notation, `%G' uses `E' instead of
     `e'.

`%o'
     This prints an unsigned octal integer.

`%s'
     This prints a string.

`%u'
     This prints an unsigned decimal integer.  (This format is of
     marginal use, because all numbers in `awk' are floating-point; it
     is provided primarily for compatibility with C.)

`%x, %X'
     These print an unsigned hexadecimal integer; `%X' uses the letters
     `A' through `F' instead of `a' through `f'.

`%%'
     This isn't a format-control letter, but it does have meaning--the
     sequence `%%' outputs one `%'; it does not consume an argument and
     it ignores any modifiers.

     NOTE: When using the integer format-control letters for values
     that are outside the range of the widest C integer type, `gawk'
     switches to the the `%g' format specifier. If `--lint' is provided
     on the command line (*note Options::), `gawk' warns about this.
     Other versions of `awk' may print invalid values or do something
     else entirely.  (d.c.)


File: gawk.info,  Node: Format Modifiers,  Next: Printf Examples,  Prev: Control Letters,  Up: Printf

4.5.3 Modifiers for `printf' Formats
------------------------------------

A format specification can also include "modifiers" that can control
how much of the item's value is printed, as well as how much space it
gets.  The modifiers come between the `%' and the format-control letter.
We will use the bullet symbol "*" in the following examples to represent
spaces in the output. Here are the possible modifiers, in the order in
which they may appear:

`N$'
     An integer constant followed by a `$' is a "positional specifier".
     Normally, format specifications are applied to arguments in the
     order given in the format string.  With a positional specifier,
     the format specification is applied to a specific argument,
     instead of what would be the next argument in the list.
     Positional specifiers begin counting with one. Thus:

          printf "%s %s\n", "don't", "panic"
          printf "%2$s %1$s\n", "panic", "don't"

     prints the famous friendly message twice.

     At first glance, this feature doesn't seem to be of much use.  It
     is in fact a `gawk' extension, intended for use in translating
     messages at runtime.  *Note Printf Ordering::, which describes how
     and why to use positional specifiers.  For now, we will not use
     them.

`-'
     The minus sign, used before the width modifier (see later on in
     this table), says to left-justify the argument within its
     specified width.  Normally, the argument is printed
     right-justified in the specified width.  Thus:

          printf "%-4s", "foo"

     prints `foo*'.

`SPACE'
     For numeric conversions, prefix positive values with a space and
     negative values with a minus sign.

`+'
     The plus sign, used before the width modifier (see later on in
     this table), says to always supply a sign for numeric conversions,
     even if the data to format is positive. The `+' overrides the
     space modifier.

`#'
     Use an "alternate form" for certain control letters.  For `%o',
     supply a leading zero.  For `%x' and `%X', supply a leading `0x'
     or `0X' for a nonzero result.  For `%e', `%E', and `%f', the
     result always contains a decimal point.  For `%g' and `%G',
     trailing zeros are not removed from the result.

`0'
     A leading `0' (zero) acts as a flag that indicates that output
     should be padded with zeros instead of spaces.  This applies even
     to non-numeric output formats.  (d.c.)  This flag only has an
     effect when the field width is wider than the value to print.

`''
     A single quote or apostrohe character is a POSIX extension to ISO
     C.  It indicates that the integer part of a floating point value,
     or the entire part of an integer decimal value, should have a
     thousands-separator character in it.  This only works in locales
     that support such characters.  For example:

          $ cat thousands.awk                                     Show source program
          -| BEGIN { printf "%'d\n", 1234567 }
          $ LC_ALL=C gawk -f thousands.awk                        Run it in "C" locale
          -| 1234567
          $ LC_ALL=en_US.UTF-8 gawk -f thousands.awk              Run in US English UTF locale
          -| 1,234,567

     For more information about locales and internationalization issues,
     see *Note Locales::.

          NOTE: The `'' flag is a nice feature, but its use complicates
          things: it now becomes difficult to use it in command-line
          programs.  For information on appropriate quoting tricks, see
          *Note Quoting::.

`WIDTH'
     This is a number specifying the desired minimum width of a field.
     Inserting any number between the `%' sign and the format-control
     character forces the field to expand to this width.  The default
     way to do this is to pad with spaces on the left.  For example:

          printf "%4s", "foo"

     prints `*foo'.

     The value of WIDTH is a minimum width, not a maximum.  If the item
     value requires more than WIDTH characters, it can be as wide as
     necessary.  Thus, the following:

          printf "%4s", "foobar"

     prints `foobar'.

     Preceding the WIDTH with a minus sign causes the output to be
     padded with spaces on the right, instead of on the left.

`.PREC'
     A period followed by an integer constant specifies the precision
     to use when printing.  The meaning of the precision varies by
     control letter:

    `%e', `%E', `%f'
          Number of digits to the right of the decimal point.

    `%g', `%G'
          Maximum number of significant digits.

    `%d', `%i', `%o', `%u', `%x', `%X'
          Minimum number of digits to print.

    `%s'
          Maximum number of characters from the string that should
          print.

     Thus, the following:

          printf "%.4s", "foobar"

     prints `foob'.

The C library `printf''s dynamic WIDTH and PREC capability (for
example, `"%*.*s"') is supported.  Instead of supplying explicit WIDTH
and/or PREC values in the format string, they are passed in the
argument list.  For example:

     w = 5
     p = 3
     s = "abcdefg"
     printf "%*.*s\n", w, p, s

is exactly equivalent to:

     s = "abcdefg"
     printf "%5.3s\n", s

Both programs output `**abc'.  Earlier versions of `awk' did not
support this capability.  If you must use such a version, you may
simulate this feature by using concatenation to build up the format
string, like so:

     w = 5
     p = 3
     s = "abcdefg"
     printf "%" w "." p "s\n", s

This is not particularly easy to read but it does work.

C programmers may be used to supplying additional `l', `L', and `h'
modifiers in `printf' format strings. These are not valid in `awk'.
Most `awk' implementations silently ignore these modifiers.  If
`--lint' is provided on the command line (*note Options::), `gawk'
warns about their use. If `--posix' is supplied, their use is a fatal
error.


File: gawk.info,  Node: Printf Examples,  Prev: Format Modifiers,  Up: Printf

4.5.4 Examples Using `printf'
-----------------------------

The following is a simple example of how to use `printf' to make an
aligned table:

     awk '{ printf "%-10s %s\n", $1, $2 }' BBS-list

This command prints the names of the bulletin boards (`$1') in the file
`BBS-list' as a string of 10 characters that are left-justified.  It
also prints the phone numbers (`$2') next on the line.  This produces
an aligned two-column table of names and phone numbers, as shown here:

     $ awk '{ printf "%-10s %s\n", $1, $2 }' BBS-list
     -| aardvark   555-5553
     -| alpo-net   555-3412
     -| barfly     555-7685
     -| bites      555-1675
     -| camelot    555-0542
     -| core       555-2912
     -| fooey      555-1234
     -| foot       555-6699
     -| macfoo     555-6480
     -| sdace      555-3430
     -| sabafoo    555-2127

In this case, the phone numbers had to be printed as strings because
the numbers are separated by a dash.  Printing the phone numbers as
numbers would have produced just the first three digits: `555'.  This
would have been pretty confusing.

It wasn't necessary to specify a width for the phone numbers because
they are last on their lines.  They don't need to have spaces after
them.

The table could be made to look even nicer by adding headings to the
tops of the columns.  This is done using the `BEGIN' pattern (*note
BEGIN/END::) so that the headers are only printed once, at the
beginning of the `awk' program:

     awk 'BEGIN { print "Name      Number"
                  print "----      ------" }
          { printf "%-10s %s\n", $1, $2 }' BBS-list

The above example mixed `print' and `printf' statements in the same
program.  Using just `printf' statements can produce the same results:

     awk 'BEGIN { printf "%-10s %s\n", "Name", "Number"
                  printf "%-10s %s\n", "----", "------" }
          { printf "%-10s %s\n", $1, $2 }' BBS-list

Printing each column heading with the same format specification used
for the column elements ensures that the headings are aligned just like
the columns.

The fact that the same format specification is used three times can be
emphasized by storing it in a variable, like this:

     awk 'BEGIN { format = "%-10s %s\n"
                  printf format, "Name", "Number"
                  printf format, "----", "------" }
          { printf format, $1, $2 }' BBS-list

At this point, it would be a worthwhile exercise to use the `printf'
statement to line up the headings and table data for the
`inventory-shipped' example that was covered earlier in the minor node
on the `print' statement (*note Print::).


File: gawk.info,  Node: Redirection,  Next: Special Files,  Prev: Printf,  Up: Printing

4.6 Redirecting Output of `print' and `printf'
==============================================

So far, the output from `print' and `printf' has gone to the standard
output, usually the terminal.  Both `print' and `printf' can also send
their output to other places.  This is called "redirection".

A redirection appears after the `print' or `printf' statement.
Redirections in `awk' are written just like redirections in shell
commands, except that they are written inside the `awk' program.

There are four forms of output redirection: output to a file, output
appended to a file, output through a pipe to another command, and output
to a coprocess.  They are all shown for the `print' statement, but they
work identically for `printf':

`print ITEMS > OUTPUT-FILE'
     This type of redirection prints the items into the output file
     named OUTPUT-FILE.  The file name OUTPUT-FILE can be any
     expression.  Its value is changed to a string and then used as a
     file name (*note Expressions::).

     When this type of redirection is used, the OUTPUT-FILE is erased
     before the first output is written to it.  Subsequent writes to
     the same OUTPUT-FILE do not erase OUTPUT-FILE, but append to it.
     (This is different from how you use redirections in shell scripts.)
     If OUTPUT-FILE does not exist, it is created.  For example, here
     is how an `awk' program can write a list of BBS names to one file
     named `name-list', and a list of phone numbers to another file
     named `phone-list':

          $ awk '{ print $2 > "phone-list"
          >        print $1 > "name-list" }' BBS-list
          $ cat phone-list
          -| 555-5553
          -| 555-3412
          ...
          $ cat name-list
          -| aardvark
          -| alpo-net
          ...

     Each output file contains one name or number per line.

`print ITEMS >> OUTPUT-FILE'
     This type of redirection prints the items into the pre-existing
     output file named OUTPUT-FILE.  The difference between this and the
     single-`>' redirection is that the old contents (if any) of
     OUTPUT-FILE are not erased.  Instead, the `awk' output is appended
     to the file.  If OUTPUT-FILE does not exist, then it is created.

`print ITEMS | COMMAND'
     It is also possible to send output to another program through a
     pipe instead of into a file.   This type of redirection opens a
     pipe to COMMAND, and writes the values of ITEMS through this pipe
     to another process created to execute COMMAND.

     The redirection argument COMMAND is actually an `awk' expression.
     Its value is converted to a string whose contents give the shell
     command to be run.  For example, the following produces two files,
     one unsorted list of BBS names, and one list sorted in reverse
     alphabetical order:

          awk '{ print $1 > "names.unsorted"
                 command = "sort -r > names.sorted"
                 print $1 | command }' BBS-list

     The unsorted list is written with an ordinary redirection, while
     the sorted list is written by piping through the `sort' utility.

     The next example uses redirection to mail a message to the mailing
     list `bug-system'.  This might be useful when trouble is
     encountered in an `awk' script run periodically for system
     maintenance:

          report = "mail bug-system"
          print "Awk script failed:", $0 | report
          m = ("at record number " FNR " of " FILENAME)
          print m | report
          close(report)

     The message is built using string concatenation and saved in the
     variable `m'.  It's then sent down the pipeline to the `mail'
     program.  (The parentheses group the items to concatenate--see
     *Note Concatenation::.)

     The `close' function is called here because it's a good idea to
     close the pipe as soon as all the intended output has been sent to
     it.  *Note Close Files And Pipes::, for more information.

     This example also illustrates the use of a variable to represent a
     FILE or COMMAND--it is not necessary to always use a string
     constant.  Using a variable is generally a good idea, because
     `awk' requires that the string value be spelled identically every
     time.

`print ITEMS |& COMMAND'
     This type of redirection prints the items to the input of COMMAND.
     The difference between this and the single-`|' redirection is that
     the output from COMMAND can be read with `getline'.  Thus COMMAND
     is a "coprocess", which works together with, but subsidiary to,
     the `awk' program.

     This feature is a `gawk' extension, and is not available in POSIX
     `awk'.  *Note Two-way I/O::, for a more complete discussion.

Redirecting output using `>', `>>', `|', or `|&' asks the system to
open a file, pipe, or coprocess only if the particular FILE or COMMAND
you specify has not already been written to by your program or if it
has been closed since it was last written to.

It is a common error to use `>' redirection for the first `print' to a
file, and then to use `>>' for subsequent output:

     # clear the file
     print "Don't panic" > "guide.txt"
     ...
     # append
     print "Avoid improbability generators" >> "guide.txt"

This is indeed how redirections must be used from the shell.  But in
`awk', it isn't necessary.  In this kind of case, a program should use
`>' for all the `print' statements, since the output file is only
opened once.

Many `awk' implementations limit the number of pipelines that an `awk'
program may have open to just one!  In `gawk', there is no such limit.
`gawk' allows a program to open as many pipelines as the underlying
operating system permits.

Advanced Notes: Piping into `sh'
--------------------------------

A particularly powerful way to use redirection is to build command lines
and pipe them into the shell, `sh'.  For example, suppose you have a
list of files brought over from a system where all the file names are
stored in uppercase, and you wish to rename them to have names in all
lowercase.  The following program is both simple and efficient:

     { printf("mv %s %s\n", $0, tolower($0)) | "sh" }

     END { close("sh") }

The `tolower' function returns its argument string with all uppercase
characters converted to lowercase (*note String Functions::).  The
program builds up a list of command lines, using the `mv' utility to
rename the files.  It then sends the list to the shell for execution.


File: gawk.info,  Node: Special Files,  Next: Close Files And Pipes,  Prev: Redirection,  Up: Printing

4.7 Special File Names in `gawk'
================================

`gawk' provides a number of special file names that it interprets
internally.  These file names provide access to standard file
descriptors, process-related information, and TCP/IP networking.

* Menu:

* Special FD::                  Special files for I/O.
* Special Process::             Special files for process information.
* Special Network::             Special files for network communications.
* Special Caveats::             Things to watch out for.


File: gawk.info,  Node: Special FD,  Next: Special Process,  Up: Special Files

4.7.1 Special Files for Standard Descriptors
--------------------------------------------

Running programs conventionally have three input and output streams
already available to them for reading and writing.  These are known as
the "standard input", "standard output", and "standard error output".
These streams are, by default, connected to your terminal, but they are
often redirected with the shell, via the `<', `<<', `>', `>>', `>&',
and `|' operators.  Standard error is typically used for writing error
messages; the reason there are two separate streams, standard output
and standard error, is so that they can be redirected separately.

In other implementations of `awk', the only way to write an error
message to standard error in an `awk' program is as follows:

     print "Serious error detected!" | "cat 1>&2"

This works by opening a pipeline to a shell command that can access the
standard error stream that it inherits from the `awk' process.  This is
far from elegant, and it is also inefficient, because it requires a
separate process.  So people writing `awk' programs often don't do
this.  Instead, they send the error messages to the terminal, like this:

     print "Serious error detected!" > "/dev/tty"

This usually has the same effect but not always: although the standard
error stream is usually the terminal, it can be redirected; when that
happens, writing to the terminal is not correct.  In fact, if `awk' is
run from a background job, it may not have a terminal at all.  Then
opening `/dev/tty' fails.

`gawk' provides special file names for accessing the three standard
streams, as well as any other inherited open files.  If the file name
matches one of these special names when `gawk' redirects input or
output, then it directly uses the stream that the file name stands for.
These special file names work for all operating systems that `gawk' has
been ported to, not just those that are POSIX-compliant:

`/dev/stdin'
     The standard input (file descriptor 0).

`/dev/stdout'
     The standard output (file descriptor 1).

`/dev/stderr'
     The standard error output (file descriptor 2).

`/dev/fd/N'
     The file associated with file descriptor N.  Such a file must be
     opened by the program initiating the `awk' execution (typically
     the shell).  Unless special pains are taken in the shell from which
     `gawk' is invoked, only descriptors 0, 1, and 2 are available.

The file names `/dev/stdin', `/dev/stdout', and `/dev/stderr' are
aliases for `/dev/fd/0', `/dev/fd/1', and `/dev/fd/2', respectively.
However, they are more self-explanatory.  The proper way to write an
error message in a `gawk' program is to use `/dev/stderr', like this:

     print "Serious error detected!" > "/dev/stderr"

Note the use of quotes around the file name.  Like any other
redirection, the value must be a string.  It is a common error to omit
the quotes, which leads to confusing results.


File: gawk.info,  Node: Special Process,  Next: Special Network,  Prev: Special FD,  Up: Special Files

4.7.2 Special Files for Process-Related Information
---------------------------------------------------

`gawk' also provides special file names that give access to information
about the running `gawk' process.  Each of these "files" provides a
single record of information.  To read them more than once, they must
first be closed with the `close' function (*note Close Files And
Pipes::).  The file names are:

`/dev/pid'
     Reading this file returns the process ID of the current process,
     in decimal form, terminated with a newline.

`/dev/ppid'
     Reading this file returns the parent process ID of the current
     process, in decimal form, terminated with a newline.

`/dev/pgrpid'
     Reading this file returns the process group ID of the current
     process, in decimal form, terminated with a newline.

`/dev/user'
     Reading this file returns a single record terminated with a
     newline.  The fields are separated with spaces.  The fields
     represent the following information:

    `$1'
          The return value of the `getuid' system call (the real user
          ID number).

    `$2'
          The return value of the `geteuid' system call (the effective
          user ID number).

    `$3'
          The return value of the `getgid' system call (the real group
          ID number).

    `$4'
          The return value of the `getegid' system call (the effective
          group ID number).

     If there are any additional fields, they are the group IDs
     returned by the `getgroups' system call.  (Multiple groups may not
     be supported on all systems.)

These special file names may be used on the command line as data files,
as well as for I/O redirections within an `awk' program.  They may not
be used as source files with the `-f' option.

     NOTE: The special files that provide process-related information
     are now considered obsolete and will disappear entirely in the
     next release of `gawk'.  `gawk' prints a warning message every
     time you use one of these files.  To obtain process-related
     information, use the `PROCINFO' array.  *Note Auto-set::.


File: gawk.info,  Node: Special Network,  Next: Special Caveats,  Prev: Special Process,  Up: Special Files

4.7.3 Special Files for Network Communications
----------------------------------------------

Starting with version 3.1 of `gawk', `awk' programs can open a two-way
TCP/IP connection, acting as either a client or a server.  This is done
using a special file name of the form:

     `/inet/PROTOCOL/LOCAL-PORT/REMOTE-HOST/REMOTE-PORT'

The PROTOCOL is one of `tcp', `udp', or `raw', and the other fields
represent the other essential pieces of information for making a
networking connection.  These file names are used with the `|&'
operator for communicating with a coprocess (*note Two-way I/O::).
This is an advanced feature, mentioned here only for completeness.
Full discussion is delayed until *Note TCP/IP Networking::.


File: gawk.info,  Node: Special Caveats,  Prev: Special Network,  Up: Special Files

4.7.4 Special File Name Caveats
-------------------------------

Here is a list of things to bear in mind when using the special file
names that `gawk' provides:

   * Recognition of these special file names is disabled if `gawk' is in
     compatibility mode (*note Options::).

   * The special files that provide process-related information are now
     considered obsolete and will disappear entirely in the next
     release of `gawk'.  `gawk' prints a warning message every time you
     use one of these files.  To obtain process-related information,
     use the `PROCINFO' array.  *Note Built-in Variables::.

   * Starting with version 3.1, `gawk' _always_ interprets these
     special file names.(1) For example, using `/dev/fd/4' for output
     actually writes on file descriptor 4, and not on a new file
     descriptor that is `dup''ed from file descriptor 4.  Most of the
     time this does not matter; however, it is important to _not_ close
     any of the files related to file descriptors 0, 1, and 2.  Doing
     so results in unpredictable behavior.

---------- Footnotes ----------

(1) Older versions of `gawk' would interpret these names internally
only if the system did not actually have a `/dev/fd' directory or any
of the other special files listed earlier.  Usually this didn't make a
difference, but sometimes it did; thus, it was decided to make `gawk''s
behavior consistent on all systems and to have it always interpret the
special file names itself.


File: gawk.info,  Node: Close Files And Pipes,  Prev: Special Files,  Up: Printing

4.8 Closing Input and Output Redirections
=========================================

If the same file name or the same shell command is used with `getline'
more than once during the execution of an `awk' program (*note
Getline::), the file is opened (or the command is executed) the first
time only.  At that time, the first record of input is read from that
file or command.  The next time the same file or command is used with
`getline', another record is read from it, and so on.

Similarly, when a file or pipe is opened for output, the file name or
command associated with it is remembered by `awk', and subsequent
writes to the same file or command are appended to the previous writes.
The file or pipe stays open until `awk' exits.

This implies that special steps are necessary in order to read the same
file again from the beginning, or to rerun a shell command (rather than
reading more output from the same command).  The `close' function makes
these things possible:

     close(FILENAME)

or:

     close(COMMAND)

The argument FILENAME or COMMAND can be any expression.  Its value must
_exactly_ match the string that was used to open the file or start the
command (spaces and other "irrelevant" characters included). For
example, if you open a pipe with this:

     "sort -r names" | getline foo

then you must close it with this:

     close("sort -r names")

Once this function call is executed, the next `getline' from that file
or command, or the next `print' or `printf' to that file or command,
reopens the file or reruns the command.  Because the expression that
you use to close a file or pipeline must exactly match the expression
used to open the file or run the command, it is good practice to use a
variable to store the file name or command.  The previous example
becomes the following:

     sortcom = "sort -r names"
     sortcom | getline foo
     ...
     close(sortcom)

This helps avoid hard-to-find typographical errors in your `awk'
programs.  Here are some of the reasons for closing an output file:

   * To write a file and read it back later on in the same `awk'
     program.  Close the file after writing it, then begin reading it
     with `getline'.

   * To write numerous files, successively, in the same `awk' program.
     If the files aren't closed, eventually `awk' may exceed a system
     limit on the number of open files in one process.  It is best to
     close each one when the program has finished writing it.

   * To make a command finish.  When output is redirected through a
     pipe, the command reading the pipe normally continues to try to
     read input as long as the pipe is open.  Often this means the
     command cannot really do its work until the pipe is closed.  For
     example, if output is redirected to the `mail' program, the
     message is not actually sent until the pipe is closed.

   * To run the same program a second time, with the same arguments.
     This is not the same thing as giving more input to the first run!

     For example, suppose a program pipes output to the `mail' program.
     If it outputs several lines redirected to this pipe without closing
     it, they make a single message of several lines.  By contrast, if
     the program closes the pipe after each line of output, then each
     line makes a separate message.

If you use more files than the system allows you to have open, `gawk'
attempts to multiplex the available open files among your data files.
`gawk''s ability to do this depends upon the facilities of your
operating system, so it may not always work.  It is therefore both good
practice and good portability advice to always use `close' on your
files when you are done with them.  In fact, if you are using a lot of
pipes, it is essential that you close commands when done. For example,
consider something like this:

     {
         ...
         command = ("grep " $1 " /some/file | my_prog -q " $3)
         while ((command | getline) > 0) {
             PROCESS OUTPUT OF command
         }
         # need close(command) here
     }

This example creates a new pipeline based on data in _each_ record.
Without the call to `close' indicated in the comment, `awk' creates
child processes to run the commands, until it eventually runs out of
file descriptors for more pipelines.

Even though each command has finished (as indicated by the end-of-file
return status from `getline'), the child process is not terminated;(1)
more importantly, the file descriptor for the pipe is not closed and
released until `close' is called or `awk' exits.

`close' will silently do nothing if given an argument that does not
represent a file, pipe or coprocess that was opened with a redirection.

Note also that `close(FILENAME)' has no "magic" effects on the implicit
loop that reads through the files named on the command line.  It is,
more likely, a close of a file that was never opened, so `awk' silently
does nothing.

When using the `|&' operator to communicate with a coprocess, it is
occasionally useful to be able to close one end of the two-way pipe
without closing the other.  This is done by supplying a second argument
to `close'.  As in any other call to `close', the first argument is the
name of the command or special file used to start the coprocess.  The
second argument should be a string, with either of the values `"to"' or
`"from"'.  Case does not matter.  As this is an advanced feature, a
more complete discussion is delayed until *Note Two-way I/O::, which
discusses it in more detail and gives an example.

Advanced Notes: Using `close''s Return Value
--------------------------------------------

In many versions of Unix `awk', the `close' function is actually a
statement.  It is a syntax error to try and use the return value from
`close': (d.c.)

     command = "..."
     command | getline info
     retval = close(command)  # syntax error in most Unix awks

`gawk' treats `close' as a function.  The return value is -1 if the
argument names something that was never opened with a redirection, or
if there is a system problem closing the file or process.  In these
cases, `gawk' sets the built-in variable `ERRNO' to a string describing
the problem.

In `gawk', when closing a pipe or coprocess (input or output), the
return value is the exit status of the command.(2) Otherwise, it is the
return value from the system's `close' or `fclose' C functions when
closing input or output files, respectively.  This value is zero if the
close succeeds, or -1 if it fails.

The POSIX standard is very vague; it says that `close' returns zero on
success and non-zero otherwise.  In general, different implementations
vary in what they report when closing pipes; thus the return value
cannot be used portably.  (d.c.)

---------- Footnotes ----------

(1) The technical terminology is rather morbid.  The finished child is
called a "zombie," and cleaning up after it is referred to as "reaping."

(2) This is a full 16-bit value as returned by the `wait' system call.
See the system manual pages for information on how to decode this value.


File: gawk.info,  Node: Expressions,  Next: Patterns and Actions,  Prev: Printing,  Up: Top

5 Expressions
*************

Expressions are the basic building blocks of `awk' patterns and
actions.  An expression evaluates to a value that you can print, test,
or pass to a function.  Additionally, an expression can assign a new
value to a variable or a field by using an assignment operator.

An expression can serve as a pattern or action statement on its own.
Most other kinds of statements contain one or more expressions that
specify the data on which to operate.  As in other languages,
expressions in `awk' include variables, array references, constants,
and function calls, as well as combinations of these with various
operators.

* Menu:

* Constants::                   String, numeric and regexp constants.
* Using Constant Regexps::      When and how to use a regexp constant.
* Variables::                   Variables give names to values for later use.
* Conversion::                  The conversion of strings to numbers and vice
                                versa.
* Arithmetic Ops::              Arithmetic operations (`+', `-',
                                etc.)
* Concatenation::               Concatenating strings.
* Assignment Ops::              Changing the value of a variable or a field.
* Increment Ops::               Incrementing the numeric value of a variable.
* Truth Values::                What is ``true'' and what is ``false''.
* Typing and Comparison::       How variables acquire types and how this
                                affects comparison of numbers and strings with
                                `<', etc.
* Boolean Ops::                 Combining comparison expressions using boolean
                                operators `||' (``or''), `&&'
                                (``and'') and `!' (``not'').
* Conditional Exp::             Conditional expressions select between two
                                subexpressions under control of a third
                                subexpression.
* Function Calls::              A function call is an expression.
* Precedence::                  How various operators nest.


File: gawk.info,  Node: Constants,  Next: Using Constant Regexps,  Up: Expressions

5.1 Constant Expressions
========================

The simplest type of expression is the "constant", which always has the
same value.  There are three types of constants: numeric, string, and
regular expression.

Each is used in the appropriate context when you need a data value that
isn't going to change.  Numeric constants can have different forms, but
are stored identically internally.

* Menu:

* Scalar Constants::            Numeric and string constants.
* Nondecimal-numbers::          What are octal and hex numbers.
* Regexp Constants::            Regular Expression constants.


File: gawk.info,  Node: Scalar Constants,  Next: Nondecimal-numbers,  Up: Constants

5.1.1 Numeric and String Constants
----------------------------------

A "numeric constant" stands for a number.  This number can be an
integer, a decimal fraction, or a number in scientific (exponential)
notation.(1) Here are some examples of numeric constants that all have
the same value:

     105
     1.05e+2
     1050e-1

A string constant consists of a sequence of characters enclosed in
double-quotation marks.  For example:

     "parrot"

represents the string whose contents are `parrot'.  Strings in `gawk'
can be of any length, and they can contain any of the possible
eight-bit ASCII characters including ASCII NUL (character code zero).
Other `awk' implementations may have difficulty with some character
codes.

---------- Footnotes ----------

(1) The internal representation of all numbers, including integers,
uses double-precision floating-point numbers.  On most modern systems,
these are in IEEE 754 standard format.


File: gawk.info,  Node: Nondecimal-numbers,  Next: Regexp Constants,  Prev: Scalar Constants,  Up: Constants

5.1.2 Octal and Hexadecimal Numbers
-----------------------------------

In `awk', all numbers are in decimal; i.e., base 10.  Many other
programming languages allow you to specify numbers in other bases, often
octal (base 8) and hexadecimal (base 16).  In octal, the numbers go 0,
1, 2, 3, 4, 5, 6, 7, 10, 11, 12, etc.  Just as `11', in decimal, is 1
times 10 plus 1, so `11', in octal, is 1 times 8, plus 1. This equals 9
in decimal.  In hexadecimal, there are 16 digits. Since the everyday
decimal number system only has ten digits (`0'-`9'), the letters `a'
through `f' are used to represent the rest.  (Case in the letters is
usually irrelevant; hexadecimal `a' and `A' have the same value.)
Thus, `11', in hexadecimal, is 1 times 16 plus 1, which equals 17 in
decimal.

Just by looking at plain `11', you can't tell what base it's in.  So,
in C, C++, and other languages derived from C, there is a special
notation to help signify the base.  Octal numbers start with a leading
`0', and hexadecimal numbers start with a leading `0x' or `0X':

`11'
     Decimal value 11.

`011'
     Octal 11, decimal value 9.

`0x11'
     Hexadecimal 11, decimal value 17.

This example shows the difference:

     $ gawk 'BEGIN { printf "%d, %d, %d\n", 011, 11, 0x11 }'
     -| 9, 11, 17

Being able to use octal and hexadecimal constants in your programs is
most useful when working with data that cannot be represented
conveniently as characters or as regular numbers, such as binary data
of various sorts.

`gawk' allows the use of octal and hexadecimal constants in your
program text.  However, such numbers in the input data are not treated
differently; doing so by default would break old programs.  (If you
really need to do this, use the `--non-decimal-data' command-line
option; *note Nondecimal Data::.)  If you have octal or hexadecimal
data, you can use the `strtonum' function (*note String Functions::) to
convert the data into a number.  Most of the time, you will want to use
octal or hexadecimal constants when working with the built-in bit
manipulation functions; see *Note Bitwise Functions::, for more
information.

Unlike some early C implementations, `8' and `9' are not valid in octal
constants; e.g., `gawk' treats `018' as decimal 18:

     $ gawk 'BEGIN { print "021 is", 021 ; print 018 }'
     -| 021 is 17
     -| 18

Octal and hexadecimal source code constants are a `gawk' extension.  If
`gawk' is in compatibility mode (*note Options::), they are not
available.

Advanced Notes: A Constant's Base Does Not Affect Its Value
-----------------------------------------------------------

Once a numeric constant has been converted internally into a number,
`gawk' no longer remembers what the original form of the constant was;
the internal value is always used.  This has particular consequences
for conversion of numbers to strings:

     $ gawk 'BEGIN { printf "0x11 is <%s>\n", 0x11 }'
     -| 0x11 is <17>


File: gawk.info,  Node: Regexp Constants,  Prev: Nondecimal-numbers,  Up: Constants

5.1.4 Regular Expression Constants
----------------------------------

A regexp constant is a regular expression description enclosed in
slashes, such as `/^beginning and end$/'.  Most regexps used in `awk'
programs are constant, but the `~' and `!~' matching operators can also
match computed or "dynamic" regexps (which are just ordinary strings or
variables that contain a regexp).


File: gawk.info,  Node: Using Constant Regexps,  Next: Variables,  Prev: Constants,  Up: Expressions

5.2 Using Regular Expression Constants
======================================

When used on the righthand side of the `~' or `!~' operators, a regexp
constant merely stands for the regexp that is to be matched.  However,
regexp constants (such as `/foo/') may be used like simple expressions.
When a regexp constant appears by itself, it has the same meaning as if
it appeared in a pattern, i.e., `($0 ~ /foo/)' (d.c.)  *Note Expression
Patterns::.  This means that the following two code segments:

     if ($0 ~ /barfly/ || $0 ~ /camelot/)
         print "found"

and:

     if (/barfly/ || /camelot/)
         print "found"

are exactly equivalent.  One rather bizarre consequence of this rule is
that the following Boolean expression is valid, but does not do what
the user probably intended:

     # note that /foo/ is on the left of the ~
     if (/foo/ ~ $1) print "found foo"

This code is "obviously" testing `$1' for a match against the regexp
`/foo/'.  But in fact, the expression `/foo/ ~ $1' actually means `($0
~ /foo/) ~ $1'.  In other words, first match the input record against
the regexp `/foo/'.  The result is either zero or one, depending upon
the success or failure of the match.  That result is then matched
against the first field in the record.  Because it is unlikely that you
would ever really want to make this kind of test, `gawk' issues a
warning when it sees this construct in a program.  Another consequence
of this rule is that the assignment statement:

     matches = /foo/

assigns either zero or one to the variable `matches', depending upon
the contents of the current input record.  This feature of the language
has never been well documented until the POSIX specification.

Constant regular expressions are also used as the first argument for
the `gensub', `sub', and `gsub' functions, and as the second argument
of the `match' function (*note String Functions::).  Modern
implementations of `awk', including `gawk', allow the third argument of
`split' to be a regexp constant, but some older implementations do not.
(d.c.)  This can lead to confusion when attempting to use regexp
constants as arguments to user-defined functions (*note User-defined::).
For example:

     function mysub(pat, repl, str, global)
     {
         if (global)
             gsub(pat, repl, str)
         else
             sub(pat, repl, str)
         return str
     }

     {
         ...
         text = "hi! hi yourself!"
         mysub(/hi/, "howdy", text, 1)
         ...
     }

In this example, the programmer wants to pass a regexp constant to the
user-defined function `mysub', which in turn passes it on to either
`sub' or `gsub'.  However, what really happens is that the `pat'
parameter is either one or zero, depending upon whether or not `$0'
matches `/hi/'.  `gawk' issues a warning when it sees a regexp constant
used as a parameter to a user-defined function, since passing a truth
value in this way is probably not what was intended.


File: gawk.info,  Node: Variables,  Next: Conversion,  Prev: Using Constant Regexps,  Up: Expressions

5.3 Variables
=============

Variables are ways of storing values at one point in your program for
use later in another part of your program.  They can be manipulated
entirely within the program text, and they can also be assigned values
on the `awk' command line.

* Menu:

* Using Variables::             Using variables in your programs.
* Assignment Options::          Setting variables on the command-line and a
                                summary of command-line syntax. This is an
                                advanced method of input.


File: gawk.info,  Node: Using Variables,  Next: Assignment Options,  Up: Variables

5.3.1 Using Variables in a Program
----------------------------------

Variables let you give names to values and refer to them later.
Variables have already been used in many of the examples.  The name of
a variable must be a sequence of letters, digits, or underscores, and
it may not begin with a digit.  Case is significant in variable names;
`a' and `A' are distinct variables.

A variable name is a valid expression by itself; it represents the
variable's current value.  Variables are given new values with
"assignment operators", "increment operators", and "decrement
operators".  *Note Assignment Ops::.

A few variables have special built-in meanings, such as `FS' (the field
separator), and `NF' (the number of fields in the current input
record).  *Note Built-in Variables::, for a list of the built-in
variables.  These built-in variables can be used and assigned just like
all other variables, but their values are also used or changed
automatically by `awk'.  All built-in variables' names are entirely
uppercase.

Variables in `awk' can be assigned either numeric or string values.
The kind of value a variable holds can change over the life of a
program.  By default, variables are initialized to the empty string,
which is zero if converted to a number.  There is no need to
"initialize" each variable explicitly in `awk', which is what you would
do in C and in most other traditional languages.


File: gawk.info,  Node: Assignment Options,  Prev: Using Variables,  Up: Variables

5.3.2 Assigning Variables on the Command Line
---------------------------------------------

Any `awk' variable can be set by including a "variable assignment"
among the arguments on the command line when `awk' is invoked (*note
Other Arguments::).  Such an assignment has the following form:

     VARIABLE=TEXT

With it, a variable is set either at the beginning of the `awk' run or
in between input files.  When the assignment is preceded with the `-v'
option, as in the following:

     -v VARIABLE=TEXT

the variable is set at the very beginning, even before the `BEGIN'
rules are run.  The `-v' option and its assignment must precede all the
file name arguments, as well as the program text.  (*Note Options::,
for more information about the `-v' option.)  Otherwise, the variable
assignment is performed at a time determined by its position among the
input file arguments--after the processing of the preceding input file
argument.  For example:

     awk '{ print $n }' n=4 inventory-shipped n=2 BBS-list

prints the value of field number `n' for all input records.  Before the
first file is read, the command line sets the variable `n' equal to
four.  This causes the fourth field to be printed in lines from the
file `inventory-shipped'.  After the first file has finished, but
before the second file is started, `n' is set to two, so that the
second field is printed in lines from `BBS-list':

     $ awk '{ print $n }' n=4 inventory-shipped n=2 BBS-list
     -| 15
     -| 24
     ...
     -| 555-5553
     -| 555-3412
     ...

Command-line arguments are made available for explicit examination by
the `awk' program in the `ARGV' array (*note ARGC and ARGV::).  `awk'
processes the values of command-line assignments for escape sequences
(*note Escape Sequences::).  (d.c.)


File: gawk.info,  Node: Conversion,  Next: Arithmetic Ops,  Prev: Variables,  Up: Expressions

5.4 Conversion of Strings and Numbers
=====================================

Strings are converted to numbers and numbers are converted to strings,
if the context of the `awk' program demands it.  For example, if the
value of either `foo' or `bar' in the expression `foo + bar' happens to
be a string, it is converted to a number before the addition is
performed.  If numeric values appear in string concatenation, they are
converted to strings.  Consider the following:

     two = 2; three = 3
     print (two three) + 4

This prints the (numeric) value 27.  The numeric values of the
variables `two' and `three' are converted to strings and concatenated
together.  The resulting string is converted back to the number 23, to
which 4 is then added.

If, for some reason, you need to force a number to be converted to a
string, concatenate the empty string, `""', with that number.  To force
a string to be converted to a number, add zero to that string.  A
string is converted to a number by interpreting any numeric prefix of
the string as numerals: `"2.5"' converts to 2.5, `"1e3"' converts to
1000, and `"25fix"' has a numeric value of 25.  Strings that can't be
interpreted as valid numbers convert to zero.

The exact manner in which numbers are converted into strings is
controlled by the `awk' built-in variable `CONVFMT' (*note Built-in
Variables::).  Numbers are converted using the `sprintf' function with
`CONVFMT' as the format specifier (*note String Functions::).

`CONVFMT''s default value is `"%.6g"', which prints a value with at
least six significant digits.  For some applications, you might want to
change it to specify more precision.  On most modern machines, 17
digits is enough to capture a floating-point number's value exactly,
most of the time.(1)

Strange results can occur if you set `CONVFMT' to a string that doesn't
tell `sprintf' how to format floating-point numbers in a useful way.
For example, if you forget the `%' in the format, `awk' converts all
numbers to the same constant string.  As a special case, if a number is
an integer, then the result of converting it to a string is _always_ an
integer, no matter what the value of `CONVFMT' may be.  Given the
following code fragment:

     CONVFMT = "%2.2f"
     a = 12
     b = a ""

`b' has the value `"12"', not `"12.00"'.  (d.c.)

Prior to the POSIX standard, `awk' used the value of `OFMT' for
converting numbers to strings.  `OFMT' specifies the output format to
use when printing numbers with `print'.  `CONVFMT' was introduced in
order to separate the semantics of conversion from the semantics of
printing.  Both `CONVFMT' and `OFMT' have the same default value:
`"%.6g"'.  In the vast majority of cases, old `awk' programs do not
change their behavior.  However, these semantics for `OFMT' are
something to keep in mind if you must port your new style program to
older implementations of `awk'.  We recommend that instead of changing
your programs, just port `gawk' itself.  *Note Print::, for more
information on the `print' statement.

Finally, once again, where you are can matter when it comes to
converting between numbers and strings.  In *Note Locales::, we
mentioned that the local character set and language (the locale) can
affect how `gawk' matches characters.  The locale also affects numeric
formats.  In particular, for `awk' programs, it affects the decimal
point character.  The `"C"' locale, and most English-language locales,
use the period character (`.') as the decimal point.  However, many (if
not most) European and non-English locales use the comma (`,') as the
decimal point character.

The POSIX standard says that `awk' always uses the period as the decimal
point when reading the `awk' program source code, and for command-line
variable assignments (*note Other Arguments::).  However, when
interpreting input data, for `print' and `printf' output, and for
number to string conversion, the local decimal point character is used.
As of version 3.1.3, `gawk' fully complies with this aspect of the
standard.  Here are some examples indicating the difference in behavior,
on a GNU/Linux system:

     $ gawk 'BEGIN { printf "%g\n", 3.1415927 }'
     -| 3.14159
     $  LC_ALL=en_DK gawk 'BEGIN { printf "%g\n", 3.1415927 }'
     -| 3,14159
     $ echo 4,321 | gawk '{ print $1 + 1 }'
     -| 5
     $ echo 4,321 | LC_ALL=en_DK gawk '{ print $1 + 1 }'
     -| 5,321

The `en_DK' locale is for English in Denmark, where the comma acts as
the decimal point separator.  In the normal `"C"' locale, `gawk' treats
`4,321' as `4', while in the Danish locale, it's treated as the full
number, `4.321'.

---------- Footnotes ----------

(1) Pathological cases can require up to 752 digits (!), but we doubt
that you need to worry about this.


File: gawk.info,  Node: Arithmetic Ops,  Next: Concatenation,  Prev: Conversion,  Up: Expressions

5.5 Arithmetic Operators
========================

The `awk' language uses the common arithmetic operators when evaluating
expressions.  All of these arithmetic operators follow normal
precedence rules and work as you would expect them to.

The following example uses a file named `grades', which contains a list
of student names as well as three test scores per student (it's a small
class):

     Pat   100 97 58
     Sandy  84 72 93
     Chris  72 92 89

This programs takes the file `grades' and prints the average of the
scores:

     $ awk '{ sum = $2 + $3 + $4 ; avg = sum / 3
     >        print $1, avg }' grades
     -| Pat 85
     -| Sandy 83
     -| Chris 84.3333

The following list provides the arithmetic operators in `awk', in order
from the highest precedence to the lowest:

`- X'
     Negation.

`+ X'
     Unary plus; the expression is converted to a number.

`X ^ Y'
`X ** Y'
     Exponentiation; X raised to the Y power.  `2 ^ 3' has the value
     eight; the character sequence `**' is equivalent to `^'.

`X * Y'
     Multiplication.

`X / Y'
     Division;  because all numbers in `awk' are floating-point
     numbers, the result is _not_ rounded to an integer--`3 / 4' has
     the value 0.75.  (It is a common mistake, especially for C
     programmers, to forget that _all_ numbers in `awk' are
     floating-point, and that division of integer-looking constants
     produces a real number, not an integer.)

`X % Y'
     Remainder; further discussion is provided in the text, just after
     this list.

`X + Y'
     Addition.

`X - Y'
     Subtraction.

Unary plus and minus have the same precedence, the multiplication
operators all have the same precedence, and addition and subtraction
have the same precedence.

When computing the remainder of `X % Y', the quotient is rounded toward
zero to an integer and multiplied by Y. This result is subtracted from
X; this operation is sometimes known as "trunc-mod."  The following
relation always holds:

     b * int(a / b) + (a % b) == a

One possibly undesirable effect of this definition of remainder is that
`X % Y' is negative if X is negative.  Thus:

     -17 % 8 = -1

In other `awk' implementations, the signedness of the remainder may be
machine-dependent.

     NOTE: The POSIX standard only specifies the use of `^' for
     exponentiation.  For maximum portability, do not use the `**'
     operator.


File: gawk.info,  Node: Concatenation,  Next: Assignment Ops,  Prev: Arithmetic Ops,  Up: Expressions

5.6 String Concatenation
========================

     It seemed like a good idea at the time.
     Brian Kernighan

There is only one string operation: concatenation.  It does not have a
specific operator to represent it.  Instead, concatenation is performed
by writing expressions next to one another, with no operator.  For
example:

     $ awk '{ print "Field number one: " $1 }' BBS-list
     -| Field number one: aardvark
     -| Field number one: alpo-net
     ...

Without the space in the string constant after the `:', the line runs
together.  For example:

     $ awk '{ print "Field number one:" $1 }' BBS-list
     -| Field number one:aardvark
     -| Field number one:alpo-net
     ...

Because string concatenation does not have an explicit operator, it is
often necessary to insure that it happens at the right time by using
parentheses to enclose the items to concatenate.  For example, the
following code fragment does not concatenate `file' and `name' as you
might expect:

     file = "file"
     name = "name"
     print "something meaningful" > file name

It is necessary to use the following:

     print "something meaningful" > (file name)

Parentheses should be used around concatenation in all but the most
common contexts, such as on the righthand side of `='.  Be careful
about the kinds of expressions used in string concatenation.  In
particular, the order of evaluation of expressions used for
concatenation is undefined in the `awk' language.  Consider this
example:

     BEGIN {
         a = "don't"
         print (a " " (a = "panic"))
     }

It is not defined whether the assignment to `a' happens before or after
the value of `a' is retrieved for producing the concatenated value.
The result could be either `don't panic', or `panic panic'.  The
precedence of concatenation, when mixed with other operators, is often
counter-intuitive.  Consider this example:

     $ awk 'BEGIN { print -12 " " -24 }'
     -| -12-24

This "obviously" is concatenating -12, a space, and -24.  But where did
the space disappear to?  The answer lies in the combination of operator
precedences and `awk''s automatic conversion rules.  To get the desired
result, write the program in the following manner:

     $ awk 'BEGIN { print -12 " " (-24) }'
     -| -12 -24

This forces `awk' to treat the `-' on the `-24' as unary.  Otherwise,
it's parsed as follows:

         -12 (`" "' - 24)
     => -12 (0 - 24)
     => -12 (-24)
     => -12-24

As mentioned earlier, when doing concatenation, _parenthesize_.
Otherwise, you're never quite sure what you'll get.


File: gawk.info,  Node: Assignment Ops,  Next: Increment Ops,  Prev: Concatenation,  Up: Expressions

5.7 Assignment Expressions
==========================

An "assignment" is an expression that stores a (usually different)
value into a variable.  For example, let's assign the value one to the
variable `z':

     z = 1

After this expression is executed, the variable `z' has the value one.
Whatever old value `z' had before the assignment is forgotten.

Assignments can also store string values.  For example, the following
stores the value `"this food is good"' in the variable `message':

     thing = "food"
     predicate = "good"
     message = "this " thing " is " predicate

This also illustrates string concatenation.  The `=' sign is called an
"assignment operator".  It is the simplest assignment operator because
the value of the righthand operand is stored unchanged.  Most operators
(addition, concatenation, and so on) have no effect except to compute a
value.  If the value isn't used, there's no reason to use the operator.
An assignment operator is different; it does produce a value, but even
if you ignore it, the assignment still makes itself felt through the
alteration of the variable.  We call this a "side effect".

The lefthand operand of an assignment need not be a variable (*note
Variables::); it can also be a field (*note Changing Fields::) or an
array element (*note Arrays::).  These are all called "lvalues", which
means they can appear on the lefthand side of an assignment operator.
The righthand operand may be any expression; it produces the new value
that the assignment stores in the specified variable, field, or array
element. (Such values are called "rvalues".)

It is important to note that variables do _not_ have permanent types.
A variable's type is simply the type of whatever value it happens to
hold at the moment.  In the following program fragment, the variable
`foo' has a numeric value at first, and a string value later on:

     foo = 1
     print foo
     foo = "bar"
     print foo

When the second assignment gives `foo' a string value, the fact that it
previously had a numeric value is forgotten.

String values that do not begin with a digit have a numeric value of
zero. After executing the following code, the value of `foo' is five:

     foo = "a string"
     foo = foo + 5

     NOTE: Using a variable as a number and then later as a string can
     be confusing and is poor programming style.  The previous two
     examples illustrate how `awk' works, _not_ how you should write
     your programs!

An assignment is an expression, so it has a value--the same value that
is assigned.  Thus, `z = 1' is an expression with the value one.  One
consequence of this is that you can write multiple assignments together,
such as:

     x = y = z = 5

This example stores the value five in all three variables (`x', `y',
and `z').  It does so because the value of `z = 5', which is five, is
stored into `y' and then the value of `y = z = 5', which is five, is
stored into `x'.

Assignments may be used anywhere an expression is called for.  For
example, it is valid to write `x != (y = 1)' to set `y' to one, and
then test whether `x' equals one.  But this style tends to make
programs hard to read; such nesting of assignments should be avoided,
except perhaps in a one-shot program.

Aside from `=', there are several other assignment operators that do
arithmetic with the old value of the variable.  For example, the
operator `+=' computes a new value by adding the righthand value to the
old value of the variable.  Thus, the following assignment adds five to
the value of `foo':

     foo += 5

This is equivalent to the following:

     foo = foo + 5

Use whichever makes the meaning of your program clearer.

There are situations where using `+=' (or any assignment operator) is
_not_ the same as simply repeating the lefthand operand in the
righthand expression.  For example:

     # Thanks to Pat Rankin for this example
     BEGIN  {
         foo[rand()] += 5
         for (x in foo)
            print x, foo[x]

         bar[rand()] = bar[rand()] + 5
         for (x in bar)
            print x, bar[x]
     }

The indices of `bar' are practically guaranteed to be different, because
`rand' returns different values each time it is called.  (Arrays and
the `rand' function haven't been covered yet.  *Note Arrays::, and see
*Note Numeric Functions::, for more information).  This example
illustrates an important fact about assignment operators: the lefthand
expression is only evaluated _once_.  It is up to the implementation as
to which expression is evaluated first, the lefthand or the righthand.
Consider this example:

     i = 1
     a[i += 2] = i + 1

The value of `a[3]' could be either two or four.

*Note table-assign-ops:: lists the arithmetic assignment operators.  In
each case, the righthand operand is an expression whose value is
converted to a number.

Operator               Effect
--------------------------------------------------------------------------
LVALUE `+=' INCREMENT  Adds INCREMENT to the value of LVALUE.
--------------------------------------------------------------------------
LVALUE `-=' DECREMENT  Subtracts DECREMENT from the value of LVALUE.
--------------------------------------------------------------------------
LVALUE `*='            Multiplies the value of LVALUE by COEFFICIENT.
COEFFICIENT
--------------------------------------------------------------------------
LVALUE `/=' DIVISOR    Divides the value of LVALUE by DIVISOR.
--------------------------------------------------------------------------
LVALUE `%=' MODULUS    Sets LVALUE to its remainder by MODULUS.
--------------------------------------------------------------------------
LVALUE `^=' POWER
--------------------------------------------------------------------------
LVALUE `**=' POWER     Raises LVALUE to the power POWER.
--------------------------------------------------------------------------

Table 5.1: Arithmetic Assignment Operators

     NOTE: Only the `^=' operator is specified by POSIX.  For maximum
     portability, do not use the `**=' operator.

Advanced Notes: Syntactic Ambiguities Between `/=' and Regular Expressions
--------------------------------------------------------------------------

There is a syntactic ambiguity between the `/=' assignment operator and
regexp constants whose first character is an `='.  (d.c.)  This is most
notable in commercial `awk' versions.  For example:

     $ awk /==/ /dev/null
     error--> awk: syntax error at source line 1
     error-->  context is
     error-->         >>> /= <<<
     error--> awk: bailing out at source line 1

A workaround is:

     awk '/[=]=/' /dev/null

`gawk' does not have this problem, nor do the other freely available
versions described in *Note Other Versions::.


File: gawk.info,  Node: Increment Ops,  Next: Truth Values,  Prev: Assignment Ops,  Up: Expressions

5.8 Increment and Decrement Operators
=====================================

"Increment" and "decrement operators" increase or decrease the value of
a variable by one.  An assignment operator can do the same thing, so
the increment operators add no power to the `awk' language; however,
they are convenient abbreviations for very common operations.

The operator used for adding one is written `++'.  It can be used to
increment a variable either before or after taking its value.  To
pre-increment a variable `v', write `++v'.  This adds one to the value
of `v'--that new value is also the value of the expression. (The
assignment expression `v += 1' is completely equivalent.)  Writing the
`++' after the variable specifies post-increment.  This increments the
variable value just the same; the difference is that the value of the
increment expression itself is the variable's _old_ value.  Thus, if
`foo' has the value four, then the expression `foo++' has the value
four, but it changes the value of `foo' to five.  In other words, the
operator returns the old value of the variable, but with the side
effect of incrementing it.

The post-increment `foo++' is nearly the same as writing `(foo += 1) -
1'.  It is not perfectly equivalent because all numbers in `awk' are
floating-point--in floating-point, `foo + 1 - 1' does not necessarily
equal `foo'.  But the difference is minute as long as you stick to
numbers that are fairly small (less than 10e12).

Fields and array elements are incremented just like variables.  (Use
`$(i++)' when you want to do a field reference and a variable increment
at the same time.  The parentheses are necessary because of the
precedence of the field reference operator `$'.)

The decrement operator `--' works just like `++', except that it
subtracts one instead of adding it.  As with `++', it can be used before
the lvalue to pre-decrement or after it to post-decrement.  Following
is a summary of increment and decrement expressions:

`++LVALUE'
     This expression increments LVALUE, and the new value becomes the
     value of the expression.

`LVALUE++'
     This expression increments LVALUE, but the value of the expression
     is the _old_ value of LVALUE.

`--LVALUE'
     This expression is like `++LVALUE', but instead of adding, it
     subtracts.  It decrements LVALUE and delivers the value that is
     the result.

`LVALUE--'
     This expression is like `LVALUE++', but instead of adding, it
     subtracts.  It decrements LVALUE.  The value of the expression is
     the _old_ value of LVALUE.

Advanced Notes: Operator Evaluation Order
-----------------------------------------

     Doctor, doctor!  It hurts when I do this!
     So don't do that!
     Groucho Marx

What happens for something like the following?

     b = 6
     print b += b++

Or something even stranger?

     b = 6
     b += ++b + b++
     print b

In other words, when do the various side effects prescribed by the
postfix operators (`b++') take effect?  When side effects happen is
"implementation defined".  In other words, it is up to the particular
version of `awk'.  The result for the first example may be 12 or 13,
and for the second, it may be 22 or 23.

In short, doing things like this is not recommended and definitely not
anything that you can rely upon for portability.  You should avoid such
things in your own programs.


File: gawk.info,  Node: Truth Values,  Next: Typing and Comparison,  Prev: Increment Ops,  Up: Expressions

5.9 True and False in `awk'
===========================

Many programming languages have a special representation for the
concepts of "true" and "false."  Such languages usually use the special
constants `true' and `false', or perhaps their uppercase equivalents.
However, `awk' is different.  It borrows a very simple concept of true
and false from C.  In `awk', any nonzero numeric value _or_ any
nonempty string value is true.  Any other value (zero or the null
string `""') is false.  The following program prints `A strange truth
value' three times:

     BEGIN {
        if (3.1415927)
            print "A strange truth value"
        if ("Four Score And Seven Years Ago")
            print "A strange truth value"
        if (j = 57)
            print "A strange truth value"
     }

There is a surprising consequence of the "nonzero or non-null" rule:
the string constant `"0"' is actually true, because it is non-null.
(d.c.)


File: gawk.info,  Node: Typing and Comparison,  Next: Boolean Ops,  Prev: Truth Values,  Up: Expressions

5.10 Variable Typing and Comparison Expressions
===============================================

     The Guide is definitive. Reality is frequently inaccurate.
     The Hitchhiker's Guide to the Galaxy

Unlike other programming languages, `awk' variables do not have a fixed
type. Instead, they can be either a number or a string, depending upon
the value that is assigned to them.

The 1992 POSIX standard introduced the concept of a "numeric string",
which is simply a string that looks like a number--for example,
`" +2"'.  This concept is used for determining the type of a variable.
The type of the variable is important because the types of two variables
determine how they are compared.  In `gawk', variable typing follows
these rules:

   * A numeric constant or the result of a numeric operation has the
     NUMERIC attribute.

   * A string constant or the result of a string operation has the
     STRING attribute.

   * Fields, `getline' input, `FILENAME', `ARGV' elements, `ENVIRON'
     elements, and the elements of an array created by `split' that are
     numeric strings have the STRNUM attribute.  Otherwise, they have
     the STRING attribute.  Uninitialized variables also have the
     STRNUM attribute.

   * Attributes propagate across assignments but are not changed by any
     use.

The last rule is particularly important. In the following program, `a'
has numeric type, even though it is later used in a string operation:

     BEGIN {
              a = 12.345
              b = a " is a cute number"
              print b
     }

When two operands are compared, either string comparison or numeric
comparison may be used. This depends upon the attributes of the
operands, according to the following symmetric matrix:

             +---------------------------------------------
             |       STRING          NUMERIC         STRNUM
     -------+---------------------------------------------
             |
     STRING  |       string          string          string
             |
     NUMERIC |       string          numeric         numeric
             |
     STRNUM  |       string          numeric         numeric
     -------+---------------------------------------------

The basic idea is that user input that looks numeric--and _only_ user
input--should be treated as numeric, even though it is actually made of
characters and is therefore also a string.  Thus, for example, the
string constant `" +3.14"' is a string, even though it looks numeric,
and is _never_ treated as number for comparison purposes.

In short, when one operand is a "pure" string, such as a string
constant, then a string comparison is performed.  Otherwise, a numeric
comparison is performed.(1)

"Comparison expressions" compare strings or numbers for relationships
such as equality.  They are written using "relational operators", which
are a superset of those in C.  *Note table-relational-ops:: describes
them.

Expression         Result
--------------------------------------------------------------------------
X `<' Y            True if X is less than Y.
--------------------------------------------------------------------------
X `<=' Y           True if X is less than or equal to Y.
--------------------------------------------------------------------------
X `>' Y            True if X is greater than Y.
--------------------------------------------------------------------------
X `>=' Y           True if X is greater than or equal to Y.
--------------------------------------------------------------------------
X `==' Y           True if X is equal to Y.
--------------------------------------------------------------------------
X `!=' Y           True if X is not equal to Y.
--------------------------------------------------------------------------
X `~' Y            True if the string X matches the regexp denoted by Y.
--------------------------------------------------------------------------
X `!~' Y           True if the string X does not match the regexp
                   denoted by Y.
--------------------------------------------------------------------------
SUBSCRIPT `in'     True if the array ARRAY has an element with the
ARRAY              subscript SUBSCRIPT.
--------------------------------------------------------------------------

Table 5.2: Relational Operators

   Comparison expressions have the value one if true and zero if false.
When comparing operands of mixed types, numeric operands are converted
to strings using the value of `CONVFMT' (*note Conversion::).

   Strings are compared by comparing the first character of each, then
the second character of each, and so on.  Thus, `"10"' is less than
`"9"'.  If there are two strings where one is a prefix of the other,
the shorter string is less than the longer one.  Thus, `"abc"' is less
than `"abcd"'.

   It is very easy to accidentally mistype the `==' operator and leave
off one of the `=' characters.  The result is still valid `awk' code,
but the program does not do what is intended:

     if (a = b)   # oops! should be a == b
        ...
     else
        ...

Unless `b' happens to be zero or the null string, the `if' part of the
test always succeeds.  Because the operators are so similar, this kind
of error is very difficult to spot when scanning the source code.

The following table of expressions illustrates the kind of comparison
`gawk' performs, as well as what the result of the comparison is:

`1.5 <= 2.0'
     numeric comparison (true)

`"abc" >= "xyz"'
     string comparison (false)

`1.5 != " +2"'
     string comparison (true)

`"1e2" < "3"'
     string comparison (true)

`a = 2; b = "2"'
`a == b'
     string comparison (true)

`a = 2; b = " +2"'

`a == b'
     string comparison (false)

In the next example:

     $ echo 1e2 3 | awk '{ print ($1 < $2) ? "true" : "false" }'
     -| false

the result is `false' because both `$1' and `$2' are user input.  They
are numeric strings--therefore both have the STRNUM attribute,
dictating a numeric comparison.  The purpose of the comparison rules
and the use of numeric strings is to attempt to produce the behavior
that is "least surprising," while still "doing the right thing."
String comparisons and regular expression comparisons are very
different.  For example:

     x == "foo"

has the value one, or is true if the variable `x' is precisely `foo'.
By contrast:

     x ~ /foo/

has the value one if `x' contains `foo', such as `"Oh, what a fool am
I!"'.

The righthand operand of the `~' and `!~' operators may be either a
regexp constant (`/.../') or an ordinary expression. In the latter
case, the value of the expression as a string is used as a dynamic
regexp (*note Regexp Usage::; also *note Computed Regexps::).

In modern implementations of `awk', a constant regular expression in
slashes by itself is also an expression.  The regexp `/REGEXP/' is an
abbreviation for the following comparison expression:

     $0 ~ /REGEXP/

One special place where `/foo/' is _not_ an abbreviation for `$0 ~
/foo/' is when it is the righthand operand of `~' or `!~'.  *Note Using
Constant Regexps::, where this is discussed in more detail.

---------- Footnotes ----------

(1) The POSIX standard is under revision.  The revised standard's rules
for typing and comparison are the same as just described for `gawk'.


File: gawk.info,  Node: Boolean Ops,  Next: Conditional Exp,  Prev: Typing and Comparison,  Up: Expressions

5.11 Boolean Expressions
========================

A "Boolean expression" is a combination of comparison expressions or
matching expressions, using the Boolean operators "or" (`||'), "and"
(`&&'), and "not" (`!'), along with parentheses to control nesting.
The truth value of the Boolean expression is computed by combining the
truth values of the component expressions.  Boolean expressions are
also referred to as "logical expressions".  The terms are equivalent.

Boolean expressions can be used wherever comparison and matching
expressions can be used.  They can be used in `if', `while', `do', and
`for' statements (*note Statements::).  They have numeric values (one
if true, zero if false) that come into play if the result of the
Boolean expression is stored in a variable or used in arithmetic.

In addition, every Boolean expression is also a valid pattern, so you
can use one as a pattern to control the execution of rules.  The
Boolean operators are:

`BOOLEAN1 && BOOLEAN2'
     True if both BOOLEAN1 and BOOLEAN2 are true.  For example, the
     following statement prints the current input record if it contains
     both `2400' and `foo':

          if ($0 ~ /2400/ && $0 ~ /foo/) print

     The subexpression BOOLEAN2 is evaluated only if BOOLEAN1 is true.
     This can make a difference when BOOLEAN2 contains expressions that
     have side effects. In the case of `$0 ~ /foo/ && ($2 == bar++)',
     the variable `bar' is not incremented if there is no substring
     `foo' in the record.

`BOOLEAN1 || BOOLEAN2'
     True if at least one of BOOLEAN1 or BOOLEAN2 is true.  For
     example, the following statement prints all records in the input
     that contain _either_ `2400' or `foo' or both:

          if ($0 ~ /2400/ || $0 ~ /foo/) print

     The subexpression BOOLEAN2 is evaluated only if BOOLEAN1 is false.
     This can make a difference when BOOLEAN2 contains expressions
     that have side effects.

`! BOOLEAN'
     True if BOOLEAN is false.  For example, the following program
     prints `no home!' in the unusual event that the `HOME' environment
     variable is not defined:

          BEGIN { if (! ("HOME" in ENVIRON))
                         print "no home!" }

     (The `in' operator is described in *Note Reference to Elements::.)

The `&&' and `||' operators are called "short-circuit" operators
because of the way they work.  Evaluation of the full expression is
"short-circuited" if the result can be determined part way through its
evaluation.

Statements that use `&&' or `||' can be continued simply by putting a
newline after them.  But you cannot put a newline in front of either of
these operators without using backslash continuation (*note
Statements/Lines::).

The actual value of an expression using the `!' operator is either one
or zero, depending upon the truth value of the expression it is applied
to.  The `!' operator is often useful for changing the sense of a flag
variable from false to true and back again. For example, the following
program is one way to print lines in between special bracketing lines:

     $1 == "START"   { interested = ! interested; next }
     interested == 1 { print }
     $1 == "END"     { interested = ! interested; next }

The variable `interested', as with all `awk' variables, starts out
initialized to zero, which is also false.  When a line is seen whose
first field is `START', the value of `interested' is toggled to true,
using `!'. The next rule prints lines as long as `interested' is true.
When a line is seen whose first field is `END', `interested' is toggled
back to false.

     NOTE: The `next' statement is discussed in *Note Next Statement::.
     `next' tells `awk' to skip the rest of the rules, get the next
     record, and start processing the rules over again at the top.  The
     reason it's there is to avoid printing the bracketing `START' and
     `END' lines.


File: gawk.info,  Node: Conditional Exp,  Next: Function Calls,  Prev: Boolean Ops,  Up: Expressions

5.12 Conditional Expressions
============================

A "conditional expression" is a special kind of expression that has
three operands.  It allows you to use one expression's value to select
one of two other expressions.  The conditional expression is the same
as in the C language, as shown here:

     SELECTOR ? IF-TRUE-EXP : IF-FALSE-EXP

There are three subexpressions.  The first, SELECTOR, is always
computed first.  If it is "true" (not zero or not null), then
IF-TRUE-EXP is computed next and its value becomes the value of the
whole expression.  Otherwise, IF-FALSE-EXP is computed next and its
value becomes the value of the whole expression.  For example, the
following expression produces the absolute value of `x':

     x >= 0 ? x : -x

Each time the conditional expression is computed, only one of
IF-TRUE-EXP and IF-FALSE-EXP is used; the other is ignored.  This is
important when the expressions have side effects.  For example, this
conditional expression examines element `i' of either array `a' or
array `b', and increments `i':

     x == y ? a[i++] : b[i++]

This is guaranteed to increment `i' exactly once, because each time
only one of the two increment expressions is executed and the other is
not.  *Note Arrays::, for more information about arrays.

As a minor `gawk' extension, a statement that uses `?:' can be
continued simply by putting a newline after either character.  However,
putting a newline in front of either character does not work without
using backslash continuation (*note Statements/Lines::).  If `--posix'
is specified (*note Options::), then this extension is disabled.


File: gawk.info,  Node: Function Calls,  Next: Precedence,  Prev: Conditional Exp,  Up: Expressions

5.13 Function Calls
===================

A "function" is a name for a particular calculation.  This enables you
to ask for it by name at any point in the program.  For example, the
function `sqrt' computes the square root of a number.

A fixed set of functions are "built-in", which means they are available
in every `awk' program.  The `sqrt' function is one of these.  *Note
Built-in::, for a list of built-in functions and their descriptions.
In addition, you can define functions for use in your program.  *Note
User-defined::, for instructions on how to do this.

The way to use a function is with a "function call" expression, which
consists of the function name followed immediately by a list of
"arguments" in parentheses.  The arguments are expressions that provide
the raw materials for the function's calculations.  When there is more
than one argument, they are separated by commas.  If there are no
arguments, just write `()' after the function name.  The following
examples show function calls with and without arguments:

     sqrt(x^2 + y^2)        one argument
     atan2(y, x)            two arguments
     rand()                 no arguments

*Caution:* Do not put any space between the function name and the
open-parenthesis!  A user-defined function name looks just like the
name of a variable--a space would make the expression look like
concatenation of a variable with an expression inside parentheses.

With built-in functions, space before the parenthesis is harmless, but
it is best not to get into the habit of using space to avoid mistakes
with user-defined functions.  Each function expects a particular number
of arguments.  For example, the `sqrt' function must be called with a
single argument, the number of which to take the square root:

     sqrt(ARGUMENT)

Some of the built-in functions have one or more optional arguments.  If
those arguments are not supplied, the functions use a reasonable
default value.  *Note Built-in::, for full details.  If arguments are
omitted in calls to user-defined functions, then those arguments are
treated as local variables and initialized to the empty string (*note
User-defined::).

Like every other expression, the function call has a value, which is
computed by the function based on the arguments you give it.  In this
example, the value of `sqrt(ARGUMENT)' is the square root of ARGUMENT.
A function can also have side effects, such as assigning values to
certain variables or doing I/O.  The following program reads numbers,
one number per line, and prints the square root of each one:

     $ awk '{ print "The square root of", $1, "is", sqrt($1) }'
     1
     -| The square root of 1 is 1
     3
     -| The square root of 3 is 1.73205
     5
     -| The square root of 5 is 2.23607
     Ctrl-d


File: gawk.info,  Node: Precedence,  Prev: Function Calls,  Up: Expressions

5.14 Operator Precedence (How Operators Nest)
=============================================

"Operator precedence" determines how operators are grouped when
different operators appear close by in one expression.  For example,
`*' has higher precedence than `+'; thus, `a + b * c' means to multiply
`b' and `c', and then add `a' to the product (i.e., `a + (b * c)').

The normal precedence of the operators can be overruled by using
parentheses.  Think of the precedence rules as saying where the
parentheses are assumed to be.  In fact, it is wise to always use
parentheses whenever there is an unusual combination of operators,
because other people who read the program may not remember what the
precedence is in this case.  Even experienced programmers occasionally
forget the exact rules, which leads to mistakes.  Explicit parentheses
help prevent any such mistakes.

When operators of equal precedence are used together, the leftmost
operator groups first, except for the assignment, conditional, and
exponentiation operators, which group in the opposite order.  Thus, `a
- b + c' groups as `(a - b) + c' and `a = b = c' groups as `a = (b =
c)'.

The precedence of prefix unary operators does not matter as long as only
unary operators are involved, because there is only one way to interpret
them: innermost first.  Thus, `$++i' means `$(++i)' and `++$x' means
`++($x)'.  However, when another operator follows the operand, then the
precedence of the unary operators can matter.  `$x^2' means `($x)^2',
but `-x^2' means `-(x^2)', because `-' has lower precedence than `^',
whereas `$' has higher precedence.  This table presents `awk''s
operators, in order of highest to lowest precedence:

`(...)'
     Grouping.

`$'
     Field.

`++ --'
     Increment, decrement.

`^ **'
     Exponentiation.  These operators group right-to-left.

`+ - !'
     Unary plus, minus, logical "not."

`* / %'
     Multiplication, division, modulus.

`+ -'
     Addition, subtraction.

`String Concatenation'
     No special symbol is used to indicate concatenation.  The operands
     are simply written side by side (*note Concatenation::).

`< <= == !='
`> >= >> | |&'
     Relational and redirection.  The relational operators and the
     redirections have the same precedence level.  Characters such as
     `>' serve both as relationals and as redirections; the context
     distinguishes between the two meanings.

     Note that the I/O redirection operators in `print' and `printf'
     statements belong to the statement level, not to expressions.  The
     redirection does not produce an expression that could be the
     operand of another operator.  As a result, it does not make sense
     to use a redirection operator near another operator of lower
     precedence without parentheses.  Such combinations (for example,
     `print foo > a ? b : c'), result in syntax errors.  The correct
     way to write this statement is `print foo > (a ? b : c)'.

`~ !~'
     Matching, nonmatching.

`in'
     Array membership.

`&&'
     Logical "and".

`||'
     Logical "or".

`?:'
     Conditional.  This operator groups right-to-left.

`= += -= *='
`/= %= ^= **='
     Assignment.  These operators group right to left.

     NOTE: The `|&', `**', and `**=' operators are not specified by
     POSIX.  For maximum portability, do not use them.


File: gawk.info,  Node: Patterns and Actions,  Next: Arrays,  Prev: Expressions,  Up: Top

6 Patterns, Actions, and Variables
**********************************

As you have already seen, each `awk' statement consists of a pattern
with an associated action.  This major node describes how you build
patterns and actions, what kinds of things you can do within actions,
and `awk''s built-in variables.

The pattern-action rules and the statements available for use within
actions form the core of `awk' programming.  In a sense, everything
covered up to here has been the foundation that programs are built on
top of.  Now it's time to start building something useful.

* Menu:

* Pattern Overview::            What goes into a pattern.
* Using Shell Variables::       How to use shell variables with `awk'.
* Action Overview::             What goes into an action.
* Statements::                  Describes the various control statements in
                                detail.
* Built-in Variables::          Summarizes the built-in variables.


File: gawk.info,  Node: Pattern Overview,  Next: Using Shell Variables,  Up: Patterns and Actions

6.1 Pattern Elements
====================

* Menu:

* Regexp Patterns::             Using regexps as patterns.
* Expression Patterns::         Any expression can be used as a pattern.
* Ranges::                      Pairs of patterns specify record ranges.
* BEGIN/END::                   Specifying initialization and cleanup rules.
* Empty::                       The empty pattern, which matches every record.

Patterns in `awk' control the execution of rules--a rule is executed
when its pattern matches the current input record.  The following is a
summary of the types of `awk' patterns:

`/REGULAR EXPRESSION/'
     A regular expression. It matches when the text of the input record
     fits the regular expression.  (*Note Regexp::.)

`EXPRESSION'
     A single expression.  It matches when its value is nonzero (if a
     number) or non-null (if a string).  (*Note Expression Patterns::.)

`PAT1, PAT2'
     A pair of patterns separated by a comma, specifying a range of
     records.  The range includes both the initial record that matches
     PAT1 and the final record that matches PAT2.  (*Note Ranges::.)

`BEGIN'
`END'
     Special patterns for you to supply startup or cleanup actions for
     your `awk' program.  (*Note BEGIN/END::.)

`EMPTY'
     The empty pattern matches every input record.  (*Note Empty::.)


File: gawk.info,  Node: Regexp Patterns,  Next: Expression Patterns,  Up: Pattern Overview

6.1.1 Regular Expressions as Patterns
-------------------------------------

Regular expressions are one of the first kinds of patterns presented in
this book.  This kind of pattern is simply a regexp constant in the
pattern part of a rule.  Its  meaning is `$0 ~ /PATTERN/'.  The pattern
matches when the input record matches the regexp.  For example:

     /foo|bar|baz/  { buzzwords++ }
     END            { print buzzwords, "buzzwords seen" }


File: gawk.info,  Node: Expression Patterns,  Next: Ranges,  Prev: Regexp Patterns,  Up: Pattern Overview

6.1.2 Expressions as Patterns
-----------------------------

Any `awk' expression is valid as an `awk' pattern.  The pattern matches
if the expression's value is nonzero (if a number) or non-null (if a
string).  The expression is reevaluated each time the rule is tested
against a new input record.  If the expression uses fields such as
`$1', the value depends directly on the new input record's text;
otherwise, it depends on only what has happened so far in the execution
of the `awk' program.

Comparison expressions, using the comparison operators described in
*Note Typing and Comparison::, are a very common kind of pattern.
Regexp matching and nonmatching are also very common expressions.  The
left operand of the `~' and `!~' operators is a string.  The right
operand is either a constant regular expression enclosed in slashes
(`/REGEXP/'), or any expression whose string value is used as a dynamic
regular expression (*note Computed Regexps::).  The following example
prints the second field of each input record whose first field is
precisely `foo':

     $ awk '$1 == "foo" { print $2 }' BBS-list

(There is no output, because there is no BBS site with the exact name
`foo'.)  Contrast this with the following regular expression match,
which accepts any record with a first field that contains `foo':

     $ awk '$1 ~ /foo/ { print $2 }' BBS-list
     -| 555-1234
     -| 555-6699
     -| 555-6480
     -| 555-2127

A regexp constant as a pattern is also a special case of an expression
pattern.  The expression `/foo/' has the value one if `foo' appears in
the current input record. Thus, as a pattern, `/foo/' matches any
record containing `foo'.

Boolean expressions are also commonly used as patterns.  Whether the
pattern matches an input record depends on whether its subexpressions
match.  For example, the following command prints all the records in
`BBS-list' that contain both `2400' and `foo':

     $ awk '/2400/ && /foo/' BBS-list
     -| fooey        555-1234     2400/1200/300     B

The following command prints all records in `BBS-list' that contain
_either_ `2400' or `foo' (or both, of course):

     $ awk '/2400/ || /foo/' BBS-list
     -| alpo-net     555-3412     2400/1200/300     A
     -| bites        555-1675     2400/1200/300     A
     -| fooey        555-1234     2400/1200/300     B
     -| foot         555-6699     1200/300          B
     -| macfoo       555-6480     1200/300          A
     -| sdace        555-3430     2400/1200/300     A
     -| sabafoo      555-2127     1200/300          C

The following command prints all records in `BBS-list' that do _not_
contain the string `foo':

     $ awk '! /foo/' BBS-list
     -| aardvark     555-5553     1200/300          B
     -| alpo-net     555-3412     2400/1200/300     A
     -| barfly       555-7685     1200/300          A
     -| bites        555-1675     2400/1200/300     A
     -| camelot      555-0542     300               C
     -| core         555-2912     1200/300          C
     -| sdace        555-3430     2400/1200/300     A

The subexpressions of a Boolean operator in a pattern can be constant
regular expressions, comparisons, or any other `awk' expressions.  Range
patterns are not expressions, so they cannot appear inside Boolean
patterns.  Likewise, the special patterns `BEGIN' and `END', which
never match any input record, are not expressions and cannot appear
inside Boolean patterns.


File: gawk.info,  Node: Ranges,  Next: BEGIN/END,  Prev: Expression Patterns,  Up: Pattern Overview

6.1.3 Specifying Record Ranges with Patterns
--------------------------------------------

A "range pattern" is made of two patterns separated by a comma, in the
form `BEGPAT, ENDPAT'.  It is used to match ranges of consecutive input
records.  The first pattern, BEGPAT, controls where the range begins,
while ENDPAT controls where the pattern ends.  For example, the
following:

     awk '$1 == "on", $1 == "off"' myfile

prints every record in `myfile' between `on'/`off' pairs, inclusive.

A range pattern starts out by matching BEGPAT against every input
record.  When a record matches BEGPAT, the range pattern is "turned on"
and the range pattern matches this record as well.  As long as the
range pattern stays turned on, it automatically matches every input
record read.  The range pattern also matches ENDPAT against every input
record; when this succeeds, the range pattern is turned off again for
the following record.  Then the range pattern goes back to checking
BEGPAT against each record.

The record that turns on the range pattern and the one that turns it
off both match the range pattern.  If you don't want to operate on
these records, you can write `if' statements in the rule's action to
distinguish them from the records you are interested in.

It is possible for a pattern to be turned on and off by the same
record. If the record satisfies both conditions, then the action is
executed for just that record.  For example, suppose there is text
between two identical markers (e.g., the `%' symbol), each on its own
line, that should be ignored.  A first attempt would be to combine a
range pattern that describes the delimited text with the `next'
statement (not discussed yet, *note Next Statement::).  This causes
`awk' to skip any further processing of the current record and start
over again with the next input record. Such a program looks like this:

     /^%$/,/^%$/    { next }
                    { print }

This program fails because the range pattern is both turned on and
turned off by the first line, which just has a `%' on it.  To
accomplish this task, write the program in the following manner, using
a flag:

     /^%$/     { skip = ! skip; next }
     skip == 1 { next } # skip lines with `skip' set

In a range pattern, the comma (`,') has the lowest precedence of all
the operators (i.e., it is evaluated last).  Thus, the following
program attempts to combine a range pattern with another, simpler test:

     echo Yes | awk '/1/,/2/ || /Yes/'

The intent of this program is `(/1/,/2/) || /Yes/'.  However, `awk'
interprets this as `/1/, (/2/ || /Yes/)'.  This cannot be changed or
worked around; range patterns do not combine with other patterns:

     $ echo Yes | gawk '(/1/,/2/) || /Yes/'
     error--> gawk: cmd. line:1: (/1/,/2/) || /Yes/
     error--> gawk: cmd. line:1:           ^ parse error
     error--> gawk: cmd. line:2: (/1/,/2/) || /Yes/
     error--> gawk: cmd. line:2:                   ^ unexpected newline


File: gawk.info,  Node: BEGIN/END,  Next: Empty,  Prev: Ranges,  Up: Pattern Overview

6.1.4 The `BEGIN' and `END' Special Patterns
--------------------------------------------

All the patterns described so far are for matching input records.  The
`BEGIN' and `END' special patterns are different.  They supply startup
and cleanup actions for `awk' programs.  `BEGIN' and `END' rules must
have actions; there is no default action for these rules because there
is no current record when they run.  `BEGIN' and `END' rules are often
referred to as "`BEGIN' and `END' blocks" by long-time `awk'
programmers.

* Menu:

* Using BEGIN/END::             How and why to use BEGIN/END rules.
* I/O And BEGIN/END::           I/O issues in BEGIN/END rules.


File: gawk.info,  Node: Using BEGIN/END,  Next: I/O And BEGIN/END,  Up: BEGIN/END

6.1.4.1 Startup and Cleanup Actions
...................................

A `BEGIN' rule is executed once only, before the first input record is
read. Likewise, an `END' rule is executed once only, after all the
input is read.  For example:

     $ awk '
     > BEGIN { print "Analysis of \"foo\"" }
     > /foo/ { ++n }
     > END   { print "\"foo\" appears", n, "times." }' BBS-list
     -| Analysis of "foo"
     -| "foo" appears 4 times.

This program finds the number of records in the input file `BBS-list'
that contain the string `foo'.  The `BEGIN' rule prints a title for the
report.  There is no need to use the `BEGIN' rule to initialize the
counter `n' to zero, since `awk' does this automatically (*note
Variables::).  The second rule increments the variable `n' every time a
record containing the pattern `foo' is read.  The `END' rule prints the
value of `n' at the end of the run.

The special patterns `BEGIN' and `END' cannot be used in ranges or with
Boolean operators (indeed, they cannot be used with any operators).  An
`awk' program may have multiple `BEGIN' and/or `END' rules.  They are
executed in the order in which they appear: all the `BEGIN' rules at
startup and all the `END' rules at termination.  `BEGIN' and `END'
rules may be intermixed with other rules.  This feature was added in
the 1987 version of `awk' and is included in the POSIX standard.  The
original (1978) version of `awk' required the `BEGIN' rule to be placed
at the beginning of the program, the `END' rule to be placed at the
end, and only allowed one of each.  This is no longer required, but it
is a good idea to follow this template in terms of program organization
and readability.

Multiple `BEGIN' and `END' rules are useful for writing library
functions, because each library file can have its own `BEGIN' and/or
`END' rule to do its own initialization and/or cleanup.  The order in
which library functions are named on the command line controls the
order in which their `BEGIN' and `END' rules are executed.  Therefore,
you have to be careful when writing such rules in library files so that
the order in which they are executed doesn't matter.  *Note Options::,
for more information on using library functions.  *Note Library
Functions::, for a number of useful library functions.

If an `awk' program has only a `BEGIN' rule and no other rules, then
the program exits after the `BEGIN' rule is run.(1)  However, if an
`END' rule exists, then the input is read, even if there are no other
rules in the program.  This is necessary in case the `END' rule checks
the `FNR' and `NR' variables.

---------- Footnotes ----------

(1) The original version of `awk' used to keep reading and ignoring
input until the end of the file was seen.


File: gawk.info,  Node: I/O And BEGIN/END,  Prev: Using BEGIN/END,  Up: BEGIN/END

6.1.4.2 Input/Output from `BEGIN' and `END' Rules
.................................................

There are several (sometimes subtle) points to remember when doing I/O
from a `BEGIN' or `END' rule.  The first has to do with the value of
`$0' in a `BEGIN' rule.  Because `BEGIN' rules are executed before any
input is read, there simply is no input record, and therefore no
fields, when executing `BEGIN' rules.  References to `$0' and the fields
yield a null string or zero, depending upon the context.  One way to
give `$0' a real value is to execute a `getline' command without a
variable (*note Getline::).  Another way is simply to assign a value to
`$0'.

The second point is similar to the first but from the other direction.
Traditionally, due largely to implementation issues, `$0' and `NF' were
_undefined_ inside an `END' rule.  The POSIX standard specifies that
`NF' is available in an `END' rule. It contains the number of fields
from the last input record.  Most probably due to an oversight, the
standard does not say that `$0' is also preserved, although logically
one would think that it should be.  In fact, `gawk' does preserve the
value of `$0' for use in `END' rules.  Be aware, however, that Unix
`awk', and possibly other implementations, do not.

The third point follows from the first two.  The meaning of `print'
inside a `BEGIN' or `END' rule is the same as always: `print $0'.  If
`$0' is the null string, then this prints an empty line.  Many long
time `awk' programmers use an unadorned `print' in `BEGIN' and `END'
rules, to mean `print ""', relying on `$0' being null.  Although one
might generally get away with this in `BEGIN' rules, it is a very bad
idea in `END' rules, at least in `gawk'.  It is also poor style, since
if an empty line is needed in the output, the program should print one
explicitly.

Finally, the `next' and `nextfile' statements are not allowed in a
`BEGIN' rule, because the implicit
read-a-record-and-match-against-the-rules loop has not started yet.
Similarly, those statements are not valid in an `END' rule, since all
the input has been read.  (*Note Next Statement::, and see *Note
Nextfile Statement::.)


File: gawk.info,  Node: Empty,  Prev: BEGIN/END,  Up: Pattern Overview

6.1.5 The Empty Pattern
-----------------------

An empty (i.e., nonexistent) pattern is considered to match _every_
input record.  For example, the program:

     awk '{ print $1 }' BBS-list

prints the first field of every record.


File: gawk.info,  Node: Using Shell Variables,  Next: Action Overview,  Prev: Pattern Overview,  Up: Patterns and Actions

6.2 Using Shell Variables in Programs
=====================================

`awk' programs are often used as components in larger programs written
in shell.  For example, it is very common to use a shell variable to
hold a pattern that the `awk' program searches for.  There are two ways
to get the value of the shell variable into the body of the `awk'
program.

The most common method is to use shell quoting to substitute the
variable's value into the program inside the script.  For example, in
the following program:

     echo -n "Enter search pattern: "
     read pattern
     awk "/$pattern/ "'{ nmatches++ }
          END { print nmatches, "found" }' /path/to/data

the `awk' program consists of two pieces of quoted text that are
concatenated together to form the program.  The first part is
double-quoted, which allows substitution of the `pattern' variable
inside the quotes.  The second part is single-quoted.

Variable substitution via quoting works, but can be potentially messy.
It requires a good understanding of the shell's quoting rules (*note
Quoting::), and it's often difficult to correctly match up the quotes
when reading the program.

A better method is to use `awk''s variable assignment feature (*note
Assignment Options::) to assign the shell variable's value to an `awk'
variable's value.  Then use dynamic regexps to match the pattern (*note
Computed Regexps::).  The following shows how to redo the previous
example using this technique:

     echo -n "Enter search pattern: "
     read pattern
     awk -v pat="$pattern" '$0 ~ pat { nmatches++ }
            END { print nmatches, "found" }' /path/to/data

Now, the `awk' program is just one single-quoted string.  The
assignment `-v pat="$pattern"' still requires double quotes, in case
there is whitespace in the value of `$pattern'.  The `awk' variable
`pat' could be named `pattern' too, but that would be more confusing.
Using a variable also provides more flexibility, since the variable can
be used anywhere inside the program--for printing, as an array
subscript, or for any other use--without requiring the quoting tricks
at every point in the program.


File: gawk.info,  Node: Action Overview,  Next: Statements,  Prev: Using Shell Variables,  Up: Patterns and Actions

6.3 Actions
===========

An `awk' program or script consists of a series of rules and function
definitions interspersed.  (Functions are described later.  *Note
User-defined::.)  A rule contains a pattern and an action, either of
which (but not both) may be omitted.  The purpose of the "action" is to
tell `awk' what to do once a match for the pattern is found.  Thus, in
outline, an `awk' program generally looks like this:

     [PATTERN] [{ ACTION }]
     [PATTERN] [{ ACTION }]
     ...
     function NAME(ARGS) { ... }
     ...

An action consists of one or more `awk' "statements", enclosed in curly
braces (`{...}').  Each statement specifies one thing to do.  The
statements are separated by newlines or semicolons.  The curly braces
around an action must be used even if the action contains only one
statement, or if it contains no statements at all.  However, if you
omit the action entirely, omit the curly braces as well.  An omitted
action is equivalent to `{ print $0 }':

     /foo/  { }     match `foo', do nothing -- empty action
     /foo/          match `foo', print the record -- omitted action

The following types of statements are supported in `awk':

Expressions
     Call functions or assign values to variables (*note
     Expressions::).  Executing this kind of statement simply computes
     the value of the expression.  This is useful when the expression
     has side effects (*note Assignment Ops::).

Control statements
     Specify the control flow of `awk' programs.  The `awk' language
     gives you C-like constructs (`if', `for', `while', and `do') as
     well as a few special ones (*note Statements::).

Compound statements
     Consist of one or more statements enclosed in curly braces.  A
     compound statement is used in order to put several statements
     together in the body of an `if', `while', `do', or `for' statement.

Input statements
     Use the `getline' command (*note Getline::).  Also supplied in
     `awk' are the `next' statement (*note Next Statement::), and the
     `nextfile' statement (*note Nextfile Statement::).

Output statements
     Such as `print' and `printf'.  *Note Printing::.

Deletion statements
     For deleting array elements.  *Note Delete::.


File: gawk.info,  Node: Statements,  Next: Built-in Variables,  Prev: Action Overview,  Up: Patterns and Actions

6.4 Control Statements in Actions
=================================

"Control statements", such as `if', `while', and so on, control the
flow of execution in `awk' programs.  Most of the control statements in
`awk' are patterned on similar statements in C.

All the control statements start with special keywords, such as `if'
and `while', to distinguish them from simple expressions.  Many control
statements contain other statements.  For example, the `if' statement
contains another statement that may or may not be executed.  The
contained statement is called the "body".  To include more than one
statement in the body, group them into a single "compound statement"
with curly braces, separating them with newlines or semicolons.

* Menu:

* If Statement::                Conditionally execute some `awk'
                                statements.
* While Statement::             Loop until some condition is satisfied.
* Do Statement::                Do specified action while looping until some
                                condition is satisfied.
* For Statement::               Another looping statement, that provides
                                initialization and increment clauses.
* Switch Statement::            Switch/case evaluation for conditional
                                execution of statements based on a value.
* Break Statement::             Immediately exit the innermost enclosing loop.
* Continue Statement::          Skip to the end of the innermost enclosing
                                loop.
* Next Statement::              Stop processing the current input record.
* Nextfile Statement::          Stop processing the current file.
* Exit Statement::              Stop execution of `awk'.


File: gawk.info,  Node: If Statement,  Next: While Statement,  Up: Statements

6.4.1 The `if'-`else' Statement
-------------------------------

The `if'-`else' statement is `awk''s decision-making statement.  It
looks like this:

     if (CONDITION) THEN-BODY [else ELSE-BODY]

The CONDITION is an expression that controls what the rest of the
statement does.  If the CONDITION is true, THEN-BODY is executed;
otherwise, ELSE-BODY is executed.  The `else' part of the statement is
optional.  The condition is considered false if its value is zero or
the null string; otherwise, the condition is true.  Refer to the
following:

     if (x % 2 == 0)
         print "x is even"
     else
         print "x is odd"

In this example, if the expression `x % 2 == 0' is true (that is, if
the value of `x' is evenly divisible by two), then the first `print'
statement is executed; otherwise, the second `print' statement is
executed.  If the `else' keyword appears on the same line as THEN-BODY
and THEN-BODY is not a compound statement (i.e., not surrounded by
curly braces), then a semicolon must separate THEN-BODY from the `else'.
To illustrate this, the previous example can be rewritten as:

     if (x % 2 == 0) print "x is even"; else
             print "x is odd"

If the `;' is left out, `awk' can't interpret the statement and it
produces a syntax error.  Don't actually write programs this way,
because a human reader might fail to see the `else' if it is not the
first thing on its line.


File: gawk.info,  Node: While Statement,  Next: Do Statement,  Prev: If Statement,  Up: Statements

6.4.2 The `while' Statement
---------------------------

In programming, a "loop" is a part of a program that can be executed
two or more times in succession.  The `while' statement is the simplest
looping statement in `awk'.  It repeatedly executes a statement as long
as a condition is true.  For example:

     while (CONDITION)
       BODY

BODY is a statement called the "body" of the loop, and CONDITION is an
expression that controls how long the loop keeps running.  The first
thing the `while' statement does is test the CONDITION.  If the
CONDITION is true, it executes the statement BODY.  (The CONDITION is
true when the value is not zero and not a null string.)  After BODY has
been executed, CONDITION is tested again, and if it is still true, BODY
is executed again.  This process repeats until the CONDITION is no
longer true.  If the CONDITION is initially false, the body of the loop
is never executed and `awk' continues with the statement following the
loop.  This example prints the first three fields of each record, one
per line:

     awk '{ i = 1
            while (i <= 3) {
                print $i
                i++
            }
     }' inventory-shipped

The body of this loop is a compound statement enclosed in braces,
containing two statements.  The loop works in the following manner:
first, the value of `i' is set to one.  Then, the `while' statement
tests whether `i' is less than or equal to three.  This is true when
`i' equals one, so the `i'-th field is printed.  Then the `i++'
increments the value of `i' and the loop repeats.  The loop terminates
when `i' reaches four.

A newline is not required between the condition and the body; however
using one makes the program clearer unless the body is a compound
statement or else is very simple.  The newline after the open-brace
that begins the compound statement is not required either, but the
program is harder to read without it.


File: gawk.info,  Node: Do Statement,  Next: For Statement,  Prev: While Statement,  Up: Statements

6.4.3 The `do'-`while' Statement
--------------------------------

The `do' loop is a variation of the `while' looping statement.  The
`do' loop executes the BODY once and then repeats the BODY as long as
the CONDITION is true.  It looks like this:

     do
       BODY
     while (CONDITION)

Even if the CONDITION is false at the start, the BODY is executed at
least once (and only once, unless executing BODY makes CONDITION true).
Contrast this with the corresponding `while' statement:

     while (CONDITION)
       BODY

This statement does not execute BODY even once if the CONDITION is
false to begin with.  The following is an example of a `do' statement:

     {      i = 1
            do {
               print $0
               i++
            } while (i <= 10)
     }

This program prints each input record 10 times.  However, it isn't a
very realistic example, since in this case an ordinary `while' would do
just as well.  This situation reflects actual experience; only
occasionally is there a real use for a `do' statement.


File: gawk.info,  Node: For Statement,  Next: Switch Statement,  Prev: Do Statement,  Up: Statements

6.4.4 The `for' Statement
-------------------------

The `for' statement makes it more convenient to count iterations of a
loop.  The general form of the `for' statement looks like this:

     for (INITIALIZATION; CONDITION; INCREMENT)
       BODY

The INITIALIZATION, CONDITION, and INCREMENT parts are arbitrary `awk'
expressions, and BODY stands for any `awk' statement.

The `for' statement starts by executing INITIALIZATION.  Then, as long
as the CONDITION is true, it repeatedly executes BODY and then
INCREMENT.  Typically, INITIALIZATION sets a variable to either zero or
one, INCREMENT adds one to it, and CONDITION compares it against the
desired number of iterations.  For example:

     awk '{ for (i = 1; i <= 3; i++)
               print $i
     }' inventory-shipped

This prints the first three fields of each input record, with one field
per line.

It isn't possible to set more than one variable in the INITIALIZATION
part without using a multiple assignment statement such as `x = y = 0'.
This makes sense only if all the initial values are equal.  (But it is
possible to initialize additional variables by writing their
assignments as separate statements preceding the `for' loop.)

The same is true of the INCREMENT part. Incrementing additional
variables requires separate statements at the end of the loop.  The C
compound expression, using C's comma operator, is useful in this
context but it is not supported in `awk'.

Most often, INCREMENT is an increment expression, as in the previous
example.  But this is not required; it can be any expression
whatsoever.  For example, the following statement prints all the powers
of two between 1 and 100:

     for (i = 1; i <= 100; i *= 2)
       print i

If there is nothing to be done, any of the three expressions in the
parentheses following the `for' keyword may be omitted.  Thus,
`for (; x > 0;)' is equivalent to `while (x > 0)'.  If the CONDITION is
omitted, it is treated as true, effectively yielding an "infinite loop"
(i.e., a loop that never terminates).

In most cases, a `for' loop is an abbreviation for a `while' loop, as
shown here:

     INITIALIZATION
     while (CONDITION) {
       BODY
       INCREMENT
     }

The only exception is when the `continue' statement (*note Continue
Statement::) is used inside the loop. Changing a `for' statement to a
`while' statement in this way can change the effect of the `continue'
statement inside the loop.

The `awk' language has a `for' statement in addition to a `while'
statement because a `for' loop is often both less work to type and more
natural to think of.  Counting the number of iterations is very common
in loops.  It can be easier to think of this counting as part of
looping rather than as something to do inside the loop.

There is an alternate version of the `for' loop, for iterating over all
the indices of an array:

     for (i in array)
         DO SOMETHING WITH array[i]

*Note Scanning an Array::, for more information on this version of the
`for' loop.


File: gawk.info,  Node: Switch Statement,  Next: Break Statement,  Prev: For Statement,  Up: Statements

6.4.5 The `switch' Statement
----------------------------

     NOTE: This node describes an experimental feature added in `gawk'
     3.1.3.  It is _not_ enabled by default. To enable it, use the
     `--enable-switch' option to `configure' when `gawk' is being
     configured and built.  *Note Additional Configuration Options::,
     for more information.

The `switch' statement allows the evaluation of an expression and the
execution of statements based on a `case' match. Case statements are
checked for a match in the order they are defined.  If no suitable
`case' is found, the `default' section is executed, if supplied.

Each `case' contains a single constant, be it numeric, string, or
regexp.  The `switch' expression is evaluated, and then each `case''s
constant is compared against the result in turn. The type of constant
determines the comparison: numeric or string do the usual comparisons.
A regexp constant does a regular expression match against the string
value of the original expression.  The general form of the `switch'
statement looks like this:

     switch (EXPRESSION) {
     case VALUE OR REGULAR EXPRESSION:
         CASE-BODY
     default:
         DEFAULT-BODY
     }

Control flow in the `switch' statement works as it does in C. Once a
match to a given case is made, case statement bodies are executed until
a `break', `continue', `next', `nextfile'  or `exit' is encountered, or
the end of the `switch' statement itself. For example:

     switch (NR * 2 + 1) {
     case 3:
     case "11":
         print NR - 1
         break

     case /2[[:digit:]]+/:
         print NR

     default:
         print NR + 1

     case -1:
         print NR * -1
     }

Note that if none of the statements specified above halt execution of a
matched `case' statement, execution falls through to the next `case'
until execution halts. In the above example, for any case value
starting with `2' followed by one or more digits, the `print' statement
is executed and then falls through into the `default' section,
executing its `print' statement. In turn, the -1 case will also be
executed since the `default' does not halt execution.


File: gawk.info,  Node: Break Statement,  Next: Continue Statement,  Prev: Switch Statement,  Up: Statements

6.4.6 The `break' Statement
---------------------------

The `break' statement jumps out of the innermost `for', `while', or
`do' loop that encloses it.  The following example finds the smallest
divisor of any integer, and also identifies prime numbers:

     # find smallest divisor of num
     {
        num = $1
        for (div = 2; div*div <= num; div++)
          if (num % div == 0)
            break
        if (num % div == 0)
          printf "Smallest divisor of %d is %d\n", num, div
        else
          printf "%d is prime\n", num
     }

When the remainder is zero in the first `if' statement, `awk'
immediately "breaks out" of the containing `for' loop.  This means that
`awk' proceeds immediately to the statement following the loop and
continues processing.  (This is very different from the `exit'
statement, which stops the entire `awk' program.  *Note Exit
Statement::.)

Th following program illustrates how the CONDITION of a `for' or
`while' statement could be replaced with a `break' inside an `if':

     # find smallest divisor of num
     {
       num = $1
       for (div = 2; ; div++) {
         if (num % div == 0) {
           printf "Smallest divisor of %d is %d\n", num, div
           break
         }
         if (div*div > num) {
           printf "%d is prime\n", num
           break
         }
       }
     }

The `break' statement has no meaning when used outside the body of a
loop.  However, although it was never documented, historical
implementations of `awk' treated the `break' statement outside of a
loop as if it were a `next' statement (*note Next Statement::).  Recent
versions of Unix `awk' no longer allow this usage.  `gawk' supports
this use of `break' only if `--traditional' has been specified on the
command line (*note Options::).  Otherwise, it is treated as an error,
since the POSIX standard specifies that `break' should only be used
inside the body of a loop.  (d.c.)


File: gawk.info,  Node: Continue Statement,  Next: Next Statement,  Prev: Break Statement,  Up: Statements

6.4.7 The `continue' Statement
------------------------------

As with `break', the `continue' statement is used only inside `for',
`while', and `do' loops.  It skips over the rest of the loop body,
causing the next cycle around the loop to begin immediately.  Contrast
this with `break', which jumps out of the loop altogether.

The `continue' statement in a `for' loop directs `awk' to skip the rest
of the body of the loop and resume execution with the
increment-expression of the `for' statement.  The following program
illustrates this fact:

     BEGIN {
          for (x = 0; x <= 20; x++) {
              if (x == 5)
                  continue
              printf "%d ", x
          }
          print ""
     }

This program prints all the numbers from 0 to 20--except for 5, for
which the `printf' is skipped.  Because the increment `x++' is not
skipped, `x' does not remain stuck at 5.  Contrast the `for' loop from
the previous example with the following `while' loop:

     BEGIN {
          x = 0
          while (x <= 20) {
              if (x == 5)
                  continue
              printf "%d ", x
              x++
          }
          print ""
     }

This program loops forever once `x' reaches 5.

The `continue' statement has no meaning when used outside the body of a
loop.  Historical versions of `awk' treated a `continue' statement
outside a loop the same way they treated a `break' statement outside a
loop: as if it were a `next' statement (*note Next Statement::).
Recent versions of Unix `awk' no longer work this way, and `gawk'
allows it only if `--traditional' is specified on the command line
(*note Options::).  Just like the `break' statement, the POSIX standard
specifies that `continue' should only be used inside the body of a loop.
(d.c.)


File: gawk.info,  Node: Next Statement,  Next: Nextfile Statement,  Prev: Continue Statement,  Up: Statements

6.4.8 The `next' Statement
--------------------------

The `next' statement forces `awk' to immediately stop processing the
current record and go on to the next record.  This means that no
further rules are executed for the current record, and the rest of the
current rule's action isn't executed.

Contrast this with the effect of the `getline' function (*note
Getline::).  That also causes `awk' to read the next record
immediately, but it does not alter the flow of control in any way
(i.e., the rest of the current action executes with a new input record).

At the highest level, `awk' program execution is a loop that reads an
input record and then tests each rule's pattern against it.  If you
think of this loop as a `for' statement whose body contains the rules,
then the `next' statement is analogous to a `continue' statement. It
skips to the end of the body of this implicit loop and executes the
increment (which reads another record).

For example, suppose an `awk' program works only on records with four
fields, and it shouldn't fail when given bad input.  To avoid
complicating the rest of the program, write a "weed out" rule near the
beginning, in the following manner:

     NF != 4 {
       err = sprintf("%s:%d: skipped: NF != 4\n", FILENAME, FNR)
       print err > "/dev/stderr"
       next
     }

Because of the `next' statement, the program's subsequent rules won't
see the bad record.  The error message is redirected to the standard
error output stream, as error messages should be.  For more detail see
*Note Special Files::.

According to the POSIX standard, the behavior is undefined if the
`next' statement is used in a `BEGIN' or `END' rule.  `gawk' treats it
as a syntax error.  Although POSIX permits it, some other `awk'
implementations don't allow the `next' statement inside function bodies
(*note User-defined::).  Just as with any other `next' statement, a
`next' statement inside a function body reads the next record and
starts processing it with the first rule in the program.  If the `next'
statement causes the end of the input to be reached, then the code in
any `END' rules is executed.  *Note BEGIN/END::.


File: gawk.info,  Node: Nextfile Statement,  Next: Exit Statement,  Prev: Next Statement,  Up: Statements

6.4.9 Using `gawk''s `nextfile' Statement
-----------------------------------------

`gawk' provides the `nextfile' statement, which is similar to the
`next' statement.  However, instead of abandoning processing of the
current record, the `nextfile' statement instructs `gawk' to stop
processing the current data file.

The `nextfile' statement is a `gawk' extension.  In most other `awk'
implementations, or if `gawk' is in compatibility mode (*note
Options::), `nextfile' is not special.

Upon execution of the `nextfile' statement, `FILENAME' is updated to
the name of the next data file listed on the command line, `FNR' is
reset to one, `ARGIND' is incremented, and processing starts over with
the first rule in the program.  (`ARGIND' hasn't been introduced yet.
*Note Built-in Variables::.)  If the `nextfile' statement causes the
end of the input to be reached, then the code in any `END' rules is
executed.  *Note BEGIN/END::.

The `nextfile' statement is useful when there are many data files to
process but it isn't necessary to process every record in every file.
Normally, in order to move on to the next data file, a program has to
continue scanning the unwanted records.  The `nextfile' statement
accomplishes this much more efficiently.

While one might think that `close(FILENAME)' would accomplish the same
as `nextfile', this isn't true.  `close' is reserved for closing files,
pipes, and coprocesses that are opened with redirections.  It is not
related to the main processing that `awk' does with the files listed in
`ARGV'.

If it's necessary to use an `awk' version that doesn't support
`nextfile', see *Note Nextfile Function::, for a user-defined function
that simulates the `nextfile' statement.

The current version of the Bell Laboratories `awk' (*note Other
Versions::) also supports `nextfile'.  However, it doesn't allow the
`nextfile' statement inside function bodies (*note User-defined::).
`gawk' does; a `nextfile' inside a function body reads the next record
and starts processing it with the first rule in the program, just as
any other `nextfile' statement.

*Caution:*  Versions of `gawk' prior to 3.0 used two words (`next
file') for the `nextfile' statement.  In version 3.0, this was changed
to one word, because the treatment of `file' was inconsistent. When it
appeared after `next', `file' was a keyword; otherwise, it was a
regular identifier.  The old usage is no longer accepted; `next file'
generates a syntax error.


File: gawk.info,  Node: Exit Statement,  Prev: Nextfile Statement,  Up: Statements

6.4.10 The `exit' Statement
---------------------------

The `exit' statement causes `awk' to immediately stop executing the
current rule and to stop processing input; any remaining input is
ignored.  The `exit' statement is written as follows:

     exit [RETURN CODE]

When an `exit' statement is executed from a `BEGIN' rule, the program
stops processing everything immediately.  No input records are read.
However, if an `END' rule is present, as part of executing the `exit'
statement, the `END' rule is executed (*note BEGIN/END::).  If `exit'
is used as part of an `END' rule, it causes the program to stop
immediately.

An `exit' statement that is not part of a `BEGIN' or `END' rule stops
the execution of any further automatic rules for the current record,
skips reading any remaining input records, and executes the `END' rule
if there is one.

In such a case, if you don't want the `END' rule to do its job, set a
variable to nonzero before the `exit' statement and check that variable
in the `END' rule.  *Note Assert Function::, for an example that does
this.

If an argument is supplied to `exit', its value is used as the exit
status code for the `awk' process.  If no argument is supplied, `exit'
returns status zero (success).  In the case where an argument is
supplied to a first `exit' statement, and then `exit' is called a
second time from an `END' rule with no argument, `awk' uses the
previously supplied exit value.  (d.c.)

For example, suppose an error condition occurs that is difficult or
impossible to handle.  Conventionally, programs report this by exiting
with a nonzero status.  An `awk' program can do this using an `exit'
statement with a nonzero argument, as shown in the following example:

     BEGIN {
            if (("date" | getline date_now) <= 0) {
              print "Can't get system date" > "/dev/stderr"
              exit 1
            }
            print "current date is", date_now
            close("date")
     }


File: gawk.info,  Node: Built-in Variables,  Prev: Statements,  Up: Patterns and Actions

6.5 Built-in Variables
======================

Most `awk' variables are available to use for your own purposes; they
never change unless your program assigns values to them, and they never
affect anything unless your program examines them.  However, a few
variables in `awk' have special built-in meanings.  `awk' examines some
of these automatically, so that they enable you to tell `awk' how to do
certain things.  Others are set automatically by `awk', so that they
carry information from the internal workings of `awk' to your program.

This minor node documents all the built-in variables of `gawk', most of
which are also documented in the chapters describing their areas of
activity.

* Menu:

* User-modified::               Built-in variables that you change to control
                                `awk'.
* Auto-set::                    Built-in variables where `awk' gives
                                you information.
* ARGC and ARGV::               Ways to use `ARGC' and `ARGV'.


File: gawk.info,  Node: User-modified,  Next: Auto-set,  Up: Built-in Variables

6.5.1 Built-in Variables That Control `awk'
-------------------------------------------

The following is an alphabetical list of variables that you can change
to control how `awk' does certain things. The variables that are
specific to `gawk' are marked with a pound sign (`#').

`BINMODE #'
     On non-POSIX systems, this variable specifies use of binary mode
     for all I/O.  Numeric values of one, two, or three specify that
     input files, output files, or all files, respectively, should use
     binary I/O.  Alternatively, string values of `"r"' or `"w"'
     specify that input files and output files, respectively, should
     use binary I/O.  A string value of `"rw"' or `"wr"' indicates that
     all files should use binary I/O.  Any other string value is
     equivalent to `"rw"', but `gawk' generates a warning message.
     `BINMODE' is described in more detail in *Note PC Using::.

     This variable is a `gawk' extension.  In other `awk'
     implementations (except `mawk', *note Other Versions::), or if
     `gawk' is in compatibility mode (*note Options::), it is not
     special.

`CONVFMT'
     This string controls conversion of numbers to strings (*note
     Conversion::).  It works by being passed, in effect, as the first
     argument to the `sprintf' function (*note String Functions::).
     Its default value is `"%.6g"'.  `CONVFMT' was introduced by the
     POSIX standard.

`FIELDWIDTHS #'
     This is a space-separated list of columns that tells `gawk' how to
     split input with fixed columnar boundaries.  Assigning a value to
     `FIELDWIDTHS' overrides the use of `FS' for field splitting.
     *Note Constant Size::, for more information.

     If `gawk' is in compatibility mode (*note Options::), then
     `FIELDWIDTHS' has no special meaning, and field-splitting
     operations occur based exclusively on the value of `FS'.

`FS'
     This is the input field separator (*note Field Separators::).  The
     value is a single-character string or a multi-character regular
     expression that matches the separations between fields in an input
     record.  If the value is the null string (`""'), then each
     character in the record becomes a separate field.  (This behavior
     is a `gawk' extension. POSIX `awk' does not specify the behavior
     when `FS' is the null string.)

     The default value is `" "', a string consisting of a single space.
     As a special exception, this value means that any sequence of
     spaces, tabs, and/or newlines is a single separator.(1)  It also
     causes spaces, tabs, and newlines at the beginning and end of a
     record to be ignored.

     You can set the value of `FS' on the command line using the `-F'
     option:

          awk -F, 'PROGRAM' INPUT-FILES

     If `gawk' is using `FIELDWIDTHS' for field splitting, assigning a
     value to `FS' causes `gawk' to return to the normal, `FS'-based
     field splitting. An easy way to do this is to simply say `FS =
     FS', perhaps with an explanatory comment.

`IGNORECASE #'
     If `IGNORECASE' is nonzero or non-null, then all string comparisons
     and all regular expression matching are case independent.  Thus,
     regexp matching with `~' and `!~', as well as the `gensub',
     `gsub', `index', `match', `split', and `sub' functions, record
     termination with `RS', and field splitting with `FS', all ignore
     case when doing their particular regexp operations.  However, the
     value of `IGNORECASE' does _not_ affect array subscripting and it
     does not affect field splitting when using a single-character
     field separator.  *Note Case-sensitivity::.

     If `gawk' is in compatibility mode (*note Options::), then
     `IGNORECASE' has no special meaning.  Thus, string and regexp
     operations are always case-sensitive.

`LINT #'
     When this variable is true (nonzero or non-null), `gawk' behaves
     as if the `--lint' command-line option is in effect.  (*note
     Options::).  With a value of `"fatal"', lint warnings become fatal
     errors.  With a value of `"invalid"', only warnings about things
     that are actually invalid are issued. (This is not fully
     implemented yet.)  Any other true value prints nonfatal warnings.
     Assigning a false value to `LINT' turns off the lint warnings.

     This variable is a `gawk' extension.  It is not special in other
     `awk' implementations.  Unlike the other special variables,
     changing `LINT' does affect the production of lint warnings, even
     if `gawk' is in compatibility mode.  Much as the `--lint' and
     `--traditional' options independently control different aspects of
     `gawk''s behavior, the control of lint warnings during program
     execution is independent of the flavor of `awk' being executed.

`OFMT'
     This string controls conversion of numbers to strings (*note
     Conversion::) for printing with the `print' statement.  It works
     by being passed as the first argument to the `sprintf' function
     (*note String Functions::).  Its default value is `"%.6g"'.
     Earlier versions of `awk' also used `OFMT' to specify the format
     for converting numbers to strings in general expressions; this is
     now done by `CONVFMT'.

`OFS'
     This is the output field separator (*note Output Separators::).
     It is output between the fields printed by a `print' statement.
     Its default value is `" "', a string consisting of a single space.

`ORS'
     This is the output record separator.  It is output at the end of
     every `print' statement.  Its default value is `"\n"', the newline
     character.  (*Note Output Separators::.)

`RS'
     This is `awk''s input record separator.  Its default value is a
     string containing a single newline character, which means that an
     input record consists of a single line of text.  It can also be
     the null string, in which case records are separated by runs of
     blank lines.  If it is a regexp, records are separated by matches
     of the regexp in the input text.  (*Note Records::.)

     The ability for `RS' to be a regular expression is a `gawk'
     extension.  In most other `awk' implementations, or if `gawk' is
     in compatibility mode (*note Options::), just the first character
     of `RS''s value is used.

`SUBSEP'
     This is the subscript separator.  It has the default value of
     `"\034"' and is used to separate the parts of the indices of a
     multidimensional array.  Thus, the expression `foo["A", "B"]'
     really accesses `foo["A\034B"]' (*note Multi-dimensional::).

`TEXTDOMAIN #'
     This variable is used for internationalization of programs at the
     `awk' level.  It sets the default text domain for specially marked
     string constants in the source text, as well as for the
     `dcgettext', `dcngettext' and `bindtextdomain' functions (*note
     Internationalization::).  The default value of `TEXTDOMAIN' is
     `"messages"'.

     This variable is a `gawk' extension.  In other `awk'
     implementations, or if `gawk' is in compatibility mode (*note
     Options::), it is not special.

---------- Footnotes ----------

(1) In POSIX `awk', newline does not count as whitespace.


File: gawk.info,  Node: Auto-set,  Next: ARGC and ARGV,  Prev: User-modified,  Up: Built-in Variables

6.5.2 Built-in Variables That Convey Information
------------------------------------------------

The following is an alphabetical list of variables that `awk' sets
automatically on certain occasions in order to provide information to
your program.  The variables that are specific to `gawk' are marked
with a pound sign (`#').

`ARGC, ARGV'
     The command-line arguments available to `awk' programs are stored
     in an array called `ARGV'.  `ARGC' is the number of command-line
     arguments present.  *Note Other Arguments::.  Unlike most `awk'
     arrays, `ARGV' is indexed from 0 to `ARGC' - 1.  In the following
     example:

          $ awk 'BEGIN {
          >         for (i = 0; i < ARGC; i++)
          >             print ARGV[i]
          >      }' inventory-shipped BBS-list
          -| awk
          -| inventory-shipped
          -| BBS-list

     `ARGV[0]' contains `"awk"', `ARGV[1]' contains
     `"inventory-shipped"', and `ARGV[2]' contains `"BBS-list"'.  The
     value of `ARGC' is three, one more than the index of the last
     element in `ARGV', because the elements are numbered from zero.

     The names `ARGC' and `ARGV', as well as the convention of indexing
     the array from 0 to `ARGC' - 1, are derived from the C language's
     method of accessing command-line arguments.

     The value of `ARGV[0]' can vary from system to system.  Also, you
     should note that the program text is _not_ included in `ARGV', nor
     are any of `awk''s command-line options.  *Note ARGC and ARGV::,
     for information about how `awk' uses these variables.

`ARGIND #'
     The index in `ARGV' of the current file being processed.  Every
     time `gawk' opens a new data file for processing, it sets `ARGIND'
     to the index in `ARGV' of the file name.  When `gawk' is
     processing the input files, `FILENAME == ARGV[ARGIND]' is always
     true.

     This variable is useful in file processing; it allows you to tell
     how far along you are in the list of data files as well as to
     distinguish between successive instances of the same file name on
     the command line.

     While you can change the value of `ARGIND' within your `awk'
     program, `gawk' automatically sets it to a new value when the next
     file is opened.

     This variable is a `gawk' extension.  In other `awk'
     implementations, or if `gawk' is in compatibility mode (*note
     Options::), it is not special.

`ENVIRON'
     An associative array that contains the values of the environment.
     The array indices are the environment variable names; the elements
     are the values of the particular environment variables.  For
     example, `ENVIRON["HOME"]' might be `/home/arnold'.  Changing this
     array does not affect the environment passed on to any programs
     that `awk' may spawn via redirection or the `system' function.

     Some operating systems may not have environment variables.  On
     such systems, the `ENVIRON' array is empty (except for
     `ENVIRON["AWKPATH"]', *note AWKPATH Variable::).

`ERRNO #'
     If a system error occurs during a redirection for `getline',
     during a read for `getline', or during a `close' operation, then
     `ERRNO' contains a string describing the error.

     `ERRNO' works similarly to the C variable `errno'.  In particular
     `gawk' _never_ clears it (sets it to zero or `""').  Thus, you
     should only expect its value to be meaningful when an I/O
     operation returns a failure value, such as `getline' returning -1.
     You are, of course, free to clear it yourself before doing an I/O
     operation.

     This variable is a `gawk' extension.  In other `awk'
     implementations, or if `gawk' is in compatibility mode (*note
     Options::), it is not special.

`FILENAME'
     The name of the file that `awk' is currently reading.  When no
     data files are listed on the command line, `awk' reads from the
     standard input and `FILENAME' is set to `"-"'.  `FILENAME' is
     changed each time a new file is read (*note Reading Files::).
     Inside a `BEGIN' rule, the value of `FILENAME' is `""', since
     there are no input files being processed yet.(1) (d.c.)  Note,
     though, that using `getline' (*note Getline::) inside a `BEGIN'
     rule can give `FILENAME' a value.

`FNR'
     The current record number in the current file.  `FNR' is
     incremented each time a new record is read (*note Getline::).  It
     is reinitialized to zero each time a new input file is started.

`NF'
     The number of fields in the current input record.  `NF' is set
     each time a new record is read, when a new field is created or
     when `$0' changes (*note Fields::).

     Unlike most of the variables described in this node, assigning a
     value to `NF' has the potential to affect `awk''s internal
     workings.  In particular, assignments to `NF' can be used to
     create or remove fields from the current record: *Note Changing
     Fields::.

`NR'
     The number of input records `awk' has processed since the
     beginning of the program's execution (*note Records::).  `NR' is
     incremented each time a new record is read.

`PROCINFO #'
     The elements of this array provide access to information about the
     running `awk' program.  The following elements (listed
     alphabetically) are guaranteed to be available:

    `PROCINFO["egid"]'
          The value of the `getegid' system call.

    `PROCINFO["euid"]'
          The value of the `geteuid' system call.

    `PROCINFO["FS"]'
          This is `"FS"' if field splitting with `FS' is in effect, or
          it is `"FIELDWIDTHS"' if field splitting with `FIELDWIDTHS'
          is in effect.

    `PROCINFO["gid"]'
          The value of the `getgid' system call.

    `PROCINFO["pgrpid"]'
          The process group ID of the current process.

    `PROCINFO["pid"]'
          The process ID of the current process.

    `PROCINFO["ppid"]'
          The parent process ID of the current process.

    `PROCINFO["uid"]'
          The value of the `getuid' system call.

    `PROCINFO["version"]'
          The version of `gawk'. This is available from version 3.1.4
          and later.

     On some systems, there may be elements in the array, `"group1"'
     through `"groupN"' for some N. N is the number of supplementary
     groups that the process has.  Use the `in' operator to test for
     these elements (*note Reference to Elements::).

     This array is a `gawk' extension.  In other `awk' implementations,
     or if `gawk' is in compatibility mode (*note Options::), it is not
     special.

`RLENGTH'
     The length of the substring matched by the `match' function (*note
     String Functions::).  `RLENGTH' is set by invoking the `match'
     function.  Its value is the length of the matched string, or -1 if
     no match is found.

`RSTART'
     The start-index in characters of the substring that is matched by
     the `match' function (*note String Functions::).  `RSTART' is set
     by invoking the `match' function.  Its value is the position of
     the string where the matched substring starts, or zero if no match
     was found.

`RT #'
     This is set each time a record is read. It contains the input text
     that matched the text denoted by `RS', the record separator.

     This variable is a `gawk' extension.  In other `awk'
     implementations, or if `gawk' is in compatibility mode (*note
     Options::), it is not special.

Advanced Notes: Changing `NR' and `FNR'
---------------------------------------

`awk' increments `NR' and `FNR' each time it reads a record, instead of
setting them to the absolute value of the number of records read.  This
means that a program can change these variables and their new values
are incremented for each record.  (d.c.)  This is demonstrated in the
following example:

     $ echo '1
     > 2
     > 3
     > 4' | awk 'NR == 2 { NR = 17 }
     > { print NR }'
     -| 1
     -| 17
     -| 18
     -| 19

Before `FNR' was added to the `awk' language (*note V7/SVR3.1::), many
`awk' programs used this feature to track the number of records in a
file by resetting `NR' to zero when `FILENAME' changed.

---------- Footnotes ----------

(1) Some early implementations of Unix `awk' initialized `FILENAME' to
`"-"', even if there were data files to be processed. This behavior was
incorrect and should not be relied upon in your programs.


File: gawk.info,  Node: ARGC and ARGV,  Prev: Auto-set,  Up: Built-in Variables

6.5.4 Using `ARGC' and `ARGV'
-----------------------------

*Note Auto-set::, presented the following program describing the
information contained in `ARGC' and `ARGV':

     $ awk 'BEGIN {
     >        for (i = 0; i < ARGC; i++)
     >            print ARGV[i]
     >      }' inventory-shipped BBS-list
     -| awk
     -| inventory-shipped
     -| BBS-list

In this example, `ARGV[0]' contains `awk', `ARGV[1]' contains
`inventory-shipped', and `ARGV[2]' contains `BBS-list'.  Notice that
the `awk' program is not entered in `ARGV'.  The other special
command-line options, with their arguments, are also not entered.  This
includes variable assignments done with the `-v' option (*note
Options::).  Normal variable assignments on the command line _are_
treated as arguments and do show up in the `ARGV' array:

     $ cat showargs.awk
     -| BEGIN {
     -|     printf "A=%d, B=%d\n", A, B
     -|     for (i = 0; i < ARGC; i++)
     -|         printf "\tARGV[%d] = %s\n", i, ARGV[i]
     -| }
     -| END   { printf "A=%d, B=%d\n", A, B }
     $ awk -v A=1 -f showargs.awk B=2 /dev/null
     -| A=1, B=0
     -|        ARGV[0] = awk
     -|        ARGV[1] = B=2
     -|        ARGV[2] = /dev/null
     -| A=1, B=2

A program can alter `ARGC' and the elements of `ARGV'.  Each time `awk'
reaches the end of an input file, it uses the next element of `ARGV' as
the name of the next input file.  By storing a different string there,
a program can change which files are read.  Use `"-"' to represent the
standard input.  Storing additional elements and incrementing `ARGC'
causes additional files to be read.

If the value of `ARGC' is decreased, that eliminates input files from
the end of the list.  By recording the old value of `ARGC' elsewhere, a
program can treat the eliminated arguments as something other than file
names.

To eliminate a file from the middle of the list, store the null string
(`""') into `ARGV' in place of the file's name.  As a special feature,
`awk' ignores file names that have been replaced with the null string.
Another option is to use the `delete' statement to remove elements from
`ARGV' (*note Delete::).

All of these actions are typically done in the `BEGIN' rule, before
actual processing of the input begins.  *Note Split Program::, and see
*Note Tee Program::, for examples of each way of removing elements from
`ARGV'.  The following fragment processes `ARGV' in order to examine,
and then remove, command-line options:

     BEGIN {
         for (i = 1; i < ARGC; i++) {
             if (ARGV[i] == "-v")
                 verbose = 1
             else if (ARGV[i] == "-d")
                 debug = 1
             else if (ARGV[i] ~ /^-?/) {
                 e = sprintf("%s: unrecognized option -- %c",
                         ARGV[0], substr(ARGV[i], 1, ,1))
                 print e > "/dev/stderr"
             } else
                 break
             delete ARGV[i]
         }
     }

To actually get the options into the `awk' program, end the `awk'
options with `--' and then supply the `awk' program's options, in the
following manner:

     awk -f myprog -- -v -d file1 file2 ...

This is not necessary in `gawk'. Unless `--posix' has been specified,
`gawk' silently puts any unrecognized options into `ARGV' for the `awk'
program to deal with.  As soon as it sees an unknown option, `gawk'
stops looking for other options that it might otherwise recognize.  The
previous example with `gawk' would be:

     gawk -f myprog -d -v file1 file2 ...

Because `-d' is not a valid `gawk' option, it and the following `-v'
are passed on to the `awk' program.


File: gawk.info,  Node: Arrays,  Next: Functions,  Prev: Patterns and Actions,  Up: Top

7 Arrays in `awk'
*****************

An "array" is a table of values called "elements".  The elements of an
array are distinguished by their indices.  "Indices" may be either
numbers or strings.

This major node describes how arrays work in `awk', how to use array
elements, how to scan through every element in an array, and how to
remove array elements.  It also describes how `awk' simulates
multidimensional arrays, as well as some of the less obvious points
about array usage.  The major node finishes with a discussion of
`gawk''s facility for sorting an array based on its indices.

`awk' maintains a single set of names that may be used for naming
variables, arrays, and functions (*note User-defined::).  Thus, you
cannot have a variable and an array with the same name in the same
`awk' program.

* Menu:

* Array Intro::                 Introduction to Arrays
* Reference to Elements::       How to examine one element of an array.
* Assigning Elements::          How to change an element of an array.
* Array Example::               Basic Example of an Array
* Scanning an Array::           A variation of the `for' statement. It
                                loops through the indices of an array's
                                existing elements.
* Delete::                      The `delete' statement removes an element
                                from an array.
* Numeric Array Subscripts::    How to use numbers as subscripts in
                                `awk'.
* Uninitialized Subscripts::    Using Uninitialized variables as subscripts.
* Multi-dimensional::           Emulating multidimensional arrays in
                                `awk'.
* Multi-scanning::              Scanning multidimensional arrays.
* Array Sorting::               Sorting array values and indices.


File: gawk.info,  Node: Array Intro,  Next: Reference to Elements,  Up: Arrays

7.1 Introduction to Arrays
==========================

The `awk' language provides one-dimensional arrays for storing groups
of related strings or numbers.  Every `awk' array must have a name.
Array names have the same syntax as variable names; any valid variable
name would also be a valid array name.  But one name cannot be used in
both ways (as an array and as a variable) in the same `awk' program.

Arrays in `awk' superficially resemble arrays in other programming
languages, but there are fundamental differences.  In `awk', it isn't
necessary to specify the size of an array before starting to use it.
Additionally, any number or string in `awk', not just consecutive
integers, may be used as an array index.

In most other languages, arrays must be "declared" before use,
including a specification of how many elements or components they
contain.  In such languages, the declaration causes a contiguous block
of memory to be allocated for that many elements.  Usually, an index in
the array must be a positive integer.  For example, the index zero
specifies the first element in the array, which is actually stored at
the beginning of the block of memory.  Index one specifies the second
element, which is stored in memory right after the first element, and
so on.  It is impossible to add more elements to the array, because it
has room only for as many elements as given in the declaration.  (Some
languages allow arbitrary starting and ending indices--e.g., `15 ..
27'--but the size of the array is still fixed when the array is
declared.)

A contiguous array of four elements might look like the following
example, conceptually, if the element values are 8, `"foo"', `""', and
30:

     +---------+---------+--------+---------+
     |    8    |  "foo"  |   ""   |    30   |    Value
     +---------+---------+--------+---------+
          0         1         2         3        Index

Only the values are stored; the indices are implicit from the order of
the values. Here, 8 is the value at index zero, because 8 appears in the
position with zero elements before it.

Arrays in `awk' are different--they are "associative".  This means that
each array is a collection of pairs: an index and its corresponding
array element value:

     Element 3     Value 30
     Element 1     Value "foo"
     Element 0     Value 8
     Element 2     Value ""

The pairs are shown in jumbled order because their order is irrelevant.

One advantage of associative arrays is that new pairs can be added at
any time.  For example, suppose a tenth element is added to the array
whose value is `"number ten"'.  The result is:

     Element 10    Value "number ten"
     Element 3     Value 30
     Element 1     Value "foo"
     Element 0     Value 8
     Element 2     Value ""

Now the array is "sparse", which just means some indices are missing.
It has elements 0-3 and 10, but doesn't have elements 4, 5, 6, 7, 8, or
9.

Another consequence of associative arrays is that the indices don't
have to be positive integers.  Any number, or even a string, can be an
index.  For example, the following is an array that translates words
from English to French:

     Element "dog" Value "chien"
     Element "cat" Value "chat"
     Element "one" Value "un"
     Element 1     Value "un"

Here we decided to translate the number one in both spelled-out and
numeric form--thus illustrating that a single array can have both
numbers and strings as indices.  In fact, array subscripts are always
strings; this is discussed in more detail in *Note Numeric Array
Subscripts::.  Here, the number `1' isn't double-quoted, since `awk'
automatically converts it to a string.

The value of `IGNORECASE' has no effect upon array subscripting.  The
identical string value used to store an array element must be used to
retrieve it.  When `awk' creates an array (e.g., with the `split'
built-in function), that array's indices are consecutive integers
starting at one.  (*Note String Functions::.)

`awk''s arrays are efficient--the time to access an element is
independent of the number of elements in the array.


File: gawk.info,  Node: Reference to Elements,  Next: Assigning Elements,  Prev: Array Intro,  Up: Arrays

7.2 Referring to an Array Element
=================================

The principal way to use an array is to refer to one of its elements.
An array reference is an expression as follows:

     ARRAY[INDEX]

Here, ARRAY is the name of an array.  The expression INDEX is the index
of the desired element of the array.

The value of the array reference is the current value of that array
element.  For example, `foo[4.3]' is an expression for the element of
array `foo' at index `4.3'.

A reference to an array element that has no recorded value yields a
value of `""', the null string.  This includes elements that have not
been assigned any value as well as elements that have been deleted
(*note Delete::).  Such a reference automatically creates that array
element, with the null string as its value.  (In some cases, this is
unfortunate, because it might waste memory inside `awk'.)

To determine whether an element exists in an array at a certain index,
use the following expression:

     INDEX in ARRAY

This expression tests whether the particular index exists, without the
side effect of creating that element if it is not present.  The
expression has the value one (true) if `ARRAY[INDEX]' exists and zero
(false) if it does not exist.  For example, this statement tests
whether the array `frequencies' contains the index `2':

     if (2 in frequencies)
         print "Subscript 2 is present."

Note that this is _not_ a test of whether the array `frequencies'
contains an element whose _value_ is two.  There is no way to do that
except to scan all the elements.  Also, this _does not_ create
`frequencies[2]', while the following (incorrect) alternative does:

     if (frequencies[2] != "")
         print "Subscript 2 is present."


File: gawk.info,  Node: Assigning Elements,  Next: Array Example,  Prev: Reference to Elements,  Up: Arrays

7.3 Assigning Array Elements
============================

Array elements can be assigned values just like `awk' variables:

     ARRAY[SUBSCRIPT] = VALUE

ARRAY is the name of an array.  The expression SUBSCRIPT is the index
of the element of the array that is assigned a value.  The expression
VALUE is the value to assign to that element of the array.


File: gawk.info,  Node: Array Example,  Next: Scanning an Array,  Prev: Assigning Elements,  Up: Arrays

7.4 Basic Array Example
=======================

The following program takes a list of lines, each beginning with a line
number, and prints them out in order of line number.  The line numbers
are not in order when they are first read--instead they are scrambled.
This program sorts the lines by making an array using the line numbers
as subscripts.  The program then prints out the lines in sorted order
of their numbers.  It is a very simple program and gets confused upon
encountering repeated numbers, gaps, or lines that don't begin with a
number:

     {
       if ($1 > max)
         max = $1
       arr[$1] = $0
     }

     END {
       for (x = 1; x <= max; x++)
         print arr[x]
     }

The first rule keeps track of the largest line number seen so far; it
also stores each line into the array `arr', at an index that is the
line's number.  The second rule runs after all the input has been read,
to print out all the lines.  When this program is run with the
following input:

     5  I am the Five man
     2  Who are you?  The new number two!
     4  . . . And four on the floor
     1  Who is number one?
     3  I three you.

Its output is:

     1  Who is number one?
     2  Who are you?  The new number two!
     3  I three you.
     4  . . . And four on the floor
     5  I am the Five man

If a line number is repeated, the last line with a given number
overrides the others.  Gaps in the line numbers can be handled with an
easy improvement to the program's `END' rule, as follows:

     END {
       for (x = 1; x <= max; x++)
         if (x in arr)
           print arr[x]
     }


File: gawk.info,  Node: Scanning an Array,  Next: Delete,  Prev: Array Example,  Up: Arrays

7.5 Scanning All Elements of an Array
=====================================

In programs that use arrays, it is often necessary to use a loop that
executes once for each element of an array.  In other languages, where
arrays are contiguous and indices are limited to positive integers,
this is easy: all the valid indices can be found by counting from the
lowest index up to the highest.  This technique won't do the job in
`awk', because any number or string can be an array index.  So `awk'
has a special kind of `for' statement for scanning an array:

     for (VAR in ARRAY)
       BODY

This loop executes BODY once for each index in ARRAY that the program
has previously used, with the variable VAR set to that index.

The following program uses this form of the `for' statement.  The first
rule scans the input records and notes which words appear (at least
once) in the input, by storing a one into the array `used' with the
word as index.  The second rule scans the elements of `used' to find
all the distinct words that appear in the input.  It prints each word
that is more than 10 characters long and also prints the number of such
words.  *Note String Functions::, for more information on the built-in
function `length'.

     # Record a 1 for each word that is used at least once
     {
         for (i = 1; i <= NF; i++)
             used[$i] = 1
     }

     # Find number of distinct words more than 10 characters long
     END {
         for (x in used)
             if (length(x) > 10) {
                 ++num_long_words
                 print x
             }
         print num_long_words, "words longer than 10 characters"
     }

*Note Word Sorting::, for a more detailed example of this type.

The order in which elements of the array are accessed by this statement
is determined by the internal arrangement of the array elements within
`awk' and cannot be controlled or changed.  This can lead to problems
if new elements are added to ARRAY by statements in the loop body; it
is not predictable whether the `for' loop will reach them.  Similarly,
changing VAR inside the loop may produce strange results.  It is best
to avoid such things.


File: gawk.info,  Node: Delete,  Next: Numeric Array Subscripts,  Prev: Scanning an Array,  Up: Arrays

7.6 The `delete' Statement
==========================

To remove an individual element of an array, use the `delete' statement:

     delete ARRAY[INDEX]

Once an array element has been deleted, any value the element once had
is no longer available. It is as if the element had never been referred
to or had been given a value.  The following is an example of deleting
elements in an array:

     for (i in frequencies)
       delete frequencies[i]

This example removes all the elements from the array `frequencies'.
Once an element is deleted, a subsequent `for' statement to scan the
array does not report that element and the `in' operator to check for
the presence of that element returns zero (i.e., false):

     delete foo[4]
     if (4 in foo)
         print "This will never be printed"

It is important to note that deleting an element is _not_ the same as
assigning it a null value (the empty string, `""').  For example:

     foo[4] = ""
     if (4 in foo)
       print "This is printed, even though foo[4] is empty"

It is not an error to delete an element that does not exist.  If
`--lint' is provided on the command line (*note Options::), `gawk'
issues a warning message when an element that is not in the array is
deleted.

All the elements of an array may be deleted with a single statement by
leaving off the subscript in the `delete' statement, as follows:

     delete ARRAY

This ability is a `gawk' extension; it is not available in
compatibility mode (*note Options::).

Using this version of the `delete' statement is about three times more
efficient than the equivalent loop that deletes each element one at a
time.

The following statement provides a portable but nonobvious way to clear
out an array:(1)

     split("", array)

The `split' function (*note String Functions::) clears out the target
array first. This call asks it to split apart the null string. Because
there is no data to split out, the function simply clears the array and
then returns.

*Caution:* Deleting an array does not change its type; you cannot
delete an array and then use the array's name as a scalar (i.e., a
regular variable). For example, the following does not work:

     a[1] = 3; delete a; a = 3

---------- Footnotes ----------

(1) Thanks to Michael Brennan for pointing this out.


File: gawk.info,  Node: Numeric Array Subscripts,  Next: Uninitialized Subscripts,  Prev: Delete,  Up: Arrays

7.7 Using Numbers to Subscript Arrays
=====================================

An important aspect about arrays to remember is that _array subscripts
are always strings_.  When a numeric value is used as a subscript, it
is converted to a string value before being used for subscripting
(*note Conversion::).  This means that the value of the built-in
variable `CONVFMT' can affect how your program accesses elements of an
array.  For example:

     xyz = 12.153
     data[xyz] = 1
     CONVFMT = "%2.2f"
     if (xyz in data)
         printf "%s is in data\n", xyz
     else
         printf "%s is not in data\n", xyz

This prints `12.15 is not in data'.  The first statement gives `xyz' a
numeric value.  Assigning to `data[xyz]' subscripts `data' with the
string value `"12.153"' (using the default conversion value of
`CONVFMT', `"%.6g"').  Thus, the array element `data["12.153"]' is
assigned the value one.  The program then changes the value of
`CONVFMT'.  The test `(xyz in data)' generates a new string value from
`xyz'--this time `"12.15"'--because the value of `CONVFMT' only allows
two significant digits.  This test fails, since `"12.15"' is a
different string from `"12.153"'.

According to the rules for conversions (*note Conversion::), integer
values are always converted to strings as integers, no matter what the
value of `CONVFMT' may happen to be.  So the usual case of the
following works:

     for (i = 1; i <= maxsub; i++)
         do something with array[i]

The "integer values always convert to strings as integers" rule has an
additional consequence for array indexing.  Octal and hexadecimal
constants (*note Nondecimal-numbers::) are converted internally into
numbers, and their original form is forgotten.  This means, for
example, that `array[17]', `array[021]', and `array[0x11]' all refer to
the same element!

As with many things in `awk', the majority of the time things work as
one would expect them to.  But it is useful to have a precise knowledge
of the actual rules which sometimes can have a subtle effect on your
programs.


File: gawk.info,  Node: Uninitialized Subscripts,  Next: Multi-dimensional,  Prev: Numeric Array Subscripts,  Up: Arrays

7.8 Using Uninitialized Variables as Subscripts
===============================================

Suppose it's necessary to write a program to print the input data in
reverse order.  A reasonable attempt to do so (with some test data)
might look like this:

     $ echo 'line 1
     > line 2
     > line 3' | awk '{ l[lines] = $0; ++lines }
     > END {
     >     for (i = lines-1; i >= 0; --i)
     >        print l[i]
     > }'
     -| line 3
     -| line 2

Unfortunately, the very first line of input data did not come out in the
output!

At first glance, this program should have worked.  The variable `lines'
is uninitialized, and uninitialized variables have the numeric value
zero.  So, `awk' should have printed the value of `l[0]'.

The issue here is that subscripts for `awk' arrays are _always_
strings. Uninitialized variables, when used as strings, have the value
`""', not zero.  Thus, `line 1' ends up stored in `l[""]'.  The
following version of the program works correctly:

     { l[lines++] = $0 }
     END {
         for (i = lines - 1; i >= 0; --i)
            print l[i]
     }

Here, the `++' forces `lines' to be numeric, thus making the "old
value" numeric zero. This is then converted to `"0"' as the array
subscript.

Even though it is somewhat unusual, the null string (`""') is a valid
array subscript.  (d.c.)  `gawk' warns about the use of the null string
as a subscript if `--lint' is provided on the command line (*note
Options::).


File: gawk.info,  Node: Multi-dimensional,  Next: Multi-scanning,  Prev: Uninitialized Subscripts,  Up: Arrays

7.9 Multidimensional Arrays
===========================

A multidimensional array is an array in which an element is identified
by a sequence of indices instead of a single index.  For example, a
two-dimensional array requires two indices.  The usual way (in most
languages, including `awk') to refer to an element of a two-dimensional
array named `grid' is with `grid[X,Y]'.

Multidimensional arrays are supported in `awk' through concatenation of
indices into one string.  `awk' converts the indices into strings
(*note Conversion::) and concatenates them together, with a separator
between them.  This creates a single string that describes the values
of the separate indices.  The combined string is used as a single index
into an ordinary, one-dimensional array.  The separator used is the
value of the built-in variable `SUBSEP'.

For example, suppose we evaluate the expression `foo[5,12] = "value"'
when the value of `SUBSEP' is `"@"'.  The numbers 5 and 12 are
converted to strings and concatenated with an `@' between them,
yielding `"5@12"'; thus, the array element `foo["5@12"]' is set to
`"value"'.

Once the element's value is stored, `awk' has no record of whether it
was stored with a single index or a sequence of indices.  The two
expressions `foo[5,12]' and `foo[5 SUBSEP 12]' are always equivalent.

The default value of `SUBSEP' is the string `"\034"', which contains a
nonprinting character that is unlikely to appear in an `awk' program or
in most input data.  The usefulness of choosing an unlikely character
comes from the fact that index values that contain a string matching
`SUBSEP' can lead to combined strings that are ambiguous.  Suppose that
`SUBSEP' is `"@"'; then `foo["a@b", "c"]' and `foo["a", "b@c"]' are
indistinguishable because both are actually stored as `foo["a@b@c"]'.

To test whether a particular index sequence exists in a
multidimensional array, use the same operator (`in') that is used for
single dimensional arrays.  Write the whole sequence of indices in
parentheses, separated by commas, as the left operand:

     (SUBSCRIPT1, SUBSCRIPT2, ...) in ARRAY

The following example treats its input as a two-dimensional array of
fields; it rotates this array 90 degrees clockwise and prints the
result.  It assumes that all lines have the same number of elements:

     {
          if (max_nf < NF)
               max_nf = NF
          max_nr = NR
          for (x = 1; x <= NF; x++)
               vector[x, NR] = $x
     }

     END {
          for (x = 1; x <= max_nf; x++) {
               for (y = max_nr; y >= 1; --y)
                    printf("%s ", vector[x, y])
               printf("\n")
          }
     }

When given the input:

     1 2 3 4 5 6
     2 3 4 5 6 1
     3 4 5 6 1 2
     4 5 6 1 2 3

the program produces the following output:

     4 3 2 1
     5 4 3 2
     6 5 4 3
     1 6 5 4
     2 1 6 5
     3 2 1 6


File: gawk.info,  Node: Multi-scanning,  Next: Array Sorting,  Prev: Multi-dimensional,  Up: Arrays

7.10 Scanning Multidimensional Arrays
=====================================

There is no special `for' statement for scanning a "multidimensional"
array. There cannot be one, because, in truth, there are no
multidimensional arrays or elements--there is only a multidimensional
_way of accessing_ an array.

However, if your program has an array that is always accessed as
multidimensional, you can get the effect of scanning it by combining
the scanning `for' statement (*note Scanning an Array::) with the
built-in `split' function (*note String Functions::).  It works in the
following manner:

     for (combined in array) {
         split(combined, separate, SUBSEP)
         ...
     }

This sets the variable `combined' to each concatenated combined index
in the array, and splits it into the individual indices by breaking it
apart where the value of `SUBSEP' appears.  The individual indices then
become the elements of the array `separate'.

Thus, if a value is previously stored in `array[1, "foo"]'; then an
element with index `"1\034foo"' exists in `array'.  (Recall that the
default value of `SUBSEP' is the character with code 034.)  Sooner or
later, the `for' statement finds that index and does an iteration with
the variable `combined' set to `"1\034foo"'.  Then the `split' function
is called as follows:

     split("1\034foo", separate, "\034")

The result is to set `separate[1]' to `"1"' and `separate[2]' to
`"foo"'.  Presto! The original sequence of separate indices is
recovered.


File: gawk.info,  Node: Array Sorting,  Prev: Multi-scanning,  Up: Arrays

7.11 Sorting Array Values and Indices with `gawk'
=================================================

The order in which an array is scanned with a `for (i in array)' loop
is essentially arbitrary.  In most `awk' implementations, sorting an
array requires writing a `sort' function.  While this can be
educational for exploring different sorting algorithms, usually that's
not the point of the program.  `gawk' provides the built-in `asort' and
`asorti' functions (*note String Functions::) for sorting arrays.  For
example:

     POPULATE THE ARRAY data
     n = asort(data)
     for (i = 1; i <= n; i++)
         DO SOMETHING WITH data[i]

After the call to `asort', the array `data' is indexed from 1 to some
number N, the total number of elements in `data'.  (This count is
`asort''s return value.)  `data[1]' <= `data[2]' <= `data[3]', and so
on.  The comparison of array elements is done using `gawk''s usual
comparison rules (*note Typing and Comparison::).

An important side effect of calling `asort' is that _the array's
original indices are irrevocably lost_.  As this isn't always
desirable, `asort' accepts a second argument:

     POPULATE THE ARRAY source
     n = asort(source, dest)
     for (i = 1; i <= n; i++)
         DO SOMETHING WITH dest[i]

In this case, `gawk' copies the `source' array into the `dest' array
and then sorts `dest', destroying its indices.  However, the `source'
array is not affected.

Often, what's needed is to sort on the values of the _indices_ instead
of the values of the elements.  To do that, starting with `gawk' 3.1.2,
use the `asorti' function.  The interface is identical to that of
`asort', except that the index values are used for sorting, and become
the values of the result array:

     { source[$0] = some_func($0) }

     END {
         n = asorti(source, dest)
         for (i = 1; i <= n; i++) {
             DO SOMETHING WITH dest[i]             Work with sorted indices directly
             ...
             DO SOMETHING WITH source[dest[i]]     Access original array via sorted indices
         }
     }

If your version of `gawk' is 3.1.0 or 3.1.1, you don't have `asorti'.
Instead, use a helper array to hold the sorted index values, and then
access the original array's elements.  It works in the following way:

     POPULATE THE ARRAY data
     # copy indices
     j = 1
     for (i in data) {
         ind[j] = i    # index value becomes element value
         j++
     }
     n = asort(ind)    # index values are now sorted
     for (i = 1; i <= n; i++) {
         DO SOMETHING WITH ind[i]           Work with sorted indices directly
         ...
         DO SOMETHING WITH data[ind[i]]     Access original array via sorted indices
     }

Sorting the array by replacing the indices provides maximal flexibility.
To traverse the elements in decreasing order, use a loop that goes from
N down to 1, either over the elements or over the indices.

Copying array indices and elements isn't expensive in terms of memory.
Internally, `gawk' maintains "reference counts" to data.  For example,
when `asort' copies the first array to the second one, there is only
one copy of the original array elements' data, even though both arrays
use the values.  Similarly, when copying the indices from `data' to
`ind', there is only one copy of the actual index strings.

We said previously that comparisons are done using `gawk''s "usual
comparison rules."  Because `IGNORECASE' affects string comparisons,
the value of `IGNORECASE' also affects sorting for both `asort' and
`asorti'.  Caveat Emptor.


File: gawk.info,  Node: Functions,  Next: Internationalization,  Prev: Arrays,  Up: Top

8 Functions
***********

This major node describes `awk''s built-in functions, which fall into
three categories: numeric, string, and I/O.  `gawk' provides additional
groups of functions to work with values that represent time, do bit
manipulation, and internationalize and localize programs.

Besides the built-in functions, `awk' has provisions for writing new
functions that the rest of a program can use.  The second half of this
major node describes these "user-defined" functions.

* Menu:

* Built-in::                    Summarizes the built-in functions.
* User-defined::                Describes User-defined functions in detail.


File: gawk.info,  Node: Built-in,  Next: User-defined,  Up: Functions

8.1 Built-in Functions
======================

"Built-in" functions are always available for your `awk' program to
call.  This minor node defines all the built-in functions in `awk';
some of these are mentioned in other sections but are summarized here
for your convenience.

* Menu:

* Calling Built-in::            How to call built-in functions.
* Numeric Functions::           Functions that work with numbers, including
                                `int', `sin' and `rand'.
* String Functions::            Functions for string manipulation, such as
                                `split', `match' and `sprintf'.
* I/O Functions::               Functions for files and shell commands.
* Time Functions::              Functions for dealing with timestamps.
* Bitwise Functions::           Functions for bitwise operations.
* I18N Functions::              Functions for string translation.


File: gawk.info,  Node: Calling Built-in,  Next: Numeric Functions,  Up: Built-in

8.1.1 Calling Built-in Functions
--------------------------------

To call one of `awk''s built-in functions, write the name of the
function followed by arguments in parentheses.  For example, `atan2(y +
z, 1)' is a call to the function `atan2' and has two arguments.

Whitespace is ignored between the built-in function name and the open
parenthesis, and it is good practice to avoid using whitespace there.
User-defined functions do not permit whitespace in this way, and it is
easier to avoid mistakes by following a simple convention that always
works--no whitespace after a function name.

Each built-in function accepts a certain number of arguments.  In some
cases, arguments can be omitted. The defaults for omitted arguments
vary from function to function and are described under the individual
functions.  In some `awk' implementations, extra arguments given to
built-in functions are ignored.  However, in `gawk', it is a fatal
error to give extra arguments to a built-in function.

When a function is called, expressions that create the function's actual
parameters are evaluated completely before the call is performed.  For
example, in the following code fragment:

     i = 4
     j = sqrt(i++)

the variable `i' is incremented to the value five before `sqrt' is
called with a value of four for its actual parameter.  The order of
evaluation of the expressions used for the function's parameters is
undefined.  Thus, avoid writing programs that assume that parameters
are evaluated from left to right or from right to left.  For example:

     i = 5
     j = atan2(i++, i *= 2)

If the order of evaluation is left to right, then `i' first becomes 6,
and then 12, and `atan2' is called with the two arguments 6 and 12.
But if the order of evaluation is right to left, `i' first becomes 10,
then 11, and `atan2' is called with the two arguments 11 and 10.


File: gawk.info,  Node: Numeric Functions,  Next: String Functions,  Prev: Calling Built-in,  Up: Built-in

8.1.2 Numeric Functions
-----------------------

The following list describes all of the built-in functions that work
with numbers.  Optional parameters are enclosed in square
brackets ([ ]):

`int(X)'
     This returns the nearest integer to X, located between X and zero
     and truncated toward zero.

     For example, `int(3)' is 3, `int(3.9)' is 3, `int(-3.9)' is -3,
     and `int(-3)' is -3 as well.

`sqrt(X)'
     This returns the positive square root of X.  `gawk' reports an
     error if X is negative.  Thus, `sqrt(4)' is 2.

`exp(X)'
     This returns the exponential of X (`e ^ X') or reports an error if
     X is out of range.  The range of values X can have depends on your
     machine's floating-point representation.

`log(X)'
     This returns the natural logarithm of X, if X is positive;
     otherwise, it reports an error.

`sin(X)'
     This returns the sine of X, with X in radians.

`cos(X)'
     This returns the cosine of X, with X in radians.

`atan2(Y, X)'
     This returns the arctangent of `Y / X' in radians.

`rand()'
     This returns a random number.  The values of `rand' are uniformly
     distributed between zero and one.  The value could be zero but is
     never one.(1)

     Often random integers are needed instead.  Following is a
     user-defined function that can be used to obtain a random
     non-negative integer less than N:

          function randint(n) {
               return int(n * rand())
          }

     The multiplication produces a random number greater than zero and
     less than `n'.  Using `int', this result is made into an integer
     between zero and `n' - 1, inclusive.

     The following example uses a similar function to produce random
     integers between one and N.  This program prints a new random
     number for each input record:

          # Function to roll a simulated die.
          function roll(n) { return 1 + int(rand() * n) }

          # Roll 3 six-sided dice and
          # print total number of points.
          {
                printf("%d points\n",
                       roll(6)+roll(6)+roll(6))
          }

     *Caution:* In most `awk' implementations, including `gawk', `rand'
     starts generating numbers from the same starting number, or
     "seed", each time you run `awk'.  Thus, a program generates the
     same results each time you run it.  The numbers are random within
     one `awk' run but predictable from run to run.  This is convenient
     for debugging, but if you want a program to do different things
     each time it is used, you must change the seed to a value that is
     different in each run.  To do this, use `srand'.

`srand([X])'
     The function `srand' sets the starting point, or seed, for
     generating random numbers to the value X.

     Each seed value leads to a particular sequence of random
     numbers.(2) Thus, if the seed is set to the same value a second
     time, the same sequence of random numbers is produced again.

     Different `awk' implementations use different random-number
     generators internally.  Don't expect the same `awk' program to
     produce the same series of random numbers when executed by
     different versions of `awk'.

     If the argument X is omitted, as in `srand()', then the current
     date and time of day are used for a seed.  This is the way to get
     random numbers that are truly unpredictable.

     The return value of `srand' is the previous seed.  This makes it
     easy to keep track of the seeds in case you need to consistently
     reproduce sequences of random numbers.

---------- Footnotes ----------

(1) The C version of `rand' is known to produce fairly poor sequences
of random numbers.  However, nothing requires that an `awk'
implementation use the C `rand' to implement the `awk' version of
`rand'.  In fact, `gawk' uses the BSD `random' function, which is
considerably better than `rand', to produce random numbers.

(2) Computer-generated random numbers really are not truly random.
They are technically known as "pseudorandom."  This means that while
the numbers in a sequence appear to be random, you can in fact generate
the same sequence of random numbers over and over again.


File: gawk.info,  Node: String Functions,  Next: I/O Functions,  Prev: Numeric Functions,  Up: Built-in

8.1.3 String-Manipulation Functions
-----------------------------------

The functions in this minor node look at or change the text of one or
more strings.  Optional parameters are enclosed in square
brackets ([ ]).  Those functions that are specific to `gawk' are marked
with a pound sign (`#'):

* Menu:

* Gory Details::                More than you want to know about `\' and
                                `&' with `sub', `gsub', and
                                `gensub'.

`asort(SOURCE [, DEST]) #'
     `asort' is a `gawk'-specific extension, returning the number of
     elements in the array SOURCE.  The contents of SOURCE are sorted
     using `gawk''s normal rules for comparing values (in particular,
     `IGNORECASE' affects the sorting) and the indices of the sorted
     values of SOURCE are replaced with sequential integers starting
     with one. If the optional array DEST is specified, then SOURCE is
     duplicated into DEST.  DEST is then sorted, leaving the indices of
     SOURCE unchanged.  For example, if the contents of `a' are as
     follows:

          a["last"] = "de"
          a["first"] = "sac"
          a["middle"] = "cul"

     A call to `asort':

          asort(a)

     results in the following contents of `a':

          a[1] = "cul"
          a[2] = "de"
          a[3] = "sac"

     The `asort' function is described in more detail in *Note Array
     Sorting::.  `asort' is a `gawk' extension; it is not available in
     compatibility mode (*note Options::).

`asorti(SOURCE [, DEST]) #'
     `asorti' is a `gawk'-specific extension, returning the number of
     elements in the array SOURCE.  It works similarly to `asort',
     however, the _indices_ are sorted, instead of the values.  As
     array indices are always strings, the comparison performed is
     always a string comparison.  (Here too, `IGNORECASE' affects the
     sorting.)

     The `asorti' function is described in more detail in *Note Array
     Sorting::.  It was added in `gawk' 3.1.2.  `asorti' is a `gawk'
     extension; it is not available in compatibility mode (*note
     Options::).

`index(IN, FIND)'
     This searches the string IN for the first occurrence of the string
     FIND, and returns the position in characters where that occurrence
     begins in the string IN.  Consider the following example:

          $ awk 'BEGIN { print index("peanut", "an") }'
          -| 3

     If FIND is not found, `index' returns zero.  (Remember that string
     indices in `awk' start at one.)

`length([STRING])'
     This returns the number of characters in STRING.  If STRING is a
     number, the length of the digit string representing that number is
     returned.  For example, `length("abcde")' is 5.  By contrast,
     `length(15 * 35)' works out to 3. In this example, 15 * 35 = 525,
     and 525 is then converted to the string `"525"', which has three
     characters.

     If no argument is supplied, `length' returns the length of `$0'.

          NOTE: In older versions of `awk', the `length' function could
          be called without any parentheses.  Doing so is marked as
          "deprecated" in the POSIX standard.  This means that while a
          program can do this, it is a feature that can eventually be
          removed from a future version of the standard.  Therefore,
          for programs to be maximally portable, always supply the
          parentheses.

     Beginning with `gawk' version 3.2, when supplied an array
     argument, the `length' function returns the number of elements in
     the array.  This is less useful than it might seem at first, as the
     array is not guaranteed to be indexed from one to the number of
     elements in it.  If `--lint' is provided on the command line
     (*note Options::), `gawk' warns that passing an array argument is
     not portable.  If `--posix' is supplied, using an array argument
     is a fatal error (*note Arrays::).

`match(STRING, REGEXP [, ARRAY])'
     The `match' function searches STRING for the longest, leftmost
     substring matched by the regular expression, REGEXP.  It returns
     the character position, or "index", at which that substring begins
     (one, if it starts at the beginning of STRING).  If no match is
     found, it returns zero.

     The REGEXP argument may be either a regexp constant (`/.../') or a
     string constant ("...").  In the latter case, the string is
     treated as a regexp to be matched.  *Note Computed Regexps::, for a
     discussion of the difference between the two forms, and the
     implications for writing your program correctly.

     The order of the first two arguments is backwards from most other
     string functions that work with regular expressions, such as `sub'
     and `gsub'.  It might help to remember that for `match', the order
     is the same as for the `~' operator: `STRING ~ REGEXP'.

     The `match' function sets the built-in variable `RSTART' to the
     index.  It also sets the built-in variable `RLENGTH' to the length
     in characters of the matched substring.  If no match is found,
     `RSTART' is set to zero, and `RLENGTH' to -1.

     For example:

          {
                 if ($1 == "FIND")
                   regex = $2
                 else {
                   where = match($0, regex)
                   if (where != 0)
                     print "Match of", regex, "found at",
                               where, "in", $0
                 }
          }

     This program looks for lines that match the regular expression
     stored in the variable `regex'.  This regular expression can be
     changed.  If the first word on a line is `FIND', `regex' is
     changed to be the second word on that line.  Therefore, if given:

          FIND ru+n
          My program runs
          but not very quickly
          FIND Melvin
          JF+KM
          This line is property of Reality Engineering Co.
          Melvin was here.

     `awk' prints:

          Match of ru+n found at 12 in My program runs
          Match of Melvin found at 1 in Melvin was here.

     If ARRAY is present, it is cleared, and then the 0th element of
     ARRAY is set to the entire portion of STRING matched by REGEXP.
     If REGEXP contains parentheses, the integer-indexed elements of
     ARRAY are set to contain the portion of STRING matching the
     corresponding parenthesized subexpression.  For example:

          $ echo foooobazbarrrrr |
          > gawk '{ match($0, /(fo+).+(bar*)/, arr)
          >           print arr[1], arr[2] }'
          -| foooo barrrrr

     In addition, beginning with `gawk' 3.1.2, multidimensional
     subscripts are available providing the start index and length of
     each matched subexpression:

          $ echo foooobazbarrrrr |
          > gawk '{ match($0, /(fo+).+(bar*)/, arr)
          >           print arr[1], arr[2]
          >           print arr[1, "start"], arr[1, "length"]
          >           print arr[2, "start"], arr[2, "length"]
          > }'
          -| foooo barrrrr
          -| 1 5
          -| 9 7

     There may not be subscripts for the start and index for every
     parenthesized subexpressions, since they may not all have matched
     text; thus they should be tested for with the `in' operator (*note
     Reference to Elements::).

     The ARRAY argument to `match' is a `gawk' extension.  In
     compatibility mode (*note Options::), using a third argument is a
     fatal error.

`split(STRING, ARRAY [, FIELDSEP])'
     This function divides STRING into pieces separated by FIELDSEP and
     stores the pieces in ARRAY.  The first piece is stored in
     `ARRAY[1]', the second piece in `ARRAY[2]', and so forth.  The
     string value of the third argument, FIELDSEP, is a regexp
     describing where to split STRING (much as `FS' can be a regexp
     describing where to split input records).  If FIELDSEP is omitted,
     the value of `FS' is used.  `split' returns the number of elements
     created.

     The `split' function splits strings into pieces in a manner
     similar to the way input lines are split into fields.  For example:

          split("cul-de-sac", a, "-")

     splits the string `cul-de-sac' into three fields using `-' as the
     separator.  It sets the contents of the array `a' as follows:

          a[1] = "cul"
          a[2] = "de"
          a[3] = "sac"

     The value returned by this call to `split' is three.

     As with input field-splitting, when the value of FIELDSEP is
     `" "', leading and trailing whitespace is ignored, and the elements
     are separated by runs of whitespace.  Also as with input
     field-splitting, if FIELDSEP is the null string, each individual
     character in the string is split into its own array element.
     (This is a `gawk'-specific extension.)

     Note, however, that `RS' has no effect on the way `split' works.
     Even though `RS = ""' causes newline to also be an input field
     separator, this does not affect how `split' splits strings.

     Modern implementations of `awk', including `gawk', allow the third
     argument to be a regexp constant (`/abc/') as well as a string.
     (d.c.)  The POSIX standard allows this as well.  *Note Computed
     Regexps::, for a discussion of the difference between using a
     string constant or a regexp constant, and the implications for
     writing your program correctly.

     Before splitting the string, `split' deletes any previously
     existing elements in the array ARRAY.

     If STRING is null, the array has no elements. (So this is a
     portable way to delete an entire array with one statement.  *Note
     Delete::.)

     If STRING does not match FIELDSEP at all (but is not null), ARRAY
     has one element only. The value of that element is the original
     STRING.

`sprintf(FORMAT, EXPRESSION1, ...)'
     This returns (without printing) the string that `printf' would
     have printed out with the same arguments (*note Printf::).  For
     example:

          pival = sprintf("pi = %.2f (approx.)", 22/7)

     assigns the string `"pi = 3.14 (approx.)"' to the variable `pival'.

`strtonum(STR) #'
     Examines STR and returns its numeric value.  If STR begins with a
     leading `0', `strtonum' assumes that STR is an octal number.  If
     STR begins with a leading `0x' or `0X', `strtonum' assumes that
     STR is a hexadecimal number.  For example:

          $ echo 0x11 |
          > gawk '{ printf "%d\n", strtonum($1) }'
          -| 17

     Using the `strtonum' function is _not_ the same as adding zero to
     a string value; the automatic coercion of strings to numbers works
     only for decimal data, not for octal or hexadecimal.(1)

     Note also that `strtonum' uses the current locale's decimal point
     for recognizing numbers.

     `strtonum' is a `gawk' extension; it is not available in
     compatibility mode (*note Options::).

`sub(REGEXP, REPLACEMENT [, TARGET])'
     The `sub' function alters the value of TARGET.  It searches this
     value, which is treated as a string, for the leftmost, longest
     substring matched by the regular expression REGEXP.  Then the
     entire string is changed by replacing the matched text with
     REPLACEMENT.  The modified string becomes the new value of TARGET.

     The REGEXP argument may be either a regexp constant (`/.../') or a
     string constant ("...").  In the latter case, the string is
     treated as a regexp to be matched.  *Note Computed Regexps::, for a
     discussion of the difference between the two forms, and the
     implications for writing your program correctly.

     This function is peculiar because TARGET is not simply used to
     compute a value, and not just any expression will do--it must be a
     variable, field, or array element so that `sub' can store a
     modified value there.  If this argument is omitted, then the
     default is to use and alter `$0'.(2) For example:

          str = "water, water, everywhere"
          sub(/at/, "ith", str)

     sets `str' to `"wither, water, everywhere"', by replacing the
     leftmost longest occurrence of `at' with `ith'.

     The `sub' function returns the number of substitutions made (either
     one or zero).

     If the special character `&' appears in REPLACEMENT, it stands for
     the precise substring that was matched by REGEXP.  (If the regexp
     can match more than one string, then this precise substring may
     vary.)  For example:

          { sub(/candidate/, "& and his wife"); print }

     changes the first occurrence of `candidate' to `candidate and his
     wife' on each input line.  Here is another example:

          $ awk 'BEGIN {
          >         str = "daabaaa"
          >         sub(/a+/, "C&C", str)
          >         print str
          > }'
          -| dCaaCbaaa

     This shows how `&' can represent a nonconstant string and also
     illustrates the "leftmost, longest" rule in regexp matching (*note
     Leftmost Longest::).

     The effect of this special character (`&') can be turned off by
     putting a backslash before it in the string.  As usual, to insert
     one backslash in the string, you must write two backslashes.
     Therefore, write `\\&' in a string constant to include a literal
     `&' in the replacement.  For example, the following shows how to
     replace the first `|' on each line with an `&':

          { sub(/\|/, "\\&"); print }

     As mentioned, the third argument to `sub' must be a variable,
     field or array reference.  Some versions of `awk' allow the third
     argument to be an expression that is not an lvalue.  In such a
     case, `sub' still searches for the pattern and returns zero or
     one, but the result of the substitution (if any) is thrown away
     because there is no place to put it.  Such versions of `awk'
     accept expressions such as the following:

          sub(/USA/, "United States", "the USA and Canada")

     For historical compatibility, `gawk' accepts erroneous code, such
     as in the previous example. However, using any other nonchangeable
     object as the third parameter causes a fatal error and your program
     will not run.

     Finally, if the REGEXP is not a regexp constant, it is converted
     into a string, and then the value of that string is treated as the
     regexp to match.

`gsub(REGEXP, REPLACEMENT [, TARGET])'
     This is similar to the `sub' function, except `gsub' replaces
     _all_ of the longest, leftmost, _nonoverlapping_ matching
     substrings it can find.  The `g' in `gsub' stands for "global,"
     which means replace everywhere.  For example:

          { gsub(/Britain/, "United Kingdom"); print }

     replaces all occurrences of the string `Britain' with `United
     Kingdom' for all input records.

     The `gsub' function returns the number of substitutions made.  If
     the variable to search and alter (TARGET) is omitted, then the
     entire input record (`$0') is used.  As in `sub', the characters
     `&' and `\' are special, and the third argument must be assignable.

`gensub(REGEXP, REPLACEMENT, HOW [, TARGET]) #'
     `gensub' is a general substitution function.  Like `sub' and
     `gsub', it searches the target string TARGET for matches of the
     regular expression REGEXP.  Unlike `sub' and `gsub', the modified
     string is returned as the result of the function and the original
     target string is _not_ changed.  If HOW is a string beginning with
     `g' or `G', then it replaces all matches of REGEXP with
     REPLACEMENT.  Otherwise, HOW is treated as a number that indicates
     which match of REGEXP to replace. If no TARGET is supplied, `$0'
     is used.

     `gensub' provides an additional feature that is not available in
     `sub' or `gsub': the ability to specify components of a regexp in
     the replacement text.  This is done by using parentheses in the
     regexp to mark the components and then specifying `\N' in the
     replacement text, where N is a digit from 1 to 9.  For example:

          $ gawk '
          > BEGIN {
          >      a = "abc def"
          >      b = gensub(/(.+) (.+)/, "\\2 \\1", "g", a)
          >      print b
          > }'
          -| def abc

     As with `sub', you must type two backslashes in order to get one
     into the string.  In the replacement text, the sequence `\0'
     represents the entire matched text, as does the character `&'.

     The following example shows how you can use the third argument to
     control which match of the regexp should be changed:

          $ echo a b c a b c |
          > gawk '{ print gensub(/a/, "AA", 2) }'
          -| a b c AA b c

     In this case, `$0' is used as the default target string.  `gensub'
     returns the new string as its result, which is passed directly to
     `print' for printing.

     If the HOW argument is a string that does not begin with `g' or
     `G', or if it is a number that is less than or equal to zero, only
     one substitution is performed.  If HOW is zero, `gawk' issues a
     warning message.

     If REGEXP does not match TARGET, `gensub''s return value is the
     original unchanged value of TARGET.

     `gensub' is a `gawk' extension; it is not available in
     compatibility mode (*note Options::).

`substr(STRING, START [, LENGTH])'
     This returns a LENGTH-character-long substring of STRING, starting
     at character number START.  The first character of a string is
     character number one.(3) For example, `substr("washington", 5, 3)'
     returns `"ing"'.

     If LENGTH is not present, this function returns the whole suffix of
     STRING that begins at character number START.  For example,
     `substr("washington", 5)' returns `"ington"'.  The whole suffix is
     also returned if LENGTH is greater than the number of characters
     remaining in the string, counting from character START.

     If START is less than one, `substr' treats it as if it was one.
     (POSIX doesn't specify what to do in this case: Unix `awk' acts
     this way, and therefore `gawk' does too.)  If START is greater
     than the number of characters in the string, `substr' returns the
     null string.  Similarly, if LENGTH is present but less than or
     equal to zero, the null string is returned.

     The string returned by `substr' _cannot_ be assigned.  Thus, it is
     a mistake to attempt to change a portion of a string, as shown in
     the following example:

          string = "abcdef"
          # try to get "abCDEf", won't work
          substr(string, 3, 3) = "CDE"

     It is also a mistake to use `substr' as the third argument of
     `sub' or `gsub':

          gsub(/xyz/, "pdq", substr($0, 5, 20))  # WRONG

     (Some commercial versions of `awk' do in fact let you use `substr'
     this way, but doing so is not portable.)

     If you need to replace bits and pieces of a string, combine
     `substr' with string concatenation, in the following manner:

          string = "abcdef"
          ...
          string = substr(string, 1, 2) "CDE" substr(string, 6)

`tolower(STRING)'
     This returns a copy of STRING, with each uppercase character in
     the string replaced with its corresponding lowercase character.
     Nonalphabetic characters are left unchanged.  For example,
     `tolower("MiXeD cAsE 123")' returns `"mixed case 123"'.

`toupper(STRING)'
     This returns a copy of STRING, with each lowercase character in
     the string replaced with its corresponding uppercase character.
     Nonalphabetic characters are left unchanged.  For example,
     `toupper("MiXeD cAsE 123")' returns `"MIXED CASE 123"'.

---------- Footnotes ----------

(1) Unless you use the `--non-decimal-data' option, which isn't
recommended.  *Note Nondecimal Data::, for more information.

(2) Note that this means that the record will first be regenerated
using the value of `OFS' if any fields have been changed, and that the
fields will be updated after the substituion, even if the operation is
a "no-op" such as `sub(/^/, "")'.

(3) This is different from C and C++, in which the first character is
number zero.


File: gawk.info,  Node: Gory Details,  Up: String Functions

8.1.3.1 More About `\' and `&' with `sub', `gsub', and `gensub'
...............................................................

When using `sub', `gsub', or `gensub', and trying to get literal
backslashes and ampersands into the replacement text, you need to
remember that there are several levels of "escape processing" going on.

First, there is the "lexical" level, which is when `awk' reads your
program and builds an internal copy of it that can be executed.  Then
there is the runtime level, which is when `awk' actually scans the
replacement string to determine what to generate.

At both levels, `awk' looks for a defined set of characters that can
come after a backslash.  At the lexical level, it looks for the escape
sequences listed in *Note Escape Sequences::.  Thus, for every `\' that
`awk' processes at the runtime level, type two backslashes at the
lexical level.  When a character that is not valid for an escape
sequence follows the `\', Unix `awk' and `gawk' both simply remove the
initial `\' and put the next character into the string. Thus, for
example, `"a\qb"' is treated as `"aqb"'.

At the runtime level, the various functions handle sequences of `\' and
`&' differently.  The situation is (sadly) somewhat complex.
Historically, the `sub' and `gsub' functions treated the two character
sequence `\&' specially; this sequence was replaced in the generated
text with a single `&'.  Any other `\' within the REPLACEMENT string
that did not precede an `&' was passed through unchanged.  This is
illustrated in *Note table-sub-escapes::.

      You type         `sub' sees          `sub' generates
      -------         ---------          --------------
          `\&'              `&'            the matched text
         `\\&'             `\&'            a literal `&'
        `\\\&'             `\&'            a literal `&'
       `\\\\&'            `\\&'            a literal `\&'
      `\\\\\&'            `\\&'            a literal `\&'
     `\\\\\\&'           `\\\&'            a literal `\\&'
         `\\q'             `\q'            a literal `\q'

Table 8.1: Historical Escape Sequence Processing for sub and gsub

This table shows both the lexical-level processing, where an odd number
of backslashes becomes an even number at the runtime level, as well as
the runtime processing done by `sub'.  (For the sake of simplicity, the
rest of the following tables only show the case of even numbers of
backslashes entered at the lexical level.)

   The problem with the historical approach is that there is no way to
get a literal `\' followed by the matched text.

   The 1992 POSIX standard attempted to fix this problem. That standard
says that `sub' and `gsub' look for either a `\' or an `&' after the
`\'. If either one follows a `\', that character is output literally.
The interpretation of `\' and `&' then becomes as shown in *Note
table-sub-posix-92::.

      You type         `sub' sees          `sub' generates
      -------         ---------          --------------
           `&'              `&'            the matched text
         `\\&'             `\&'            a literal `&'
       `\\\\&'            `\\&'            a literal `\', then the matched text
     `\\\\\\&'           `\\\&'            a literal `\&'

Table 8.2: 1992 POSIX Rules for sub and gsub Escape Sequence Processing

This appears to solve the problem.  Unfortunately, the phrasing of the
standard is unusual. It says, in effect, that `\' turns off the special
meaning of any following character, but for anything other than `\' and
`&', such special meaning is undefined.  This wording leads to two
problems:

   * Backslashes must now be doubled in the REPLACEMENT string, breaking
     historical `awk' programs.

   * To make sure that an `awk' program is portable, _every_ character
     in the REPLACEMENT string must be preceded with a backslash.(1)

   Because of the problems just listed, in 1996, the `gawk' maintainer
submitted proposed text for a revised standard that reverts to rules
that correspond more closely to the original existing practice. The
proposed rules have special cases that make it possible to produce a
`\' preceding the matched text. This is shown in *Note
table-sub-proposed::.

      You type         `sub' sees         `sub' generates
      -------         ---------         --------------
     `\\\\\\&'           `\\\&'            a literal `\&'
       `\\\\&'            `\\&'            a literal `\', followed by the matched text
         `\\&'             `\&'            a literal `&'
         `\\q'             `\q'            a literal `\q'
        `\\\\'             `\\'            `\\'

Table 8.3: Propsosed rules for sub and backslash

   In a nutshell, at the runtime level, there are now three special
sequences of characters (`\\\&', `\\&' and `\&') whereas historically
there was only one.  However, as in the historical case, any `\' that
is not part of one of these three sequences is not special and appears
in the output literally.

   `gawk' 3.0 and 3.1 follow these proposed POSIX rules for `sub' and
`gsub'.  The POSIX standard took much longer to be revised than was
expected in 1996.  The 2001 standard does not follow the above rules.
Instead, the rules there are somewhat simpler.  The results are similar
except for one case.

   The 2001 POSIX rules state that `\&' in the replacement string
produces a literal `&', `\\' produces a literal `\', and `\' followed
by anything else is not special; the `\' is placed straight into the
output.  These rules are presented in *Note table-posix-2001-sub::.

      You type         `sub' sees         `sub' generates
      -------         ---------         --------------
     `\\\\\\&'           `\\\&'            a literal `\&'
       `\\\\&'            `\\&'            a literal `\', followed by the matched text
         `\\&'             `\&'            a literal `&'
         `\\q'             `\q'            a literal `\q'
        `\\\\'             `\\'            `\'

Table 8.4: POSIX 2001 rules for sub

   The only case where the difference is noticeable is the last one:
`\\\\' is seen as `\\' and produces `\' instead of `\\'.

   Starting with version 3.1.4, `gawk' follows the POSIX rules when
`--posix' is specified (*note Options::). Otherwise, it continues to
follow the 1996 proposed rules, since, as of this writing, that has
been its behavior for over seven years.

     NOTE: At the next major release, `gawk' will switch to using the
     POSIX 2001 rules by default.

   The rules for `gensub' are considerably simpler. At the runtime
level, whenever `gawk' sees a `\', if the following character is a
digit, then the text that matched the corresponding parenthesized
subexpression is placed in the generated output.  Otherwise, no matter
what character follows the `\', it appears in the generated text and
the `\' does not, as shown in *Note table-gensub-escapes::.

       You type          `gensub' sees         `gensub' generates
       -------          ------------         -----------------
           `&'                    `&'            the matched text
         `\\&'                   `\&'            a literal `&'
        `\\\\'                   `\\'            a literal `\'
       `\\\\&'                  `\\&'            a literal `\', then the matched text
     `\\\\\\&'                 `\\\&'            a literal `\&'
         `\\q'                   `\q'            a literal `q'

Table 8.5: Escape Sequence Processing for gensub

   Because of the complexity of the lexical and runtime level processing
and the special cases for `sub' and `gsub', we recommend the use of
`gawk' and `gensub' when you have to do substitutions.

Advanced Notes: Matching the Null String
----------------------------------------

In `awk', the `*' operator can match the null string.  This is
particularly important for the `sub', `gsub', and `gensub' functions.
For example:

     $ echo abc | awk '{ gsub(/m*/, "X"); print }'
     -| XaXbXcX

Although this makes a certain amount of sense, it can be surprising.

---------- Footnotes ----------

(1) This consequence was certainly unintended.


File: gawk.info,  Node: I/O Functions,  Next: Time Functions,  Prev: String Functions,  Up: Built-in

8.1.5 Input/Output Functions
----------------------------

The following functions relate to input/output (I/O).  Optional
parameters are enclosed in square brackets ([ ]):

`close(FILENAME [, HOW])'
     Close the file FILENAME for input or output. Alternatively, the
     argument may be a shell command that was used for creating a
     coprocess, or for redirecting to or from a pipe; then the
     coprocess or pipe is closed.  *Note Close Files And Pipes::, for
     more information.

     When closing a coprocess, it is occasionally useful to first close
     one end of the two-way pipe and then to close the other.  This is
     done by providing a second argument to `close'.  This second
     argument should be one of the two string values `"to"' or `"from"',
     indicating which end of the pipe to close.  Case in the string does
     not matter.  *Note Two-way I/O::, which discusses this feature in
     more detail and gives an example.

`fflush([FILENAME])'
     Flush any buffered output associated with FILENAME, which is
     either a file opened for writing or a shell command for
     redirecting output to a pipe or coprocess.

     Many utility programs "buffer" their output; i.e., they save
     information to write to a disk file or terminal in memory until
     there is enough for it to be worthwhile to send the data to the
     output device.  This is often more efficient than writing every
     little bit of information as soon as it is ready.  However,
     sometimes it is necessary to force a program to "flush" its
     buffers; that is, write the information to its destination, even
     if a buffer is not full.  This is the purpose of the `fflush'
     function--`gawk' also buffers its output and the `fflush' function
     forces `gawk' to flush its buffers.

     `fflush' was added to the Bell Laboratories research version of
     `awk' in 1994; it is not part of the POSIX standard and is not
     available if `--posix' has been specified on the command line
     (*note Options::).

     `gawk' extends the `fflush' function in two ways.  The first is to
     allow no argument at all. In this case, the buffer for the
     standard output is flushed.  The second is to allow the null string
     (`""') as the argument. In this case, the buffers for _all_ open
     output files and pipes are flushed.

     `fflush' returns zero if the buffer is successfully flushed;
     otherwise, it returns -1.  In the case where all buffers are
     flushed, the return value is zero only if all buffers were flushed
     successfully.  Otherwise, it is -1, and `gawk' warns about the
     problem FILENAME.

     `gawk' also issues a warning message if you attempt to flush a
     file or pipe that was opened for reading (such as with `getline'),
     or if FILENAME is not an open file, pipe, or coprocess.  In such a
     case, `fflush' returns -1, as well.

`system(COMMAND)'
     Executes operating-system commands and then returns to the `awk'
     program.  The `system' function executes the command given by the
     string COMMAND.  It returns the status returned by the command
     that was executed as its value.

     For example, if the following fragment of code is put in your `awk'
     program:

          END {
               system("date | mail -s 'awk run done' root")
          }

     the system administrator is sent mail when the `awk' program
     finishes processing input and begins its end-of-input processing.

     Note that redirecting `print' or `printf' into a pipe is often
     enough to accomplish your task.  If you need to run many commands,
     it is more efficient to simply print them down a pipeline to the
     shell:

          while (MORE STUFF TO DO)
              print COMMAND | "/bin/sh"
          close("/bin/sh")

     However, if your `awk' program is interactive, `system' is useful
     for cranking up large self-contained programs, such as a shell or
     an editor.  Some operating systems cannot implement the `system'
     function.  `system' causes a fatal error if it is not supported.

Advanced Notes: Interactive Versus Noninteractive Buffering
-----------------------------------------------------------

As a side point, buffering issues can be even more confusing, depending
upon whether your program is "interactive", i.e., communicating with a
user sitting at a keyboard.(1)

Interactive programs generally "line buffer" their output; i.e., they
write out every line.  Noninteractive programs wait until they have a
full buffer, which may be many lines of output.  Here is an example of
the difference:

     $ awk '{ print $1 + $2 }'
     1 1
     -| 2
     2 3
     -| 5
     Ctrl-d

Each line of output is printed immediately. Compare that behavior with
this example:

     $ awk '{ print $1 + $2 }' | cat
     1 1
     2 3
     Ctrl-d
     -| 2
     -| 5

Here, no output is printed until after the `Ctrl-d' is typed, because
it is all buffered and sent down the pipe to `cat' in one shot.

Advanced Notes: Controlling Output Buffering with `system'
----------------------------------------------------------

The `fflush' function provides explicit control over output buffering
for individual files and pipes.  However, its use is not portable to
many other `awk' implementations.  An alternative method to flush output
buffers is to call `system' with a null string as its argument:

     system("")   # flush output

`gawk' treats this use of the `system' function as a special case and
is smart enough not to run a shell (or other command interpreter) with
the empty command.  Therefore, with `gawk', this idiom is not only
useful, it is also efficient.  While this method should work with other
`awk' implementations, it does not necessarily avoid starting an
unnecessary shell.  (Other implementations may only flush the buffer
associated with the standard output and not necessarily all buffered
output.)

If you think about what a programmer expects, it makes sense that
`system' should flush any pending output.  The following program:

     BEGIN {
          print "first print"
          system("echo system echo")
          print "second print"
     }

must print:

     first print
     system echo
     second print

and not:

     system echo
     first print
     second print

If `awk' did not flush its buffers before calling `system', you would
see the latter (undesirable) output.

---------- Footnotes ----------

(1) A program is interactive if the standard output is connected to a
terminal device.


File: gawk.info,  Node: Time Functions,  Next: Bitwise Functions,  Prev: I/O Functions,  Up: Built-in

8.1.8 Using `gawk''s Timestamp Functions
----------------------------------------

`awk' programs are commonly used to process log files containing
timestamp information, indicating when a particular log record was
written.  Many programs log their timestamp in the form returned by the
`time' system call, which is the number of seconds since a particular
epoch.  On POSIX-compliant systems, it is the number of seconds since
1970-01-01 00:00:00 UTC, not counting leap seconds.(1) All known
POSIX-compliant systems support timestamps from 0 through 2^31 - 1,
which is sufficient to represent times through 2038-01-19 03:14:07 UTC.
Many systems support a wider range of timestamps, including negative
timestamps that represent times before the epoch.

In order to make it easier to process such log files and to produce
useful reports, `gawk' provides the following functions for working
with timestamps.  They are `gawk' extensions; they are not specified in
the POSIX standard, nor are they in any other known version of `awk'.(2)
Optional parameters are enclosed in square brackets ([ ]):

`systime()'
     This function returns the current time as the number of seconds
     since the system epoch.  On POSIX systems, this is the number of
     seconds since 1970-01-01 00:00:00 UTC, not counting leap seconds.
     It may be a different number on other systems.

`mktime(DATESPEC)'
     This function turns DATESPEC into a timestamp in the same form as
     is returned by `systime'.  It is similar to the function of the
     same name in ISO C.  The argument, DATESPEC, is a string of the
     form `"YYYY MM DD HH MM SS [DST]"'.  The string consists of six or
     seven numbers representing, respectively, the full year including
     century, the month from 1 to 12, the day of the month from 1 to
     31, the hour of the day from 0 to 23, the minute from 0 to 59, the
     second from 0 to 60,(3) and an optional daylight-savings flag.

     The values of these numbers need not be within the ranges
     specified; for example, an hour of -1 means 1 hour before midnight.
     The origin-zero Gregorian calendar is assumed, with year 0
     preceding year 1 and year -1 preceding year 0.  The time is
     assumed to be in the local timezone.  If the daylight-savings flag
     is positive, the time is assumed to be daylight savings time; if
     zero, the time is assumed to be standard time; and if negative
     (the default), `mktime' attempts to determine whether daylight
     savings time is in effect for the specified time.

     If DATESPEC does not contain enough elements or if the resulting
     time is out of range, `mktime' returns -1.

`strftime([FORMAT [, TIMESTAMP]])'
     This function returns a string.  It is similar to the function of
     the same name in ISO C.  The time specified by TIMESTAMP is used to
     produce a string, based on the contents of the FORMAT string.  The
     TIMESTAMP is in the same format as the value returned by the
     `systime' function.  If no TIMESTAMP argument is supplied, `gawk'
     uses the current time of day as the timestamp.  If no FORMAT
     argument is supplied, `strftime' uses `"%a %b %d %H:%M:%S %Z %Y"'.
     This format string produces output that is (almost) equivalent to
     that of the `date' utility.  (Versions of `gawk' prior to 3.0
     require the FORMAT argument.)

The `systime' function allows you to compare a timestamp from a log
file with the current time of day.  In particular, it is easy to
determine how long ago a particular record was logged.  It also allows
you to produce log records using the "seconds since the epoch" format.

The `mktime' function allows you to convert a textual representation of
a date and time into a timestamp.   This makes it easy to do
before/after comparisons of dates and times, particularly when dealing
with date and time data coming from an external source, such as a log
file.

The `strftime' function allows you to easily turn a timestamp into
human-readable information.  It is similar in nature to the `sprintf'
function (*note String Functions::), in that it copies nonformat
specification characters verbatim to the returned string, while
substituting date and time values for format specifications in the
FORMAT string.

`strftime' is guaranteed by the 1999 ISO C standard(4) to support the
following date format specifications:

`%a'
     The locale's abbreviated weekday name.

`%A'
     The locale's full weekday name.

`%b'
     The locale's abbreviated month name.

`%B'
     The locale's full month name.

`%c'
     The locale's "appropriate" date and time representation.  (This is
     `%A %B %d %T %Y' in the `"C"' locale.)

`%C'
     The century.  This is the year divided by 100 and truncated to the
     next lower integer.

`%d'
     The day of the month as a decimal number (01-31).

`%D'
     Equivalent to specifying `%m/%d/%y'.

`%e'
     The day of the month, padded with a space if it is only one digit.

`%F'
     Equivalent to specifying `%Y-%m-%d'.  This is the ISO 8601 date
     format.

`%g'
     The year modulo 100 of the ISO week number, as a decimal number
     (00-99).  For example, January 1, 1993 is in week 53 of 1992.
     Thus, the year of its ISO week number is 1992, even though its
     year is 1993.  Similarly, December 31, 1973 is in week 1 of 1974.
     Thus, the year of its ISO week number is 1974, even though its
     year is 1973.

`%G'
     The full year of the ISO week number, as a decimal number.

`%h'
     Equivalent to `%b'.

`%H'
     The hour (24-hour clock) as a decimal number (00-23).

`%I'
     The hour (12-hour clock) as a decimal number (01-12).

`%j'
     The day of the year as a decimal number (001-366).

`%m'
     The month as a decimal number (01-12).

`%M'
     The minute as a decimal number (00-59).

`%n'
     A newline character (ASCII LF).

`%p'
     The locale's equivalent of the AM/PM designations associated with
     a 12-hour clock.

`%r'
     The locale's 12-hour clock time.  (This is `%I:%M:%S %p' in the
     `"C"' locale.)

`%R'
     Equivalent to specifying `%H:%M'.

`%S'
     The second as a decimal number (00-60).

`%t'
     A TAB character.

`%T'
     Equivalent to specifying `%H:%M:%S'.

`%u'
     The weekday as a decimal number (1-7).  Monday is day one.

`%U'
     The week number of the year (the first Sunday as the first day of
     week one) as a decimal number (00-53).

`%V'
     The week number of the year (the first Monday as the first day of
     week one) as a decimal number (01-53).  The method for determining
     the week number is as specified by ISO 8601.  (To wit: if the week
     containing January 1 has four or more days in the new year, then
     it is week one; otherwise it is week 53 of the previous year and
     the next week is week one.)

`%w'
     The weekday as a decimal number (0-6).  Sunday is day zero.

`%W'
     The week number of the year (the first Monday as the first day of
     week one) as a decimal number (00-53).

`%x'
     The locale's "appropriate" date representation.  (This is `%A %B
     %d %Y' in the `"C"' locale.)

`%X'
     The locale's "appropriate" time representation.  (This is `%T' in
     the `"C"' locale.)

`%y'
     The year modulo 100 as a decimal number (00-99).

`%Y'
     The full year as a decimal number (e.g., 1995).

`%z'
     The timezone offset in a +HHMM format (e.g., the format necessary
     to produce RFC 822/RFC 1036 date headers).

`%Z'
     The time zone name or abbreviation; no characters if no time zone
     is determinable.

`%Ec %EC %Ex %EX %Ey %EY %Od %Oe %OH'
`%OI %Om %OM %OS %Ou %OU %OV %Ow %OW %Oy'
     "Alternate representations" for the specifications that use only
     the second letter (`%c', `%C', and so on).(5) (These facilitate
     compliance with the POSIX `date' utility.)

`%%'
     A literal `%'.

If a conversion specifier is not one of the above, the behavior is
undefined.(6)

Informally, a "locale" is the geographic place in which a program is
meant to run.  For example, a common way to abbreviate the date
September 4, 1991 in the United States is "9/4/91."  In many countries
in Europe, however, it is abbreviated "4.9.91."  Thus, the `%x'
specification in a `"US"' locale might produce `9/4/91', while in a
`"EUROPE"' locale, it might produce `4.9.91'.  The ISO C standard
defines a default `"C"' locale, which is an environment that is typical
of what most C programmers are used to.

A public-domain C version of `strftime' is supplied with `gawk' for
systems that are not yet fully standards-compliant.  It supports all of
the just listed format specifications.  If that version is used to
compile `gawk' (*note Installation::), then the following additional
format specifications are available:

`%k'
     The hour (24-hour clock) as a decimal number (0-23).  Single-digit
     numbers are padded with a space.

`%l'
     The hour (12-hour clock) as a decimal number (1-12).  Single-digit
     numbers are padded with a space.

`%N'
     The "Emperor/Era" name.  Equivalent to `%C'.

`%o'
     The "Emperor/Era" year.  Equivalent to `%y'.

`%s'
     The time as a decimal timestamp in seconds since the epoch.

`%v'
     The date in VMS format (e.g., `20-JUN-1991').

Additionally, the alternate representations are recognized but their
normal representations are used.

This example is an `awk' implementation of the POSIX `date' utility.
Normally, the `date' utility prints the current date and time of day in
a well-known format.  However, if you provide an argument to it that
begins with a `+', `date' copies nonformat specifier characters to the
standard output and interprets the current time according to the format
specifiers in the string.  For example:

     $ date '+Today is %A, %B %d, %Y.'
     -| Today is Thursday, September 14, 2000.

Here is the `gawk' version of the `date' utility.  It has a shell
"wrapper" to handle the `-u' option, which requires that `date' run as
if the time zone is set to UTC:

     #! /bin/sh
     #
     # date --- approximate the P1003.2 'date' command

     case $1 in
     -u)  TZ=UTC0     # use UTC
          export TZ
          shift ;;
     esac

     gawk 'BEGIN  {
         format = "%a %b %d %H:%M:%S %Z %Y"
         exitval = 0

         if (ARGC > 2)
             exitval = 1
         else if (ARGC == 2) {
             format = ARGV[1]
             if (format ~ /^\+/)
                 format = substr(format, 2)   # remove leading +
         }
         print strftime(format)
         exit exitval
     }' "$@"

---------- Footnotes ----------

(1) *Note Glossary::, especially the entries "Epoch" and "UTC."

(2) The GNU `date' utility can also do many of the things described
here.  Its use may be preferable for simple time-related operations in
shell scripts.

(3) Occasionally there are minutes in a year with a leap second, which
is why the seconds can go up to 60.

(4) As this is a recent standard, not every system's `strftime'
necessarily supports all of the conversions listed here.

(5) If you don't understand any of this, don't worry about it; these
facilities are meant to make it easier to "internationalize" programs.
Other internationalization features are described in *Note
Internationalization::.

(6) This is because ISO C leaves the behavior of the C version of
`strftime' undefined and `gawk' uses the system's version of `strftime'
if it's there.  Typically, the conversion specifier either does not
appear in the returned string or appears literally.


File: gawk.info,  Node: Bitwise Functions,  Next: I18N Functions,  Prev: Time Functions,  Up: Built-in

8.1.9 Bit-Manipulation Functions of `gawk'
------------------------------------------

     I can explain it for you, but I can't understand it for you.
     Anonymous

Many languages provide the ability to perform "bitwise" operations on
two integer numbers.  In other words, the operation is performed on
each successive pair of bits in the operands.  Three common operations
are bitwise AND, OR, and XOR.  The operations are described in *Note
table-bitwise-ops::.

                     Bit Operator
               |  AND  |   OR  |  XOR
               |--+--+--+--+--+--
     Operands  | 0 | 1 | 0 | 1 | 0 | 1
     ---------+--+--+--+--+--+--
         0     | 0   0 | 0   1 | 0   1
         1     | 0   1 | 1   1 | 1   0

Table 8.6: Bitwise Operations

   As you can see, the result of an AND operation is 1 only when _both_
bits are 1.  The result of an OR operation is 1 if _either_ bit is 1.
The result of an XOR operation is 1 if either bit is 1, but not both.
The next operation is the "complement"; the complement of 1 is 0 and
the complement of 0 is 1. Thus, this operation "flips" all the bits of
a given value.

   Finally, two other common operations are to shift the bits left or
right.  For example, if you have a bit string `10111001' and you shift
it right by three bits, you end up with `00010111'.(1) If you start over
again with `10111001' and shift it left by three bits, you end up with
`11001000'.  `gawk' provides built-in functions that implement the
bitwise operations just described. They are:

`and(V1, V2)'          Returns the bitwise AND of the values provided by V1
                       and V2.
`or(V1, V2)'           Returns the bitwise OR of the values provided by V1
                       and V2.
`xor(V1, V2)'          Returns the bitwise XOR of the values provided by V1
                       and V2.
`compl(VAL)'           Returns the bitwise complement of VAL.
`lshift(VAL, COUNT)'   Returns the value of VAL, shifted left by COUNT bits.
`rshift(VAL, COUNT)'   Returns the value of VAL, shifted right by COUNT bits.

   For all of these functions, first the double-precision
floating-point value is converted to the widest C unsigned integer
type, then the bitwise operation is performed.  If the result cannot be
represented exactly as a C `double', leading nonzero bits are removed
one by one until it can be represented exactly.  The result is then
converted back into a C `double'.  (If you don't understand this
paragraph, don't worry about it.)

   Here is a user-defined function (*note User-defined::) that
illustrates the use of these functions:

     # bits2str --- turn a byte into readable 1's and 0's

     function bits2str(bits,        data, mask)
     {
         if (bits == 0)
             return "0"

         mask = 1
         for (; bits != 0; bits = rshift(bits, 1))
             data = (and(bits, mask) ? "1" : "0") data

         while ((length(data) % 8) != 0)
             data = "0" data

         return data
     }

     BEGIN {
         printf "123 = %s\n", bits2str(123)
         printf "0123 = %s\n", bits2str(0123)
         printf "0x99 = %s\n", bits2str(0x99)
         comp = compl(0x99)
         printf "compl(0x99) = %#x = %s\n", comp, bits2str(comp)
         shift = lshift(0x99, 2)
         printf "lshift(0x99, 2) = %#x = %s\n", shift, bits2str(shift)
         shift = rshift(0x99, 2)
         printf "rshift(0x99, 2) = %#x = %s\n", shift, bits2str(shift)
     }

This program produces the following output when run:

     $ gawk -f testbits.awk
     -| 123 = 01111011
     -| 0123 = 01010011
     -| 0x99 = 10011001
     -| compl(0x99) = 0xffffff66 = 11111111111111111111111101100110
     -| lshift(0x99, 2) = 0x264 = 0000001001100100
     -| rshift(0x99, 2) = 0x26 = 00100110

The `bits2str' function turns a binary number into a string.  The
number `1' represents a binary value where the rightmost bit is set to
1.  Using this mask, the function repeatedly checks the rightmost bit.
ANDing the mask with the value indicates whether the rightmost bit is 1
or not. If so, a `"1"' is concatenated onto the front of the string.
Otherwise, a `"0"' is added.  The value is then shifted right by one
bit and the loop continues until there are no more 1 bits.

If the initial value is zero it returns a simple `"0"'.  Otherwise, at
the end, it pads the value with zeros to represent multiples of 8-bit
quantities. This is typical in modern computers.

The main code in the `BEGIN' rule shows the difference between the
decimal and octal values for the same numbers (*note
Nondecimal-numbers::), and then demonstrates the results of the
`compl', `lshift', and `rshift' functions.

---------- Footnotes ----------

(1) This example shows that 0's come in on the left side. For `gawk',
this is always true, but in some languages, it's possible to have the
left side fill with 1's. Caveat emptor.


File: gawk.info,  Node: I18N Functions,  Prev: Bitwise Functions,  Up: Built-in

8.1.10 Using `gawk''s String-Translation Functions
--------------------------------------------------

`gawk' provides facilities for internationalizing `awk' programs.
These include the functions described in the following list.  The
descriptions here are purposely brief.  *Note Internationalization::,
for the full story.  Optional parameters are enclosed in square
brackets ([ ]):

`dcgettext(STRING [, DOMAIN [, CATEGORY]])'
     This function returns the translation of STRING in text domain
     DOMAIN for locale category CATEGORY.  The default value for DOMAIN
     is the current value of `TEXTDOMAIN'.  The default value for
     CATEGORY is `"LC_MESSAGES"'.

`dcngettext(STRING1, STRING2, NUMBER [, DOMAIN [, CATEGORY]])'
     This function returns the plural form used for NUMBER of the
     translation of STRING1 and STRING2 in text domain DOMAIN for
     locale category CATEGORY. STRING1 is the English singular variant
     of a message, and STRING2 the English plural variant of the same
     message.  The default value for DOMAIN is the current value of
     `TEXTDOMAIN'.  The default value for CATEGORY is `"LC_MESSAGES"'.

`bindtextdomain(DIRECTORY [, DOMAIN])'
     This function allows you to specify the directory in which `gawk'
     will look for message translation files, in case they will not or
     cannot be placed in the "standard" locations (e.g., during
     testing).  It returns the directory in which DOMAIN is "bound."

     The default DOMAIN is the value of `TEXTDOMAIN'.  If DIRECTORY is
     the null string (`""'), then `bindtextdomain' returns the current
     binding for the given DOMAIN.


File: gawk.info,  Node: User-defined,  Prev: Built-in,  Up: Functions

8.2 User-Defined Functions
==========================

Complicated `awk' programs can often be simplified by defining your own
functions.  User-defined functions can be called just like built-in
ones (*note Function Calls::), but it is up to you to define them,
i.e., to tell `awk' what they should do.

* Menu:

* Definition Syntax::           How to write definitions and what they mean.
* Function Example::            An example function definition and what it
                                does.
* Function Caveats::            Things to watch out for.
* Return Statement::            Specifying the value a function returns.
* Dynamic Typing::              How variable types can change at runtime.


File: gawk.info,  Node: Definition Syntax,  Next: Function Example,  Up: User-defined

8.2.1 Function Definition Syntax
--------------------------------

Definitions of functions can appear anywhere between the rules of an
`awk' program.  Thus, the general form of an `awk' program is extended
to include sequences of rules _and_ user-defined function definitions.
There is no need to put the definition of a function before all uses of
the function.  This is because `awk' reads the entire program before
starting to execute any of it.

The definition of a function named NAME looks like this:

     function NAME(PARAMETER-LIST)
     {
          BODY-OF-FUNCTION
     }

NAME is the name of the function to define.  A valid function name is
like a valid variable name: a sequence of letters, digits, and
underscores that doesn't start with a digit.  Within a single `awk'
program, any particular name can only be used as a variable, array, or
function.

PARAMETER-LIST is a list of the function's arguments and local variable
names, separated by commas.  When the function is called, the argument
names are used to hold the argument values given in the call.  The
local variables are initialized to the empty string.  A function cannot
have two parameters with the same name, nor may it have a parameter
with the same name as the function itself.

The BODY-OF-FUNCTION consists of `awk' statements.  It is the most
important part of the definition, because it says what the function
should actually _do_.  The argument names exist to give the body a way
to talk about the arguments; local variables exist to give the body
places to keep temporary values.

Argument names are not distinguished syntactically from local variable
names. Instead, the number of arguments supplied when the function is
called determines how many argument variables there are.  Thus, if three
argument values are given, the first three names in PARAMETER-LIST are
arguments and the rest are local variables.

It follows that if the number of arguments is not the same in all calls
to the function, some of the names in PARAMETER-LIST may be arguments
on some occasions and local variables on others.  Another way to think
of this is that omitted arguments default to the null string.

Usually when you write a function, you know how many names you intend to
use for arguments and how many you intend to use as local variables.
It is conventional to place some extra space between the arguments and
the local variables, in order to document how your function is supposed
to be used.

During execution of the function body, the arguments and local variable
values hide, or "shadow", any variables of the same names used in the
rest of the program.  The shadowed variables are not accessible in the
function definition, because there is no way to name them while their
names have been taken away for the local variables.  All other variables
used in the `awk' program can be referenced or set normally in the
function's body.

The arguments and local variables last only as long as the function body
is executing.  Once the body finishes, you can once again access the
variables that were shadowed while the function was running.

The function body can contain expressions that call functions.  They
can even call this function, either directly or by way of another
function.  When this happens, we say the function is "recursive".  The
act of a function calling itself is called "recursion".

In many `awk' implementations, including `gawk', the keyword `function'
may be abbreviated `func'.  However, POSIX only specifies the use of
the keyword `function'.  This actually has some practical implications.
If `gawk' is in POSIX-compatibility mode (*note Options::), then the
following statement does _not_ define a function:

     func foo() { a = sqrt($1) ; print a }

Instead it defines a rule that, for each record, concatenates the value
of the variable `func' with the return value of the function `foo'.  If
the resulting string is non-null, the action is executed.  This is
probably not what is desired.  (`awk' accepts this input as
syntactically valid, because functions may be used before they are
defined in `awk' programs.)

To ensure that your `awk' programs are portable, always use the keyword
`function' when defining a function.


File: gawk.info,  Node: Function Example,  Next: Function Caveats,  Prev: Definition Syntax,  Up: User-defined

8.2.2 Function Definition Examples
----------------------------------

Here is an example of a user-defined function, called `myprint', that
takes a number and prints it in a specific format:

     function myprint(num)
     {
          printf "%6.3g\n", num
     }

To illustrate, here is an `awk' rule that uses our `myprint' function:

     $3 > 0     { myprint($3) }

This program prints, in our special format, all the third fields that
contain a positive number in our input.  Therefore, when given the
following:

      1.2   3.4    5.6   7.8
      9.10 11.12 -13.14 15.16
     17.18 19.20  21.22 23.24

this program, using our function to format the results, prints:

        5.6
       21.2

This function deletes all the elements in an array:

     function delarray(a,    i)
     {
         for (i in a)
            delete a[i]
     }

When working with arrays, it is often necessary to delete all the
elements in an array and start over with a new list of elements (*note
Delete::).  Instead of having to repeat this loop everywhere that you
need to clear out an array, your program can just call `delarray'.
(This guarantees portability.  The use of `delete ARRAY' to delete the
contents of an entire array is a nonstandard extension.)

The following is an example of a recursive function.  It takes a string
as an input parameter and returns the string in backwards order.
Recursive functions must always have a test that stops the recursion.
In this case, the recursion terminates when the starting position is
zero, i.e., when there are no more characters left in the string.

     function rev(str, start)
     {
         if (start == 0)
             return ""

         return (substr(str, start, 1) rev(str, start - 1))
     }

If this function is in a file named `rev.awk', it can be tested this
way:

     $ echo "Don't Panic!" |
     > gawk --source '{ print rev($0, length($0)) }' -f rev.awk
     -| !cinaP t'noD

The C `ctime' function takes a timestamp and returns it in a string,
formatted in a well-known fashion.  The following example uses the
built-in `strftime' function (*note Time Functions::) to create an
`awk' version of `ctime':

     # ctime.awk
     #
     # awk version of C ctime(3) function

     function ctime(ts,    format)
     {
         format = "%a %b %d %H:%M:%S %Z %Y"
         if (ts == 0)
             ts = systime()       # use current time as default
         return strftime(format, ts)
     }


File: gawk.info,  Node: Function Caveats,  Next: Return Statement,  Prev: Function Example,  Up: User-defined

8.2.3 Calling User-Defined Functions
------------------------------------

"Calling a function" means causing the function to run and do its job.
A function call is an expression and its value is the value returned by
the function.

A function call consists of the function name followed by the arguments
in parentheses.  `awk' expressions are what you write in the call for
the arguments.  Each time the call is executed, these expressions are
evaluated, and the values are the actual arguments.  For example, here
is a call to `foo' with three arguments (the first being a string
concatenation):

     foo(x y, "lose", 4 * z)

*Caution:* Whitespace characters (spaces and tabs) are not allowed
between the function name and the open-parenthesis of the argument list.
If you write whitespace by mistake, `awk' might think that you mean to
concatenate a variable with an expression in parentheses.  However, it
notices that you used a function name and not a variable name, and
reports an error.

When a function is called, it is given a _copy_ of the values of its
arguments.  This is known as "call by value".  The caller may use a
variable as the expression for the argument, but the called function
does not know this--it only knows what value the argument had.  For
example, if you write the following code:

     foo = "bar"
     z = myfunc(foo)

then you should not think of the argument to `myfunc' as being "the
variable `foo'."  Instead, think of the argument as the string value
`"bar"'.  If the function `myfunc' alters the values of its local
variables, this has no effect on any other variables.  Thus, if `myfunc'
does this:

     function myfunc(str)
     {
       print str
       str = "zzz"
       print str
     }

to change its first argument variable `str', it does _not_ change the
value of `foo' in the caller.  The role of `foo' in calling `myfunc'
ended when its value (`"bar"') was computed.  If `str' also exists
outside of `myfunc', the function body cannot alter this outer value,
because it is shadowed during the execution of `myfunc' and cannot be
seen or changed from there.

However, when arrays are the parameters to functions, they are _not_
copied.  Instead, the array itself is made available for direct
manipulation by the function.  This is usually called "call by
reference".  Changes made to an array parameter inside the body of a
function _are_ visible outside that function.

     NOTE: Changing an array parameter inside a function can be very
     dangerous if you do not watch what you are doing.  For example:

          function changeit(array, ind, nvalue)
          {
               array[ind] = nvalue
          }

          BEGIN {
              a[1] = 1; a[2] = 2; a[3] = 3
              changeit(a, 2, "two")
              printf "a[1] = %s, a[2] = %s, a[3] = %s\n",
                      a[1], a[2], a[3]
          }

     prints `a[1] = 1, a[2] = two, a[3] = 3', because `changeit' stores
     `"two"' in the second element of `a'.

Some `awk' implementations allow you to call a function that has not
been defined. They only report a problem at runtime when the program
actually tries to call the function. For example:

     BEGIN {
         if (0)
             foo()
         else
             bar()
     }
     function bar() { ... }
     # note that `foo' is not defined

Because the `if' statement will never be true, it is not really a
problem that `foo' has not been defined.  Usually, though, it is a
problem if a program calls an undefined function.

If `--lint' is specified (*note Options::), `gawk' reports calls to
undefined functions.

Some `awk' implementations generate a runtime error if you use the
`next' statement (*note Next Statement::) inside a user-defined
function.  `gawk' does not have this limitation.


File: gawk.info,  Node: Return Statement,  Next: Dynamic Typing,  Prev: Function Caveats,  Up: User-defined

8.2.4 The `return' Statement
----------------------------

The body of a user-defined function can contain a `return' statement.
This statement returns control to the calling part of the `awk'
program.  It can also be used to return a value for use in the rest of
the `awk' program.  It looks like this:

     return [EXPRESSION]

The EXPRESSION part is optional.  If it is omitted, then the returned
value is undefined, and therefore, unpredictable.

A `return' statement with no value expression is assumed at the end of
every function definition.  So if control reaches the end of the
function body, then the function returns an unpredictable value.  `awk'
does _not_ warn you if you use the return value of such a function.

Sometimes, you want to write a function for what it does, not for what
it returns.  Such a function corresponds to a `void' function in C or
to a `procedure' in Pascal.  Thus, it may be appropriate to not return
any value; simply bear in mind that if you use the return value of such
a function, you do so at your own risk.

The following is an example of a user-defined function that returns a
value for the largest number among the elements of an array:

     function maxelt(vec,   i, ret)
     {
          for (i in vec) {
               if (ret == "" || vec[i] > ret)
                    ret = vec[i]
          }
          return ret
     }

You call `maxelt' with one argument, which is an array name.  The local
variables `i' and `ret' are not intended to be arguments; while there
is nothing to stop you from passing more than one argument to `maxelt',
the results would be strange.  The extra space before `i' in the
function parameter list indicates that `i' and `ret' are not supposed
to be arguments.  You should follow this convention when defining
functions.

The following program uses the `maxelt' function.  It loads an array,
calls `maxelt', and then reports the maximum number in that array:

     function maxelt(vec,   i, ret)
     {
          for (i in vec) {
               if (ret == "" || vec[i] > ret)
                    ret = vec[i]
          }
          return ret
     }

     # Load all fields of each record into nums.
     {
          for(i = 1; i <= NF; i++)
               nums[NR, i] = $i
     }

     END {
          print maxelt(nums)
     }

Given the following input:

      1 5 23 8 16
     44 3 5 2 8 26
     256 291 1396 2962 100
     -6 467 998 1101
     99385 11 0 225

the program reports (predictably) that `99385' is the largest number in
the array.


File: gawk.info,  Node: Dynamic Typing,  Prev: Return Statement,  Up: User-defined

8.2.5 Functions and Their Effects on Variable Typing
----------------------------------------------------

`awk' is a very fluid language.  It is possible that `awk' can't tell
if an identifier represents a regular variable or an array until
runtime.  Here is an annotated sample program:

     function foo(a)
     {
         a[1] = 1   # parameter is an array
     }

     BEGIN {
         b = 1
         foo(b)  # invalid: fatal type mismatch

         foo(x)  # x uninitialized, becomes an array dynamically
         x = 1   # now not allowed, runtime error
     }

Usually, such things aren't a big issue, but it's worth being aware of
them.


File: gawk.info,  Node: Internationalization,  Next: Advanced Features,  Prev: Functions,  Up: Top

9 Internationalization with `gawk'
**********************************

Once upon a time, computer makers wrote software that worked only in
English.  Eventually, hardware and software vendors noticed that if
their systems worked in the native languages of non-English-speaking
countries, they were able to sell more systems.  As a result,
internationalization and localization of programs and software systems
became a common practice.

Until recently, the ability to provide internationalization was largely
restricted to programs written in C and C++.  This major node describes
the underlying library `gawk' uses for internationalization, as well as
how `gawk' makes internationalization features available at the `awk'
program level.  Having internationalization available at the `awk' level
gives software developers additional flexibility--they are no longer
required to write in C when internationalization is a requirement.

* Menu:

* I18N and L10N::               Internationalization and Localization.
* Explaining gettext::          How GNU `gettext' works.
* Programmer i18n::             Features for the programmer.
* Translator i18n::             Features for the translator.
* I18N Example::                A simple i18n example.
* Gawk I18N::                   `gawk' is also internationalized.


File: gawk.info,  Node: I18N and L10N,  Next: Explaining gettext,  Up: Internationalization

9.1 Internationalization and Localization
=========================================

"Internationalization" means writing (or modifying) a program once, in
such a way that it can use multiple languages without requiring further
source-code changes.  "Localization" means providing the data necessary
for an internationalized program to work in a particular language.
Most typically, these terms refer to features such as the language used
for printing error messages, the language used to read responses, and
information related to how numerical and monetary values are printed
and read.


File: gawk.info,  Node: Explaining gettext,  Next: Programmer i18n,  Prev: I18N and L10N,  Up: Internationalization

9.2 GNU `gettext'
=================

The facilities in GNU `gettext' focus on messages; strings printed by a
program, either directly or via formatting with `printf' or
`sprintf'.(1)

When using GNU `gettext', each application has its own "text domain".
This is a unique name, such as `kpilot' or `gawk', that identifies the
application.  A complete application may have multiple
components--programs written in C or C++, as well as scripts written in
`sh' or `awk'.  All of the components use the same text domain.

To make the discussion concrete, assume we're writing an application
named `guide'.  Internationalization consists of the following steps,
in this order:

  1. The programmer goes through the source for all of `guide''s
     components and marks each string that is a candidate for
     translation.  For example, `"`-F': option required"' is a good
     candidate for translation.  A table with strings of option names
     is not (e.g., `gawk''s `--profile' option should remain the same,
     no matter what the local language).

  2. The programmer indicates the application's text domain (`"guide"')
     to the `gettext' library, by calling the `textdomain' function.

  3. Messages from the application are extracted from the source code
     and collected into a portable object file (`guide.po'), which
     lists the strings and their translations.  The translations are
     initially empty.  The original (usually English) messages serve as
     the key for lookup of the translations.

  4. For each language with a translator, `guide.po' is copied and
     translations are created and shipped with the application.

  5. Each language's `.po' file is converted into a binary message
     object (`.mo') file.  A message object file contains the original
     messages and their translations in a binary format that allows
     fast lookup of translations at runtime.

  6. When `guide' is built and installed, the binary translation files
     are installed in a standard place.

  7. For testing and development, it is possible to tell `gettext' to
     use `.mo' files in a different directory than the standard one by
     using the `bindtextdomain' function.

  8. At runtime, `guide' looks up each string via a call to `gettext'.
     The returned string is the translated string if available, or the
     original string if not.

  9. If necessary, it is possible to access messages from a different
     text domain than the one belonging to the application, without
     having to switch the application's default text domain back and
     forth.

In C (or C++), the string marking and dynamic translation lookup are
accomplished by wrapping each string in a call to `gettext':

     printf(gettext("Don't Panic!\n"));

The tools that extract messages from source code pull out all strings
enclosed in calls to `gettext'.

The GNU `gettext' developers, recognizing that typing `gettext' over
and over again is both painful and ugly to look at, use the macro `_'
(an underscore) to make things easier:

     /* In the standard header file: */
     #define _(str) gettext(str)

     /* In the program text: */
     printf(_("Don't Panic!\n"));

This reduces the typing overhead to just three extra characters per
string and is considerably easier to read as well.  There are locale
"categories" for different types of locale-related information.  The
defined locale categories that `gettext' knows about are:

`LC_MESSAGES'
     Text messages.  This is the default category for `gettext'
     operations, but it is possible to supply a different one
     explicitly, if necessary.  (It is almost never necessary to supply
     a different category.)

`LC_COLLATE'
     Text-collation information; i.e., how different characters and/or
     groups of characters sort in a given language.

`LC_CTYPE'
     Character-type information (alphabetic, digit, upper- or
     lowercase, and so on).  This information is accessed via the POSIX
     character classes in regular expressions, such as `/[[:alnum:]]/'
     (*note Regexp Operators::).

`LC_MONETARY'
     Monetary information, such as the currency symbol, and whether the
     symbol goes before or after a number.

`LC_NUMERIC'
     Numeric information, such as which characters to use for the
     decimal point and the thousands separator.(2)

`LC_RESPONSE'
     Response information, such as how "yes" and "no" appear in the
     local language, and possibly other information as well.

`LC_TIME'
     Time- and date-related information, such as 12- or 24-hour clock,
     month printed before or after day in a date, local month
     abbreviations, and so on.

`LC_ALL'
     All of the above.  (Not too useful in the context of `gettext'.)

---------- Footnotes ----------

(1) For some operating systems, the `gawk' port doesn't support GNU
`gettext'.  This applies most notably to the PC operating systems.  As
such, these features are not available if you are using one of those
operating systems.  Sorry.

(2) Americans use a comma every three decimal places and a period for
the decimal point, while many Europeans do exactly the opposite:
`1,234.56' versus `1.234,56'.


File: gawk.info,  Node: Programmer i18n,  Next: Translator i18n,  Prev: Explaining gettext,  Up: Internationalization

9.3 Internationalizing `awk' Programs
=====================================

`gawk' provides the following variables and functions for
internationalization:

`TEXTDOMAIN'
     This variable indicates the application's text domain.  For
     compatibility with GNU `gettext', the default value is
     `"messages"'.

`_"your message here"'
     String constants marked with a leading underscore are candidates
     for translation at runtime.  String constants without a leading
     underscore are not translated.

`dcgettext(STRING [, DOMAIN [, CATEGORY]])'
     This built-in function returns the translation of STRING in text
     domain DOMAIN for locale category CATEGORY.  The default value for
     DOMAIN is the current value of `TEXTDOMAIN'.  The default value
     for CATEGORY is `"LC_MESSAGES"'.

     If you supply a value for CATEGORY, it must be a string equal to
     one of the known locale categories described in *Note Explaining
     gettext::.  You must also supply a text domain.  Use `TEXTDOMAIN'
     if you want to use the current domain.

     *Caution:* The order of arguments to the `awk' version of the
     `dcgettext' function is purposely different from the order for the
     C version.  The `awk' version's order was chosen to be simple and
     to allow for reasonable `awk'-style default arguments.

`dcngettext(STRING1, STRING2, NUMBER [, DOMAIN [, CATEGORY]])'
     This built-in function returns the plural form used for NUMBER of
     the translation of STRING1 and STRING2 in text domain DOMAIN for
     locale category CATEGORY. STRING1 is the English singular variant
     of a message, and STRING2 the English plural variant of the same
     message.  The default value for DOMAIN is the current value of
     `TEXTDOMAIN'.  The default value for CATEGORY is `"LC_MESSAGES"'.

     The same remarks as for the `dcgettext' function apply.

`bindtextdomain(DIRECTORY [, DOMAIN])'
     This built-in function allows you to specify the directory in which
     `gettext' looks for `.mo' files, in case they will not or cannot
     be placed in the standard locations (e.g., during testing).  It
     returns the directory in which DOMAIN is "bound."

     The default DOMAIN is the value of `TEXTDOMAIN'.  If DIRECTORY is
     the null string (`""'), then `bindtextdomain' returns the current
     binding for the given DOMAIN.

To use these facilities in your `awk' program, follow the steps
outlined in *Note Explaining gettext::, like so:

  1. Set the variable `TEXTDOMAIN' to the text domain of your program.
     This is best done in a `BEGIN' rule (*note BEGIN/END::), or it can
     also be done via the `-v' command-line option (*note Options::):

          BEGIN {
              TEXTDOMAIN = "guide"
              ...
          }

  2. Mark all translatable strings with a leading underscore (`_')
     character.  It _must_ be adjacent to the opening quote of the
     string.  For example:

          print _"hello, world"
          x = _"you goofed"
          printf(_"Number of users is %d\n", nusers)

  3. If you are creating strings dynamically, you can still translate
     them, using the `dcgettext' built-in function:

          message = nusers " users logged in"
          message = dcgettext(message, "adminprog")
          print message

     Here, the call to `dcgettext' supplies a different text domain
     (`"adminprog"') in which to find the message, but it uses the
     default `"LC_MESSAGES"' category.

  4. During development, you might want to put the `.mo' file in a
     private directory for testing.  This is done with the
     `bindtextdomain' built-in function:

          BEGIN {
             TEXTDOMAIN = "guide"   # our text domain
             if (Testing) {
                 # where to find our files
                 bindtextdomain("testdir")
                 # joe is in charge of adminprog
                 bindtextdomain("../joe/testdir", "adminprog")
             }
             ...
          }


*Note I18N Example::, for an example program showing the steps to create
and use translations from `awk'.


File: gawk.info,  Node: Translator i18n,  Next: I18N Example,  Prev: Programmer i18n,  Up: Internationalization

9.4 Translating `awk' Programs
==============================

Once a program's translatable strings have been marked, they must be
extracted to create the initial `.po' file.  As part of translation, it
is often helpful to rearrange the order in which arguments to `printf'
are output.

`gawk''s `--gen-po' command-line option extracts the messages and is
discussed next.  After that, `printf''s ability to rearrange the order
for `printf' arguments at runtime is covered.

* Menu:

* String Extraction::           Extracting marked strings.
* Printf Ordering::             Rearranging `printf' arguments.
* I18N Portability::            `awk'-level portability issues.


File: gawk.info,  Node: String Extraction,  Next: Printf Ordering,  Up: Translator i18n

9.4.1 Extracting Marked Strings
-------------------------------

Once your `awk' program is working, and all the strings have been
marked and you've set (and perhaps bound) the text domain, it is time
to produce translations.  First, use the `--gen-po' command-line option
to create the initial `.po' file:

     $ gawk --gen-po -f guide.awk > guide.po

When run with `--gen-po', `gawk' does not execute your program.
Instead, it parses it as usual and prints all marked strings to
standard output in the format of a GNU `gettext' Portable Object file.
Also included in the output are any constant strings that appear as the
first argument to `dcgettext' or as the first and second argument to
`dcngettext'.(1) *Note I18N Example::, for the full list of steps to go
through to create and test translations for `guide'.

---------- Footnotes ----------

(1) Starting with `gettext' version 0.11.5, the `xgettext' utility that
comes with GNU `gettext' can handle `.awk' files.


File: gawk.info,  Node: Printf Ordering,  Next: I18N Portability,  Prev: String Extraction,  Up: Translator i18n

9.4.2 Rearranging `printf' Arguments
------------------------------------

Format strings for `printf' and `sprintf' (*note Printf::) present a
special problem for translation.  Consider the following:(1)

     printf(_"String `%s' has %d characters\n",
               string, length(string)))

A possible German translation for this might be:

     "%d Zeichen lang ist die Zeichenkette `%s'\n"

The problem should be obvious: the order of the format specifications
is different from the original!  Even though `gettext' can return the
translated string at runtime, it cannot change the argument order in
the call to `printf'.

To solve this problem, `printf' format specificiers may have an
additional optional element, which we call a "positional specifier".
For example:

     "%2$d Zeichen lang ist die Zeichenkette `%1$s'\n"

Here, the positional specifier consists of an integer count, which
indicates which argument to use, and a `$'. Counts are one-based, and
the format string itself is _not_ included.  Thus, in the following
example, `string' is the first argument and `length(string)' is the
second:

     $ gawk 'BEGIN {
     >     string = "Dont Panic"
     >     printf _"%2$d characters live in \"%1$s\"\n",
     >                         string, length(string)
     > }'
     -| 10 characters live in "Dont Panic"

If present, positional specifiers come first in the format
specification, before the flags, the field width, and/or the precision.

Positional specifiers can be used with the dynamic field width and
precision capability:

     $ gawk 'BEGIN {
     >    printf("%*.*s\n", 10, 20, "hello")
     >    printf("%3$*2$.*1$s\n", 20, 10, "hello")
     > }'
     -|      hello
     -|      hello

     NOTE: When using `*' with a positional specifier, the `*' comes
     first, then the integer position, and then the `$'.  This is
     somewhat counterintutive.

`gawk' does not allow you to mix regular format specifiers and those
with positional specifiers in the same string:

     $ gawk 'BEGIN { printf _"%d %3$s\n", 1, 2, "hi" }'
     error--> gawk: cmd. line:1: fatal: must use `count$' on all formats or none

     NOTE: There are some pathological cases that `gawk' may fail to
     diagnose.  In such cases, the output may not be what you expect.
     It's still a bad idea to try mixing them, even if `gawk' doesn't
     detect it.

Although positional specifiers can be used directly in `awk' programs,
their primary purpose is to help in producing correct translations of
format strings into languages different from the one in which the
program is first written.

---------- Footnotes ----------

(1) This example is borrowed from the GNU `gettext' manual.


File: gawk.info,  Node: I18N Portability,  Prev: Printf Ordering,  Up: Translator i18n

9.4.3 `awk' Portability Issues
------------------------------

`gawk''s internationalization features were purposely chosen to have as
little impact as possible on the portability of `awk' programs that use
them to other versions of `awk'.  Consider this program:

     BEGIN {
         TEXTDOMAIN = "guide"
         if (Test_Guide)   # set with -v
             bindtextdomain("/test/guide/messages")
         print _"don't panic!"
     }

As written, it won't work on other versions of `awk'.  However, it is
actually almost portable, requiring very little change:

   * Assignments to `TEXTDOMAIN' won't have any effect, since
     `TEXTDOMAIN' is not special in other `awk' implementations.

   * Non-GNU versions of `awk' treat marked strings as the
     concatenation of a variable named `_' with the string following
     it.(1) Typically, the variable `_' has the null string (`""') as
     its value, leaving the original string constant as the result.

   * By defining "dummy" functions to replace `dcgettext', `dcngettext'
     and `bindtextdomain', the `awk' program can be made to run, but
     all the messages are output in the original language.  For example:

          function bindtextdomain(dir, domain)
          {
              return dir
          }

          function dcgettext(string, domain, category)
          {
              return string
          }

          function dcngettext(string1, string2, number, domain, category)
          {
              return (number == 1 ? string1 : string2)
          }

   * The use of positional specifications in `printf' or `sprintf' is
     _not_ portable.  To support `gettext' at the C level, many
     systems' C versions of `sprintf' do support positional specifiers.
     But it works only if enough arguments are supplied in the
     function call.  Many versions of `awk' pass `printf' formats and
     arguments unchanged to the underlying C library version of
     `sprintf', but only one format and argument at a time.  What
     happens if a positional specification is used is anybody's guess.
     However, since the positional specifications are primarily for use
     in _translated_ format strings, and since non-GNU `awk's never
     retrieve the translated string, this should not be a problem in
     practice.

---------- Footnotes ----------

(1) This is good fodder for an "Obfuscated `awk'" contest.


File: gawk.info,  Node: I18N Example,  Next: Gawk I18N,  Prev: Translator i18n,  Up: Internationalization

9.5 A Simple Internationalization Example
=========================================

Now let's look at a step-by-step example of how to internationalize and
localize a simple `awk' program, using `guide.awk' as our original
source:

     BEGIN {
         TEXTDOMAIN = "guide"
         bindtextdomain(".")  # for testing
         print _"Don't Panic"
         print _"The Answer Is", 42
         print "Pardon me, Zaphod who?"
     }

Run `gawk --gen-po' to create the `.po' file:

     $ gawk --gen-po -f guide.awk > guide.po

This produces:

     #: guide.awk:4
     msgid "Don't Panic"
     msgstr ""

     #: guide.awk:5
     msgid "The Answer Is"
     msgstr ""

This original portable object file is saved and reused for each language
into which the application is translated.  The `msgid' is the original
string and the `msgstr' is the translation.

     NOTE: Strings not marked with a leading underscore do not appear
     in the `guide.po' file.

Next, the messages must be translated.  Here is a translation to a
hypothetical dialect of English, called "Mellow":(1)

     $ cp guide.po guide-mellow.po
     ADD TRANSLATIONS TO guide-mellow.po ...

Following are the translations:

     #: guide.awk:4
     msgid "Don't Panic"
     msgstr "Hey man, relax!"

     #: guide.awk:5
     msgid "The Answer Is"
     msgstr "Like, the scoop is"

The next step is to make the directory to hold the binary message object
file and then to create the `guide.mo' file.  The directory layout
shown here is standard for GNU `gettext' on GNU/Linux systems.  Other
versions of `gettext' may use a different layout:

     $ mkdir en_US en_US/LC_MESSAGES

The `msgfmt' utility does the conversion from human-readable `.po' file
to machine-readable `.mo' file.  By default, `msgfmt' creates a file
named `messages'.  This file must be renamed and placed in the proper
directory so that `gawk' can find it:

     $ msgfmt guide-mellow.po
     $ mv messages en_US/LC_MESSAGES/guide.mo

Finally, we run the program to test it:

     $ gawk -f guide.awk
     -| Hey man, relax!
     -| Like, the scoop is 42
     -| Pardon me, Zaphod who?

If the three replacement functions for `dcgettext', `dcngettext' and
`bindtextdomain' (*note I18N Portability::) are in a file named
`libintl.awk', then we can run `guide.awk' unchanged as follows:

     $ gawk --posix -f guide.awk -f libintl.awk
     -| Don't Panic
     -| The Answer Is 42
     -| Pardon me, Zaphod who?

---------- Footnotes ----------

(1) Perhaps it would be better if it were called "Hippy." Ah, well.


File: gawk.info,  Node: Gawk I18N,  Prev: I18N Example,  Up: Internationalization

9.6 `gawk' Can Speak Your Language
==================================

As of version 3.1, `gawk' itself has been internationalized using the
GNU `gettext' package.  (GNU `gettext' is described in complete detail
in *Note Top::.)  As of this writing, the latest version of GNU
`gettext' is version 0.11.5
(ftp://ftp.gnu.org/gnu/gettext/gettext-0.11.5.tar.gz).

If a translation of `gawk''s messages exists, then `gawk' produces
usage messages, warnings, and fatal errors in the local language.


File: gawk.info,  Node: Advanced Features,  Next: Invoking Gawk,  Prev: Internationalization,  Up: Top

10 Advanced Features of `gawk'
******************************

     Write documentation as if whoever reads it is a violent psychopath
     who knows where you live.
     Steve English, as quoted by Peter Langston

This major node discusses advanced features in `gawk'.  It's a bit of a
"grab bag" of items that are otherwise unrelated to each other.  First,
a command-line option allows `gawk' to recognize nondecimal numbers in
input data, not just in `awk' programs.  Next, two-way I/O, discussed
briefly in earlier parts of this Info file, is described in full
detail, along with the basics of TCP/IP networking and BSD portal
files.  Finally, `gawk' can "profile" an `awk' program, making it
possible to tune it for performance.

*Note Dynamic Extensions::, discusses the ability to dynamically add
new built-in functions to `gawk'.  As this feature is still immature
and likely to change, its description is relegated to an appendix.

* Menu:

* Nondecimal Data::             Allowing nondecimal input data.
* Two-way I/O::                 Two-way communications with another process.
* TCP/IP Networking::           Using `gawk' for network programming.
* Portal Files::                Using `gawk' with BSD portals.
* Profiling::                   Profiling your `awk' programs.


File: gawk.info,  Node: Nondecimal Data,  Next: Two-way I/O,  Up: Advanced Features

10.1 Allowing Nondecimal Input Data
===================================

If you run `gawk' with the `--non-decimal-data' option, you can have
nondecimal constants in your input data:

     $ echo 0123 123 0x123 |
     > gawk --non-decimal-data '{ printf "%d, %d, %d\n",
     >                                         $1, $2, $3 }'
     -| 83, 123, 291

For this feature to work, write your program so that `gawk' treats your
data as numeric:

     $ echo 0123 123 0x123 | gawk '{ print $1, $2, $3 }'
     -| 0123 123 0x123

The `print' statement treats its expressions as strings.  Although the
fields can act as numbers when necessary, they are still strings, so
`print' does not try to treat them numerically.  You may need to add
zero to a field to force it to be treated as a number.  For example:

     $ echo 0123 123 0x123 | gawk --non-decimal-data '
     > { print $1, $2, $3
     >   print $1 + 0, $2 + 0, $3 + 0 }'
     -| 0123 123 0x123
     -| 83 123 291

Because it is common to have decimal data with leading zeros, and
because using it could lead to surprising results, the default is to
leave this facility disabled.  If you want it, you must explicitly
request it.

*Caution:* _Use of this option is not recommended._ It can break old
programs very badly.  Instead, use the `strtonum' function to convert
your data (*note Nondecimal-numbers::).  This makes your programs
easier to write and easier to read, and leads to less surprising
results.


File: gawk.info,  Node: Two-way I/O,  Next: TCP/IP Networking,  Prev: Nondecimal Data,  Up: Advanced Features

10.2 Two-Way Communications with Another Process
================================================

     From: brennan@whidbey.com (Mike Brennan)
     Newsgroups: comp.lang.awk
     Subject: Re: Learn the SECRET to Attract Women Easily
     Date: 4 Aug 1997 17:34:46 GMT
     Message-ID: <5s53rm$eca@news.whidbey.com>

     On 3 Aug 1997 13:17:43 GMT, Want More Dates???
     <tracy78@kilgrona.com> wrote:
     >Learn the SECRET to Attract Women Easily
     >
     >The SCENT(tm)  Pheromone Sex Attractant For Men to Attract Women

     The scent of awk programmers is a lot more attractive to women than
     the scent of perl programmers.
     --
     Mike Brennan

It is often useful to be able to send data to a separate program for
processing and then read the result.  This can always be done with
temporary files:

     # write the data for processing
     tempfile = ("mydata." PROCINFO["pid"])
     while (NOT DONE WITH DATA)
         print DATA | ("subprogram > " tempfile)
     close("subprogram > " tempfile)

     # read the results, remove tempfile when done
     while ((getline newdata < tempfile) > 0)
         PROCESS newdata APPROPRIATELY
     close(tempfile)
     system("rm " tempfile)

This works, but not elegantly.  Among other things, it requires that
the program be run in a directory that cannot be shared among users;
for example, `/tmp' will not do, as another user might happen to be
using a temporary file with the same name.

Starting with version 3.1 of `gawk', it is possible to open a _two-way_
pipe to another process.  The second process is termed a "coprocess",
since it runs in parallel with `gawk'.  The two-way connection is
created using the new `|&' operator (borrowed from the Korn shell,
`ksh'):(1)

     do {
         print DATA |& "subprogram"
         "subprogram" |& getline results
     } while (DATA LEFT TO PROCESS)
     close("subprogram")

The first time an I/O operation is executed using the `|&' operator,
`gawk' creates a two-way pipeline to a child process that runs the
other program.  Output created with `print' or `printf' is written to
the program's standard input, and output from the program's standard
output can be read by the `gawk' program using `getline'.  As is the
case with processes started by `|', the subprogram can be any program,
or pipeline of programs, that can be started by the shell.

There are some cautionary items to be aware of:

   * As the code inside `gawk' currently stands, the coprocess's
     standard error goes to the same place that the parent `gawk''s
     standard error goes. It is not possible to read the child's
     standard error separately.

   * I/O buffering may be a problem.  `gawk' automatically flushes all
     output down the pipe to the child process.  However, if the
     coprocess does not flush its output, `gawk' may hang when doing a
     `getline' in order to read the coprocess's results.  This could
     lead to a situation known as "deadlock", where each process is
     waiting for the other one to do something.

It is possible to close just one end of the two-way pipe to a
coprocess, by supplying a second argument to the `close' function of
either `"to"' or `"from"' (*note Close Files And Pipes::).  These
strings tell `gawk' to close the end of the pipe that sends data to the
process or the end that reads from it, respectively.

This is particularly necessary in order to use the system `sort'
utility as part of a coprocess; `sort' must read _all_ of its input
data before it can produce any output.  The `sort' program does not
receive an end-of-file indication until `gawk' closes the write end of
the pipe.

When you have finished writing data to the `sort' utility, you can
close the `"to"' end of the pipe, and then start reading sorted data
via `getline'.  For example:

     BEGIN {
         command = "LC_ALL=C sort"
         n = split("abcdefghijklmnopqrstuvwxyz", a, "")

         for (i = n; i > 0; i--)
             print a[i] |& command
         close(command, "to")

         while ((command |& getline line) > 0)
             print "got", line
         close(command)
     }

This program writes the letters of the alphabet in reverse order, one
per line, down the two-way pipe to `sort'.  It then closes the write
end of the pipe, so that `sort' receives an end-of-file indication.
This causes `sort' to sort the data and write the sorted data back to
the `gawk' program.  Once all of the data has been read, `gawk'
terminates the coprocess and exits.

As a side note, the assignment `LC_ALL=C' in the `sort' command ensures
traditional Unix (ASCII) sorting from `sort'.

Beginning with `gawk' 3.1.2, you may use Pseudo-ttys (ptys) for two-way
communication instead of pipes, if your system supports them.  This is
done on a per-command basis, by setting a special element in the
`PROCINFO' array (*note Auto-set::), like so:

     command = "sort -nr"           # command, saved in variable for convenience
     PROCINFO[command, "pty"] = 1   # update PROCINFO
     print ... |& command       # start two-way pipe
     ...

Using ptys avoids the buffer deadlock issues described earlier, at some
loss in performance.  If your system does not have ptys, or if all the
system's ptys are in use, `gawk' automatically falls back to using
regular pipes.

---------- Footnotes ----------

(1) This is very different from the same operator in the C shell, `csh'.


File: gawk.info,  Node: TCP/IP Networking,  Next: Portal Files,  Prev: Two-way I/O,  Up: Advanced Features

10.3 Using `gawk' for Network Programming
=========================================

     `EMISTERED': A host is a host from coast to coast,
     and no-one can talk to host that's close,
     unless the host that isn't close
     is busy hung or dead.

In addition to being able to open a two-way pipeline to a coprocess on
the same system (*note Two-way I/O::), it is possible to make a two-way
connection to another process on another system across an IP networking
connection.

You can think of this as just a _very long_ two-way pipeline to a
coprocess.  The way `gawk' decides that you want to use TCP/IP
networking is by recognizing special file names that begin with
`/inet/'.

The full syntax of the special file name is
`/inet/PROTOCOL/LOCAL-PORT/REMOTE-HOST/REMOTE-PORT'.  The components
are:

PROTOCOL
     The protocol to use over IP.  This must be either `tcp', `udp', or
     `raw', for a TCP, UDP, or raw IP connection, respectively.  The
     use of TCP is recommended for most applications.

     *Caution:* The use of raw sockets is not currently supported in
     version 3.1 of `gawk'.

LOCAL-PORT
     The local TCP or UDP port number to use.  Use a port number of `0'
     when you want the system to pick a port. This is what you should do
     when writing a TCP or UDP client.  You may also use a well-known
     service name, such as `smtp' or `http', in which case `gawk'
     attempts to determine the predefined port number using the C
     `getservbyname' function.

REMOTE-HOST
     The IP address or fully-qualified domain name of the Internet host
     to which you want to connect.

REMOTE-PORT
     The TCP or UDP port number to use on the given REMOTE-HOST.
     Again, use `0' if you don't care, or else a well-known service
     name.

Consider the following very simple example:

     BEGIN {
       Service = "/inet/tcp/0/localhost/daytime"
       Service |& getline
       print $0
       close(Service)
     }

This program reads the current date and time from the local system's
TCP `daytime' server.  It then prints the results and closes the
connection.

Because this topic is extensive, the use of `gawk' for TCP/IP
programming is documented separately.  *Note Top::, for a much more
complete introduction and discussion, as well as extensive examples.


File: gawk.info,  Node: Portal Files,  Next: Profiling,  Prev: TCP/IP Networking,  Up: Advanced Features

10.4 Using `gawk' with BSD Portals
==================================

Similar to the `/inet' special files, if `gawk' is configured with the
`--enable-portals' option (*note Quick Installation::), then `gawk'
treats files whose pathnames begin with `/p' as 4.4 BSD-style portals.

When used with the `|&' operator, `gawk' opens the file for two-way
communications.  The operating system's portal mechanism then manages
creating the process associated with the portal and the corresponding
communications with the portal's process.


File: gawk.info,  Node: Profiling,  Prev: Portal Files,  Up: Advanced Features

10.5 Profiling Your `awk' Programs
==================================

Beginning with version 3.1 of `gawk', you may produce execution traces
of your `awk' programs.  This is done with a specially compiled version
of `gawk', called `pgawk' ("profiling `gawk'").

`pgawk' is identical in every way to `gawk', except that when it has
finished running, it creates a profile of your program in a file named
`awkprof.out'.  Because it is profiling, it also executes up to 45%
slower than `gawk' normally does.

As shown in the following example, the `--profile' option can be used
to change the name of the file where `pgawk' will write the profile:

     $ pgawk --profile=myprog.prof -f myprog.awk data1 data2

In the above example, `pgawk' places the profile in `myprog.prof'
instead of in `awkprof.out'.

Regular `gawk' also accepts this option.  When called with just
`--profile', `gawk' "pretty prints" the program into `awkprof.out',
without any execution counts.  You may supply an option to `--profile'
to change the file name.  Here is a sample session showing a simple
`awk' program, its input data, and the results from running `pgawk'.
First, the `awk' program:

     BEGIN { print "First BEGIN rule" }

     END { print "First END rule" }

     /foo/ {
         print "matched /foo/, gosh"
         for (i = 1; i <= 3; i++)
             sing()
     }

     {
         if (/foo/)
             print "if is true"
         else
             print "else is true"
     }

     BEGIN { print "Second BEGIN rule" }

     END { print "Second END rule" }

     function sing(    dummy)
     {
         print "I gotta be me!"
     }

Following is the input data:

     foo
     bar
     baz
     foo
     junk

Here is the `awkprof.out' that results from running `pgawk' on this
program and data (this example also illustrates that `awk' programmers
sometimes have to work late):

             # gawk profile, created Sun Aug 13 00:00:15 2000

             # BEGIN block(s)

             BEGIN {
          1          print "First BEGIN rule"
          1          print "Second BEGIN rule"
             }

             # Rule(s)

          5  /foo/   { # 2
          2          print "matched /foo/, gosh"
          6          for (i = 1; i <= 3; i++) {
          6                  sing()
                     }
             }

          5  {
          5          if (/foo/) { # 2
          2                  print "if is true"
          3          } else {
          3                  print "else is true"
                     }
             }

             # END block(s)

             END {
          1          print "First END rule"
          1          print "Second END rule"
             }

             # Functions, listed alphabetically

          6  function sing(dummy)
             {
          6          print "I gotta be me!"
             }

This example illustrates many of the basic rules for profiling output.
The rules are as follows:

   * The program is printed in the order `BEGIN' rule, pattern/action
     rules, `END' rule and functions, listed alphabetically.  Multiple
     `BEGIN' and `END' rules are merged together.

   * Pattern-action rules have two counts.  The first count, to the
     left of the rule, shows how many times the rule's pattern was
     _tested_.  The second count, to the right of the rule's opening
     left brace in a comment, shows how many times the rule's action
     was _executed_.  The difference between the two indicates how many
     times the rule's pattern evaluated to false.

   * Similarly, the count for an `if'-`else' statement shows how many
     times the condition was tested.  To the right of the opening left
     brace for the `if''s body is a count showing how many times the
     condition was true.  The count for the `else' indicates how many
     times the test failed.

   * The count for a loop header (such as `for' or `while') shows how
     many times the loop test was executed.  (Because of this, you
     can't just look at the count on the first statement in a rule to
     determine how many times the rule was executed.  If the first
     statement is a loop, the count is misleading.)

   * For user-defined functions, the count next to the `function'
     keyword indicates how many times the function was called.  The
     counts next to the statements in the body show how many times
     those statements were executed.

   * The layout uses "K&R" style with tabs.  Braces are used
     everywhere, even when the body of an `if', `else', or loop is only
     a single statement.

   * Parentheses are used only where needed, as indicated by the
     structure of the program and the precedence rules.  For example,
     `(3 + 5) * 4' means add three plus five, then multiply the total
     by four.  However, `3 + 5 * 4' has no parentheses, and means `3 +
     (5 * 4)'.

   * All string concatenations are parenthesized too.  (This could be
     made a bit smarter.)

   * Parentheses are used around the arguments to `print' and `printf'
     only when the `print' or `printf' statement is followed by a
     redirection.  Similarly, if the target of a redirection isn't a
     scalar, it gets parenthesized.

   * `pgawk' supplies leading comments in front of the `BEGIN' and
     `END' rules, the pattern/action rules, and the functions.


The profiled version of your program may not look exactly like what you
typed when you wrote it.  This is because `pgawk' creates the profiled
version by "pretty printing" its internal representation of the
program.  The advantage to this is that `pgawk' can produce a standard
representation.  The disadvantage is that all source-code comments are
lost, as are the distinctions among multiple `BEGIN' and `END' rules.
Also, things such as:

     /foo/

come out as:

     /foo/   {
         print $0
     }

which is correct, but possibly surprising.

Besides creating profiles when a program has completed, `pgawk' can
produce a profile while it is running.  This is useful if your `awk'
program goes into an infinite loop and you want to see what has been
executed.  To use this feature, run `pgawk' in the background:

     $ pgawk -f myprog &
     [1] 13992

The shell prints a job number and process ID number; in this case,
13992.  Use the `kill' command to send the `USR1' signal to `pgawk':

     $ kill -USR1 13992

As usual, the profiled version of the program is written to
`awkprof.out', or to a different file if you use the `--profile' option.

Along with the regular profile, as shown earlier, the profile includes
a trace of any active functions:

     # Function Call Stack:

     #   3. baz
     #   2. bar
     #   1. foo
     # -- main --

You may send `pgawk' the `USR1' signal as many times as you like.  Each
time, the profile and function call trace are appended to the output
profile file.

If you use the `HUP' signal instead of the `USR1' signal, `pgawk'
produces the profile and the function call trace and then exits.

When `pgawk' runs on MS-DOS or MS-Windows, it uses the `INT' and `QUIT'
signals for producing the profile and, in the case of the `INT' signal,
`pgawk' exits.  This is because these systems don't support the `kill'
command, so the only signals you can deliver to a program are those
generated by the keyboard.  The `INT' signal is generated by the
`Ctrl-<C>' or `Ctrl-<BREAK>' key, while the `QUIT' signal is generated
by the `Ctrl-<\>' key.


File: gawk.info,  Node: Invoking Gawk,  Next: Library Functions,  Prev: Advanced Features,  Up: Top

11 Running `awk' and `gawk'
***************************

This major node covers how to run awk, both POSIX-standard and
`gawk'-specific command-line options, and what `awk' and `gawk' do with
non-option arguments.  It then proceeds to cover how `gawk' searches
for source files, obsolete options and/or features, and known bugs in
`gawk'.  This major node rounds out the discussion of `awk' as a
program and as a language.

While a number of the options and features described here were
discussed in passing earlier in the book, this major node provides the
full details.

* Menu:

* Command Line::                How to run `awk'.
* Options::                     Command-line options and their meanings.
* Other Arguments::             Input file names and variable assignments.
* AWKPATH Variable::            Searching directories for `awk'
                                programs.
* Obsolete::                    Obsolete Options and/or features.
* Undocumented::                Undocumented Options and Features.
* Known Bugs::                  Known Bugs in `gawk'.


File: gawk.info,  Node: Command Line,  Next: Options,  Up: Invoking Gawk

11.1 Invoking `awk'
===================

There are two ways to run `awk'--with an explicit program or with one
or more program files.  Here are templates for both of them; items
enclosed in [...] in these templates are optional:

     awk [OPTIONS] -f progfile [`--'] FILE ...
     awk [OPTIONS] [`--'] 'PROGRAM' FILE ...

Besides traditional one-letter POSIX-style options, `gawk' also
supports GNU long options.

It is possible to invoke `awk' with an empty program:

     awk '' datafile1 datafile2

Doing so makes little sense, though; `awk' exits silently when given an
empty program.  (d.c.)  If `--lint' has been specified on the command
line, `gawk' issues a warning that the program is empty.


File: gawk.info,  Node: Options,  Next: Other Arguments,  Prev: Command Line,  Up: Invoking Gawk

11.2 Command-Line Options
=========================

Options begin with a dash and consist of a single character.  GNU-style
long options consist of two dashes and a keyword.  The keyword can be
abbreviated, as long as the abbreviation allows the option to be
uniquely identified.  If the option takes an argument, then the keyword
is either immediately followed by an equals sign (`=') and the
argument's value, or the keyword and the argument's value are separated
by whitespace.  If a particular option with a value is given more than
once, it is the last value that counts.

Each long option for `gawk' has a corresponding POSIX-style option.
The long and short options are interchangeable in all contexts.  The
options and their meanings are as follows:

`-F FS'
`--field-separator FS'
     Sets the `FS' variable to FS (*note Field Separators::).

`-f SOURCE-FILE'
`--file SOURCE-FILE'
     Indicates that the `awk' program is to be found in SOURCE-FILE
     instead of in the first non-option argument.

`-v VAR=VAL'
`--assign VAR=VAL'
     Sets the variable VAR to the value VAL _before_ execution of the
     program begins.  Such variable values are available inside the
     `BEGIN' rule (*note Other Arguments::).

     The `-v' option can only set one variable, but it can be used more
     than once, setting another variable each time, like this: `awk
     -v foo=1 -v bar=2 ...'.

     *Caution:*  Using `-v' to set the values of the built-in variables
     may lead to surprising results.  `awk' will reset the values of
     those variables as it needs to, possibly ignoring any predefined
     value you may have given.

`-mf N'
`-mr N'
     Sets various memory limits to the value N.  The `f' flag sets the
     maximum number of fields and the `r' flag sets the maximum record
     size.  These two flags and the `-m' option are from the Bell
     Laboratories research version of Unix `awk'.  They are provided
     for compatibility but otherwise ignored by `gawk', since `gawk'
     has no predefined limits.  (The Bell Laboratories `awk' no longer
     needs these options; it continues to accept them to avoid breaking
     old programs.)

`-W GAWK-OPT'
     Following the POSIX standard, implementation-specific options are
     supplied as arguments to the `-W' option.  These options also have
     corresponding GNU-style long options.  Note that the long options
     may be abbreviated, as long as the abbreviations remain unique.
     The full list of `gawk'-specific options is provided next.

`--'
     Signals the end of the command-line options.  The following
     arguments are not treated as options even if they begin with `-'.
     This interpretation of `--' follows the POSIX argument parsing
     conventions.

     This is useful if you have file names that start with `-', or in
     shell scripts, if you have file names that will be specified by
     the user that could start with `-'.

The previous list described options mandated by the POSIX standard, as
well as options available in the Bell Laboratories version of `awk'.
The following list describes `gawk'-specific options:

`-W compat'
`-W traditional'
`--compat'
`--traditional'
     Specifies "compatibility mode", in which the GNU extensions to the
     `awk' language are disabled, so that `gawk' behaves just like the
     Bell Laboratories research version of Unix `awk'.  `--traditional'
     is the preferred form of this option.  *Note POSIX/GNU::, which
     summarizes the extensions.  Also see *Note Compatibility Mode::.

`-W copyright'
`--copyright'
     Print the short version of the General Public License and then
     exit.

`-W copyleft'
`--copyleft'
     Just like `--copyright'.  This option may disappear in a future
     version of `gawk'.

`-W dump-variables[=FILE]'
`--dump-variables[=FILE]'
     Prints a sorted list of global variables, their types, and final
     values to FILE.  If no FILE is provided, `gawk' prints this list
     to the file named `awkvars.out' in the current directory.

     Having a list of all global variables is a good way to look for
     typographical errors in your programs.  You would also use this
     option if you have a large program with a lot of functions, and
     you want to be sure that your functions don't inadvertently use
     global variables that you meant to be local.  (This is a
     particularly easy mistake to make with simple variable names like
     `i', `j', etc.)

`-W exec FILE'
`--exec FILE'
     Similar to `-f', reads `awk' program text from FILE.  There are
     two differences.  The fist is that this option also terminates
     option processing; anything else on the command line is passed on
     directly to the `awk' program.  The second is that command line
     variable assignments of the form `VAR=VALUE' are disallowed.

     This option is particularly necessary for World Wide Web CGI
     applications that pass arguments through the URL; using this
     option prevents a malicious (or other) user from passing in
     options, assignments, or `awk' source code (via `--source') to the
     CGI application.  This option should be used with `#!' scripts
     (*note Executable Scripts::), like so:

          #! /usr/local/bin/gawk --exec

          AWK PROGRAM HERE ...

`-W gen-po'
`--gen-po'
     Analyzes the source program and generates a GNU `gettext' Portable
     Object file on standard output for all string constants that have
     been marked for translation.  *Note Internationalization::, for
     information about this option.

`-W help'
`-W usage'
`--help'
`--usage'
     Prints a "usage" message summarizing the short and long style
     options that `gawk' accepts and then exit.

`-W lint[=fatal]'
`--lint[=fatal]'
     Warns about constructs that are dubious or nonportable to other
     `awk' implementations.  Some warnings are issued when `gawk' first
     reads your program.  Others are issued at runtime, as your program
     executes.  With an optional argument of `fatal', lint warnings
     become fatal errors.  This may be drastic, but its use will
     certainly encourage the development of cleaner `awk' programs.
     With an optional argument of `invalid', only warnings about things
     that are actually invalid are issued. (This is not fully
     implemented yet.)

`-W lint-old'
`--lint-old'
     Warns about constructs that are not available in the original
     version of `awk' from Version 7 Unix (*note V7/SVR3.1::).

`-W non-decimal-data'
`--non-decimal-data'
     Enable automatic interpretation of octal and hexadecimal values in
     input data (*note Nondecimal Data::).

     *Caution:* This option can severely break old programs.  Use with
     care.

`-W posix'
`--posix'
     Operates in strict POSIX mode.  This disables all `gawk'
     extensions (just like `--traditional') and adds the following
     additional restrictions:

        * `\x' escape sequences are not recognized (*note Escape
          Sequences::).

        * Newlines do not act as whitespace to separate fields when
          `FS' is equal to a single space (*note Fields::).

        * Newlines are not allowed after `?' or `:' (*note Conditional
          Exp::).

        * The synonym `func' for the keyword `function' is not
          recognized (*note Definition Syntax::).

        * The `**' and `**=' operators cannot be used in place of `^'
          and `^=' (*note Arithmetic Ops::, and also *note Assignment
          Ops::).

        * Specifying `-Ft' on the command-line does not set the value
          of `FS' to be a single TAB character (*note Field
          Separators::).

        * The `fflush' built-in function is not supported (*note I/O
          Functions::).

     If you supply both `--traditional' and `--posix' on the command
     line, `--posix' takes precedence. `gawk' also issues a warning if
     both options are supplied.

`-W profile[=FILE]'
`--profile[=FILE]'
     Enable profiling of `awk' programs (*note Profiling::).  By
     default, profiles are created in a file named `awkprof.out'.  The
     optional FILE argument allows you to specify a different file name
     for the profile file.

     When run with `gawk', the profile is just a "pretty printed"
     version of the program.  When run with `pgawk', the profile
     contains execution counts for each statement in the program in the
     left margin, and function call counts for each function.

`-W re-interval'
`--re-interval'
     Allows interval expressions (*note Regexp Operators::) in regexps.
     Because interval expressions were traditionally not available in
     `awk', `gawk' does not provide them by default. This prevents old
     `awk' programs from breaking.

`-W source PROGRAM-TEXT'
`--source PROGRAM-TEXT'
     Allows you to mix source code in files with source code that you
     enter on the command line.  Program source code is taken from the
     PROGRAM-TEXT.  This is particularly useful when you have library
     functions that you want to use from your command-line programs
     (*note AWKPATH Variable::).

`-W version'
`--version'
     Prints version information for this particular copy of `gawk'.
     This allows you to determine if your copy of `gawk' is up to date
     with respect to whatever the Free Software Foundation is currently
     distributing.  It is also useful for bug reports (*note Bugs::).

As long as program text has been supplied, any other options are
flagged as invalid with a warning message but are otherwise ignored.

In compatibility mode, as a special case, if the value of FS supplied
to the `-F' option is `t', then `FS' is set to the TAB character
(`"\t"').  This is true only for `--traditional' and not for `--posix'
(*note Field Separators::).

The `-f' option may be used more than once on the command line.  If it
is, `awk' reads its program source from all of the named files, as if
they had been concatenated together into one big file.  This is useful
for creating libraries of `awk' functions.  These functions can be
written once and then retrieved from a standard place, instead of
having to be included into each individual program.  (As mentioned in
*Note Definition Syntax::, function names must be unique.)

Library functions can still be used, even if the program is entered at
the terminal, by specifying `-f /dev/tty'.  After typing your program,
type `Ctrl-d' (the end-of-file character) to terminate it.  (You may
also use `-f -' to read program source from the standard input but then
you will not be able to also use the standard input as a source of
data.)

Because it is clumsy using the standard `awk' mechanisms to mix source
file and command-line `awk' programs, `gawk' provides the `--source'
option.  This does not require you to pre-empt the standard input for
your source code; it allows you to easily mix command-line and library
source code (*note AWKPATH Variable::).

If no `-f' or `--source' option is specified, then `gawk' uses the
first non-option command-line argument as the text of the program
source code.

If the environment variable `POSIXLY_CORRECT' exists, then `gawk'
behaves in strict POSIX mode, exactly as if you had supplied the
`--posix' command-line option.  Many GNU programs look for this
environment variable to turn on strict POSIX mode. If `--lint' is
supplied on the command line and `gawk' turns on POSIX mode because of
`POSIXLY_CORRECT', then it issues a warning message indicating that
POSIX mode is in effect.  You would typically set this variable in your
shell's startup file.  For a Bourne-compatible shell (such as `bash'),
you would add these lines to the `.profile' file in your home directory:

     POSIXLY_CORRECT=true
     export POSIXLY_CORRECT

For a `csh'-compatible shell,(1) you would add this line to the
`.login' file in your home directory:

     setenv POSIXLY_CORRECT true

Having `POSIXLY_CORRECT' set is not recommended for daily use, but it
is good for testing the portability of your programs to other
environments.

---------- Footnotes ----------

(1) Not recommended.


File: gawk.info,  Node: Other Arguments,  Next: AWKPATH Variable,  Prev: Options,  Up: Invoking Gawk

11.3 Other Command-Line Arguments
=================================

Any additional arguments on the command line are normally treated as
input files to be processed in the order specified.   However, an
argument that has the form `VAR=VALUE', assigns the value VALUE to the
variable VAR--it does not specify a file at all.  (This was discussed
earlier in *Note Assignment Options::.)

All these arguments are made available to your `awk' program in the
`ARGV' array (*note Built-in Variables::).  Command-line options and
the program text (if present) are omitted from `ARGV'.  All other
arguments, including variable assignments, are included.   As each
element of `ARGV' is processed, `gawk' sets the variable `ARGIND' to
the index in `ARGV' of the current element.

The distinction between file name arguments and variable-assignment
arguments is made when `awk' is about to open the next input file.  At
that point in execution, it checks the file name to see whether it is
really a variable assignment; if so, `awk' sets the variable instead of
reading a file.

Therefore, the variables actually receive the given values after all
previously specified files have been read.  In particular, the values of
variables assigned in this fashion are _not_ available inside a `BEGIN'
rule (*note BEGIN/END::), because such rules are run before `awk'
begins scanning the argument list.

The variable values given on the command line are processed for escape
sequences (*note Escape Sequences::).  (d.c.)

In some earlier implementations of `awk', when a variable assignment
occurred before any file names, the assignment would happen _before_
the `BEGIN' rule was executed.  `awk''s behavior was thus inconsistent;
some command-line assignments were available inside the `BEGIN' rule,
while others were not.  Unfortunately, some applications came to depend
upon this "feature."  When `awk' was changed to be more consistent, the
`-v' option was added to accommodate applications that depended upon
the old behavior.

The variable assignment feature is most useful for assigning to
variables such as `RS', `OFS', and `ORS', which control input and
output formats before scanning the data files.  It is also useful for
controlling state if multiple passes are needed over a data file.  For
example:

     awk 'pass == 1  { PASS 1 STUFF }
          pass == 2  { PASS 2 STUFF }' pass=1 mydata pass=2 mydata

Given the variable assignment feature, the `-F' option for setting the
value of `FS' is not strictly necessary.  It remains for historical
compatibility.


File: gawk.info,  Node: AWKPATH Variable,  Next: Obsolete,  Prev: Other Arguments,  Up: Invoking Gawk

11.4 The `AWKPATH' Environment Variable
=======================================

The previous minor node described how `awk' program files can be named
on the command-line with the `-f' option.  In most `awk'
implementations, you must supply a precise path name for each program
file, unless the file is in the current directory.  But in `gawk', if
the file name supplied to the `-f' option does not contain a `/', then
`gawk' searches a list of directories (called the "search path"), one
by one, looking for a file with the specified name.

The search path is a string consisting of directory names separated by
colons.  `gawk' gets its search path from the `AWKPATH' environment
variable.  If that variable does not exist, `gawk' uses a default path,
`.:/usr/local/share/awk'.(1) (Programs written for use by system
administrators should use an `AWKPATH' variable that does not include
the current directory, `.'.)

The search path feature is particularly useful for building libraries
of useful `awk' functions.  The library files can be placed in a
standard directory in the default path and then specified on the
command line with a short file name.  Otherwise, the full file name
would have to be typed for each file.

By using both the `--source' and `-f' options, your command-line `awk'
programs can use facilities in `awk' library files (*note Library
Functions::).  Path searching is not done if `gawk' is in compatibility
mode.  This is true for both `--traditional' and `--posix'.  *Note
Options::.

     NOTE: If you want files in the current directory to be found, you
     must include the current directory in the path, either by including
     `.' explicitly in the path or by writing a null entry in the path.
     (A null entry is indicated by starting or ending the path with a
     colon or by placing two colons next to each other (`::').)  If the
     current directory is not included in the path, then files cannot be
     found in the current directory.  This path search mechanism is
     identical to the shell's.

Starting with version 3.0, if `AWKPATH' is not defined in the
environment, `gawk' places its default search path into
`ENVIRON["AWKPATH"]'. This makes it easy to determine the actual search
path that `gawk' will use from within an `awk' program.

While you can change `ENVIRON["AWKPATH"]' within your `awk' program,
this has no effect on the running program's behavior.  This makes
sense: the `AWKPATH' environment variable is used to find the program
source files.  Once your program is running, all the files have been
found, and `gawk' no longer needs to use `AWKPATH'.

---------- Footnotes ----------

(1) Your version of `gawk' may use a different directory; it will
depend upon how `gawk' was built and installed. The actual directory is
the value of `$(datadir)' generated when `gawk' was configured.  You
probably don't need to worry about this, though.


File: gawk.info,  Node: Obsolete,  Next: Undocumented,  Prev: AWKPATH Variable,  Up: Invoking Gawk

11.5 Obsolete Options and/or Features
=====================================

This minor node describes features and/or command-line options from
previous releases of `gawk' that are either not available in the
current version or that are still supported but deprecated (meaning that
they will _not_ be in the next release).

For version 3.1 of `gawk', there are no deprecated command-line options
from the previous version of `gawk'.  The use of `next file' (two
words) for `nextfile' was deprecated in `gawk' 3.0 but still worked.
Starting with version 3.1, the two-word usage is no longer accepted.

The process-related special files described in *Note Special Process::,
work as described, but are now considered deprecated.  `gawk' prints a
warning message every time they are used.  (Use `PROCINFO' instead; see
*Note Auto-set::.)  They will be removed from the next release of
`gawk'.


File: gawk.info,  Node: Undocumented,  Next: Known Bugs,  Prev: Obsolete,  Up: Invoking Gawk

11.6 Undocumented Options and Features
======================================

     Use the Source, Luke!
     Obi-Wan

This minor node intentionally left blank.


File: gawk.info,  Node: Known Bugs,  Prev: Undocumented,  Up: Invoking Gawk

11.7 Known Bugs in `gawk'
=========================

   * The `-F' option for changing the value of `FS' (*note Options::)
     is not necessary given the command-line variable assignment
     feature; it remains only for backward compatibility.

   * Syntactically invalid single-character programs tend to overflow
     the parse stack, generating a rather unhelpful message.  Such
     programs are surprisingly difficult to diagnose in the completely
     general case, and the effort to do so really is not worth it.


File: gawk.info,  Node: Library Functions,  Next: Sample Programs,  Prev: Invoking Gawk,  Up: Top

12 A Library of `awk' Functions
*******************************

*Note User-defined::, describes how to write your own `awk' functions.
Writing functions is important, because it allows you to encapsulate
algorithms and program tasks in a single place.  It simplifies
programming, making program development more manageable, and making
programs more readable.

One valuable way to learn a new programming language is to _read_
programs in that language.  To that end, this major node and *Note
Sample Programs::, provide a good-sized body of code for you to read,
and hopefully, to learn from.

This major node presents a library of useful `awk' functions.  Many of
the sample programs presented later in this Info file use these
functions.  The functions are presented here in a progression from
simple to complex.

*Note Extract Program::, presents a program that you can use to extract
the source code for these example library functions and programs from
the Texinfo source for this Info file.  (This has already been done as
part of the `gawk' distribution.)

If you have written one or more useful, general-purpose `awk' functions
and would like to contribute them to the author's collection of `awk'
programs, see *Note How To Contribute::, for more information.

The programs in this major node and in *Note Sample Programs::, freely
use features that are `gawk'-specific.  Rewriting these programs for
different implementations of awk is pretty straightforward.

Diagnostic error messages are sent to `/dev/stderr'.  Use `| "cat
1>&2"' instead of `> "/dev/stderr"' if your system does not have a
`/dev/stderr', or if you cannot use `gawk'.

A number of programs use `nextfile' (*note Nextfile Statement::) to
skip any remaining input in the input file.  *Note Nextfile Function::,
shows you how to write a function that does the same thing.

Finally, some of the programs choose to ignore upper- and lowercase
distinctions in their input. They do so by assigning one to
`IGNORECASE'.  You can achieve almost the same effect(1) by adding the
following rule to the beginning of the program:

     # ignore case
     { $0 = tolower($0) }

Also, verify that all regexp and string constants used in comparisons
use only lowercase letters.

* Menu:

* Library Names::               How to best name private global variables in
                                library functions.
* General Functions::           Functions that are of general use.
* Data File Management::        Functions for managing command-line data
                                files.
* Getopt Function::             A function for processing command-line
                                arguments.
* Passwd Functions::            Functions for getting user information.
* Group Functions::             Functions for getting group information.

---------- Footnotes ----------

(1) The effects are not identical.  Output of the transformed record
will be in all lowercase, while `IGNORECASE' preserves the original
contents of the input record.


File: gawk.info,  Node: Library Names,  Next: General Functions,  Up: Library Functions

12.1 Naming Library Function Global Variables
=============================================

Due to the way the `awk' language evolved, variables are either
"global" (usable by the entire program) or "local" (usable just by a
specific function).  There is no intermediate state analogous to
`static' variables in C.

Library functions often need to have global variables that they can use
to preserve state information between calls to the function--for
example, `getopt''s variable `_opti' (*note Getopt Function::).  Such
variables are called "private", since the only functions that need to
use them are the ones in the library.

When writing a library function, you should try to choose names for your
private variables that will not conflict with any variables used by
either another library function or a user's main program.  For example,
a name like `i' or `j' is not a good choice, because user programs
often use variable names like these for their own purposes.

The example programs shown in this major node all start the names of
their private variables with an underscore (`_').  Users generally
don't use leading underscores in their variable names, so this
convention immediately decreases the chances that the variable name
will be accidentally shared with the user's program.

In addition, several of the library functions use a prefix that helps
indicate what function or set of functions use the variables--for
example, `_pw_byname' in the user database routines (*note Passwd
Functions::).  This convention is recommended, since it even further
decreases the chance of inadvertent conflict among variable names.
Note that this convention is used equally well for variable names and
for private function names as well.(1)

As a final note on variable naming, if a function makes global variables
available for use by a main program, it is a good convention to start
that variable's name with a capital letter--for example, `getopt''s
`Opterr' and `Optind' variables (*note Getopt Function::).  The leading
capital letter indicates that it is global, while the fact that the
variable name is not all capital letters indicates that the variable is
not one of `awk''s built-in variables, such as `FS'.

It is also important that _all_ variables in library functions that do
not need to save state are, in fact, declared local.(2) If this is not
done, the variable could accidentally be used in the user's program,
leading to bugs that are very difficult to track down:

     function lib_func(x, y,    l1, l2)
     {
         ...
         USE VARIABLE some_var   # some_var should be local
         ...                   # but is not by oversight
     }

A different convention, common in the Tcl community, is to use a single
associative array to hold the values needed by the library function(s),
or "package."  This significantly decreases the number of actual global
names in use.  For example, the functions described in *Note Passwd
Functions::, might have used array elements `PW_data["inited"]',
`PW_data["total"]', `PW_data["count"]', and `PW_data["awklib"]',
instead of `_pw_inited', `_pw_awklib', `_pw_total', and `_pw_count'.

The conventions presented in this minor node are exactly that:
conventions. You are not required to write your programs this way--we
merely recommend that you do so.

---------- Footnotes ----------

(1) While all the library routines could have been rewritten to use
this convention, this was not done, in order to show how my own `awk'
programming style has evolved and to provide some basis for this
discussion.

(2) `gawk''s `--dump-variables' command-line option is useful for
verifying this.


File: gawk.info,  Node: General Functions,  Next: Data File Management,  Prev: Library Names,  Up: Library Functions

12.2 General Programming
========================

This minor node presents a number of functions that are of general
programming use.

* Menu:

* Nextfile Function::           Two implementations of a `nextfile'
                                function.
* Strtonum Function::           A replacement for the built-in `strtonum'
                                function.
* Assert Function::             A function for assertions in `awk'
                                programs.
* Round Function::              A function for rounding if `sprintf' does
                                not do it correctly.
* Cliff Random Function::       The Cliff Random Number Generator.
* Ordinal Functions::           Functions for using characters as numbers and
                                vice versa.
* Join Function::               A function to join an array into a string.
* Gettimeofday Function::       A function to get formatted times.


File: gawk.info,  Node: Nextfile Function,  Next: Strtonum Function,  Up: General Functions

12.2.1 Implementing `nextfile' as a Function
--------------------------------------------

The `nextfile' statement, presented in *Note Nextfile Statement::, is a
`gawk'-specific extension--it is not available in most other
implementations of `awk'.  This minor node shows two versions of a
`nextfile' function that you can use to simulate `gawk''s `nextfile'
statement if you cannot use `gawk'.

A first attempt at writing a `nextfile' function is as follows:

     # nextfile --- skip remaining records in current file
     # this should be read in before the "main" awk program

     function nextfile()    { _abandon_ = FILENAME; next }
     _abandon_ == FILENAME  { next }

Because it supplies a rule that must be executed first, this file should
be included before the main program. This rule compares the current
data file's name (which is always in the `FILENAME' variable) to a
private variable named `_abandon_'.  If the file name matches, then the
action part of the rule executes a `next' statement to go on to the
next record.  (The use of `_' in the variable name is a convention.  It
is discussed more fully in *Note Library Names::.)

The use of the `next' statement effectively creates a loop that reads
all the records from the current data file.  The end of the file is
eventually reached and a new data file is opened, changing the value of
`FILENAME'.  Once this happens, the comparison of `_abandon_' to
`FILENAME' fails, and execution continues with the first rule of the
"real" program.

The `nextfile' function itself simply sets the value of `_abandon_' and
then executes a `next' statement to start the loop.

This initial version has a subtle problem.  If the same data file is
listed _twice_ on the commandline, one right after the other or even
with just a variable assignment between them, this code skips right
through the file a second time, even though it should stop when it gets
to the end of the first occurrence.  A second version of `nextfile'
that remedies this problem is shown here:

     # nextfile --- skip remaining records in current file
     # correctly handle successive occurrences of the same file
     # this should be read in before the "main" awk program

     function nextfile()   { _abandon_ = FILENAME; next }

     _abandon_ == FILENAME {
           if (FNR == 1)
               _abandon_ = ""
           else
               next
     }

The `nextfile' function has not changed.  It makes `_abandon_' equal to
the current file name and then executes a `next' statement.  The `next'
statement reads the next record and increments `FNR' so that `FNR' is
guaranteed to have a value of at least two.  However, if `nextfile' is
called for the last record in the file, then `awk' closes the current
data file and moves on to the next one.  Upon doing so, `FILENAME' is
set to the name of the new file and `FNR' is reset to one.  If this
next file is the same as the previous one, `_abandon_' is still equal
to `FILENAME'.  However, `FNR' is equal to one, telling us that this is
a new occurrence of the file and not the one we were reading when the
`nextfile' function was executed.  In that case, `_abandon_' is reset
to the empty string, so that further executions of this rule fail
(until the next time that `nextfile' is called).

If `FNR' is not one, then we are still in the original data file and
the program executes a `next' statement to skip through it.

An important question to ask at this point is: given that the
functionality of `nextfile' can be provided with a library file, why is
it built into `gawk'?  Adding features for little reason leads to
larger, slower programs that are harder to maintain.  The answer is
that building `nextfile' into `gawk' provides significant gains in
efficiency.  If the `nextfile' function is executed at the beginning of
a large data file, `awk' still has to scan the entire file, splitting
it up into records, just to skip over it.  The built-in `nextfile' can
simply close the file immediately and proceed to the next one, which
saves a lot of time.  This is particularly important in `awk', because
`awk' programs are generally I/O-bound (i.e., they spend most of their
time doing input and output, instead of performing computations).


File: gawk.info,  Node: Strtonum Function,  Next: Assert Function,  Prev: Nextfile Function,  Up: General Functions

12.2.2 Converting Strings To Numbers
------------------------------------

The `strtonum' function (*note String Functions::) is a `gawk'
extension.  The following function provides an implementation for other
versions of `awk':

     # strtonum --- convert string to number
     function mystrtonum(str,        ret, chars, n, i, k, c)
     {
         if (str ~ /^0[0-7]*$/) {
             # octal
             n = length(str)
             ret = 0
             for (i = 1; i <= n; i++) {
                 c = substr(str, i, 1)
                 if ((k = index("01234567", c)) > 0)
                     k-- # adjust for 1-basing in awk

                 ret = ret * 8 + k
             }
         } else if (str ~ /^0[xX][0-9a-fA-f]+/) {
             # hexadecimal
             str = substr(str, 3)    # lop off leading 0x
             n = length(str)
             ret = 0
             for (i = 1; i <= n; i++) {
                 c = substr(str, i, 1)
                 c = tolower(c)
                 if ((k = index("0123456789", c)) > 0)
                     k-- # adjust for 1-basing in awk
                 else if ((k = index("abcdef", c)) > 0)
                     k += 9

                 ret = ret * 16 + k
             }
         } else if (str ~ /^[-+]?([0-9]+([.][0-9]*([Ee][0-9]+)?)?|([.][0-9]+([Ee][-+]?[0-9]+)?))$/) {
             # decimal number, possibly floating point
             ret = str + 0
         } else
             ret = "NOT-A-NUMBER"

         return ret
     }

     # BEGIN {     # gawk test harness
     #     a[1] = "25"
     #     a[2] = ".31"
     #     a[3] = "0123"
     #     a[4] = "0xdeadBEEF"
     #     a[5] = "123.45"
     #     a[6] = "1.e3"
     #     a[7] = "1.32"
     #     a[7] = "1.32E2"
     #
     #     for (i = 1; i in a; i++)
     #         print a[i], strtonum(a[i]), mystrtonum(a[i])
     # }

The function first looks for C-style octal numbers (base 8).  If the
input string matches a regular expression describing octal numbers,
then `mystrtonum' loops through each character in the string.  It sets
`k' to the index in `"01234567"' of the current octal digit.  Since the
return value is one-based, the `k--' adjusts `k' so it can be used in
computing the return value.

Similar logic applies to the code that checks for and converts a
hexadecimal value, which starts with `0x' or `0X'.  The use of
`tolower' simplifies the computation for finding the correct numeric
value for each hexadecimal digit.

Finally, if the string matches the (rather complicated) regex for a
regular decimal integer or floating-point numer, the computation `ret =
str + 0' lets `awk' convert the value to a number.

A commented-out test program is included, so that the function can be
tested with `gawk' and the results compared to the built-in `strtonum'
function.


File: gawk.info,  Node: Assert Function,  Next: Round Function,  Prev: Strtonum Function,  Up: General Functions

12.2.3 Assertions
-----------------

When writing large programs, it is often useful to know that a
condition or set of conditions is true.  Before proceeding with a
particular computation, you make a statement about what you believe to
be the case.  Such a statement is known as an "assertion".  The C
language provides an `<assert.h>' header file and corresponding
`assert' macro that the programmer can use to make assertions.  If an
assertion fails, the `assert' macro arranges to print a diagnostic
message describing the condition that should have been true but was
not, and then it kills the program.  In C, using `assert' looks this:

     #include <assert.h>

     int myfunc(int a, double b)
     {
          assert(a <= 5 && b >= 17.1);
          ...
     }

If the assertion fails, the program prints a message similar to this:

     prog.c:5: assertion failed: a <= 5 && b >= 17.1

The C language makes it possible to turn the condition into a string
for use in printing the diagnostic message.  This is not possible in
`awk', so this `assert' function also requires a string version of the
condition that is being tested.  Following is the function:

     # assert --- assert that a condition is true. Otherwise exit.
     function assert(condition, string)
     {
         if (! condition) {
             printf("%s:%d: assertion failed: %s\n",
                 FILENAME, FNR, string) > "/dev/stderr"
             _assert_exit = 1
             exit 1
         }
     }

     END {
         if (_assert_exit)
             exit 1
     }

The `assert' function tests the `condition' parameter. If it is false,
it prints a message to standard error, using the `string' parameter to
describe the failed condition.  It then sets the variable
`_assert_exit' to one and executes the `exit' statement.  The `exit'
statement jumps to the `END' rule. If the `END' rules finds
`_assert_exit' to be true, it exits immediately.

The purpose of the test in the `END' rule is to keep any other `END'
rules from running.  When an assertion fails, the program should exit
immediately.  If no assertions fail, then `_assert_exit' is still false
when the `END' rule is run normally, and the rest of the program's
`END' rules execute.  For all of this to work correctly, `assert.awk'
must be the first source file read by `awk'.  The function can be used
in a program in the following way:

     function myfunc(a, b)
     {
          assert(a <= 5 && b >= 17.1, "a <= 5 && b >= 17.1")
          ...
     }

If the assertion fails, you see a message similar to the following:

     mydata:1357: assertion failed: a <= 5 && b >= 17.1

There is a small problem with this version of `assert'.  An `END' rule
is automatically added to the program calling `assert'.  Normally, if a
program consists of just a `BEGIN' rule, the input files and/or
standard input are not read. However, now that the program has an `END'
rule, `awk' attempts to read the input data files or standard input
(*note Using BEGIN/END::), most likely causing the program to hang as
it waits for input.

There is a simple workaround to this: make sure the `BEGIN' rule always
ends with an `exit' statement.


File: gawk.info,  Node: Round Function,  Next: Cliff Random Function,  Prev: Assert Function,  Up: General Functions

12.2.4 Rounding Numbers
-----------------------

The way `printf' and `sprintf' (*note Printf::) perform rounding often
depends upon the system's C `sprintf' subroutine.  On many machines,
`sprintf' rounding is "unbiased," which means it doesn't always round a
trailing `.5' up, contrary to naive expectations.  In unbiased
rounding, `.5' rounds to even, rather than always up, so 1.5 rounds to
2 but 4.5 rounds to 4.  This means that if you are using a format that
does rounding (e.g., `"%.0f"'), you should check what your system does.
The following function does traditional rounding; it might be useful
if your awk's `printf' does unbiased rounding:

     # round.awk --- do normal rounding
     function round(x,   ival, aval, fraction)
     {
        ival = int(x)    # integer part, int() truncates

        # see if fractional part
        if (ival == x)   # no fraction
           return x

        if (x < 0) {
           aval = -x     # absolute value
           ival = int(aval)
           fraction = aval - ival
           if (fraction >= .5)
              return int(x) - 1   # -2.5 --> -3
           else
              return int(x)       # -2.3 --> -2
        } else {
           fraction = x - ival
           if (fraction >= .5)
              return ival + 1
           else
              return ival
        }
     }

     # test harness
     { print $0, round($0) }


File: gawk.info,  Node: Cliff Random Function,  Next: Ordinal Functions,  Prev: Round Function,  Up: General Functions

12.2.5 The Cliff Random Number Generator
----------------------------------------

The Cliff random number generator(1) is a very simple random number
generator that "passes the noise sphere test for randomness by showing
no structure."  It is easily programmed, in less than 10 lines of `awk'
code:

     # cliff_rand.awk --- generate Cliff random numbers
     BEGIN { _cliff_seed = 0.1 }

     function cliff_rand()
     {
         _cliff_seed = (100 * log(_cliff_seed)) % 1
         if (_cliff_seed < 0)
             _cliff_seed = - _cliff_seed
         return _cliff_seed
     }

This algorithm requires an initial "seed" of 0.1.  Each new value uses
the current seed as input for the calculation.  If the built-in `rand'
function (*note Numeric Functions::) isn't random enough, you might try
using this function instead.

---------- Footnotes ----------

(1) `http://mathworld.wolfram.com/CliffRandomNumberGenerator.hmtl'


File: gawk.info,  Node: Ordinal Functions,  Next: Join Function,  Prev: Cliff Random Function,  Up: General Functions

12.2.6 Translating Between Characters and Numbers
-------------------------------------------------

One commercial implementation of `awk' supplies a built-in function,
`ord', which takes a character and returns the numeric value for that
character in the machine's character set.  If the string passed to
`ord' has more than one character, only the first one is used.

The inverse of this function is `chr' (from the function of the same
name in Pascal), which takes a number and returns the corresponding
character.  Both functions are written very nicely in `awk'; there is
no real reason to build them into the `awk' interpreter:

     # ord.awk --- do ord and chr

     # Global identifiers:
     #    _ord_:        numerical values indexed by characters
     #    _ord_init:    function to initialize _ord_
     BEGIN    { _ord_init() }

     function _ord_init(    low, high, i, t)
     {
         low = sprintf("%c", 7) # BEL is ascii 7
         if (low == "\a") {    # regular ascii
             low = 0
             high = 127
         } else if (sprintf("%c", 128 + 7) == "\a") {
             # ascii, mark parity
             low = 128
             high = 255
         } else {        # ebcdic(!)
             low = 0
             high = 255
         }

         for (i = low; i <= high; i++) {
             t = sprintf("%c", i)
             _ord_[t] = i
         }
     }

Some explanation of the numbers used by `chr' is worthwhile.  The most
prominent character set in use today is ASCII. Although an 8-bit byte
can hold 256 distinct values (from 0 to 255), ASCII only defines
characters that use the values from 0 to 127.(1) In the now distant
past, at least one minicomputer manufacturer used ASCII, but with mark
parity, meaning that the leftmost bit in the byte is always 1.  This
means that on those systems, characters have numeric values from 128 to
255.  Finally, large mainframe systems use the EBCDIC character set,
which uses all 256 values.  While there are other character sets in use
on some older systems, they are not really worth worrying about:

     function ord(str,    c)
     {
         # only first character is of interest
         c = substr(str, 1, 1)
         return _ord_[c]
     }

     function chr(c)
     {
         # force c to be numeric by adding 0
         return sprintf("%c", c + 0)
     }

     #### test code ####
     # BEGIN    \
     # {
     #    for (;;) {
     #        printf("enter a character: ")
     #        if (getline var <= 0)
     #            break
     #        printf("ord(%s) = %d\n", var, ord(var))
     #    }
     # }

An obvious improvement to these functions is to move the code for the
`_ord_init' function into the body of the `BEGIN' rule.  It was written
this way initially for ease of development.  There is a "test program"
in a `BEGIN' rule, to test the function.  It is commented out for
production use.

---------- Footnotes ----------

(1) ASCII has been extended in many countries to use the values from
128 to 255 for country-specific characters.  If your  system uses these
extensions, you can simplify `_ord_init' to simply loop from 0 to 255.


File: gawk.info,  Node: Join Function,  Next: Gettimeofday Function,  Prev: Ordinal Functions,  Up: General Functions

12.2.7 Merging an Array into a String
-------------------------------------

When doing string processing, it is often useful to be able to join all
the strings in an array into one long string.  The following function,
`join', accomplishes this task.  It is used later in several of the
application programs (*note Sample Programs::).

Good function design is important; this function needs to be general
but it should also have a reasonable default behavior.  It is called
with an array as well as the beginning and ending indices of the
elements in the array to be merged.  This assumes that the array
indices are numeric--a reasonable assumption since the array was likely
created with `split' (*note String Functions::):

     # join.awk --- join an array into a string
     function join(array, start, end, sep,    result, i)
     {
         if (sep == "")
            sep = " "
         else if (sep == SUBSEP) # magic value
            sep = ""
         result = array[start]
         for (i = start + 1; i <= end; i++)
             result = result sep array[i]
         return result
     }

An optional additional argument is the separator to use when joining the
strings back together.  If the caller supplies a nonempty value, `join'
uses it; if it is not supplied, it has a null value.  In this case,
`join' uses a single blank as a default separator for the strings.  If
the value is equal to `SUBSEP', then `join' joins the strings with no
separator between them.  `SUBSEP' serves as a "magic" value to indicate
that there should be no separation between the component strings.(1)

---------- Footnotes ----------

(1) It would be nice if `awk' had an assignment operator for
concatenation.  The lack of an explicit operator for concatenation
makes string operations more difficult than they really need to be.


File: gawk.info,  Node: Gettimeofday Function,  Prev: Join Function,  Up: General Functions

12.2.8 Managing the Time of Day
-------------------------------

The `systime' and `strftime' functions described in *Note Time
Functions::, provide the minimum functionality necessary for dealing
with the time of day in human readable form.  While `strftime' is
extensive, the control formats are not necessarily easy to remember or
intuitively obvious when reading a program.

The following function, `gettimeofday', populates a user-supplied array
with preformatted time information.  It returns a string with the
current time formatted in the same way as the `date' utility:

     # gettimeofday.awk --- get the time of day in a usable format

     # Returns a string in the format of output of date(1)
     # Populates the array argument time with individual values:
     #    time["second"]       -- seconds (0 - 59)
     #    time["minute"]       -- minutes (0 - 59)
     #    time["hour"]         -- hours (0 - 23)
     #    time["althour"]      -- hours (0 - 12)
     #    time["monthday"]     -- day of month (1 - 31)
     #    time["month"]        -- month of year (1 - 12)
     #    time["monthname"]    -- name of the month
     #    time["shortmonth"]   -- short name of the month
     #    time["year"]         -- year modulo 100 (0 - 99)
     #    time["fullyear"]     -- full year
     #    time["weekday"]      -- day of week (Sunday = 0)
     #    time["altweekday"]   -- day of week (Monday = 0)
     #    time["dayname"]      -- name of weekday
     #    time["shortdayname"] -- short name of weekday
     #    time["yearday"]      -- day of year (0 - 365)
     #    time["timezone"]     -- abbreviation of timezone name
     #    time["ampm"]         -- AM or PM designation
     #    time["weeknum"]      -- week number, Sunday first day
     #    time["altweeknum"]   -- week number, Monday first day

     function gettimeofday(time,    ret, now, i)
     {
         # get time once, avoids unnecessary system calls
         now = systime()

         # return date(1)-style output
         ret = strftime("%a %b %d %H:%M:%S %Z %Y", now)

         # clear out target array
         delete time

         # fill in values, force numeric values to be
         # numeric by adding 0
         time["second"]       = strftime("%S", now) + 0
         time["minute"]       = strftime("%M", now) + 0
         time["hour"]         = strftime("%H", now) + 0
         time["althour"]      = strftime("%I", now) + 0
         time["monthday"]     = strftime("%d", now) + 0
         time["month"]        = strftime("%m", now) + 0
         time["monthname"]    = strftime("%B", now)
         time["shortmonth"]   = strftime("%b", now)
         time["year"]         = strftime("%y", now) + 0
         time["fullyear"]     = strftime("%Y", now) + 0
         time["weekday"]      = strftime("%w", now) + 0
         time["altweekday"]   = strftime("%u", now) + 0
         time["dayname"]      = strftime("%A", now)
         time["shortdayname"] = strftime("%a", now)
         time["yearday"]      = strftime("%j", now) + 0
         time["timezone"]     = strftime("%Z", now)
         time["ampm"]         = strftime("%p", now)
         time["weeknum"]      = strftime("%U", now) + 0
         time["altweeknum"]   = strftime("%W", now) + 0

         return ret
     }

The string indices are easier to use and read than the various formats
required by `strftime'.  The `alarm' program presented in *Note Alarm
Program::, uses this function.  A more general design for the
`gettimeofday' function would have allowed the user to supply an
optional timestamp value to use instead of the current time.


File: gawk.info,  Node: Data File Management,  Next: Getopt Function,  Prev: General Functions,  Up: Library Functions

12.3 Data File Management
=========================

This minor node presents functions that are useful for managing
command-line data files.

* Menu:

* Filetrans Function::          A function for handling data file transitions.
* Rewind Function::             A function for rereading the current file.
* File Checking::               Checking that data files are readable.
* Empty Files::                 Checking for zero-length files.
* Ignoring Assigns::            Treating assignments as file names.


File: gawk.info,  Node: Filetrans Function,  Next: Rewind Function,  Up: Data File Management

12.3.1 Noting Data File Boundaries
----------------------------------

The `BEGIN' and `END' rules are each executed exactly once at the
beginning and end of your `awk' program, respectively (*note
BEGIN/END::).  We (the `gawk' authors) once had a user who mistakenly
thought that the `BEGIN' rule is executed at the beginning of each data
file and the `END' rule is executed at the end of each data file.  When
informed that this was not the case, the user requested that we add new
special patterns to `gawk', named `BEGIN_FILE' and `END_FILE', that
would have the desired behavior.  He even supplied us the code to do so.

Adding these special patterns to `gawk' wasn't necessary; the job can
be done cleanly in `awk' itself, as illustrated by the following
library program.  It arranges to call two user-supplied functions,
`beginfile' and `endfile', at the beginning and end of each data file.
Besides solving the problem in only nine(!) lines of code, it does so
_portably_; this works with any implementation of `awk':

     # transfile.awk
     #
     # Give the user a hook for filename transitions
     #
     # The user must supply functions beginfile() and endfile()
     # that each take the name of the file being started or
     # finished, respectively.

     FILENAME != _oldfilename \
     {
         if (_oldfilename != "")
             endfile(_oldfilename)
         _oldfilename = FILENAME
         beginfile(FILENAME)
     }

     END   { endfile(FILENAME) }

This file must be loaded before the user's "main" program, so that the
rule it supplies is executed first.

This rule relies on `awk''s `FILENAME' variable that automatically
changes for each new data file.  The current file name is saved in a
private variable, `_oldfilename'.  If `FILENAME' does not equal
`_oldfilename', then a new data file is being processed and it is
necessary to call `endfile' for the old file.  Because `endfile' should
only be called if a file has been processed, the program first checks
to make sure that `_oldfilename' is not the null string.  The program
then assigns the current file name to `_oldfilename' and calls
`beginfile' for the file.  Because, like all `awk' variables,
`_oldfilename' is initialized to the null string, this rule executes
correctly even for the first data file.

The program also supplies an `END' rule to do the final processing for
the last file.  Because this `END' rule comes before any `END' rules
supplied in the "main" program, `endfile' is called first.  Once again
the value of multiple `BEGIN' and `END' rules should be clear.

This version has same problem as the first version of `nextfile' (*note
Nextfile Function::).  If the same data file occurs twice in a row on
the command line, then `endfile' and `beginfile' are not executed at
the end of the first pass and at the beginning of the second pass.  The
following version solves the problem:

     # ftrans.awk --- handle data file transitions
     #
     # user supplies beginfile() and endfile() functions
     FNR == 1 {
         if (_filename_ != "")
             endfile(_filename_)
         _filename_ = FILENAME
         beginfile(FILENAME)
     }

     END  { endfile(_filename_) }

*Note Wc Program::, shows how this library function can be used and how
it simplifies writing the main program.


File: gawk.info,  Node: Rewind Function,  Next: File Checking,  Prev: Filetrans Function,  Up: Data File Management

12.3.2 Rereading the Current File
---------------------------------

Another request for a new built-in function was for a `rewind' function
that would make it possible to reread the current file.  The requesting
user didn't want to have to use `getline' (*note Getline::) inside a
loop.

However, as long as you are not in the `END' rule, it is quite easy to
arrange to immediately close the current input file and then start over
with it from the top.  For lack of a better name, we'll call it
`rewind':

     # rewind.awk --- rewind the current file and start over
     function rewind(    i)
     {
         # shift remaining arguments up
         for (i = ARGC; i > ARGIND; i--)
             ARGV[i] = ARGV[i-1]

         # make sure gawk knows to keep going
         ARGC++

         # make current file next to get done
         ARGV[ARGIND+1] = FILENAME

         # do it
         nextfile
     }

This code relies on the `ARGIND' variable (*note Auto-set::), which is
specific to `gawk'.  If you are not using `gawk', you can use ideas
presented in *Note Filetrans Function::, to either update `ARGIND' on
your own or modify this code as appropriate.

The `rewind' function also relies on the `nextfile' keyword (*note
Nextfile Statement::).  *Note Nextfile Function::, for a function
version of `nextfile'.


File: gawk.info,  Node: File Checking,  Next: Empty Files,  Prev: Rewind Function,  Up: Data File Management

12.3.3 Checking for Readable Data Files
---------------------------------------

Normally, if you give `awk' a data file that isn't readable, it stops
with a fatal error.  There are times when you might want to just ignore
such files and keep going.  You can do this by prepending the following
program to your `awk' program:

     # readable.awk --- library file to skip over unreadable files
     BEGIN {
         for (i = 1; i < ARGC; i++) {
             if (ARGV[i] ~ /^[A-Za-z_][A-Za-z0-9_]*=.*/ \
                 || ARGV[i] == "-")
                 continue    # assignment or standard input
             else if ((getline junk < ARGV[i]) < 0) # unreadable
                 delete ARGV[i]
             else
                 close(ARGV[i])
         }
     }

In `gawk', the `getline' won't be fatal (unless `--posix' is in force).
Removing the element from `ARGV' with `delete' skips the file (since
it's no longer in the list).


File: gawk.info,  Node: Empty Files,  Next: Ignoring Assigns,  Prev: File Checking,  Up: Data File Management

12.3.4 Checking For Zero-length Files
-------------------------------------

All known `awk' implementations silently skip over zero-length files.
This is a by-product of `awk''s implicit
read-a-record-and-match-against-the-rules loop: when `awk' tries to
read a record from an empty file, it immediately receives an end of
file indication, closes the file, and proceeds on to the next
command-line data file, _without_ executing any user-level `awk'
program code.

Using `gawk''s `ARGIND' variable (*note Built-in Variables::), it is
possible to detect when an empty data file has been skipped.  Similar
to the library file presented in *Note Filetrans Function::, the
following library file calls a function named `zerofile' that the user
must provide.  The arguments passed are the file name and the position
in `ARGV' where it was found:

     # zerofile.awk --- library file to process empty input files
     BEGIN { Argind = 0 }

     ARGIND > Argind + 1 {
         for (Argind++; Argind < ARGIND; Argind++)
             zerofile(ARGV[Argind], Argind)
     }

     ARGIND != Argind { Argind = ARGIND }

     END {
         if (ARGIND > Argind)
             for (Argind++; Argind <= ARGIND; Argind++)
                 zerofile(ARGV[Argind], Argind)
     }

The user-level variable `Argind' allows the `awk' program to track its
progress through `ARGV'.  Whenever the program detects that `ARGIND' is
greater than `Argind + 1', it means that one or more empty files were
skipped.  The action then calls `zerofile' for each such file,
incrementing `Argind' along the way.

The `Argind != ARGIND' rule simply keeps `Argind' up to date in the
normal case.

Finally, the `END' rule catches the case of any empty files at the end
of the command-line arguments.  Note that the test in the condition of
the `for' loop uses the `<=' operator, not `<'.

As an exercise, you might consider whether this same problem can be
solved without relying on `gawk''s `ARGIND' variable.

As a second exercise, revise this code to handle the case where an
intervening value in `ARGV' is a variable assignment.


File: gawk.info,  Node: Ignoring Assigns,  Prev: Empty Files,  Up: Data File Management

12.3.5 Treating Assignments as File Names
-----------------------------------------

Occasionally, you might not want `awk' to process command-line variable
assignments (*note Assignment Options::).  In particular, if you have
file names that contain an `=' character, `awk' treats the file name as
an assignment, and does not process it.

Some users have suggested an additional command-line option for `gawk'
to disable command-line assignments.  However, some simple programming
with a library file does the trick:

     # noassign.awk --- library file to avoid the need for a
     # special option that disables command-line assignments
     function disable_assigns(argc, argv,    i)
     {
         for (i = 1; i < argc; i++)
             if (argv[i] ~ /^[A-Za-z_][A-Za-z_0-9]*=.*/)
                 argv[i] = ("./" argv[i])
     }

     BEGIN {
         if (No_command_assign)
             disable_assigns(ARGC, ARGV)
     }

You then run your program this way:

     awk -v No_command_assign=1 -f noassign.awk -f yourprog.awk *

The function works by looping through the arguments.  It prepends `./'
to any argument that matches the form of a variable assignment, turning
that argument into a file name.

The use of `No_command_assign' allows you to disable command-line
assignments at invocation time, by giving the variable a true value.
When not set, it is initially zero (i.e., false), so the command-line
arguments are left alone.


File: gawk.info,  Node: Getopt Function,  Next: Passwd Functions,  Prev: Data File Management,  Up: Library Functions

12.4 Processing Command-Line Options
====================================

Most utilities on POSIX compatible systems take options, or "switches,"
on the command line that can be used to change the way a program
behaves.  `awk' is an example of such a program (*note Options::).
Often, options take "arguments"; i.e., data that the program needs to
correctly obey the command-line option.  For example, `awk''s `-F'
option requires a string to use as the field separator.  The first
occurrence on the command line of either `--' or a string that does not
begin with `-' ends the options.

Modern Unix systems provide a C function named `getopt' for processing
command-line arguments.  The programmer provides a string describing the
one-letter options. If an option requires an argument, it is followed
in the string with a colon.  `getopt' is also passed the count and
values of the command-line arguments and is called in a loop.  `getopt'
processes the command-line arguments for option letters.  Each time
around the loop, it returns a single character representing the next
option letter that it finds, or `?' if it finds an invalid option.
When it returns -1, there are no options left on the command line.

When using `getopt', options that do not take arguments can be grouped
together.  Furthermore, options that take arguments require that the
argument is present.  The argument can immediately follow the option
letter, or it can be a separate command-line argument.

Given a hypothetical program that takes three command-line options,
`-a', `-b', and `-c', where `-b' requires an argument, all of the
following are valid ways of invoking the program:

     prog -a -b foo -c data1 data2 data3
     prog -ac -bfoo -- data1 data2 data3
     prog -acbfoo data1 data2 data3

Notice that when the argument is grouped with its option, the rest of
the argument is considered to be the option's argument.  In this
example, `-acbfoo' indicates that all of the `-a', `-b', and `-c'
options were supplied, and that `foo' is the argument to the `-b'
option.

`getopt' provides four external variables that the programmer can use:

`optind'
     The index in the argument value array (`argv') where the first
     nonoption command-line argument can be found.

`optarg'
     The string value of the argument to an option.

`opterr'
     Usually `getopt' prints an error message when it finds an invalid
     option.  Setting `opterr' to zero disables this feature.  (An
     application might want to print its own error message.)

`optopt'
     The letter representing the command-line option.

The following C fragment shows how `getopt' might process command-line
arguments for `awk':

     int
     main(int argc, char *argv[])
     {
         ...
         /* print our own message */
         opterr = 0;
         while ((c = getopt(argc, argv, "v:f:F:W:")) != -1) {
             switch (c) {
             case 'f':    /* file */
                 ...
                 break;
             case 'F':    /* field separator */
                 ...
                 break;
             case 'v':    /* variable assignment */
                 ...
                 break;
             case 'W':    /* extension */
                 ...
                 break;
             case '?':
             default:
                 usage();
                 break;
             }
         }
         ...
     }

As a side point, `gawk' actually uses the GNU `getopt_long' function to
process both normal and GNU-style long options (*note Options::).

The abstraction provided by `getopt' is very useful and is quite handy
in `awk' programs as well.  Following is an `awk' version of `getopt'.
This function highlights one of the greatest weaknesses in `awk', which
is that it is very poor at manipulating single characters.  Repeated
calls to `substr' are necessary for accessing individual characters
(*note String Functions::).(1)

The discussion that follows walks through the code a bit at a time:

     # getopt.awk --- do C library getopt(3) function in awk
     # External variables:
     #    Optind -- index in ARGV of first nonoption argument
     #    Optarg -- string value of argument to current option
     #    Opterr -- if nonzero, print our own diagnostic
     #    Optopt -- current option letter

     # Returns:
     #    -1     at end of options
     #    ?      for unrecognized option
     #    <c>    a character representing the current option

     # Private Data:
     #    _opti  -- index in multi-flag option, e.g., -abc

The function starts out with a list of the global variables it uses,
what the return values are, what they mean, and any global variables
that are "private" to this library function.  Such documentation is
essential for any program, and particularly for library functions.

The `getopt' function first checks that it was indeed called with a
string of options (the `options' parameter).  If `options' has a zero
length, `getopt' immediately returns -1:

     function getopt(argc, argv, options,    thisopt, i)
     {
         if (length(options) == 0)    # no options given
             return -1

         if (argv[Optind] == "--") {  # all done
             Optind++
             _opti = 0
             return -1
         } else if (argv[Optind] !~ /^-[^: \t\n\f\r\v\b]/) {
             _opti = 0
             return -1
         }

The next thing to check for is the end of the options.  A `--' ends the
command-line options, as does any command-line argument that does not
begin with a `-'.  `Optind' is used to step through the array of
command-line arguments; it retains its value across calls to `getopt',
because it is a global variable.

The regular expression that is used, `/^-[^: \t\n\f\r\v\b]/', is
perhaps a bit of overkill; it checks for a `-' followed by anything
that is not whitespace and not a colon.  If the current command-line
argument does not match this pattern, it is not an option, and it ends
option processing:

         if (_opti == 0)
             _opti = 2
         thisopt = substr(argv[Optind], _opti, 1)
         Optopt = thisopt
         i = index(options, thisopt)
         if (i == 0) {
             if (Opterr)
                 printf("%c -- invalid option\n",
                                       thisopt) > "/dev/stderr"
             if (_opti >= length(argv[Optind])) {
                 Optind++
                 _opti = 0
             } else
                 _opti++
             return "?"
         }

The `_opti' variable tracks the position in the current command-line
argument (`argv[Optind]').  If multiple options are grouped together
with one `-' (e.g., `-abx'), it is necessary to return them to the user
one at a time.

If `_opti' is equal to zero, it is set to two, which is the index in
the string of the next character to look at (we skip the `-', which is
at position one).  The variable `thisopt' holds the character, obtained
with `substr'.  It is saved in `Optopt' for the main program to use.

If `thisopt' is not in the `options' string, then it is an invalid
option.  If `Opterr' is nonzero, `getopt' prints an error message on
the standard error that is similar to the message from the C version of
`getopt'.

Because the option is invalid, it is necessary to skip it and move on
to the next option character.  If `_opti' is greater than or equal to
the length of the current command-line argument, it is necessary to
move on to the next argument, so `Optind' is incremented and `_opti' is
reset to zero. Otherwise, `Optind' is left alone and `_opti' is merely
incremented.

In any case, because the option is invalid, `getopt' returns `?'.  The
main program can examine `Optopt' if it needs to know what the invalid
option letter actually is. Continuing on:

         if (substr(options, i + 1, 1) == ":") {
             # get option argument
             if (length(substr(argv[Optind], _opti + 1)) > 0)
                 Optarg = substr(argv[Optind], _opti + 1)
             else
                 Optarg = argv[++Optind]
             _opti = 0
         } else
             Optarg = ""

If the option requires an argument, the option letter is followed by a
colon in the `options' string.  If there are remaining characters in the
current command-line argument (`argv[Optind]'), then the rest of that
string is assigned to `Optarg'.  Otherwise, the next command-line
argument is used (`-xFOO' versus `-x FOO'). In either case, `_opti' is
reset to zero, because there are no more characters left to examine in
the current command-line argument. Continuing:

         if (_opti == 0 || _opti >= length(argv[Optind])) {
             Optind++
             _opti = 0
         } else
             _opti++
         return thisopt
     }

Finally, if `_opti' is either zero or greater than the length of the
current command-line argument, it means this element in `argv' is
through being processed, so `Optind' is incremented to point to the
next element in `argv'.  If neither condition is true, then only
`_opti' is incremented, so that the next option letter can be processed
on the next call to `getopt'.

The `BEGIN' rule initializes both `Opterr' and `Optind' to one.
`Opterr' is set to one, since the default behavior is for `getopt' to
print a diagnostic message upon seeing an invalid option.  `Optind' is
set to one, since there's no reason to look at the program name, which
is in `ARGV[0]':

     BEGIN {
         Opterr = 1    # default is to diagnose
         Optind = 1    # skip ARGV[0]

         # test program
         if (_getopt_test) {
             while ((_go_c = getopt(ARGC, ARGV, "ab:cd")) != -1)
                 printf("c = <%c>, optarg = <%s>\n",
                                            _go_c, Optarg)
             printf("non-option arguments:\n")
             for (; Optind < ARGC; Optind++)
                 printf("\tARGV[%d] = <%s>\n",
                                         Optind, ARGV[Optind])
         }
     }

The rest of the `BEGIN' rule is a simple test program.  Here is the
result of two sample runs of the test program:

     $ awk -f getopt.awk -v _getopt_test=1 -- -a -cbARG bax -x
     -| c = <a>, optarg = <>
     -| c = <c>, optarg = <>
     -| c = <b>, optarg = <ARG>
     -| non-option arguments:
     -|         ARGV[3] = <bax>
     -|         ARGV[4] = <-x>

     $ awk -f getopt.awk -v _getopt_test=1 -- -a -x -- xyz abc
     -| c = <a>, optarg = <>
     error--> x -- invalid option
     -| c = <?>, optarg = <>
     -| non-option arguments:
     -|         ARGV[4] = <xyz>
     -|         ARGV[5] = <abc>

In both runs, the first `--' terminates the arguments to `awk', so that
it does not try to interpret the `-a', etc., as its own options.
Several of the sample programs presented in *Note Sample Programs::,
use `getopt' to process their arguments.

---------- Footnotes ----------

(1) This function was written before `gawk' acquired the ability to
split strings into single characters using `""' as the separator.  We
have left it alone, since using `substr' is more portable.


File: gawk.info,  Node: Passwd Functions,  Next: Group Functions,  Prev: Getopt Function,  Up: Library Functions

12.5 Reading the User Database
==============================

The `PROCINFO' array (*note Built-in Variables::) provides access to
the current user's real and effective user and group ID numbers, and if
available, the user's supplementary group set.  However, because these
are numbers, they do not provide very useful information to the average
user.  There needs to be some way to find the user information
associated with the user and group ID numbers.  This minor node
presents a suite of functions for retrieving information from the user
database.  *Note Group Functions::, for a similar suite that retrieves
information from the group database.

The POSIX standard does not define the file where user information is
kept.  Instead, it provides the `<pwd.h>' header file and several C
language subroutines for obtaining user information.  The primary
function is `getpwent', for "get password entry."  The "password" comes
from the original user database file, `/etc/passwd', which stores user
information, along with the encrypted passwords (hence the name).

While an `awk' program could simply read `/etc/passwd' directly, this
file may not contain complete information about the system's set of
users.(1) To be sure you are able to produce a readable and complete
version of the user database, it is necessary to write a small C
program that calls `getpwent'.  `getpwent' is defined as returning a
pointer to a `struct passwd'.  Each time it is called, it returns the
next entry in the database.  When there are no more entries, it returns
`NULL', the null pointer.  When this happens, the C program should call
`endpwent' to close the database.  Following is `pwcat', a C program
that "cats" the password database:

     /*
      * pwcat.c
      *
      * Generate a printable version of the password database
      */
     #include <stdio.h>
     #include <pwd.h>

     int
     main(argc, argv)
     int argc;
     char **argv;
     {
         struct passwd *p;

         while ((p = getpwent()) != NULL)
             printf("%s:%s:%ld:%ld:%s:%s:%s\n",
                 p->pw_name, p->pw_passwd, (long) p->pw_uid,
                 (long) p->pw_gid, p->pw_gecos, p->pw_dir, p->pw_shell);

         endpwent();
         return 0;
     }

If you don't understand C, don't worry about it.  The output from
`pwcat' is the user database, in the traditional `/etc/passwd' format
of colon-separated fields.  The fields are:

Login name           The user's login name.
Encrypted password   The user's encrypted password.  This may not be
                     available on some systems.
User-ID              The user's numeric user ID number.
Group-ID             The user's numeric group ID number.
Full name            The user's full name, and perhaps other
                     information associated with the user.
Home directory       The user's login (or "home") directory
                     (familiar to shell programmers as `$HOME').
Login shell          The program that is run when the user logs in.
                     This is usually a shell, such as `bash'.

A few lines representative of `pwcat''s output are as follows:

     $ pwcat
     -| root:3Ov02d5VaUPB6:0:1:Operator:/:/bin/sh
     -| nobody:*:65534:65534::/:
     -| daemon:*:1:1::/:
     -| sys:*:2:2::/:/bin/csh
     -| bin:*:3:3::/bin:
     -| arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/sh
     -| miriam:yxaay:112:10:Miriam Robbins:/home/miriam:/bin/sh
     -| andy:abcca2:113:10:Andy Jacobs:/home/andy:/bin/sh
     ...

With that introduction, following is a group of functions for getting
user information.  There are several functions here, corresponding to
the C functions of the same names:

     # passwd.awk --- access password file information
     BEGIN {
         # tailor this to suit your system
         _pw_awklib = "/usr/local/libexec/awk/"
     }

     function _pw_init(    oldfs, oldrs, olddol0, pwcat, using_fw)
     {
         if (_pw_inited)
             return

         oldfs = FS
         oldrs = RS
         olddol0 = $0
         using_fw = (PROCINFO["FS"] == "FIELDWIDTHS")
         FS = ":"
         RS = "\n"

         pwcat = _pw_awklib "pwcat"
         while ((pwcat | getline) > 0) {
             _pw_byname[$1] = $0
             _pw_byuid[$3] = $0
             _pw_bycount[++_pw_total] = $0
         }
         close(pwcat)
         _pw_count = 0
         _pw_inited = 1
         FS = oldfs
         if (using_fw)
             FIELDWIDTHS = FIELDWIDTHS
         RS = oldrs
         $0 = olddol0
     }

The `BEGIN' rule sets a private variable to the directory where `pwcat'
is stored.  Because it is used to help out an `awk' library routine, we
have chosen to put it in `/usr/local/libexec/awk'; however, you might
want it to be in a different directory on your system.

The function `_pw_init' keeps three copies of the user information in
three associative arrays.  The arrays are indexed by username
(`_pw_byname'), by user ID number (`_pw_byuid'), and by order of
occurrence (`_pw_bycount').  The variable `_pw_inited' is used for
efficiency; `_pw_init' needs only to be called once.

Because this function uses `getline' to read information from `pwcat',
it first saves the values of `FS', `RS', and `$0'.  It notes in the
variable `using_fw' whether field splitting with `FIELDWIDTHS' is in
effect or not.  Doing so is necessary, since these functions could be
called from anywhere within a user's program, and the user may have his
or her own way of splitting records and fields.

The `using_fw' variable checks `PROCINFO["FS"]', which is
`"FIELDWIDTHS"' if field splitting is being done with `FIELDWIDTHS'.
This makes it possible to restore the correct field-splitting mechanism
later.  The test can only be true for `gawk'.  It is false if using
`FS' or on some other `awk' implementation.

The main part of the function uses a loop to read database lines, split
the line into fields, and then store the line into each array as
necessary.  When the loop is done, `_pw_init' cleans up by closing the
pipeline, setting `_pw_inited' to one, and restoring `FS' (and
`FIELDWIDTHS' if necessary), `RS', and `$0'.  The use of `_pw_count' is
explained shortly.

The `getpwnam' function takes a username as a string argument. If that
user is in the database, it returns the appropriate line. Otherwise, it
returns the null string:

     function getpwnam(name)
     {
         _pw_init()
         if (name in _pw_byname)
             return _pw_byname[name]
         return ""
     }

Similarly, the `getpwuid' function takes a user ID number argument. If
that user number is in the database, it returns the appropriate line.
Otherwise, it returns the null string:

     function getpwuid(uid)
     {
         _pw_init()
         if (uid in _pw_byuid)
             return _pw_byuid[uid]
         return ""
     }

The `getpwent' function simply steps through the database, one entry at
a time.  It uses `_pw_count' to track its current position in the
`_pw_bycount' array:

     function getpwent()
     {
         _pw_init()
         if (_pw_count < _pw_total)
             return _pw_bycount[++_pw_count]
         return ""
     }

The `endpwent' function resets `_pw_count' to zero, so that subsequent
calls to `getpwent' start over again:

     function endpwent()
     {
         _pw_count = 0
     }

A conscious design decision in this suite was made that each subroutine
calls `_pw_init' to initialize the database arrays.  The overhead of
running a separate process to generate the user database, and the I/O
to scan it, are only incurred if the user's main program actually calls
one of these functions.  If this library file is loaded along with a
user's program, but none of the routines are ever called, then there is
no extra runtime overhead.  (The alternative is move the body of
`_pw_init' into a `BEGIN' rule, which always runs `pwcat'.  This
simplifies the code but runs an extra process that may never be needed.)

In turn, calling `_pw_init' is not too expensive, because the
`_pw_inited' variable keeps the program from reading the data more than
once.  If you are worried about squeezing every last cycle out of your
`awk' program, the check of `_pw_inited' could be moved out of
`_pw_init' and duplicated in all the other functions.  In practice,
this is not necessary, since most `awk' programs are I/O-bound, and it
clutters up the code.

The `id' program in *Note Id Program::, uses these functions.

---------- Footnotes ----------

(1) It is often the case that password information is stored in a
network database.


File: gawk.info,  Node: Group Functions,  Prev: Passwd Functions,  Up: Library Functions

12.6 Reading the Group Database
===============================

Much of the discussion presented in *Note Passwd Functions::, applies
to the group database as well.  Although there has traditionally been a
well-known file (`/etc/group') in a well-known format, the POSIX
standard only provides a set of C library routines (`<grp.h>' and
`getgrent') for accessing the information.  Even though this file may
exist, it likely does not have complete information.  Therefore, as
with the user database, it is necessary to have a small C program that
generates the group database as its output.

`grcat', a C program that "cats" the group database, is as follows:

     /*
      * grcat.c
      *
      * Generate a printable version of the group database
      */
     #include <stdio.h>
     #include <grp.h>

     int
     main(argc, argv)
     int argc;
     char **argv;
     {
         struct group *g;
         int i;

         while ((g = getgrent()) != NULL) {
             printf("%s:%s:%ld:", g->gr_name, g->gr_passwd,
                                          (long) g->gr_gid);
             for (i = 0; g->gr_mem[i] != NULL; i++) {
                 printf("%s", g->gr_mem[i]);
                 if (g->gr_mem[i+1] != NULL)
                     putchar(',');
             }
             putchar('\n');
         }
         endgrent();
         return 0;
     }

Each line in the group database represents one group.  The fields are
separated with colons and represent the following information:

Group name           The group's name.
Group password       The group's encrypted password. In practice,
                     this field is never used; it is usually empty
                     or set to `*'.
Group-ID              The group's numeric group ID number; this
                     number should be unique within the file.
Group member list     A comma-separated list of usernames.  These
                     users are members of the group.  Modern Unix
                     systems allow users to be members of several
                     groups simultaneously.  If your system does,
                     then there are elements `"group1"' through
                     `"groupN"' in `PROCINFO' for those group ID
                     numbers.  (Note that `PROCINFO' is a `gawk'
                     extension; *note Built-in Variables::.)

Here is what running `grcat' might produce:

     $ grcat
     -| wheel:*:0:arnold
     -| nogroup:*:65534:
     -| daemon:*:1:
     -| kmem:*:2:
     -| staff:*:10:arnold,miriam,andy
     -| other:*:20:
     ...

Here are the functions for obtaining information from the group
database.  There are several, modeled after the C library functions of
the same names:

     # group.awk --- functions for dealing with the group file
     BEGIN    \
     {
         # Change to suit your system
         _gr_awklib = "/usr/local/libexec/awk/"
     }

     function _gr_init(    oldfs, oldrs, olddol0, grcat,
                                  using_fw, n, a, i)
     {
         if (_gr_inited)
             return

         oldfs = FS
         oldrs = RS
         olddol0 = $0
         using_fw = (PROCINFO["FS"] == "FIELDWIDTHS")
         FS = ":"
         RS = "\n"

         grcat = _gr_awklib "grcat"
         while ((grcat | getline) > 0) {
             if ($1 in _gr_byname)
                 _gr_byname[$1] = _gr_byname[$1] "," $4
             else
                 _gr_byname[$1] = $0
             if ($3 in _gr_bygid)
                 _gr_bygid[$3] = _gr_bygid[$3] "," $4
             else
                 _gr_bygid[$3] = $0

             n = split($4, a, "[ \t]*,[ \t]*")
             for (i = 1; i <= n; i++)
                 if (a[i] in _gr_groupsbyuser)
                     _gr_groupsbyuser[a[i]] = \
                         _gr_groupsbyuser[a[i]] " " $1
                 else
                     _gr_groupsbyuser[a[i]] = $1

             _gr_bycount[++_gr_count] = $0
         }
         close(grcat)
         _gr_count = 0
         _gr_inited++
         FS = oldfs
         if (using_fw)
             FIELDWIDTHS = FIELDWIDTHS
         RS = oldrs
         $0 = olddol0
     }

The `BEGIN' rule sets a private variable to the directory where `grcat'
is stored.  Because it is used to help out an `awk' library routine, we
have chosen to put it in `/usr/local/libexec/awk'.  You might want it
to be in a different directory on your system.

These routines follow the same general outline as the user database
routines (*note Passwd Functions::).  The `_gr_inited' variable is used
to ensure that the database is scanned no more than once.  The
`_gr_init' function first saves `FS', `FIELDWIDTHS', `RS', and `$0',
and then sets `FS' and `RS' to the correct values for scanning the
group information.

The group information is stored is several associative arrays.  The
arrays are indexed by group name (`_gr_byname'), by group ID number
(`_gr_bygid'), and by position in the database (`_gr_bycount').  There
is an additional array indexed by username (`_gr_groupsbyuser'), which
is a space-separated list of groups to which each user belongs.

Unlike the user database, it is possible to have multiple records in the
database for the same group.  This is common when a group has a large
number of members.  A pair of such entries might look like the
following:

     tvpeople:*:101:johnny,jay,arsenio
     tvpeople:*:101:david,conan,tom,joan

For this reason, `_gr_init' looks to see if a group name or group ID
number is already seen.  If it is, then the usernames are simply
concatenated onto the previous list of users.  (There is actually a
subtle problem with the code just presented.  Suppose that the first
time there were no names. This code adds the names with a leading
comma. It also doesn't check that there is a `$4'.)

Finally, `_gr_init' closes the pipeline to `grcat', restores `FS' (and
`FIELDWIDTHS' if necessary), `RS', and `$0', initializes `_gr_count' to
zero (it is used later), and makes `_gr_inited' nonzero.

The `getgrnam' function takes a group name as its argument, and if that
group exists, it is returned. Otherwise, `getgrnam' returns the null
string:

     function getgrnam(group)
     {
         _gr_init()
         if (group in _gr_byname)
             return _gr_byname[group]
         return ""
     }

The `getgrgid' function is similar, it takes a numeric group ID and
looks up the information associated with that group ID:

     function getgrgid(gid)
     {
         _gr_init()
         if (gid in _gr_bygid)
             return _gr_bygid[gid]
         return ""
     }

The `getgruser' function does not have a C counterpart. It takes a
username and returns the list of groups that have the user as a member:

     function getgruser(user)
     {
         _gr_init()
         if (user in _gr_groupsbyuser)
             return _gr_groupsbyuser[user]
         return ""
     }

The `getgrent' function steps through the database one entry at a time.
It uses `_gr_count' to track its position in the list:

     function getgrent()
     {
         _gr_init()
         if (++_gr_count in _gr_bycount)
             return _gr_bycount[_gr_count]
         return ""
     }

The `endgrent' function resets `_gr_count' to zero so that `getgrent'
can start over again:

     function endgrent()
     {
         _gr_count = 0
     }

As with the user database routines, each function calls `_gr_init' to
initialize the arrays.  Doing so only incurs the extra overhead of
running `grcat' if these functions are used (as opposed to moving the
body of `_gr_init' into a `BEGIN' rule).

Most of the work is in scanning the database and building the various
associative arrays.  The functions that the user calls are themselves
very simple, relying on `awk''s associative arrays to do work.

The `id' program in *Note Id Program::, uses these functions.


File: gawk.info,  Node: Sample Programs,  Next: Language History,  Prev: Library Functions,  Up: Top

13 Practical `awk' Programs
***************************

*Note Library Functions::, presents the idea that reading programs in a
language contributes to learning that language.  This major node
continues that theme, presenting a potpourri of `awk' programs for your
reading enjoyment.

Many of these programs use the library functions presented in *Note
Library Functions::.

* Menu:

* Running Examples::            How to run these examples.
* Clones::                      Clones of common utilities.
* Miscellaneous Programs::      Some interesting `awk' programs.


File: gawk.info,  Node: Running Examples,  Next: Clones,  Up: Sample Programs

13.1 Running the Example Programs
=================================

To run a given program, you would typically do something like this:

     awk -f PROGRAM -- OPTIONS FILES

Here, PROGRAM is the name of the `awk' program (such as `cut.awk'),
OPTIONS are any command-line options for the program that start with a
`-', and FILES are the actual data files.

If your system supports the `#!' executable interpreter mechanism
(*note Executable Scripts::), you can instead run your program directly:

     cut.awk -c1-8 myfiles > results

If your `awk' is not `gawk', you may instead need to use this:

     cut.awk -- -c1-8 myfiles > results


File: gawk.info,  Node: Clones,  Next: Miscellaneous Programs,  Prev: Running Examples,  Up: Sample Programs

13.2 Reinventing Wheels for Fun and Profit
==========================================

This minor node presents a number of POSIX utilities that are
implemented in `awk'.  Reinventing these programs in `awk' is often
enjoyable, because the algorithms can be very clearly expressed, and
the code is usually very concise and simple.  This is true because
`awk' does so much for you.

It should be noted that these programs are not necessarily intended to
replace the installed versions on your system.  Instead, their purpose
is to illustrate `awk' language programming for "real world" tasks.

The programs are presented in alphabetical order.

* Menu:

* Cut Program::                 The `cut' utility.
* Egrep Program::               The `egrep' utility.
* Id Program::                  The `id' utility.
* Split Program::               The `split' utility.
* Tee Program::                 The `tee' utility.
* Uniq Program::                The `uniq' utility.
* Wc Program::                  The `wc' utility.


File: gawk.info,  Node: Cut Program,  Next: Egrep Program,  Up: Clones

13.2.1 Cutting out Fields and Columns
-------------------------------------

The `cut' utility selects, or "cuts," characters or fields from its
standard input and sends them to its standard output.  Fields are
separated by tabs by default, but you may supply a command-line option
to change the field "delimiter" (i.e., the field-separator character).
`cut''s definition of fields is less general than `awk''s.

A common use of `cut' might be to pull out just the login name of
logged-on users from the output of `who'.  For example, the following
pipeline generates a sorted, unique list of the logged-on users:

     who | cut -c1-8 | sort | uniq

The options for `cut' are:

`-c LIST'
     Use LIST as the list of characters to cut out.  Items within the
     list may be separated by commas, and ranges of characters can be
     separated with dashes.  The list `1-8,15,22-35' specifies
     characters 1 through 8, 15, and 22 through 35.

`-f LIST'
     Use LIST as the list of fields to cut out.

`-d DELIM'
     Use DELIM as the field-separator character instead of the tab
     character.

`-s'
     Suppress printing of lines that do not contain the field delimiter.

The `awk' implementation of `cut' uses the `getopt' library function
(*note Getopt Function::) and the `join' library function (*note Join
Function::).

The program begins with a comment describing the options, the library
functions needed, and a `usage' function that prints out a usage
message and exits.  `usage' is called if invalid arguments are supplied:

     # cut.awk --- implement cut in awk
     # Options:
     #    -f list     Cut fields
     #    -d c        Field delimiter character
     #    -c list     Cut characters
     #
     #    -s          Suppress lines without the delimiter
     #
     # Requires getopt and join library functions

     function usage(    e1, e2)
     {
         e1 = "usage: cut [-f list] [-d c] [-s] [files...]"
         e2 = "usage: cut [-c list] [files...]"
         print e1 > "/dev/stderr"
         print e2 > "/dev/stderr"
         exit 1
     }

The variables `e1' and `e2' are used so that the function fits nicely
on the screen.

Next comes a `BEGIN' rule that parses the command-line options.  It
sets `FS' to a single TAB character, because that is `cut''s default
field separator.  The output field separator is also set to be the same
as the input field separator.  Then `getopt' is used to step through
the command-line options.  Exactly one of the variables `by_fields' or
`by_chars' is set to true, to indicate that processing should be done
by fields or by characters, respectively.  When cutting by characters,
the output field separator is set to the null string:

     BEGIN    \
     {
         FS = "\t"    # default
         OFS = FS
         while ((c = getopt(ARGC, ARGV, "sf:c:d:")) != -1) {
             if (c == "f") {
                 by_fields = 1
                 fieldlist = Optarg
             } else if (c == "c") {
                 by_chars = 1
                 fieldlist = Optarg
                 OFS = ""
             } else if (c == "d") {
                 if (length(Optarg) > 1) {
                     printf("Using first character of %s" \
                     " for delimiter\n", Optarg) > "/dev/stderr"
                     Optarg = substr(Optarg, 1, 1)
                 }
                 FS = Optarg
                 OFS = FS
                 if (FS == " ")    # defeat awk semantics
                     FS = "[ ]"
             } else if (c == "s")
                 suppress++
             else
                 usage()
         }

         for (i = 1; i < Optind; i++)
             ARGV[i] = ""

Special care is taken when the field delimiter is a space.  Using a
single space (`" "') for the value of `FS' is incorrect--`awk' would
separate fields with runs of spaces, tabs, and/or newlines, and we want
them to be separated with individual spaces.  Also, note that after
`getopt' is through, we have to clear out all the elements of `ARGV'
from 1 to `Optind', so that `awk' does not try to process the
command-line options as file names.

After dealing with the command-line options, the program verifies that
the options make sense.  Only one or the other of `-c' and `-f' should
be used, and both require a field list.  Then the program calls either
`set_fieldlist' or `set_charlist' to pull apart the list of fields or
characters:

         if (by_fields && by_chars)
             usage()

         if (by_fields == 0 && by_chars == 0)
             by_fields = 1    # default

         if (fieldlist == "") {
             print "cut: needs list for -c or -f" > "/dev/stderr"
             exit 1
         }

         if (by_fields)
             set_fieldlist()
         else
             set_charlist()
     }

`set_fieldlist'  is used to split the field list apart at the commas
and into an array.  Then, for each element of the array, it looks to
see if it is actually a range, and if so, splits it apart. The range is
verified to make sure the first number is smaller than the second.
Each number in the list is added to the `flist' array, which simply
lists the fields that will be printed.  Normal field splitting is used.
The program lets `awk' handle the job of doing the field splitting:

     function set_fieldlist(        n, m, i, j, k, f, g)
     {
         n = split(fieldlist, f, ",")
         j = 1    # index in flist
         for (i = 1; i <= n; i++) {
             if (index(f[i], "-") != 0) { # a range
                 m = split(f[i], g, "-")
                 if (m != 2 || g[1] >= g[2]) {
                     printf("bad field list: %s\n",
                                       f[i]) > "/dev/stderr"
                     exit 1
                 }
                 for (k = g[1]; k <= g[2]; k++)
                     flist[j++] = k
             } else
                 flist[j++] = f[i]
         }
         nfields = j - 1
     }

The `set_charlist' function is more complicated than `set_fieldlist'.
The idea here is to use `gawk''s `FIELDWIDTHS' variable (*note Constant
Size::), which describes constant-width input.  When using a character
list, that is exactly what we have.

Setting up `FIELDWIDTHS' is more complicated than simply listing the
fields that need to be printed.  We have to keep track of the fields to
print and also the intervening characters that have to be skipped.  For
example, suppose you wanted characters 1 through 8, 15, and 22 through
35.  You would use `-c 1-8,15,22-35'.  The necessary value for
`FIELDWIDTHS' is `"8 6 1 6 14"'.  This yields five fields, and the
fields to print are `$1', `$3', and `$5'.  The intermediate fields are
"filler", which is stuff in between the desired data.  `flist' lists
the fields to print, and `t' tracks the complete field list, including
filler fields:

     function set_charlist(    field, i, j, f, g, t,
                               filler, last, len)
     {
         field = 1   # count total fields
         n = split(fieldlist, f, ",")
         j = 1       # index in flist
         for (i = 1; i <= n; i++) {
             if (index(f[i], "-") != 0) { # range
                 m = split(f[i], g, "-")
                 if (m != 2 || g[1] >= g[2]) {
                     printf("bad character list: %s\n",
                                    f[i]) > "/dev/stderr"
                     exit 1
                 }
                 len = g[2] - g[1] + 1
                 if (g[1] > 1)  # compute length of filler
                     filler = g[1] - last - 1
                 else
                     filler = 0
                 if (filler)
                     t[field++] = filler
                 t[field++] = len  # length of field
                 last = g[2]
                 flist[j++] = field - 1
             } else {
                 if (f[i] > 1)
                     filler = f[i] - last - 1
                 else
                     filler = 0
                 if (filler)
                     t[field++] = filler
                 t[field++] = 1
                 last = f[i]
                 flist[j++] = field - 1
             }
         }
         FIELDWIDTHS = join(t, 1, field - 1)
         nfields = j - 1
     }

Next is the rule that actually processes the data.  If the `-s' option
is given, then `suppress' is true.  The first `if' statement makes sure
that the input record does have the field separator.  If `cut' is
processing fields, `suppress' is true, and the field separator
character is not in the record, then the record is skipped.

If the record is valid, then `gawk' has split the data into fields,
either using the character in `FS' or using fixed-length fields and
`FIELDWIDTHS'.  The loop goes through the list of fields that should be
printed.  The corresponding field is printed if it contains data.  If
the next field also has data, then the separator character is written
out between the fields:

     {
         if (by_fields && suppress && index($0, FS) != 0)
             next

         for (i = 1; i <= nfields; i++) {
             if ($flist[i] != "") {
                 printf "%s", $flist[i]
                 if (i < nfields && $flist[i+1] != "")
                     printf "%s", OFS
             }
         }
         print ""
     }

This version of `cut' relies on `gawk''s `FIELDWIDTHS' variable to do
the character-based cutting.  While it is possible in other `awk'
implementations to use `substr' (*note String Functions::), it is also
extremely painful.  The `FIELDWIDTHS' variable supplies an elegant
solution to the problem of picking the input line apart by characters.


File: gawk.info,  Node: Egrep Program,  Next: Id Program,  Prev: Cut Program,  Up: Clones

13.2.2 Searching for Regular Expressions in Files
-------------------------------------------------

The `egrep' utility searches files for patterns.  It uses regular
expressions that are almost identical to those available in `awk'
(*note Regexp::).  It is used in the following manner:

     egrep [ OPTIONS ] 'PATTERN' FILES ...

The PATTERN is a regular expression.  In typical usage, the regular
expression is quoted to prevent the shell from expanding any of the
special characters as file name wildcards.  Normally, `egrep' prints
the lines that matched.  If multiple file names are provided on the
command line, each output line is preceded by the name of the file and
a colon.

The options to `egrep' are as follows:

`-c'
     Print out a count of the lines that matched the pattern, instead
     of the lines themselves.

`-s'
     Be silent.  No output is produced and the exit value indicates
     whether the pattern was matched.

`-v'
     Invert the sense of the test. `egrep' prints the lines that do
     _not_ match the pattern and exits successfully if the pattern is
     not matched.

`-i'
     Ignore case distinctions in both the pattern and the input data.

`-l'
     Only print (list) the names of the files that matched, not the
     lines that matched.

`-e PATTERN'
     Use PATTERN as the regexp to match.  The purpose of the `-e'
     option is to allow patterns that start with a `-'.

This version uses the `getopt' library function (*note Getopt
Function::) and the file transition library program (*note Filetrans
Function::).

The program begins with a descriptive comment and then a `BEGIN' rule
that processes the command-line arguments with `getopt'.  The `-i'
(ignore case) option is particularly easy with `gawk'; we just use the
`IGNORECASE' built-in variable (*note Built-in Variables::):

     # egrep.awk --- simulate egrep in awk
     # Options:
     #    -c    count of lines
     #    -s    silent - use exit value
     #    -v    invert test, success if no match
     #    -i    ignore case
     #    -l    print filenames only
     #    -e    argument is pattern
     #
     # Requires getopt and file transition library functions

     BEGIN {
         while ((c = getopt(ARGC, ARGV, "ce:svil")) != -1) {
             if (c == "c")
                 count_only++
             else if (c == "s")
                 no_print++
             else if (c == "v")
                 invert++
             else if (c == "i")
                 IGNORECASE = 1
             else if (c == "l")
                 filenames_only++
             else if (c == "e")
                 pattern = Optarg
             else
                 usage()
         }

Next comes the code that handles the `egrep'-specific behavior. If no
pattern is supplied with `-e', the first nonoption on the command line
is used.  The `awk' command-line arguments up to `ARGV[Optind]' are
cleared, so that `awk' won't try to process them as files.  If no files
are specified, the standard input is used, and if multiple files are
specified, we make sure to note this so that the file names can precede
the matched lines in the output:

         if (pattern == "")
             pattern = ARGV[Optind++]

         for (i = 1; i < Optind; i++)
             ARGV[i] = ""
         if (Optind >= ARGC) {
             ARGV[1] = "-"
             ARGC = 2
         } else if (ARGC - Optind > 1)
             do_filenames++

     #    if (IGNORECASE)
     #        pattern = tolower(pattern)
     }

The last two lines are commented out, since they are not needed in
`gawk'.  They should be uncommented if you have to use another version
of `awk'.

The next set of lines should be uncommented if you are not using
`gawk'.  This rule translates all the characters in the input line into
lowercase if the `-i' option is specified.(1) The rule is commented out
since it is not necessary with `gawk':

     #{
     #    if (IGNORECASE)
     #        $0 = tolower($0)
     #}

The `beginfile' function is called by the rule in `ftrans.awk' when
each new file is processed.  In this case, it is very simple; all it
does is initialize a variable `fcount' to zero. `fcount' tracks how
many lines in the current file matched the pattern (naming the
parameter `junk' shows we know that `beginfile' is called with a
parameter, but that we're not interested in its value):

     function beginfile(junk)
     {
         fcount = 0
     }

The `endfile' function is called after each file has been processed.
It affects the output only when the user wants a count of the number of
lines that matched.  `no_print' is true only if the exit status is
desired.  `count_only' is true if line counts are desired.  `egrep'
therefore only prints line counts if printing and counting are enabled.
The output format must be adjusted depending upon the number of files to
process.  Finally, `fcount' is added to `total', so that we know the
total number of lines that matched the pattern:

     function endfile(file)
     {
         if (! no_print && count_only)
             if (do_filenames)
                 print file ":" fcount
             else
                 print fcount

         total += fcount
     }

The following rule does most of the work of matching lines. The variable
`matches' is true if the line matched the pattern. If the user wants
lines that did not match, the sense of `matches' is inverted using the
`!' operator. `fcount' is incremented with the value of `matches',
which is either one or zero, depending upon a successful or
unsuccessful match.  If the line does not match, the `next' statement
just moves on to the next record.

A number of additional tests are made, but they are only done if we are
not counting lines.  First, if the user only wants exit status
(`no_print' is true), then it is enough to know that _one_ line in this
file matched, and we can skip on to the next file with `nextfile'.
Similarly, if we are only printing file names, we can print the file
name, and then skip to the next file with `nextfile'.  Finally, each
line is printed, with a leading file name and colon if necessary:

     {
         matches = ($0 ~ pattern)
         if (invert)
             matches = ! matches

         fcount += matches    # 1 or 0

         if (! matches)
             next

         if (! count_only) {
             if (no_print)
                 nextfile

             if (filenames_only) {
                 print FILENAME
                 nextfile
             }

             if (do_filenames)
                 print FILENAME ":" $0
             else
                 print
         }
     }

The `END' rule takes care of producing the correct exit status. If
there are no matches, the exit status is one; otherwise it is zero:

     END    \
     {
         if (total == 0)
             exit 1
         exit 0
     }

The `usage' function prints a usage message in case of invalid options,
and then exits:

     function usage(    e)
     {
         e = "Usage: egrep [-csvil] [-e pat] [files ...]"
         e = e "\n\tegrep [-csvil] pat [files ...]"
         print e > "/dev/stderr"
         exit 1
     }

The variable `e' is used so that the function fits nicely on the
printed page.

Just a note on programming style: you may have noticed that the `END'
rule uses backslash continuation, with the open brace on a line by
itself.  This is so that it more closely resembles the way functions
are written.  Many of the examples in this major node use this style.
You can decide for yourself if you like writing your `BEGIN' and `END'
rules this way or not.

---------- Footnotes ----------

(1) It also introduces a subtle bug; if a match happens, we output the
translated line, not the original.


File: gawk.info,  Node: Id Program,  Next: Split Program,  Prev: Egrep Program,  Up: Clones

13.2.3 Printing out User Information
------------------------------------

The `id' utility lists a user's real and effective user ID numbers,
real and effective group ID numbers, and the user's group set, if any.
`id' only prints the effective user ID and group ID if they are
different from the real ones.  If possible, `id' also supplies the
corresponding user and group names.  The output might look like this:

     $ id
     -| uid=2076(arnold) gid=10(staff) groups=10(staff),4(tty)

This information is part of what is provided by `gawk''s `PROCINFO'
array (*note Built-in Variables::).  However, the `id' utility provides
a more palatable output than just individual numbers.

Here is a simple version of `id' written in `awk'.  It uses the user
database library functions (*note Passwd Functions::) and the group
database library functions (*note Group Functions::):

The program is fairly straightforward.  All the work is done in the
`BEGIN' rule.  The user and group ID numbers are obtained from
`PROCINFO'.  The code is repetitive.  The entry in the user database
for the real user ID number is split into parts at the `:'. The name is
the first field.  Similar code is used for the effective user ID number
and the group numbers:

     # id.awk --- implement id in awk
     #
     # Requires user and group library functions
     # output is:
     # uid=12(foo) euid=34(bar) gid=3(baz) \
     #             egid=5(blat) groups=9(nine),2(two),1(one)

     BEGIN    \
     {
         uid = PROCINFO["uid"]
         euid = PROCINFO["euid"]
         gid = PROCINFO["gid"]
         egid = PROCINFO["egid"]

         printf("uid=%d", uid)
         pw = getpwuid(uid)
         if (pw != "") {
             split(pw, a, ":")
             printf("(%s)", a[1])
         }

         if (euid != uid) {
             printf(" euid=%d", euid)
             pw = getpwuid(euid)
             if (pw != "") {
                 split(pw, a, ":")
                 printf("(%s)", a[1])
             }
         }

         printf(" gid=%d", gid)
         pw = getgrgid(gid)
         if (pw != "") {
             split(pw, a, ":")
             printf("(%s)", a[1])
         }

         if (egid != gid) {
             printf(" egid=%d", egid)
             pw = getgrgid(egid)
             if (pw != "") {
                 split(pw, a, ":")
                 printf("(%s)", a[1])
             }
         }

         for (i = 1; ("group" i) in PROCINFO; i++) {
             if (i == 1)
                 printf(" groups=")
             group = PROCINFO["group" i]
             printf("%d", group)
             pw = getgrgid(group)
             if (pw != "") {
                 split(pw, a, ":")
                 printf("(%s)", a[1])
             }
             if (("group" (i+1)) in PROCINFO)
                 printf(",")
         }

         print ""
     }

The test in the `for' loop is worth noting.  Any supplementary groups
in the `PROCINFO' array have the indices `"group1"' through `"groupN"'
for some N, i.e., the total number of supplementary groups.  However,
we don't know in advance how many of these groups there are.

This loop works by starting at one, concatenating the value with
`"group"', and then using `in' to see if that value is in the array.
Eventually, `i' is incremented past the last group in the array and the
loop exits.

The loop is also correct if there are _no_ supplementary groups; then
the condition is false the first time it's tested, and the loop body
never executes.


File: gawk.info,  Node: Split Program,  Next: Tee Program,  Prev: Id Program,  Up: Clones

13.2.4 Splitting a Large File into Pieces
-----------------------------------------

The `split' program splits large text files into smaller pieces.  Usage
is as follows:

     split [-COUNT] file [ PREFIX ]

By default, the output files are named `xaa', `xab', and so on. Each
file has 1000 lines in it, with the likely exception of the last file.
To change the number of lines in each file, supply a number on the
command line preceded with a minus; e.g., `-500' for files with 500
lines in them instead of 1000.  To change the name of the output files
to something like `myfileaa', `myfileab', and so on, supply an
additional argument that specifies the file name prefix.

Here is a version of `split' in `awk'. It uses the `ord' and `chr'
functions presented in *Note Ordinal Functions::.

The program first sets its defaults, and then tests to make sure there
are not too many arguments.  It then looks at each argument in turn.
The first argument could be a minus sign followed by a number. If it
is, this happens to look like a negative number, so it is made
positive, and that is the count of lines.  The data file name is
skipped over and the final argument is used as the prefix for the
output file names:

     # split.awk --- do split in awk
     #
     # Requires ord and chr library functions
     # usage: split [-num] [file] [outname]

     BEGIN {
         outfile = "x"    # default
         count = 1000
         if (ARGC > 4)
             usage()

         i = 1
         if (ARGV[i] ~ /^-[0-9]+$/) {
             count = -ARGV[i]
             ARGV[i] = ""
             i++
         }
         # test argv in case reading from stdin instead of file
         if (i in ARGV)
             i++    # skip data file name
         if (i in ARGV) {
             outfile = ARGV[i]
             ARGV[i] = ""
         }

         s1 = s2 = "a"
         out = (outfile s1 s2)
     }

The next rule does most of the work. `tcount' (temporary count) tracks
how many lines have been printed to the output file so far. If it is
greater than `count', it is time to close the current file and start a
new one.  `s1' and `s2' track the current suffixes for the file name. If
they are both `z', the file is just too big.  Otherwise, `s1' moves to
the next letter in the alphabet and `s2' starts over again at `a':

     {
         if (++tcount > count) {
             close(out)
             if (s2 == "z") {
                 if (s1 == "z") {
                     printf("split: %s is too large to split\n",
                            FILENAME) > "/dev/stderr"
                     exit 1
                 }
                 s1 = chr(ord(s1) + 1)
                 s2 = "a"
             }
             else
                 s2 = chr(ord(s2) + 1)
             out = (outfile s1 s2)
             tcount = 1
         }
         print > out
     }

The `usage' function simply prints an error message and exits:

     function usage(   e)
     {
         e = "usage: split [-num] [file] [outname]"
         print e > "/dev/stderr"
         exit 1
     }

The variable `e' is used so that the function fits nicely on the screen.

This program is a bit sloppy; it relies on `awk' to automatically close
the last file instead of doing it in an `END' rule.  It also assumes
that letters are contiguous in the character set, which isn't true for
EBCDIC systems.


File: gawk.info,  Node: Tee Program,  Next: Uniq Program,  Prev: Split Program,  Up: Clones

13.2.5 Duplicating Output into Multiple Files
---------------------------------------------

The `tee' program is known as a "pipe fitting."  `tee' copies its
standard input to its standard output and also duplicates it to the
files named on the command line.  Its usage is as follows:

     tee [-a] file ...

The `-a' option tells `tee' to append to the named files, instead of
truncating them and starting over.

The `BEGIN' rule first makes a copy of all the command-line arguments
into an array named `copy'.  `ARGV[0]' is not copied, since it is not
needed.  `tee' cannot use `ARGV' directly, since `awk' attempts to
process each file name in `ARGV' as input data.

If the first argument is `-a', then the flag variable `append' is set
to true, and both `ARGV[1]' and `copy[1]' are deleted. If `ARGC' is
less than two, then no file names were supplied and `tee' prints a
usage message and exits.  Finally, `awk' is forced to read the standard
input by setting `ARGV[1]' to `"-"' and `ARGC' to two:

     # tee.awk --- tee in awk
     BEGIN    \
     {
         for (i = 1; i < ARGC; i++)
             copy[i] = ARGV[i]

         if (ARGV[1] == "-a") {
             append = 1
             delete ARGV[1]
             delete copy[1]
             ARGC--
         }
         if (ARGC < 2) {
             print "usage: tee [-a] file ..." > "/dev/stderr"
             exit 1
         }
         ARGV[1] = "-"
         ARGC = 2
     }

The single rule does all the work.  Since there is no pattern, it is
executed for each line of input.  The body of the rule simply prints the
line into each file on the command line, and then to the standard
output:

     {
         # moving the if outside the loop makes it run faster
         if (append)
             for (i in copy)
                 print >> copy[i]
         else
             for (i in copy)
                 print > copy[i]
         print
     }

It is also possible to write the loop this way:

     for (i in copy)
         if (append)
             print >> copy[i]
         else
             print > copy[i]

This is more concise but it is also less efficient.  The `if' is tested
for each record and for each output file.  By duplicating the loop
body, the `if' is only tested once for each input record.  If there are
N input records and M output files, the first method only executes N
`if' statements, while the second executes N`*'M `if' statements.

Finally, the `END' rule cleans up by closing all the output files:

     END    \
     {
         for (i in copy)
             close(copy[i])
     }


File: gawk.info,  Node: Uniq Program,  Next: Wc Program,  Prev: Tee Program,  Up: Clones

13.2.6 Printing Nonduplicated Lines of Text
-------------------------------------------

The `uniq' utility reads sorted lines of data on its standard input,
and by default removes duplicate lines.  In other words, it only prints
unique lines--hence the name.  `uniq' has a number of options. The
usage is as follows:

     uniq [-udc [-N]] [+N] [ INPUT FILE [ OUTPUT FILE ]]

The options for `uniq' are:

`-d'
     Pnly print only repeated lines.

`-u'
     Print only nonrepeated lines.

`-c'
     Count lines. This option overrides `-d' and `-u'.  Both repeated
     and nonrepeated lines are counted.

`-N'
     Skip N fields before comparing lines.  The definition of fields is
     similar to `awk''s default: nonwhitespace characters separated by
     runs of spaces and/or tabs.

`+N'
     Skip N characters before comparing lines.  Any fields specified
     with `-N' are skipped first.

`INPUT FILE'
     Data is read from the input file named on the command line,
     instead of from the standard input.

`OUTPUT FILE'
     The generated output is sent to the named output file, instead of
     to the standard output.

Normally `uniq' behaves as if both the `-d' and `-u' options are
provided.

`uniq' uses the `getopt' library function (*note Getopt Function::) and
the `join' library function (*note Join Function::).

The program begins with a `usage' function and then a brief outline of
the options and their meanings in a comment.  The `BEGIN' rule deals
with the command-line arguments and options. It uses a trick to get
`getopt' to handle options of the form `-25', treating such an option
as the option letter `2' with an argument of `5'. If indeed two or more
digits are supplied (`Optarg' looks like a number), `Optarg' is
concatenated with the option digit and then the result is added to zero
to make it into a number.  If there is only one digit in the option,
then `Optarg' is not needed. In this case, `Optind' must be decremented
so that `getopt' processes it next time.  This code is admittedly a bit
tricky.

If no options are supplied, then the default is taken, to print both
repeated and nonrepeated lines.  The output file, if provided, is
assigned to `outputfile'.  Early on, `outputfile' is initialized to the
standard output, `/dev/stdout':

     # uniq.awk --- do uniq in awk
     #
     # Requires getopt and join library functions
     function usage(    e)
     {
         e = "Usage: uniq [-udc [-n]] [+n] [ in [ out ]]"
         print e > "/dev/stderr"
         exit 1
     }

     # -c    count lines. overrides -d and -u
     # -d    only repeated lines
     # -u    only non-repeated lines
     # -n    skip n fields
     # +n    skip n characters, skip fields first

     BEGIN   \
     {
         count = 1
         outputfile = "/dev/stdout"
         opts = "udc0:1:2:3:4:5:6:7:8:9:"
         while ((c = getopt(ARGC, ARGV, opts)) != -1) {
             if (c == "u")
                 non_repeated_only++
             else if (c == "d")
                 repeated_only++
             else if (c == "c")
                 do_count++
             else if (index("0123456789", c) != 0) {
                 # getopt requires args to options
                 # this messes us up for things like -5
                 if (Optarg ~ /^[0-9]+$/)
                     fcount = (c Optarg) + 0
                 else {
                     fcount = c + 0
                     Optind--
                 }
             } else
                 usage()
         }

         if (ARGV[Optind] ~ /^\+[0-9]+$/) {
             charcount = substr(ARGV[Optind], 2) + 0
             Optind++
         }

         for (i = 1; i < Optind; i++)
             ARGV[i] = ""

         if (repeated_only == 0 && non_repeated_only == 0)
             repeated_only = non_repeated_only = 1

         if (ARGC - Optind == 2) {
             outputfile = ARGV[ARGC - 1]
             ARGV[ARGC - 1] = ""
         }
     }

The following function, `are_equal', compares the current line, `$0',
to the previous line, `last'.  It handles skipping fields and
characters.  If no field count and no character count are specified,
`are_equal' simply returns one or zero depending upon the result of a
simple string comparison of `last' and `$0'.  Otherwise, things get more
complicated.  If fields have to be skipped, each line is broken into an
array using `split' (*note String Functions::); the desired fields are
then joined back into a line using `join'.  The joined lines are stored
in `clast' and `cline'.  If no fields are skipped, `clast' and `cline'
are set to `last' and `$0', respectively.  Finally, if characters are
skipped, `substr' is used to strip off the leading `charcount'
characters in `clast' and `cline'.  The two strings are then compared
and `are_equal' returns the result:

     function are_equal(    n, m, clast, cline, alast, aline)
     {
         if (fcount == 0 && charcount == 0)
             return (last == $0)

         if (fcount > 0) {
             n = split(last, alast)
             m = split($0, aline)
             clast = join(alast, fcount+1, n)
             cline = join(aline, fcount+1, m)
         } else {
             clast = last
             cline = $0
         }
         if (charcount) {
             clast = substr(clast, charcount + 1)
             cline = substr(cline, charcount + 1)
         }

         return (clast == cline)
     }

The following two rules are the body of the program.  The first one is
executed only for the very first line of data.  It sets `last' equal to
`$0', so that subsequent lines of text have something to be compared to.

The second rule does the work. The variable `equal' is one or zero,
depending upon the results of `are_equal''s comparison. If `uniq' is
counting repeated lines, and the lines are equal, then it increments
the `count' variable.  Otherwise, it prints the line and resets `count',
since the two lines are not equal.

If `uniq' is not counting, and if the lines are equal, `count' is
incremented.  Nothing is printed, since the point is to remove
duplicates.  Otherwise, if `uniq' is counting repeated lines and more
than one line is seen, or if `uniq' is counting nonrepeated lines and
only one line is seen, then the line is printed, and `count' is reset.

Finally, similar logic is used in the `END' rule to print the final
line of input data:

     NR == 1 {
         last = $0
         next
     }

     {
         equal = are_equal()

         if (do_count) {    # overrides -d and -u
             if (equal)
                 count++
             else {
                 printf("%4d %s\n", count, last) > outputfile
                 last = $0
                 count = 1    # reset
             }
             next
         }

         if (equal)
             count++
         else {
             if ((repeated_only && count > 1) ||
                 (non_repeated_only && count == 1))
                     print last > outputfile
             last = $0
             count = 1
         }
     }

     END {
         if (do_count)
             printf("%4d %s\n", count, last) > outputfile
         else if ((repeated_only && count > 1) ||
                 (non_repeated_only && count == 1))
             print last > outputfile
     }


File: gawk.info,  Node: Wc Program,  Prev: Uniq Program,  Up: Clones

13.2.7 Counting Things
----------------------

The `wc' (word count) utility counts lines, words, and characters in
one or more input files. Its usage is as follows:

     wc [-lwc] [ FILES ... ]

If no files are specified on the command line, `wc' reads its standard
input. If there are multiple files, it also prints total counts for all
the files.  The options and their meanings are shown in the following
list:

`-l'
     Count only lines.

`-w'
     Count only words.  A "word" is a contiguous sequence of
     nonwhitespace characters, separated by spaces and/or tabs.
     Luckily, this is the normal way `awk' separates fields in its
     input data.

`-c'
     Count only characters.

Implementing `wc' in `awk' is particularly elegant, since `awk' does a
lot of the work for us; it splits lines into words (i.e., fields) and
counts them, it counts lines (i.e., records), and it can easily tell us
how long a line is.

This uses the `getopt' library function (*note Getopt Function::) and
the file-transition functions (*note Filetrans Function::).

This version has one notable difference from traditional versions of
`wc': it always prints the counts in the order lines, words, and
characters.  Traditional versions note the order of the `-l', `-w', and
`-c' options on the command line, and print the counts in that order.

The `BEGIN' rule does the argument processing.  The variable
`print_total' is true if more than one file is named on the command
line:

     # wc.awk --- count lines, words, characters

     # Options:
     #    -l    only count lines
     #    -w    only count words
     #    -c    only count characters
     #
     # Default is to count lines, words, characters
     #
     # Requires getopt and file transition library functions

     BEGIN {
         # let getopt print a message about
         # invalid options. we ignore them
         while ((c = getopt(ARGC, ARGV, "lwc")) != -1) {
             if (c == "l")
                 do_lines = 1
             else if (c == "w")
                 do_words = 1
             else if (c == "c")
                 do_chars = 1
         }
         for (i = 1; i < Optind; i++)
             ARGV[i] = ""

         # if no options, do all
         if (! do_lines && ! do_words && ! do_chars)
             do_lines = do_words = do_chars = 1

         print_total = (ARGC - i > 2)
     }

The `beginfile' function is simple; it just resets the counts of lines,
words, and characters to zero, and saves the current file name in
`fname':

     function beginfile(file)
     {
         chars = lines = words = 0
         fname = FILENAME
     }

The `endfile' function adds the current file's numbers to the running
totals of lines, words, and characters.(1)  It then prints out those
numbers for the file that was just read. It relies on `beginfile' to
reset the numbers for the following data file:

     function endfile(file)
     {
         tchars += chars
         tlines += lines
         twords += words
         if (do_lines)
             printf "\t%d", lines
         if (do_words)
             printf "\t%d", words
         if (do_chars)
             printf "\t%d", chars
         printf "\t%s\n", fname
     }

There is one rule that is executed for each line. It adds the length of
the record, plus one, to `chars'.  Adding one plus the record length is
needed because the newline character separating records (the value of
`RS') is not part of the record itself, and thus not included in its
length.  Next, `lines' is incremented for each line read, and `words'
is incremented by the value of `NF', which is the number of "words" on
this line:

     # do per line
     {
         chars += length($0) + 1    # get newline
         lines++
         words += NF
     }

Finally, the `END' rule simply prints the totals for all the files:

     END {
         if (print_total) {
             if (do_lines)
                 printf "\t%d", tlines
             if (do_words)
                 printf "\t%d", twords
             if (do_chars)
                 printf "\t%d", tchars
             print "\ttotal"
         }
     }

---------- Footnotes ----------

(1) `wc' can't just use the value of `FNR' in `endfile'. If you examine
the code in *Note Filetrans Function::, you will see that `FNR' has
already been reset by the time `endfile' is called.


File: gawk.info,  Node: Miscellaneous Programs,  Prev: Clones,  Up: Sample Programs

13.3 A Grab Bag of `awk' Programs
=================================

This minor node is a large "grab bag" of miscellaneous programs.  We
hope you find them both interesting and enjoyable.

* Menu:

* Dupword Program::             Finding duplicated words in a document.
* Alarm Program::               An alarm clock.
* Translate Program::           A program similar to the `tr' utility.
* Labels Program::              Printing mailing labels.
* Word Sorting::                A program to produce a word usage count.
* History Sorting::             Eliminating duplicate entries from a history
                                file.
* Extract Program::             Pulling out programs from Texinfo source
                                files.
* Simple Sed::                  A Simple Stream Editor.
* Igawk Program::               A wrapper for `awk' that includes
                                files.


File: gawk.info,  Node: Dupword Program,  Next: Alarm Program,  Up: Miscellaneous Programs

13.3.1 Finding Duplicated Words in a Document
---------------------------------------------

A common error when writing large amounts of prose is to accidentally
duplicate words.  Typically you will see this in text as something like
"the the program does the following..."  When the text is online, often
the duplicated words occur at the end of one line and the beginning of
another, making them very difficult to spot.

This program, `dupword.awk', scans through a file one line at a time
and looks for adjacent occurrences of the same word.  It also saves the
last word on a line (in the variable `prev') for comparison with the
first word on the next line.

The first two statements make sure that the line is all lowercase, so
that, for example, "The" and "the" compare equal to each other.  The
next statement replaces nonalphanumeric and nonwhitespace characters
with spaces, so that punctuation does not affect the comparison either.
The characters are replaced with spaces so that formatting controls
don't create nonsense words (e.g., the Texinfo `@code{NF}' becomes
`codeNF' if punctuation is simply deleted).  The record is then resplit
into fields, yielding just the actual words on the line, and ensuring
that there are no empty fields.

If there are no fields left after removing all the punctuation, the
current record is skipped.  Otherwise, the program loops through each
word, comparing it to the previous one:

     # dupword.awk --- find duplicate words in text
     {
         $0 = tolower($0)
         gsub(/[^[:alnum:][:blank:]]/, " ");
         $0 = $0         # re-split
         if (NF == 0)
             next
         if ($1 == prev)
             printf("%s:%d: duplicate %s\n",
                 FILENAME, FNR, $1)
         for (i = 2; i <= NF; i++)
             if ($i == $(i-1))
                 printf("%s:%d: duplicate %s\n",
                     FILENAME, FNR, $i)
         prev = $NF
     }


File: gawk.info,  Node: Alarm Program,  Next: Translate Program,  Prev: Dupword Program,  Up: Miscellaneous Programs

13.3.2 An Alarm Clock Program
-----------------------------

     Nothing cures insomnia like a ringing alarm clock.
     Arnold Robbins

The following program is a simple "alarm clock" program.  You give it a
time of day and an optional message.  At the specified time, it prints
the message on the standard output. In addition, you can give it the
number of times to repeat the message as well as a delay between
repetitions.

This program uses the `gettimeofday' function from *Note Gettimeofday
Function::.

All the work is done in the `BEGIN' rule.  The first part is argument
checking and setting of defaults: the delay, the count, and the message
to print.  If the user supplied a message without the ASCII BEL
character (known as the "alert" character, `"\a"'), then it is added to
the message.  (On many systems, printing the ASCII BEL generates an
audible alert. Thus when the alarm goes off, the system calls attention
to itself in case the user is not looking at the computer or terminal.)
Here is the program:

     # alarm.awk --- set an alarm
     #
     # Requires gettimeofday library function
     # usage: alarm time [ "message" [ count [ delay ] ] ]

     BEGIN    \
     {
         # Initial argument sanity checking
         usage1 = "usage: alarm time ['message' [count [delay]]]"
         usage2 = sprintf("\t(%s) time ::= hh:mm", ARGV[1])

         if (ARGC < 2) {
             print usage1 > "/dev/stderr"
             print usage2 > "/dev/stderr"
             exit 1
         } else if (ARGC == 5) {
             delay = ARGV[4] + 0
             count = ARGV[3] + 0
             message = ARGV[2]
         } else if (ARGC == 4) {
             count = ARGV[3] + 0
             message = ARGV[2]
         } else if (ARGC == 3) {
             message = ARGV[2]
         } else if (ARGV[1] !~ /[0-9]?[0-9]:[0-9][0-9]/) {
             print usage1 > "/dev/stderr"
             print usage2 > "/dev/stderr"
             exit 1
         }

         # set defaults for once we reach the desired time
         if (delay == 0)
             delay = 180    # 3 minutes
         if (count == 0)
             count = 5
         if (message == "")
             message = sprintf("\aIt is now %s!\a", ARGV[1])
         else if (index(message, "\a") == 0)
             message = "\a" message "\a"

The next minor node of code turns the alarm time into hours and minutes,
converts it (if necessary) to a 24-hour clock, and then turns that time
into a count of the seconds since midnight.  Next it turns the current
time into a count of seconds since midnight.  The difference between
the two is how long to wait before setting off the alarm:

         # split up alarm time
         split(ARGV[1], atime, ":")
         hour = atime[1] + 0    # force numeric
         minute = atime[2] + 0  # force numeric

         # get current broken down time
         gettimeofday(now)

         # if time given is 12-hour hours and it's after that
         # hour, e.g., `alarm 5:30' at 9 a.m. means 5:30 p.m.,
         # then add 12 to real hour
         if (hour < 12 && now["hour"] > hour)
             hour += 12

         # set target time in seconds since midnight
         target = (hour * 60 * 60) + (minute * 60)

         # get current time in seconds since midnight
         current = (now["hour"] * 60 * 60) + \
                    (now["minute"] * 60) + now["second"]

         # how long to sleep for
         naptime = target - current
         if (naptime <= 0) {
             print "time is in the past!" > "/dev/stderr"
             exit 1
         }

Finally, the program uses the `system' function (*note I/O Functions::)
to call the `sleep' utility.  The `sleep' utility simply pauses for the
given number of seconds.  If the exit status is not zero, the program
assumes that `sleep' was interrupted and exits. If `sleep' exited with
an OK status (zero), then the program prints the message in a loop,
again using `sleep' to delay for however many seconds are necessary:

         # zzzzzz..... go away if interrupted
         if (system(sprintf("sleep %d", naptime)) != 0)
             exit 1

         # time to notify!
         command = sprintf("sleep %d", delay)
         for (i = 1; i <= count; i++) {
             print message
             # if sleep command interrupted, go away
             if (system(command) != 0)
                 break
         }

         exit 0
     }


File: gawk.info,  Node: Translate Program,  Next: Labels Program,  Prev: Alarm Program,  Up: Miscellaneous Programs

13.3.3 Transliterating Characters
---------------------------------

The system `tr' utility transliterates characters.  For example, it is
often used to map uppercase letters into lowercase for further
processing:

     GENERATE DATA | tr 'A-Z' 'a-z' | PROCESS DATA ...

`tr' requires two lists of characters.(1)  When processing the input,
the first character in the first list is replaced with the first
character in the second list, the second character in the first list is
replaced with the second character in the second list, and so on.  If
there are more characters in the "from" list than in the "to" list, the
last character of the "to" list is used for the remaining characters in
the "from" list.

Some time ago, a user proposed that a transliteration function should
be added to `gawk'.  The following program was written to prove that
character transliteration could be done with a user-level function.
This program is not as complete as the system `tr' utility but it does
most of the job.

The `translate' program demonstrates one of the few weaknesses of
standard `awk': dealing with individual characters is very painful,
requiring repeated use of the `substr', `index', and `gsub' built-in
functions (*note String Functions::).(2) There are two functions.  The
first, `stranslate', takes three arguments:

`from'
     A list of characters from which to translate.

`to'
     A list of characters to which to translate.

`target'
     The string on which to do the translation.

Associative arrays make the translation part fairly easy. `t_ar' holds
the "to" characters, indexed by the "from" characters.  Then a simple
loop goes through `from', one character at a time.  For each character
in `from', if the character appears in `target', `gsub' is used to
change it to the corresponding `to' character.

The `translate' function simply calls `stranslate' using `$0' as the
target.  The main program sets two global variables, `FROM' and `TO',
from the command line, and then changes `ARGV' so that `awk' reads from
the standard input.

Finally, the processing rule simply calls `translate' for each record:

     # translate.awk --- do tr-like stuff
     # Bugs: does not handle things like: tr A-Z a-z, it has
     # to be spelled out. However, if `to' is shorter than `from',
     # the last character in `to' is used for the rest of `from'.

     function stranslate(from, to, target,     lf, lt, t_ar, i, c)
     {
         lf = length(from)
         lt = length(to)
         for (i = 1; i <= lt; i++)
             t_ar[substr(from, i, 1)] = substr(to, i, 1)
         if (lt < lf)
             for (; i <= lf; i++)
                 t_ar[substr(from, i, 1)] = substr(to, lt, 1)
         for (i = 1; i <= lf; i++) {
             c = substr(from, i, 1)
             if (index(target, c) > 0)
                 gsub(c, t_ar[c], target)
         }
         return target
     }

     function translate(from, to)
     {
         return $0 = stranslate(from, to, $0)
     }

     # main program
     BEGIN {
         if (ARGC < 3) {
             print "usage: translate from to" > "/dev/stderr"
             exit
         }
         FROM = ARGV[1]
         TO = ARGV[2]
         ARGC = 2
         ARGV[1] = "-"
     }

     {
         translate(FROM, TO)
         print
     }

While it is possible to do character transliteration in a user-level
function, it is not necessarily efficient, and we (the `gawk' authors)
started to consider adding a built-in function.  However, shortly after
writing this program, we learned that the System V Release 4 `awk' had
added the `toupper' and `tolower' functions (*note String Functions::).
These functions handle the vast majority of the cases where character
transliteration is necessary, and so we chose to simply add those
functions to `gawk' as well and then leave well enough alone.

An obvious improvement to this program would be to set up the `t_ar'
array only once, in a `BEGIN' rule. However, this assumes that the
"from" and "to" lists will never change throughout the lifetime of the
program.

---------- Footnotes ----------

(1) On some older System V systems, `tr' may require that the lists be
written as range expressions enclosed in square brackets (`[a-z]') and
quoted, to prevent the shell from attempting a file name expansion.
This is not a feature.

(2) This program was written before `gawk' acquired the ability to
split each character in a string into separate array elements.


File: gawk.info,  Node: Labels Program,  Next: Word Sorting,  Prev: Translate Program,  Up: Miscellaneous Programs

13.3.4 Printing Mailing Labels
------------------------------

Here is a "real world"(1) program.  This script reads lists of names and
addresses and generates mailing labels.  Each page of labels has 20
labels on it, 2 across and 10 down.  The addresses are guaranteed to be
no more than 5 lines of data.  Each address is separated from the next
by a blank line.

The basic idea is to read 20 labels worth of data.  Each line of each
label is stored in the `line' array.  The single rule takes care of
filling the `line' array and printing the page when 20 labels have been
read.

The `BEGIN' rule simply sets `RS' to the empty string, so that `awk'
splits records at blank lines (*note Records::).  It sets `MAXLINES' to
100, since 100 is the maximum number of lines on the page (20 * 5 =
100).

Most of the work is done in the `printpage' function.  The label lines
are stored sequentially in the `line' array.  But they have to print
horizontally; `line[1]' next to `line[6]', `line[2]' next to `line[7]',
and so on.  Two loops are used to accomplish this.  The outer loop,
controlled by `i', steps through every 10 lines of data; this is each
row of labels.  The inner loop, controlled by `j', goes through the
lines within the row.  As `j' goes from 0 to 4, `i+j' is the `j'-th
line in the row, and `i+j+5' is the entry next to it.  The output ends
up looking something like this:

     line 1          line 6
     line 2          line 7
     line 3          line 8
     line 4          line 9
     line 5          line 10
     ...

As a final note, an extra blank line is printed at lines 21 and 61, to
keep the output lined up on the labels.  This is dependent on the
particular brand of labels in use when the program was written.  You
will also note that there are 2 blank lines at the top and 2 blank
lines at the bottom.

The `END' rule arranges to flush the final page of labels; there may
not have been an even multiple of 20 labels in the data:

     # labels.awk --- print mailing labels

     # Each label is 5 lines of data that may have blank lines.
     # The label sheets have 2 blank lines at the top and 2 at
     # the bottom.

     BEGIN    { RS = "" ; MAXLINES = 100 }

     function printpage(    i, j)
     {
         if (Nlines <= 0)
             return

         printf "\n\n"        # header

         for (i = 1; i <= Nlines; i += 10) {
             if (i == 21 || i == 61)
                 print ""
             for (j = 0; j < 5; j++) {
                 if (i + j > MAXLINES)
                     break
                 printf "   %-41s %s\n", line[i+j], line[i+j+5]
             }
             print ""
         }

         printf "\n\n"        # footer

         for (i in line)
             line[i] = ""
     }

     # main rule
     {
         if (Count >= 20) {
             printpage()
             Count = 0
             Nlines = 0
         }
         n = split($0, a, "\n")
         for (i = 1; i <= n; i++)
             line[++Nlines] = a[i]
         for (; i <= 5; i++)
             line[++Nlines] = ""
         Count++
     }

     END    \
     {
         printpage()
     }

---------- Footnotes ----------

(1) "Real world" is defined as "a program actually used to get
something done."


File: gawk.info,  Node: Word Sorting,  Next: History Sorting,  Prev: Labels Program,  Up: Miscellaneous Programs

13.3.5 Generating Word-Usage Counts
-----------------------------------

The following `awk' program prints the number of occurrences of each
word in its input.  It illustrates the associative nature of `awk'
arrays by using strings as subscripts.  It also demonstrates the `for
INDEX in ARRAY' mechanism.  Finally, it shows how `awk' is used in
conjunction with other utility programs to do a useful task of some
complexity with a minimum of effort.  Some explanations follow the
program listing:

     # Print list of word frequencies
     {
         for (i = 1; i <= NF; i++)
             freq[$i]++
     }

     END {
         for (word in freq)
             printf "%s\t%d\n", word, freq[word]
     }

This program has two rules.  The first rule, because it has an empty
pattern, is executed for every input line.  It uses `awk''s
field-accessing mechanism (*note Fields::) to pick out the individual
words from the line, and the built-in variable `NF' (*note Built-in
Variables::) to know how many fields are available.  For each input
word, it increments an element of the array `freq' to reflect that the
word has been seen an additional time.

The second rule, because it has the pattern `END', is not executed
until the input has been exhausted.  It prints out the contents of the
`freq' table that has been built up inside the first action.  This
program has several problems that would prevent it from being useful by
itself on real text files:

   * Words are detected using the `awk' convention that fields are
     separated just by whitespace.  Other characters in the input
     (except newlines) don't have any special meaning to `awk'.  This
     means that punctuation characters count as part of words.

   * The `awk' language considers upper- and lowercase characters to be
     distinct.  Therefore, "bartender" and "Bartender" are not treated
     as the same word.  This is undesirable, since in normal text, words
     are capitalized if they begin sentences, and a frequency analyzer
     should not be sensitive to capitalization.

   * The output does not come out in any useful order.  You're more
     likely to be interested in which words occur most frequently or in
     having an alphabetized table of how frequently each word occurs.

The way to solve these problems is to use some of `awk''s more advanced
features.  First, we use `tolower' to remove case distinctions.  Next,
we use `gsub' to remove punctuation characters.  Finally, we use the
system `sort' utility to process the output of the `awk' script.  Here
is the new version of the program:

     # wordfreq.awk --- print list of word frequencies

     {
         $0 = tolower($0)    # remove case distinctions
         # remove punctuation
         gsub(/[^[:alnum:]_[:blank:]]/, "", $0)
         for (i = 1; i <= NF; i++)
             freq[$i]++
     }

     END {
         for (word in freq)
             printf "%s\t%d\n", word, freq[word]
     }

Assuming we have saved this program in a file named `wordfreq.awk', and
that the data is in `file1', the following pipeline:

     awk -f wordfreq.awk file1 | sort -k 2nr

produces a table of the words appearing in `file1' in order of
decreasing frequency.  The `awk' program suitably massages the data and
produces a word frequency table, which is not ordered.

The `awk' script's output is then sorted by the `sort' utility and
printed on the terminal.  The options given to `sort' specify a sort
that uses the second field of each input line (skipping one field),
that the sort keys should be treated as numeric quantities (otherwise
`15' would come before `5'), and that the sorting should be done in
descending (reverse) order.

The `sort' could even be done from within the program, by changing the
`END' action to:

     END {
         sort = "sort -k 2nr"
         for (word in freq)
             printf "%s\t%d\n", word, freq[word] | sort
         close(sort)
     }

This way of sorting must be used on systems that do not have true pipes
at the command-line (or batch-file) level.  See the general operating
system documentation for more information on how to use the `sort'
program.


File: gawk.info,  Node: History Sorting,  Next: Extract Program,  Prev: Word Sorting,  Up: Miscellaneous Programs

13.3.6 Removing Duplicates from Unsorted Text
---------------------------------------------

The `uniq' program (*note Uniq Program::), removes duplicate lines from
_sorted_ data.

Suppose, however, you need to remove duplicate lines from a data file
but that you want to preserve the order the lines are in.  A good
example of this might be a shell history file.  The history file keeps
a copy of all the commands you have entered, and it is not unusual to
repeat a command several times in a row.  Occasionally you might want
to compact the history by removing duplicate entries.  Yet it is
desirable to maintain the order of the original commands.

This simple program does the job.  It uses two arrays.  The `data'
array is indexed by the text of each line.  For each line, `data[$0]'
is incremented.  If a particular line has not been seen before, then
`data[$0]' is zero.  In this case, the text of the line is stored in
`lines[count]'.  Each element of `lines' is a unique command, and the
indices of `lines' indicate the order in which those lines are
encountered.  The `END' rule simply prints out the lines, in order:

     # histsort.awk --- compact a shell history file
     # Thanks to Byron Rakitzis for the general idea
     {
         if (data[$0]++ == 0)
             lines[++count] = $0
     }

     END {
         for (i = 1; i <= count; i++)
             print lines[i]
     }

This program also provides a foundation for generating other useful
information.  For example, using the following `print' statement in the
`END' rule indicates how often a particular command is used:

     print data[lines[i]], lines[i]

This works because `data[$0]' is incremented each time a line is seen.


File: gawk.info,  Node: Extract Program,  Next: Simple Sed,  Prev: History Sorting,  Up: Miscellaneous Programs

13.3.7 Extracting Programs from Texinfo Source Files
----------------------------------------------------

The nodes *Note Library Functions::, and *Note Sample Programs::, are
the top level nodes for a large number of `awk' programs.  If you want
to experiment with these programs, it is tedious to have to type them
in by hand.  Here we present a program that can extract parts of a
Texinfo input file into separate files.

This Info file is written in Texinfo, the GNU project's document
formatting language.  A single Texinfo source file can be used to
produce both printed and online documentation.  The Texinfo language is
described fully, starting with *Note Top::.

For our purposes, it is enough to know three things about Texinfo input
files:

   * The "at" symbol (`@') is special in Texinfo, much as the backslash
     (`\') is in C or `awk'.  Literal `@' symbols are represented in
     Texinfo source files as `@@'.

   * Comments start with either `@c' or `@comment'.  The
     file-extraction program works by using special comments that start
     at the beginning of a line.

   * Lines containing `@group' and `@end group' commands bracket
     example text that should not be split across a page boundary.
     (Unfortunately, TeX isn't always smart enough to do things exactly
     right, and we have to give it some help.)

The following program, `extract.awk', reads through a Texinfo source
file and does two things, based on the special comments.  Upon seeing
`@c system ...', it runs a command, by extracting the command text from
the control line and passing it on to the `system' function (*note I/O
Functions::).  Upon seeing `@c file FILENAME', each subsequent line is
sent to the file FILENAME, until `@c endfile' is encountered.  The
rules in `extract.awk' match either `@c' or `@comment' by letting the
`omment' part be optional.  Lines containing `@group' and `@end group'
are simply removed.  `extract.awk' uses the `join' library function
(*note Join Function::).

The example programs in the online Texinfo source for `GAWK: Effective
AWK Programming' (`gawk.texi') have all been bracketed inside `file' and
`endfile' lines.  The `gawk' distribution uses a copy of `extract.awk'
to extract the sample programs and install many of them in a standard
directory where `gawk' can find them.  The Texinfo file looks something
like this:

     ...
     This program has a @code{BEGIN} rule,
     that prints a nice message:

     @example
     @c file examples/messages.awk
     BEGIN @{ print "Don't panic!" @}
     @c end file
     @end example

     It also prints some final advice:

     @example
     @c file examples/messages.awk
     END @{ print "Always avoid bored archeologists!" @}
     @c end file
     @end example
     ...

`extract.awk' begins by setting `IGNORECASE' to one, so that mixed
upper- and lowercase letters in the directives won't matter.

The first rule handles calling `system', checking that a command is
given (`NF' is at least three) and also checking that the command exits
with a zero exit status, signifying OK:

     # extract.awk --- extract files and run programs
     #                 from texinfo files
     BEGIN    { IGNORECASE = 1 }

     /^@c(omment)?[ \t]+system/    \
     {
         if (NF < 3) {
             e = (FILENAME ":" FNR)
             e = (e  ": badly formed `system' line")
             print e > "/dev/stderr"
             next
         }
         $1 = ""
         $2 = ""
         stat = system($0)
         if (stat != 0) {
             e = (FILENAME ":" FNR)
             e = (e ": warning: system returned " stat)
             print e > "/dev/stderr"
         }
     }

The variable `e' is used so that the function fits nicely on the screen.

The second rule handles moving data into files.  It verifies that a
file name is given in the directive.  If the file named is not the
current file, then the current file is closed.  Keeping the current file
open until a new file is encountered allows the use of the `>'
redirection for printing the contents, keeping open file management
simple.

The `for' loop does the work.  It reads lines using `getline' (*note
Getline::).  For an unexpected end of file, it calls the
`unexpected_eof' function.  If the line is an "endfile" line, then it
breaks out of the loop.  If the line is an `@group' or `@end group'
line, then it ignores it and goes on to the next line.  Similarly,
comments within examples are also ignored.

Most of the work is in the following few lines.  If the line has no `@'
symbols, the program can print it directly.  Otherwise, each leading
`@' must be stripped off.  To remove the `@' symbols, the line is split
into separate elements of the array `a', using the `split' function
(*note String Functions::).  The `@' symbol is used as the separator
character.  Each element of `a' that is empty indicates two successive
`@' symbols in the original line.  For each two empty elements (`@@' in
the original file), we have to add a single `@' symbol back in.

When the processing of the array is finished, `join' is called with the
value of `SUBSEP', to rejoin the pieces back into a single line.  That
line is then printed to the output file:

     /^@c(omment)?[ \t]+file/    \
     {
         if (NF != 3) {
             e = (FILENAME ":" FNR ": badly formed `file' line")
             print e > "/dev/stderr"
             next
         }
         if ($3 != curfile) {
             if (curfile != "")
                 close(curfile)
             curfile = $3
         }

         for (;;) {
             if ((getline line) <= 0)
                 unexpected_eof()
             if (line ~ /^@c(omment)?[ \t]+endfile/)
                 break
             else if (line ~ /^@(end[ \t]+)?group/)
                 continue
             else if (line ~ /^@c(omment+)?[ \t]+/)
                 continue
             if (index(line, "@") == 0) {
                 print line > curfile
                 continue
             }
             n = split(line, a, "@")
             # if a[1] == "", means leading @,
             # don't add one back in.
             for (i = 2; i <= n; i++) {
                 if (a[i] == "") { # was an @@
                     a[i] = "@"
                     if (a[i+1] == "")
                         i++
                 }
             }
             print join(a, 1, n, SUBSEP) > curfile
         }
     }

An important thing to note is the use of the `>' redirection.  Output
done with `>' only opens the file once; it stays open and subsequent
output is appended to the file (*note Redirection::).  This makes it
easy to mix program text and explanatory prose for the same sample
source file (as has been done here!) without any hassle.  The file is
only closed when a new data file name is encountered or at the end of
the input file.

Finally, the function `unexpected_eof' prints an appropriate error
message and then exits.  The `END' rule handles the final cleanup,
closing the open file:

     function unexpected_eof() {
         printf("%s:%d: unexpected EOF or error\n",
             FILENAME, FNR) > "/dev/stderr"
         exit 1
     }

     END {
         if (curfile)
             close(curfile)
     }


File: gawk.info,  Node: Simple Sed,  Next: Igawk Program,  Prev: Extract Program,  Up: Miscellaneous Programs

13.3.8 A Simple Stream Editor
-----------------------------

The `sed' utility is a stream editor, a program that reads a stream of
data, makes changes to it, and passes it on.  It is often used to make
global changes to a large file or to a stream of data generated by a
pipeline of commands.  While `sed' is a complicated program in its own
right, its most common use is to perform global substitutions in the
middle of a pipeline:

     command1 < orig.data | sed 's/old/new/g' | command2 > result

Here, `s/old/new/g' tells `sed' to look for the regexp `old' on each
input line and globally replace it with the text `new', i.e., all the
occurrences on a line.  This is similar to `awk''s `gsub' function
(*note String Functions::).

The following program, `awksed.awk', accepts at least two command-line
arguments: the pattern to look for and the text to replace it with. Any
additional arguments are treated as data file names to process. If none
are provided, the standard input is used:

     # awksed.awk --- do s/foo/bar/g using just print
     #    Thanks to Michael Brennan for the idea
     function usage()
     {
         print "usage: awksed pat repl [files...]" > "/dev/stderr"
         exit 1
     }

     BEGIN {
         # validate arguments
         if (ARGC < 3)
             usage()

         RS = ARGV[1]
         ORS = ARGV[2]

         # don't use arguments as files
         ARGV[1] = ARGV[2] = ""
     }

     # look ma, no hands!
     {
         if (RT == "")
             printf "%s", $0
         else
             print
     }

The program relies on `gawk''s ability to have `RS' be a regexp, as
well as on the setting of `RT' to the actual text that terminates the
record (*note Records::).

The idea is to have `RS' be the pattern to look for. `gawk'
automatically sets `$0' to the text between matches of the pattern.
This is text that we want to keep, unmodified.  Then, by setting `ORS'
to the replacement text, a simple `print' statement outputs the text we
want to keep, followed by the replacement text.

There is one wrinkle to this scheme, which is what to do if the last
record doesn't end with text that matches `RS'.  Using a `print'
statement unconditionally prints the replacement text, which is not
correct.  However, if the file did not end in text that matches `RS',
`RT' is set to the null string.  In this case, we can print `$0' using
`printf' (*note Printf::).

The `BEGIN' rule handles the setup, checking for the right number of
arguments and calling `usage' if there is a problem. Then it sets `RS'
and `ORS' from the command-line arguments and sets `ARGV[1]' and
`ARGV[2]' to the null string, so that they are not treated as file names
(*note ARGC and ARGV::).

The `usage' function prints an error message and exits.  Finally, the
single rule handles the printing scheme outlined above, using `print'
or `printf' as appropriate, depending upon the value of `RT'.


File: gawk.info,  Node: Igawk Program,  Prev: Simple Sed,  Up: Miscellaneous Programs

13.3.9 An Easy Way to Use Library Functions
-------------------------------------------

Using library functions in `awk' can be very beneficial. It encourages
code reuse and the writing of general functions. Programs are smaller
and therefore clearer.  However, using library functions is only easy
when writing `awk' programs; it is painful when running them, requiring
multiple `-f' options.  If `gawk' is unavailable, then so too is the
`AWKPATH' environment variable and the ability to put `awk' functions
into a library directory (*note Options::).  It would be nice to be
able to write programs in the following manner:

     # library functions
     @include getopt.awk
     @include join.awk
     ...

     # main program
     BEGIN {
         while ((c = getopt(ARGC, ARGV, "a:b:cde")) != -1)
             ...
         ...
     }

The following program, `igawk.sh', provides this service.  It simulates
`gawk''s searching of the `AWKPATH' variable and also allows "nested"
includes; i.e., a file that is included with `@include' can contain
further `@include' statements.  `igawk' makes an effort to only include
files once, so that nested includes don't accidentally include a
library function twice.

`igawk' should behave just like `gawk' externally.  This means it
should accept all of `gawk''s command-line arguments, including the
ability to have multiple source files specified via `-f', and the
ability to mix command-line and library source files.

The program is written using the POSIX Shell (`sh') command
language.(1) It works as follows:

  1. Loop through the arguments, saving anything that doesn't represent
     `awk' source code for later, when the expanded program is run.

  2. For any arguments that do represent `awk' text, put the arguments
     into a shell variable that will be expanded.  There are two cases:

       a. Literal text, provided with `--source' or `--source='.  This
          text is just appended directly.

       b. Source file names, provided with `-f'.  We use a neat trick
          and append `@include FILENAME' to the shell variable's
          contents.  Since the file-inclusion program works the way
          `gawk' does, this gets the text of the file included into the
          program at the correct point.

  3. Run an `awk' program (naturally) over the shell variable's
     contents to expand `@include' statements.  The expanded program is
     placed in a second shell variable.

  4. Run the expanded program with `gawk' and any other original
     command-line arguments that the user supplied (such as the data
     file names).

This program uses shell variables extensively; for storing command line
arguments, the text of the `awk' program that will expand the user's
program, for the user's original program, and for the expanded program.
Doing so removes some potential problems that might arise were we to
use temporary files instead, at the cost of making the script somewhat
more complicated.

The initial part of the program turns on shell tracing if the first
argument is `debug'.

The next part loops through all the command-line arguments.  There are
several cases of interest:

`--'
     This ends the arguments to `igawk'.  Anything else should be
     passed on to the user's `awk' program without being evaluated.

`-W'
     This indicates that the next option is specific to `gawk'.  To make
     argument processing easier, the `-W' is appended to the front of
     the remaining arguments and the loop continues.  (This is an `sh'
     programming trick.  Don't worry about it if you are not familiar
     with `sh'.)

`-v, -F'
     These are saved and passed on to `gawk'.

`-f, --file, --file=, -Wfile='
     The file name is appended to the shell variable `program' with an
     `@include' statement.  The `expr' utility is used to remove the
     leading option part of the argument (e.g., `--file=').  (Typical
     `sh' usage would be to use the `echo' and `sed' utilities to do
     this work.  Unfortunately, some versions of `echo' evaluate escape
     sequences in their arguments, possibly mangling the program text.
     Using `expr' avoids this problem.)

`--source, --source=, -Wsource='
     The source text is appended to `program'.

`--version, -Wversion'
     `igawk' prints its version number, runs `gawk --version' to get
     the `gawk' version information, and then exits.

If none of the `-f', `--file', `-Wfile', `--source', or `-Wsource'
arguments are supplied, then the first nonoption argument should be the
`awk' program.  If there are no command-line arguments left, `igawk'
prints an error message and exits.  Otherwise, the first argument is
appended to `program'.  In any case, after the arguments have been
processed, `program' contains the complete text of the original `awk'
program.

The program is as follows:

     #! /bin/sh
     # igawk --- like gawk but do @include processing
     if [ "$1" = debug ]
     then
         set -x
         shift
     fi

     # A literal newline, so that program text is formmatted correctly
     n='
     '

     # Initialize variables to empty
     program=
     opts=

     while [ $# -ne 0 ] # loop over arguments
     do
         case $1 in
         --)     shift; break;;

         -W)     shift
                 # The ${x?'message here'} construct prints a
                 # diagnostic if $x is the null string
                 set -- -W"${@?'missing operand'}"
                 continue;;

         -[vF])  opts="$opts $1 '${2?'missing operand'}'"
                 shift;;

         -[vF]*) opts="$opts '$1'" ;;

         -f)     program="$program$n@include ${2?'missing operand'}"
                 shift;;

         -f*)    f=`expr "$1" : '-f\(.*\)'`
                 program="$program$n@include $f";;

         -[W-]file=*)
                 f=`expr "$1" : '-.file=\(.*\)'`
                 program="$program$n@include $f";;

         -[W-]file)
                 program="$program$n@include ${2?'missing operand'}"
                 shift;;

         -[W-]source=*)
                 t=`expr "$1" : '-.source=\(.*\)'`
                 program="$program$n$t";;

         -[W-]source)
                 program="$program$n${2?'missing operand'}"
                 shift;;

         -[W-]version)
                 echo igawk: version 2.0 1>&2
                 gawk --version
                 exit 0 ;;

         -[W-]*) opts="$opts '$1'" ;;

         *)      break;;
         esac
         shift
     done

     if [ -z "$program" ]
     then
          program=${1?'missing program'}
          shift
     fi

     # At this point, `program' has the program.

The `awk' program to process `@include' directives is stored in the
shell variable `expand_prog'.  Doing this keeps the shell script
readable.  The `awk' program reads through the user's program, one line
at a time, using `getline' (*note Getline::).  The input file names and
`@include' statements are managed using a stack.  As each `@include' is
encountered, the current file name is "pushed" onto the stack and the
file named in the `@include' directive becomes the current file name.
As each file is finished, the stack is "popped," and the previous input
file becomes the current input file again.  The process is started by
making the original file the first one on the stack.

The `pathto' function does the work of finding the full path to a file.
It simulates `gawk''s behavior when searching the `AWKPATH'
environment variable (*note AWKPATH Variable::).  If a file name has a
`/' in it, no path search is done. Otherwise, the file name is
concatenated with the name of each directory in the path, and an
attempt is made to open the generated file name.  The only way to test
if a file can be read in `awk' is to go ahead and try to read it with
`getline'; this is what `pathto' does.(2) If the file can be read, it
is closed and the file name is returned:

     expand_prog='

     function pathto(file,    i, t, junk)
     {
         if (index(file, "/") != 0)
             return file

         for (i = 1; i <= ndirs; i++) {
             t = (pathlist[i] "/" file)
             if ((getline junk < t) > 0) {
                 # found it
                 close(t)
                 return t
             }
         }
         return ""
     }

The main program is contained inside one `BEGIN' rule.  The first thing
it does is set up the `pathlist' array that `pathto' uses.  After
splitting the path on `:', null elements are replaced with `"."', which
represents the current directory:

     BEGIN {
         path = ENVIRON["AWKPATH"]
         ndirs = split(path, pathlist, ":")
         for (i = 1; i <= ndirs; i++) {
             if (pathlist[i] == "")
                 pathlist[i] = "."
         }

The stack is initialized with `ARGV[1]', which will be `/dev/stdin'.
The main loop comes next.  Input lines are read in succession. Lines
that do not start with `@include' are printed verbatim.  If the line
does start with `@include', the file name is in `$2'.  `pathto' is
called to generate the full path.  If it cannot, then we print an error
message and continue.

The next thing to check is if the file is included already.  The
`processed' array is indexed by the full file name of each included
file and it tracks this information for us.  If the file is seen again,
a warning message is printed. Otherwise, the new file name is pushed
onto the stack and processing continues.

Finally, when `getline' encounters the end of the input file, the file
is closed and the stack is popped.  When `stackptr' is less than zero,
the program is done:

         stackptr = 0
         input[stackptr] = ARGV[1] # ARGV[1] is first file

         for (; stackptr >= 0; stackptr--) {
             while ((getline < input[stackptr]) > 0) {
                 if (tolower($1) != "@include") {
                     print
                     continue
                 }
                 fpath = pathto($2)
                 if (fpath == "") {
                     printf("igawk:%s:%d: cannot find %s\n",
                         input[stackptr], FNR, $2) > "/dev/stderr"
                     continue
                 }
                 if (! (fpath in processed)) {
                     processed[fpath] = input[stackptr]
                     input[++stackptr] = fpath  # push onto stack
                 } else
                     print $2, "included in", input[stackptr],
                         "already included in",
                         processed[fpath] > "/dev/stderr"
             }
             close(input[stackptr])
         }
     }'  # close quote ends `expand_prog' variable

     processed_program=`gawk -- "$expand_prog" /dev/stdin <<EOF
     $program
     EOF
     `

The shell construct `COMMAND << MARKER' is called a "here document".
Everything in the shell script up to the MARKER is fed to COMMAND as
input.  The shell processes the contents of the here document for
variable and command substitution (and possibly other things as well,
depending upon the shell).

The shell construct ``...`' is called "command substitution".  The
output of the command between the two backquotes (grave accents) is
substituted into the command line.  It is saved as a single string,
even if the results contain whitespace.

The expanded program is saved in the variable `processed_program'.
It's done in these steps:

  1. Run `gawk' with the `@include'-processing program (the value of
     the `expand_prog' shell variable) on standard input.

  2. Standard input is the contents of the user's program, from the
     shell variable `program'.  Its contents are fed to `gawk' via a
     here document.

  3. The results of this processing are saved in the shell variable
     `processed_program' by using command substitution.

The last step is to call `gawk' with the expanded program, along with
the original options and command-line arguments that the user supplied.

     eval gawk $opts -- '"$processed_program"' '"$@"'

The `eval' command is a shell construct that reruns the shell's parsing
process.  This keeps things properly quoted.

This version of `igawk' represents my fourth attempt at this program.
There are four key simplifications that make the program work better:

   * Using `@include' even for the files named with `-f' makes building
     the initial collected `awk' program much simpler; all the
     `@include' processing can be done once.

   * Not trying to save the line read with `getline' in the `pathto'
     function when testing for the file's accessibility for use with
     the main program simplifies things considerably.

   * Using a `getline' loop in the `BEGIN' rule does it all in one
     place.  It is not necessary to call out to a separate loop for
     processing nested `@include' statements.

   * Instead of saving the expanded program in a temporary file,
     putting it in a shell variable avoids some potential security
     problems.  This has the disadvantage that the script relies upon
     more features of the `sh' language, making it harder to follow for
     those who aren't familiar with `sh'.

Also, this program illustrates that it is often worthwhile to combine
`sh' and `awk' programming together.  You can usually accomplish quite
a lot, without having to resort to low-level programming in C or C++,
and it is frequently easier to do certain kinds of string and argument
manipulation using the shell than it is in `awk'.

Finally, `igawk' shows that it is not always necessary to add new
features to a program; they can often be layered on top.  With `igawk',
there is no real reason to build `@include' processing into `gawk'
itself.

As an additional example of this, consider the idea of having two files
in a directory in the search path:

`default.awk'
     This file contains a set of default library functions, such as
     `getopt' and `assert'.

`site.awk'
     This file contains library functions that are specific to a site or
     installation; i.e., locally developed functions.  Having a
     separate file allows `default.awk' to change with new `gawk'
     releases, without requiring the system administrator to update it
     each time by adding the local functions.

One user suggested that `gawk' be modified to automatically read these
files upon startup.  Instead, it would be very simple to modify `igawk'
to do this. Since `igawk' can process nested `@include' directives,
`default.awk' could simply contain `@include' statements for the
desired library functions.

---------- Footnotes ----------

(1) Fully explaining the `sh' language is beyond the scope of this
book. We provide some minimal explanations, but see a good shell
programming book if you wish to understand things in more depth.

(2) On some very old versions of `awk', the test `getline junk < t' can
loop forever if the file exists but is empty.  Caveat emptor.


File: gawk.info,  Node: Language History,  Next: Installation,  Prev: Sample Programs,  Up: Top

Appendix A The Evolution of the `awk' Language
**********************************************

This Info file describes the GNU implementation of `awk', which follows
the POSIX specification.  Many long-time `awk' users learned `awk'
programming with the original `awk' implementation in Version 7 Unix.
(This implementation was the basis for `awk' in Berkeley Unix, through
4.3-Reno.  Subsequent versions of Berkeley Unix, and systems derived
from 4.4BSD-Lite, use various versions of `gawk' for their `awk'.)
This major node briefly describes the evolution of the `awk' language,
with cross-references to other parts of the Info file where you can
find more information.

* Menu:

* V7/SVR3.1::                   The major changes between V7 and System V
                                Release 3.1.
* SVR4::                        Minor changes between System V Releases 3.1
                                and 4.
* POSIX::                       New features from the POSIX standard.
* BTL::                         New features from the Bell Laboratories
                                version of `awk'.
* POSIX/GNU::                   The extensions in `gawk' not in POSIX
                                `awk'.
* Contributors::                The major contributors to `gawk'.


File: gawk.info,  Node: V7/SVR3.1,  Next: SVR4,  Up: Language History

A.1 Major Changes Between V7 and SVR3.1
=======================================

The `awk' language evolved considerably between the release of Version
7 Unix (1978) and the new version that was first made generally
available in System V Release 3.1 (1987).  This minor node summarizes
the changes, with cross-references to further details:

   * The requirement for `;' to separate rules on a line (*note
     Statements/Lines::).

   * User-defined functions and the `return' statement (*note
     User-defined::).

   * The `delete' statement (*note Delete::).

   * The `do'-`while' statement (*note Do Statement::).

   * The built-in functions `atan2', `cos', `sin', `rand', and `srand'
     (*note Numeric Functions::).

   * The built-in functions `gsub', `sub', and `match' (*note String
     Functions::).

   * The built-in functions `close' and `system' (*note I/O
     Functions::).

   * The `ARGC', `ARGV', `FNR', `RLENGTH', `RSTART', and `SUBSEP'
     built-in variables (*note Built-in Variables::).

   * The conditional expression using the ternary operator `?:' (*note
     Conditional Exp::).

   * The exponentiation operator `^' (*note Arithmetic Ops::) and its
     assignment operator form `^=' (*note Assignment Ops::).

   * C-compatible operator precedence, which breaks some old `awk'
     programs (*note Precedence::).

   * Regexps as the value of `FS' (*note Field Separators::) and as the
     third argument to the `split' function (*note String Functions::).

   * Dynamic regexps as operands of the `~' and `!~' operators (*note
     Regexp Usage::).

   * The escape sequences `\b', `\f', and `\r' (*note Escape
     Sequences::).  (Some vendors have updated their old versions of
     `awk' to recognize `\b', `\f', and `\r', but this is not something
     you can rely on.)

   * Redirection of input for the `getline' function (*note Getline::).

   * Multiple `BEGIN' and `END' rules (*note BEGIN/END::).

   * Multidimensional arrays (*note Multi-dimensional::).


File: gawk.info,  Node: SVR4,  Next: POSIX,  Prev: V7/SVR3.1,  Up: Language History

A.2 Changes Between SVR3.1 and SVR4
===================================

The System V Release 4 (1989) version of Unix `awk' added these features
(some of which originated in `gawk'):

   * The `ENVIRON' variable (*note Built-in Variables::).

   * Multiple `-f' options on the command line (*note Options::).

   * The `-v' option for assigning variables before program execution
     begins (*note Options::).

   * The `--' option for terminating command-line options.

   * The `\a', `\v', and `\x' escape sequences (*note Escape
     Sequences::).

   * A defined return value for the `srand' built-in function (*note
     Numeric Functions::).

   * The `toupper' and `tolower' built-in string functions for case
     translation (*note String Functions::).

   * A cleaner specification for the `%c' format-control letter in the
     `printf' function (*note Control Letters::).

   * The ability to dynamically pass the field width and precision
     (`"%*.*d"') in the argument list of the `printf' function (*note
     Control Letters::).

   * The use of regexp constants, such as `/foo/', as expressions, where
     they are equivalent to using the matching operator, as in `$0 ~
     /foo/' (*note Using Constant Regexps::).

   * Processing of escape sequences inside command-line variable
     assignments (*note Assignment Options::).


File: gawk.info,  Node: POSIX,  Next: BTL,  Prev: SVR4,  Up: Language History

A.3 Changes Between SVR4 and POSIX `awk'
========================================

The POSIX Command Language and Utilities standard for `awk' (1992)
introduced the following changes into the language:

   * The use of `-W' for implementation-specific options (*note
     Options::).

   * The use of `CONVFMT' for controlling the conversion of numbers to
     strings (*note Conversion::).

   * The concept of a numeric string and tighter comparison rules to go
     with it (*note Typing and Comparison::).

   * More complete documentation of many of the previously undocumented
     features of the language.

The following common extensions are not permitted by the POSIX standard:

   * `\x' escape sequences are not recognized (*note Escape
     Sequences::).

   * Newlines do not act as whitespace to separate fields when `FS' is
     equal to a single space (*note Fields::).

   * Newlines are not allowed after `?' or `:' (*note Conditional
     Exp::).

   * The synonym `func' for the keyword `function' is not recognized
     (*note Definition Syntax::).

   * The operators `**' and `**=' cannot be used in place of `^' and
     `^=' (*note Arithmetic Ops::, and *Note Assignment Ops::).

   * Specifying `-Ft' on the command line does not set the value of
     `FS' to be a single TAB character (*note Field Separators::).

   * The `fflush' built-in function is not supported (*note I/O
     Functions::).


File: gawk.info,  Node: BTL,  Next: POSIX/GNU,  Prev: POSIX,  Up: Language History

A.4 Extensions in the Bell Laboratories `awk'
=============================================

Brian Kernighan, one of the original designers of Unix `awk', has made
his version available via his home page (*note Other Versions::).  This
minor node describes extensions in his version of `awk' that are not in
POSIX `awk':

   * The `-mf N' and `-mr N' command-line options to set the maximum
     number of fields and the maximum record size, respectively (*note
     Options::).  As a side note, his `awk' no longer needs these
     options; it continues to accept them to avoid breaking old
     programs.

   * The `fflush' built-in function for flushing buffered output (*note
     I/O Functions::).

   * The `**' and `**=' operators (*note Arithmetic Ops:: and *Note
     Assignment Ops::).

   * The use of `func' as an abbreviation for `function' (*note
     Definition Syntax::).


The Bell Laboratories `awk' also incorporates the following extensions,
originally developed for `gawk':

   * The `\x' escape sequence (*note Escape Sequences::).

   * The `/dev/stdin', `/dev/stdout', and `/dev/stderr' special files
     (*note Special Files::).

   * The ability for `FS' and for the third argument to `split' to be
     null strings (*note Single Character Fields::).

   * The `nextfile' statement (*note Nextfile Statement::).

   * The ability to delete all of an array at once with `delete ARRAY'
     (*note Delete::).


File: gawk.info,  Node: POSIX/GNU,  Next: Contributors,  Prev: BTL,  Up: Language History

A.5 Extensions in `gawk' Not in POSIX `awk'
===========================================

The GNU implementation, `gawk', adds a large number of features.  This
minor node lists them in the order they were added to `gawk'.  They can
all be disabled with either the `--traditional' or `--posix' options
(*note Options::).

Version 2.10 of `gawk' introduced the following features:

   * The `AWKPATH' environment variable for specifying a path search for
     the `-f' command-line option (*note Options::).

   * The `IGNORECASE' variable and its effects (*note
     Case-sensitivity::).

   * The `/dev/stdin', `/dev/stdout', `/dev/stderr' and `/dev/fd/N'
     special file names (*note Special Files::).

Version 2.13 of `gawk' introduced the following features:

   * The `FIELDWIDTHS' variable and its effects (*note Constant Size::).

   * The `systime' and `strftime' built-in functions for obtaining and
     printing timestamps (*note Time Functions::).

   * The `-W lint' option to provide error and portability checking for
     both the source code and at runtime (*note Options::).

   * The `-W compat' option to turn off the GNU extensions (*note
     Options::).

   * The `-W posix' option for full POSIX compliance (*note Options::).

Version 2.14 of `gawk' introduced the following feature:

   * The `next file' statement for skipping to the next data file
     (*note Nextfile Statement::).

Version 2.15 of `gawk' introduced the following features:

   * The `ARGIND' variable, which tracks the movement of `FILENAME'
     through `ARGV'  (*note Built-in Variables::).

   * The `ERRNO' variable, which contains the system error message when
     `getline' returns -1 or `close' fails (*note Built-in Variables::).

   * The `/dev/pid', `/dev/ppid', `/dev/pgrpid', and `/dev/user' file
     name interpretation (*note Special Files::).

   * The ability to delete all of an array at once with `delete ARRAY'
     (*note Delete::).

   * The ability to use GNU-style long-named options that start with
     `--' (*note Options::).

   * The `--source' option for mixing command-line and library-file
     source code (*note Options::).

Version 3.0 of `gawk' introduced the following features:

   * `IGNORECASE' changed, now applying to string comparison as well as
     regexp operations (*note Case-sensitivity::).

   * The `RT' variable that contains the input text that matched `RS'
     (*note Records::).

   * Full support for both POSIX and GNU regexps (*note Regexp::).

   * The `gensub' function for more powerful text manipulation (*note
     String Functions::).

   * The `strftime' function acquired a default time format, allowing
     it to be called with no arguments (*note Time Functions::).

   * The ability for `FS' and for the third argument to `split' to be
     null strings (*note Single Character Fields::).

   * The ability for `RS' to be a regexp (*note Records::).

   * The `next file' statement became `nextfile' (*note Nextfile
     Statement::).

   * The `--lint-old' option to warn about constructs that are not
     available in the original Version 7 Unix version of `awk' (*note
     V7/SVR3.1::).

   * The `-m' option and the `fflush' function from the Bell
     Laboratories research version of `awk' (*note Options::; also
     *note I/O Functions::).

   * The `--re-interval' option to provide interval expressions in
     regexps (*note Regexp Operators::).

   * The `--traditional' option was added as a better name for
     `--compat' (*note Options::).

   * The use of GNU Autoconf to control the configuration process
     (*note Quick Installation::).

   * Amiga support (*note Amiga Installation::).


Version 3.1 of `gawk' introduced the following features:

   * The `BINMODE' special variable for non-POSIX systems, which allows
     binary I/O for input and/or output files (*note PC Using::).

   * The `LINT' special variable, which dynamically controls lint
     warnings (*note Built-in Variables::).

   * The `PROCINFO' array for providing process-related information
     (*note Built-in Variables::).

   * The `TEXTDOMAIN' special variable for setting an application's
     internationalization text domain (*note Built-in Variables::, and
     *Note Internationalization::).

   * The ability to use octal and hexadecimal constants in `awk'
     program source code (*note Nondecimal-numbers::).

   * The `|&' operator for two-way I/O to a coprocess (*note Two-way
     I/O::).

   * The `/inet' special files for TCP/IP networking using `|&' (*note
     TCP/IP Networking::).

   * The optional second argument to `close' that allows closing one end
     of a two-way pipe to a coprocess (*note Two-way I/O::).

   * The optional third argument to the `match' function for capturing
     text-matching subexpressions within a regexp (*note String
     Functions::).

   * Positional specifiers in `printf' formats for making translations
     easier (*note Printf Ordering::).

   * The `asort' and `asorti' functions for sorting arrays (*note Array
     Sorting::).

   * The `bindtextdomain', `dcgettext' and `dcngettext' functions for
     internationalization (*note Programmer i18n::).

   * The `extension' built-in function and the ability to add new
     built-in functions dynamically (*note Dynamic Extensions::).

   * The `mktime' built-in function for creating timestamps (*note Time
     Functions::).

   * The `and', `or', `xor', `compl', `lshift', `rshift', and
     `strtonum' built-in functions (*note Bitwise Functions::).

   * The support for `next file' as two words was removed completely
     (*note Nextfile Statement::).

   * The `--dump-variables' option to print a list of all global
     variables (*note Options::).

   * The `--gen-po' command-line option and the use of a leading
     underscore to mark strings that should be translated (*note String
     Extraction::).

   * The `--non-decimal-data' option to allow non-decimal input data
     (*note Nondecimal Data::).

   * The `--profile' option and `pgawk', the profiling version of
     `gawk', for producing execution profiles of `awk' programs (*note
     Profiling::).

   * The `--enable-portals' configuration option to enable special
     treatment of pathnames that begin with `/p' as BSD portals (*note
     Portal Files::).

   * The use of GNU Automake to help in standardizing the configuration
     process (*note Quick Installation::).

   * The use of GNU `gettext' for `gawk''s own message output (*note
     Gawk I18N::).

   * BeOS support (*note BeOS Installation::).

   * Tandem support (*note Tandem Installation::).

   * The Atari port became officially unsupported (*note Atari
     Installation::).

   * The source code now uses new-style function definitions, with
     `ansi2knr' to convert the code on systems with old compilers.

   * The `--disable-lint' configuration option to disable lint checking
     at compile time (*note Additional Configuration Options::).

   * POSIX compliance for `sub' and `gsub' (*note Gory Details::).

   * The `--exec' option, for use in CGI scripts.  (*note Options::).

   * The `length' function was extended to accept an array argument and
     return the number of elements in the array (*note String
     Functions::).



File: gawk.info,  Node: Contributors,  Prev: POSIX/GNU,  Up: Language History

A.6 Major Contributors to `gawk'
================================

     Always give credit where credit is due.
     Anonymous

This minor node names the major contributors to `gawk' and/or this
Info file, in approximate chronological order:

   * Dr. Alfred V. Aho, Dr. Peter J. Weinberger, and Dr. Brian W.
     Kernighan, all of Bell Laboratories, designed and implemented Unix
     `awk', from which `gawk' gets the majority of its feature set.

   * Paul Rubin did the initial design and implementation in 1986, and
     wrote the first draft (around 40 pages) of this Info file.

   * Jay Fenlason finished the initial implementation.

   * Diane Close revised the first draft of this Info file, bringing it
     to around 90 pages.

   * Richard Stallman helped finish the implementation and the initial
     draft of this Info file.  He is also the founder of the FSF and
     the GNU project.

   * John Woods contributed parts of the code (mostly fixes) in the
     initial version of `gawk'.

   * In 1988, David Trueman took over primary maintenance of `gawk',
     making it compatible with "new" `awk', and greatly improving its
     performance.

   * Pat Rankin provided the VMS port and its documentation.

   * Conrad Kwok, Scott Garfinkle, and Kent Williams did the initial
     ports to MS-DOS with various versions of MSC.

   * Hal Peterson provided help in porting `gawk' to Cray systems.

   * Kai Uwe Rommel provided the initial port to OS/2 and its
     documentation.

   * Michal Jaegermann provided the port to Atari systems and its
     documentation.  He continues to provide portability checking with
     DEC Alpha systems, and has done a lot of work to make sure `gawk'
     works on non-32-bit systems.

   * Fred Fish provided the port to Amiga systems and its documentation.

   * Scott Deifik currently maintains the MS-DOS port.

   * Juan Grigera maintains the port to Windows32 systems.

   * Dr. Darrel Hankerson acts as coordinator for the various ports to
     different PC platforms and creates binary distributions for
     various PC operating systems.  He is also instrumental in keeping
     the documentation up to date for the various PC platforms.

   * Christos Zoulas provided the `extension' built-in function for
     dynamically adding new modules.

   * Ju"rgen Kahrs contributed the initial version of the TCP/IP
     networking code and documentation, and motivated the inclusion of
     the `|&' operator.

   * Stephen Davies provided the port to Tandem systems and its
     documentation.

   * Martin Brown provided the port to BeOS and its documentation.

   * Arno Peters did the initial work to convert `gawk' to use GNU
     Automake and `gettext'.

   * Alan J. Broder provided the initial version of the `asort' function
     as well as the code for the new optional third argument to the
     `match' function.

   * Andreas Buening updated the `gawk' port for OS/2.

     Isamu Hasegawa, of IBM in Japan, contributed support for multibyte
     characters.

     Michael Benzinger contributed the initial code for `switch'
     statements.

     Patrick T.J. McPhee contributed the code for dynamic loading in
     Windows32 environments.

   * Arnold Robbins has been working on `gawk' since 1988, at first
     helping David Trueman, and as the primary maintainer since around
     1994.


File: gawk.info,  Node: Installation,  Next: Notes,  Prev: Language History,  Up: Top

Appendix B Installing `gawk'
****************************

This appendix provides instructions for installing `gawk' on the
various platforms that are supported by the developers.  The primary
developer supports GNU/Linux (and Unix), whereas the other ports are
contributed.  *Note Bugs::, for the electronic mail addresses of the
people who did the respective ports.

* Menu:

* Gawk Distribution::           What is in the `gawk' distribution.
* Unix Installation::           Installing `gawk' under various
                                versions of Unix.
* Non-Unix Installation::       Installation on Other Operating Systems.
* Unsupported::                 Systems whose ports are no longer supported.
* Bugs::                        Reporting Problems and Bugs.
* Other Versions::              Other freely available `awk'
                                implementations.


File: gawk.info,  Node: Gawk Distribution,  Next: Unix Installation,  Up: Installation

B.1 The `gawk' Distribution
===========================

This minor node describes how to get the `gawk' distribution, how to
extract it, and then what is in the various files and subdirectories.

* Menu:

* Getting::                     How to get the distribution.
* Extracting::                  How to extract the distribution.
* Distribution contents::       What is in the distribution.


File: gawk.info,  Node: Getting,  Next: Extracting,  Up: Gawk Distribution

B.1.1 Getting the `gawk' Distribution
-------------------------------------

There are three ways to get GNU software:

   * Copy it from someone else who already has it.

   * Order `gawk' directly from the Free Software Foundation.  Software
     distributions are available for Gnu/Linux, Unix, and MS-Windows,
     in several CD packages.  Their address is:

          Free Software Foundation
          51 Franklin Street, Fifth Floor
          Boston, MA  02110-1301 USA
          Phone: +1-617-542-5942
          Fax (including Japan): +1-617-542-2652
          Email: <gnu@gnu.org>
          URL: `http://www.gnu.org'

     Ordering from the FSF directly contributes to the support of the
     foundation and to the production of more free software.

   * Retrieve `gawk' by using anonymous `ftp' to the Internet host
     `ftp.gnu.org', in the directory `/gnu/gawk'.

The GNU software archive is mirrored around the world.  The up-to-date
list of mirror sites is available from the main FSF web site
(http://www.gnu.org/order/ftp.html).  Try to use one of the mirrors;
they will be less busy, and you can usually find one closer to your
site.


File: gawk.info,  Node: Extracting,  Next: Distribution contents,  Prev: Getting,  Up: Gawk Distribution

B.1.2 Extracting the Distribution
---------------------------------

`gawk' is distributed as a `tar' file compressed with the GNU Zip
program, `gzip'.

Once you have the distribution (for example, `gawk-3.1.5.tar.gz'), use
`gzip' to expand the file and then use `tar' to extract it.  You can
use the following pipeline to produce the `gawk' distribution:

     # Under System V, add 'o' to the tar options
     gzip -d -c gawk-3.1.5.tar.gz | tar -xvpf -

This creates a directory named `gawk-3.1.5' in the current directory.

The distribution file name is of the form `gawk-V.R.P.tar.gz'.  The V
represents the major version of `gawk', the R represents the current
release of version V, and the P represents a "patch level", meaning
that minor bugs have been fixed in the release.  The current patch
level is 5, but when retrieving distributions, you should get the
version with the highest version, release, and patch level.  (Note,
however, that patch levels greater than or equal to 80 denote "beta" or
nonproduction software; you might not want to retrieve such a version
unless you don't mind experimenting.)  If you are not on a Unix system,
you need to make other arrangements for getting and extracting the
`gawk' distribution.  You should consult a local expert.


File: gawk.info,  Node: Distribution contents,  Prev: Extracting,  Up: Gawk Distribution

B.1.3 Contents of the `gawk' Distribution
-----------------------------------------

The `gawk' distribution has a number of C source files, documentation
files, subdirectories, and files related to the configuration process
(*note Unix Installation::), as well as several subdirectories related
to different non-Unix operating systems:

Various `.c', `.y', and `.h' files
     The actual `gawk' source code.

`README'
`README_d/README.*'
     Descriptive files: `README' for `gawk' under Unix and the rest for
     the various hardware and software combinations.

`INSTALL'
     A file providing an overview of the configuration and installation
     process.

`ChangeLog'
     A detailed list of source code changes as bugs are fixed or
     improvements made.

`NEWS'
     A list of changes to `gawk' since the last release or patch.

`COPYING'
     The GNU General Public License.

`FUTURES'
     A brief list of features and changes being contemplated for future
     releases, with some indication of the time frame for the feature,
     based on its difficulty.

`LIMITATIONS'
     A list of those factors that limit `gawk''s performance.  Most of
     these depend on the hardware or operating system software and are
     not limits in `gawk' itself.

`POSIX.STD'
     A description of one area in which the POSIX standard for `awk' is
     incorrect as well as how `gawk' handles the problem.

`doc/awkforai.txt'
     A short article describing why `gawk' is a good language for AI
     (Artificial Intelligence) programming.

`doc/README.card'
`doc/ad.block'
`doc/awkcard.in'
`doc/cardfonts'
`doc/colors'
`doc/macros'
`doc/no.colors'
`doc/setter.outline'
     The `troff' source for a five-color `awk' reference card.  A
     modern version of `troff' such as GNU `troff' (`groff') is needed
     to produce the color version. See the file `README.card' for
     instructions if you have an older `troff'.

`doc/gawk.1'
     The `troff' source for a manual page describing `gawk'.  This is
     distributed for the convenience of Unix users.

`doc/gawk.texi'
     The Texinfo source file for this Info file.  It should be
     processed with TeX to produce a printed document, and with
     `makeinfo' to produce an Info or HTML file.

`doc/gawk.info'
     The generated Info file for this Info file.

`doc/gawkinet.texi'
     The Texinfo source file for *Note Top::.  It should be processed
     with TeX to produce a printed document and with `makeinfo' to
     produce an Info or HTML file.

`doc/gawkinet.info'
     The generated Info file for `TCP/IP Internetworking with `gawk''.

`doc/igawk.1'
     The `troff' source for a manual page describing the `igawk'
     program presented in *Note Igawk Program::.

`doc/Makefile.in'
     The input file used during the configuration process to generate
     the actual `Makefile' for creating the documentation.

`Makefile.am'
`*/Makefile.am'
     Files used by the GNU `automake' software for generating the
     `Makefile.in' files used by `autoconf' and `configure'.

`Makefile.in'
`acconfig.h'
`acinclude.m4'
`aclocal.m4'
`configh.in'
`configure.in'
`configure'
`custom.h'
`missing_d/*'
`m4/*'
     These files and subdirectories are used when configuring `gawk'
     for various Unix systems.  They are explained in *Note Unix
     Installation::.

`po/*'
     The `po' library contains message translations.

`awklib/extract.awk'
`awklib/Makefile.am'
`awklib/Makefile.in'
`awklib/eg/*'
     The `awklib' directory contains a copy of `extract.awk' (*note
     Extract Program::), which can be used to extract the sample
     programs from the Texinfo source file for this Info file. It also
     contains a `Makefile.in' file, which `configure' uses to generate
     a `Makefile'.  `Makefile.am' is used by GNU Automake to create
     `Makefile.in'.  The library functions from *Note Library
     Functions::, and the `igawk' program from *Note Igawk Program::,
     are included as ready-to-use files in the `gawk' distribution.
     They are installed as part of the installation process.  The rest
     of the programs in this Info file are available in appropriate
     subdirectories of `awklib/eg'.

`unsupported/atari/*'
     Files needed for building `gawk' on an Atari ST (*note Atari
     Installation::, for details).

`unsupported/tandem/*'
     Files needed for building `gawk' on a Tandem (*note Tandem
     Installation::, for details).

`posix/*'
     Files needed for building `gawk' on POSIX-compliant systems.

`pc/*'
     Files needed for building `gawk' under MS-DOS, MS Windows and OS/2
     (*note PC Installation::, for details).

`vms/*'
     Files needed for building `gawk' under VMS (*note VMS
     Installation::, for details).

`test/*'
     A test suite for `gawk'.  You can use `make check' from the
     top-level `gawk' directory to run your version of `gawk' against
     the test suite.  If `gawk' successfully passes `make check', then
     you can be confident of a successful port.


File: gawk.info,  Node: Unix Installation,  Next: Non-Unix Installation,  Prev: Gawk Distribution,  Up: Installation

B.2 Compiling and Installing `gawk' on Unix
===========================================

Usually, you can compile and install `gawk' by typing only two
commands.  However, if you use an unusual system, you may need to
configure `gawk' for your system yourself.

* Menu:

* Quick Installation::               Compiling `gawk' under Unix.
* Additional Configuration Options:: Other compile-time options.
* Configuration Philosophy::         How it's all supposed to work.


File: gawk.info,  Node: Quick Installation,  Next: Additional Configuration Options,  Up: Unix Installation

B.2.1 Compiling `gawk' for Unix
-------------------------------

After you have extracted the `gawk' distribution, `cd' to
`gawk-3.1.5'.  Like most GNU software, `gawk' is configured
automatically for your Unix system by running the `configure' program.
This program is a Bourne shell script that is generated automatically
using GNU `autoconf'.  (The `autoconf' software is described fully
starting with *Note Top::.)

To configure `gawk', simply run `configure':

     sh ./configure

This produces a `Makefile' and `config.h' tailored to your system.  The
`config.h' file describes various facts about your system.  You might
want to edit the `Makefile' to change the `CFLAGS' variable, which
controls the command-line options that are passed to the C compiler
(such as optimization levels or compiling for debugging).

Alternatively, you can add your own values for most `make' variables on
the command line, such as `CC' and `CFLAGS', when running `configure':

     CC=cc CFLAGS=-g sh ./configure

See the file `INSTALL' in the `gawk' distribution for all the details.

After you have run `configure' and possibly edited the `Makefile', type:

     make

Shortly thereafter, you should have an executable version of `gawk'.
That's all there is to it!  To verify that `gawk' is working properly,
run `make check'.  All of the tests should succeed.  If these steps do
not work, or if any of the tests fail, check the files in the
`README_d' directory to see if you've found a known problem.  If the
failure is not described there, please send in a bug report (*note
Bugs::.)


File: gawk.info,  Node: Additional Configuration Options,  Next: Configuration Philosophy,  Prev: Quick Installation,  Up: Unix Installation

B.2.2 Additional Configuration Options
--------------------------------------

There are several additional options you may use on the `configure'
command line when compiling `gawk' from scratch, including:

`--enable-portals'
     Treat pathnames that begin with `/p' as BSD portal files when
     doing two-way I/O with the `|&' operator (*note Portal Files::).

`--enable-switch'
     Enable the recognition and execution of C-style `switch' statements
     in `awk' programs (*note Switch Statement::.)

`--disable-lint'
     This option disables all lint checking within `gawk'.  The
     `--lint' and `--lint-old' options (*note Options::) are accepted,
     but silently do nothing.  Similarly, setting the `LINT' variable
     (*note User-modified::) has no effect on the running `awk' program.

     When used with GCC's automatic dead-code-elimination, this option
     cuts almost 200K bytes off the size of the `gawk' executable on
     GNU/Linux x86 systems.  Results on other systems and with other
     compilers are likely to vary.  Using this option may bring you
     some slight performance improvement.

     Using this option will cause some of the tests in the test suite
     to fail.  This option may be removed at a later date.

`--disable-nls'
     Disable all message-translation facilities.  This is usually not
     desirable, but it may bring you some slight performance
     improvement.

As of version 3.1.5, the `--with-included-gettext' configuration option
is no longer available, since `gawk' expects the GNU `gettext' library
to be installed as an external library.


File: gawk.info,  Node: Configuration Philosophy,  Prev: Additional Configuration Options,  Up: Unix Installation

B.2.3 The Configuration Process
-------------------------------

This minor node is of interest only if you know something about using
the C language and the Unix operating system.

The source code for `gawk' generally attempts to adhere to formal
standards wherever possible.  This means that `gawk' uses library
routines that are specified by the ISO C standard and by the POSIX
operating system interface standard.  When using an ISO C compiler,
function prototypes are used to help improve the compile-time checking.

Many Unix systems do not support all of either the ISO or the POSIX
standards.  The `missing_d' subdirectory in the `gawk' distribution
contains replacement versions of those functions that are most likely
to be missing.

The `config.h' file that `configure' creates contains definitions that
describe features of the particular operating system where you are
attempting to compile `gawk'.  The three things described by this file
are: what header files are available, so that they can be correctly
included, what (supposedly) standard functions are actually available
in your C libraries, and various miscellaneous facts about your variant
of Unix.  For example, there may not be an `st_blksize' element in the
`stat' structure.  In this case, `HAVE_ST_BLKSIZE' is undefined.

It is possible for your C compiler to lie to `configure'. It may do so
by not exiting with an error when a library function is not available.
To get around this, edit the file `custom.h'.  Use an `#ifdef' that is
appropriate for your system, and either `#define' any constants that
`configure' should have defined but didn't, or `#undef' any constants
that `configure' defined and should not have.  `custom.h' is
automatically included by `config.h'.

It is also possible that the `configure' program generated by
`autoconf' will not work on your system in some other fashion.  If you
do have a problem, the file `configure.in' is the input for `autoconf'.
You may be able to change this file and generate a new version of
`configure' that works on your system (*note Bugs::, for information on
how to report problems in configuring `gawk').  The same mechanism may
be used to send in updates to `configure.in' and/or `custom.h'.


File: gawk.info,  Node: Non-Unix Installation,  Next: Unsupported,  Prev: Unix Installation,  Up: Installation

B.3 Installation on Other Operating Systems
===========================================

This minor node describes how to install `gawk' on various non-Unix
systems.

* Menu:

* Amiga Installation::          Installing `gawk' on an Amiga.
* BeOS Installation::           Installing `gawk' on BeOS.
* PC Installation::             Installing and Compiling `gawk' on
                                MS-DOS and OS/2.
* VMS Installation::            Installing `gawk' on VMS.


File: gawk.info,  Node: Amiga Installation,  Next: BeOS Installation,  Up: Non-Unix Installation

B.3.1 Installing `gawk' on an Amiga
-----------------------------------

You can install `gawk' on an Amiga system using a Unix emulation
environment, available via anonymous `ftp' from `ftp.ninemoons.com' in
the directory `pub/ade/current'.  This includes a shell based on
`pdksh'.  The primary component of this environment is a Unix emulation
library, `ixemul.lib'.

A more complete distribution for the Amiga is available on the Geek
Gadgets CD-ROM, available from:

     CRONUS
     1840 E. Warner Road #105-265
     Tempe, AZ 85284  USA
     US Toll Free: (800) 804-0833
     Phone: +1-602-491-0442
     FAX: +1-602-491-0048
     Email: <info@ninemoons.com>
     WWW: `http://www.ninemoons.com'
     Anonymous `ftp' site: `ftp.ninemoons.com'

Once you have the distribution, you can configure `gawk' simply by
running `configure':

     configure -v m68k-amigaos

Then run `make' and you should be all set!  If these steps do not work,
please send in a bug report (*note Bugs::).


File: gawk.info,  Node: BeOS Installation,  Next: PC Installation,  Prev: Amiga Installation,  Up: Non-Unix Installation

B.3.2 Installing `gawk' on BeOS
-------------------------------

Since BeOS DR9, all the tools that you should need to build `gawk' are
included with BeOS. The process is basically identical to the Unix
process of running `configure' and then `make'. Full instructions are
given below.

You can compile `gawk' under BeOS by extracting the standard sources
and running `configure'. You _must_ specify the location prefix for the
installation directory. For BeOS DR9 and beyond, the best directory to
use is `/boot/home/config', so the `configure' command is:

     configure --prefix=/boot/home/config

This installs the compiled application into `/boot/home/config/bin',
which is already specified in the standard `PATH'.

Once the configuration process is completed, you can run `make', and
then `make install':

     $ make
     ...
     $ make install

BeOS uses `bash' as its shell; thus, you use `gawk' the same way you
would under Unix.  If these steps do not work, please send in a bug
report (*note Bugs::).


File: gawk.info,  Node: PC Installation,  Next: VMS Installation,  Prev: BeOS Installation,  Up: Non-Unix Installation

B.3.3 Installation on PC Operating Systems
------------------------------------------

This minor node covers installation and usage of `gawk' on x86 machines
running DOS, any version of Windows, or OS/2.  In this minor node, the
term "Windows32" refers to any of Windows-95/98/ME/NT/2000.

The limitations of DOS (and DOS shells under Windows or OS/2) has meant
that various "DOS extenders" are often used with programs such as
`gawk'.  The varying capabilities of Microsoft Windows 3.1 and
Windows32 can add to the confusion.  For an overview of the
considerations, please refer to `README_d/README.pc' in the
distribution.

* Menu:

* PC Binary Installation::      Installing a prepared distribution.
* PC Compiling::                Compiling `gawk' for MS-DOS, Windows32,
                                and OS/2.
* PC Dynamic::                  Compiling `gawk' for dynamic libraries.
* PC Using::                    Running `gawk' on MS-DOS, Windows32 and
                                OS/2.
* Cygwin::                      Building and running `gawk' for
                                Cygwin.


File: gawk.info,  Node: PC Binary Installation,  Next: PC Compiling,  Up: PC Installation

B.3.3.1 Installing a Prepared Distribution for PC Systems
.........................................................

If you have received a binary distribution prepared by the DOS
maintainers, then `gawk' and the necessary support files appear under
the `gnu' directory, with executables in `gnu/bin', libraries in
`gnu/lib/awk', and manual pages under `gnu/man'.  This is designed for
easy installation to a `/gnu' directory on your drive--however, the
files can be installed anywhere provided `AWKPATH' is set properly.
Regardless of the installation directory, the first line of `igawk.cmd'
and `igawk.bat' (in `gnu/bin') may need to be edited.

The binary distribution contains a separate file describing the
contents. In particular, it may include more than one version of the
`gawk' executable.

OS/2 (32 bit, EMX) binary distributions are prepared for the `/usr'
directory of your preferred drive. Set `UNIXROOT' to your installation
drive (e.g., `e:') if you want to install `gawk' onto another drive
than the hardcoded default `c:'. Executables appear in `/usr/bin',
libraries under `/usr/share/awk', manual pages under `/usr/man',
Texinfo documentation under `/usr/info' and NLS files under
`/usr/share/locale'.  If you already have a file `/usr/info/dir' from
another package _do not overwrite it!_ Instead enter the following
commands at your prompt (replace `x:' by your installation drive):

     install-info --info-dir=x:/usr/info x:/usr/info/gawk.info
     install-info --info-dir=x:/usr/info x:/usr/info/gawkinet.info

However, the files can be installed anywhere provided `AWKPATH' is set
properly.

The binary distribution may contain a separate file containing
additional or more detailed installation instructions.


File: gawk.info,  Node: PC Compiling,  Next: PC Dynamic,  Prev: PC Binary Installation,  Up: PC Installation

B.3.3.2 Compiling `gawk' for PC Operating Systems
.................................................

`gawk' can be compiled for MS-DOS, Windows32, and OS/2 using the GNU
development tools from DJ Delorie (DJGPP; MS-DOS only) or Eberhard
Mattes (EMX; MS-DOS, Windows32 and OS/2).  Microsoft Visual C/C++ can
be used to build a Windows32 version, and Microsoft C/C++ can be used
to build 16-bit versions for MS-DOS and OS/2.  (As of `gawk' 3.1.2, the
MSC version doesn't work. However, the maintainer is working on fixing
it.)  The file `README_d/README.pc' in the `gawk' distribution contains
additional notes, and `pc/Makefile' contains important information on
compilation options.

To build `gawk' for MS-DOS, Windows32, and OS/2 (16 bit only; for 32 bit
(EMX) you can use the `configure' script and skip the following
paragraphs; for details see below), copy the files in the `pc'
directory (_except_ for `ChangeLog') to the directory with the rest of
the `gawk' sources. The `Makefile' contains a configuration section
with comments and may need to be edited in order to work with your
`make' utility.

The `Makefile' contains a number of targets for building various MS-DOS,
Windows32, and OS/2 versions. A list of targets is printed if the `make'
command is given without a target. As an example, to build `gawk' using
the DJGPP tools, enter `make djgpp'.  (The DJGPP tools may be found at
`ftp://ftp.delorie.com/pub/djgpp/current/v2gnu/'.)

Using `make' to run the standard tests and to install `gawk' requires
additional Unix-like tools, including `sh', `sed', and `cp'. In order
to run the tests, the `test/*.ok' files may need to be converted so
that they have the usual DOS-style end-of-line markers. Most of the
tests work properly with Stewartson's shell along with the companion
utilities or appropriate GNU utilities.  However, some editing of
`test/Makefile' is required. It is recommended that you copy the file
`pc/Makefile.tst' over the file `test/Makefile' as a replacement.
Details can be found in `README_d/README.pc' and in the file
`pc/Makefile.tst'.

The 32 bit EMX version of `gawk' works "out of the box" under OS/2.  In
principle, it is possible to compile `gawk' the following way:

     $ ./configure
     $ make

This is not recommended, though. To get an OMF executable you should
use the following commands at your `sh' prompt:

     $ CPPFLAGS="-D__ST_MT_ERRNO__"
     $ export CPPFLAGS
     $ CFLAGS="-O2 -Zomf -Zmt"
     $ export CFLAGS
     $ LDFLAGS="-s -Zcrtdll -Zlinker /exepack:2 -Zlinker /pm:vio -Zstack 0x6000"
     $ export LDFLAGS
     $ RANLIB="echo"
     $ export RANLIB
     $ ./configure --prefix=c:/usr --without-included-gettext
     $ make AR=emxomfar

These are just suggestions. You may use any other set of
(self-consistent) environment variables and compiler flags.

To get an FHS-compliant file hierarchy it is recommended to use the
additional `configure' options `--infodir=c:/usr/share/info',
`--mandir=c:/usr/share/man' and `--libexecdir=c:/usr/lib'.

If you use GCC 2.95 it is recommended to use also:

     $ LIBS="-lgcc"
     $ export LIBS

You can also get an `a.out' executable if you prefer:

     $ CPPFLAGS="-D__ST_MT_ERRNO__"
     $ export CPPFLAGS
     $ CFLAGS="-O2 -Zmt"
     $ export CFLAGS
     $ LDFLAGS="-s -Zstack 0x6000"
     $ LIBS="-lgcc"
     $ unset RANLIB
     $ ./configure --prefix=c:/usr
     $ make

     NOTE: Versions later than GCC 2.95, i.e., GCC 3.x using the
     Innotek libc were not tested.

     NOTE: Even if the compiled `gawk.exe' (`a.out') executable
     contains a DOS header, it does _not_ work under DOS. To compile an
     executable that runs under DOS, `"-DPIPES_SIMULATED"' must be
     added to `CPPFLAGS'.  But then some nonstandard extensions of
     `gawk' (e.g., `|&') do not work!

After compilation the internal tests can be performed. Enter `make
check CMP="diff -a"' at your command prompt. All tests except for the
`pid' test are expected to work properly.  The `pid' test fails because
child processes are not started by `fork()'.

`make install' works as expected.

     NOTE: Most OS/2 ports of GNU `make' are not able to handle the
     Makefiles of this package. If you encounter any problems with
     `make' try GNU Make 3.79.1 or later versions. You should find the
     latest version on `http://www.unixos2.org/sw/pub/binary/make/' or
     on `ftp://hobbes.nmsu.edu/pub/os2/'.


File: gawk.info,  Node: PC Dynamic,  Next: PC Using,  Prev: PC Compiling,  Up: PC Installation

B.3.3.3 Compiling `gawk' For Dynamic Libraries
..............................................

To compile `gawk' with dynamic extension support, uncomment the
definitions of `DYN_FLAGS', `DYN_EXP', `DYN_OBJ', and `DYN_MAKEXP' in
the configuration section of the `Makefile'. There are two definitions
for `DYN_MAKEXP': pick the one that matches your target.

To build some of the example extension libraries, `cd' to the extension
directory and copy `Makefile.pc' to `Makefile'. You can then build
using the same two targets. To run the example `awk' scripts, you'll
need to either change the call to the `extension' function to match the
name of the library (for instance, change `"./ordchr.so"' to
`"ordchr.dll"' or simply `"ordchr"'), or rename the library to match
the call (for instance, rename `ordchr.dll' to `ordchr.so').

If you build `gawk.exe' with one compiler but want to build an
extension library with the other, you need to copy the import library.
Visual C uses a library called `gawk.lib', while MinGW uses a library
called `libgawk.a'. These files are equivalent and will interoperate if
you give them the correct name.  The resulting shared libraries are
also interoperable.

To create your own extension library, you can use the examples as
models, but you're essentially on your own. Post to `comp.lang.awk' or
send electronic mail to <ptjm@interlog.com> if you have problems getting
started. If you need to access functions or variables which are not
exported by `gawk.exe', add them to `gawkw32.def' and rebuild. You
should also add `ATTRIBUTE_EXPORTED' to the declaration in `awk.h' of
any variables you add to `gawkw32.def'.

Note that extension libraries have the name of the `awk' executable
embedded in them at link time, so they will work only with `gawk.exe'.
In particular, they won't work if you rename `gawk.exe' to `awk.exe' or
if you try to use `pgawk.exe'. You can perform profiling by temporarily
renaming `pgawk.exe' to `gawk.exe'. You can resolve this problem by
changing the program name in the definition of `DYN_MAKEXP' for your
compiler.

On Windows32, libraries are sought first in the current directory, then
in the directory containing `gawk.exe', and finally through the `PATH'
environment variable.


File: gawk.info,  Node: PC Using,  Next: Cygwin,  Prev: PC Dynamic,  Up: PC Installation

B.3.3.4 Using `gawk' on PC Operating Systems
............................................

With the exception of the Cygwin environment, the `|&' operator and
TCP/IP networking (*note TCP/IP Networking::) are not supported for
MS-DOS or MS-Windows. EMX (OS/2 only) does support at least the `|&'
operator.

The OS/2 and MS-DOS versions of `gawk' search for program files as
described in *Note AWKPATH Variable::.  However, semicolons (rather
than colons) separate elements in the `AWKPATH' variable. If `AWKPATH'
is not set or is empty, then the default search path for OS/2 (16 bit)
and MS-DOS versions is `".;c:/lib/awk;c:/gnu/lib/awk"'.

The search path for OS/2 (32 bit, EMX) is determined by the prefix
directory (most likely `/usr' or `c:/usr') that has been specified as
an option of the `configure' script like it is the case for the Unix
versions.  If `c:/usr' is the prefix directory then the default search
path contains `.' and `c:/usr/share/awk'.  Additionally, to support
binary distributions of `gawk' for OS/2 systems whose drive `c:' might
not support long file names or might not exist at all, there is a
special environment variable. If `UNIXROOT' specifies a drive then this
specific drive is also searched for program files.  E.g., if `UNIXROOT'
is set to `e:' the complete default search path is
`".;c:/usr/share/awk;e:/usr/share/awk"'.

An `sh'-like shell (as opposed to `command.com' under MS-DOS or
`cmd.exe' under OS/2) may be useful for `awk' programming.  Ian
Stewartson has written an excellent shell for MS-DOS and OS/2, Daisuke
Aoyama has ported GNU `bash' to MS-DOS using the DJGPP tools, and
several shells are available for OS/2, including `ksh'.  The file
`README_d/README.pc' in the `gawk' distribution contains information on
these shells.  Users of Stewartson's shell on DOS should examine its
documentation for handling command lines; in particular, the setting
for `gawk' in the shell configuration may need to be changed and the
`ignoretype' option may also be of interest.

Under OS/2 and DOS, `gawk' (and many other text programs) silently
translate end-of-line `"\r\n"' to `"\n"' on input and `"\n"' to
`"\r\n"' on output.  A special `BINMODE' variable allows control over
these translations and is interpreted as follows:

   * If `BINMODE' is `"r"', or `(BINMODE & 1)' is nonzero, then binary
     mode is set on read (i.e., no translations on reads).

   * If `BINMODE' is `"w"', or `(BINMODE & 2)' is nonzero, then binary
     mode is set on write (i.e., no translations on writes).

   * If `BINMODE' is `"rw"' or `"wr"', binary mode is set for both read
     and write (same as `(BINMODE & 3)').

   * `BINMODE=NON-NULL-STRING' is the same as `BINMODE=3' (i.e., no
     translations on reads or writes).  However, `gawk' issues a warning
     message if the string is not one of `"rw"' or `"wr"'.

The modes for standard input and standard output are set one time only
(after the command line is read, but before processing any of the `awk'
program).  Setting `BINMODE' for standard input or standard output is
accomplished by using an appropriate `-v BINMODE=N' option on the
command line.  `BINMODE' is set at the time a file or pipe is opened
and cannot be changed mid-stream.

The name `BINMODE' was chosen to match `mawk' (*note Other Versions::).
Both `mawk' and `gawk' handle `BINMODE' similarly; however, `mawk' adds
a `-W BINMODE=N' option and an environment variable that can set
`BINMODE', `RS', and `ORS'.  The files `binmode[1-3].awk' (under
`gnu/lib/awk' in some of the prepared distributions) have been chosen
to match `mawk''s `-W BINMODE=N' option.  These can be changed or
discarded; in particular, the setting of `RS' giving the fewest
"surprises" is open to debate.  `mawk' uses `RS = "\r\n"' if binary
mode is set on read, which is appropriate for files with the DOS-style
end-of-line.

To illustrate, the following examples set binary mode on writes for
standard output and other files, and set `ORS' as the "usual" DOS-style
end-of-line:

     gawk -v BINMODE=2 -v ORS="\r\n" ...

or:

     gawk -v BINMODE=w -f binmode2.awk ...

These give the same result as the `-W BINMODE=2' option in `mawk'.  The
following changes the record separator to `"\r\n"' and sets binary mode
on reads, but does not affect the mode on standard input:

     gawk -v RS="\r\n" --source "BEGIN { BINMODE = 1 }" ...

or:

     gawk -f binmode1.awk ...

With proper quoting, in the first example the setting of `RS' can be
moved into the `BEGIN' rule.


File: gawk.info,  Node: Cygwin,  Prev: PC Using,  Up: PC Installation

B.3.3.5 Using `gawk' In The Cygwin Environment
..............................................

`gawk' can be used "out of the box" under Windows if you are using the
Cygwin environment.(1) This environment provides an excellent
simulation of Unix, using the GNU tools, such as `bash', the GNU
Compiler Collection (GCC), GNU Make, and other GNU tools.  Compilation
and installation for Cygwin is the same as for a Unix system:

     tar -xvpzf gawk-3.1.5.tar.gz
     cd gawk-3.1.5
     ./configure
     make

When compared to GNU/Linux on the same system, the `configure' step on
Cygwin takes considerably longer.  However, it does finish, and then
the `make' proceeds as usual.

     NOTE: The `|&' operator and TCP/IP networking (*note TCP/IP
     Networking::) are fully supported in the Cygwin environment.  This
     is not true for any other environment for MS-DOS or MS-Windows.

---------- Footnotes ----------

(1) `http://www.cygwin.com'


File: gawk.info,  Node: VMS Installation,  Prev: PC Installation,  Up: Non-Unix Installation

B.3.4 How to Compile and Install `gawk' on VMS
----------------------------------------------

This node describes how to compile and install `gawk' under VMS.

* Menu:

* VMS Compilation::             How to compile `gawk' under VMS.
* VMS Installation Details::    How to install `gawk' under VMS.
* VMS Running::                 How to run `gawk' under VMS.
* VMS POSIX::                   Alternate instructions for VMS POSIX.


File: gawk.info,  Node: VMS Compilation,  Next: VMS Installation Details,  Up: VMS Installation

B.3.4.1 Compiling `gawk' on VMS
...............................

To compile `gawk' under VMS, there is a `DCL' command procedure that
issues all the necessary `CC' and `LINK' commands. There is also a
`Makefile' for use with the `MMS' utility.  From the source directory,
use either:

     $ @[.VMS]VMSBUILD.COM

or:

     $ MMS/DESCRIPTION=[.VMS]DESCRIP.MMS GAWK

Depending upon which C compiler you are using, follow one of the sets
of instructions in this table:

VAX C V3.x
     Use either `vmsbuild.com' or `descrip.mms' as is.  These use
     `CC/OPTIMIZE=NOLINE', which is essential for Version 3.0.

VAX C V2.x
     You must have Version 2.3 or 2.4; older ones won't work.  Edit
     either `vmsbuild.com' or `descrip.mms' according to the comments
     in them.  For `vmsbuild.com', this just entails removing two `!'
     delimiters.  Also edit `config.h' (which is a copy of file
     `[.config]vms-conf.h') and comment out or delete the two lines
     `#define __STDC__ 0' and `#define VAXC_BUILTINS' near the end.

GNU C
     Edit `vmsbuild.com' or `descrip.mms'; the changes are different
     from those for VAX C V2.x but equally straightforward.  No changes
     to `config.h' are needed.

DEC C
     Edit `vmsbuild.com' or `descrip.mms' according to their comments.
     No changes to `config.h' are needed.

`gawk' has been tested under VAX/VMS 5.5-1 using VAX C V3.2, and GNU C
1.40 and 2.3.  It should work without modifications for VMS V4.6 and up.


File: gawk.info,  Node: VMS Installation Details,  Next: VMS Running,  Prev: VMS Compilation,  Up: VMS Installation

B.3.4.2 Installing `gawk' on VMS
................................

To install `gawk', all you need is a "foreign" command, which is a
`DCL' symbol whose value begins with a dollar sign. For example:

     $ GAWK :== $disk1:[gnubin]GAWK

Substitute the actual location of `gawk.exe' for `$disk1:[gnubin]'. The
symbol should be placed in the `login.com' of any user who wants to run
`gawk', so that it is defined every time the user logs on.
Alternatively, the symbol may be placed in the system-wide
`sylogin.com' procedure, which allows all users to run `gawk'.

Optionally, the help entry can be loaded into a VMS help library:

     $ LIBRARY/HELP SYS$HELP:HELPLIB [.VMS]GAWK.HLP

(You may want to substitute a site-specific help library rather than
the standard VMS library `HELPLIB'.)  After loading the help text, the
command:

     $ HELP GAWK

provides information about both the `gawk' implementation and the `awk'
programming language.

The logical name `AWK_LIBRARY' can designate a default location for
`awk' program files.  For the `-f' option, if the specified file name
has no device or directory path information in it, `gawk' looks in the
current directory first, then in the directory specified by the
translation of `AWK_LIBRARY' if the file is not found.  If, after
searching in both directories, the file still is not found, `gawk'
appends the suffix `.awk' to the filename and retries the file search.
If `AWK_LIBRARY' is not defined, that portion of the file search fails
benignly.


File: gawk.info,  Node: VMS Running,  Next: VMS POSIX,  Prev: VMS Installation Details,  Up: VMS Installation

B.3.4.3 Running `gawk' on VMS
.............................

Command-line parsing and quoting conventions are significantly different
on VMS, so examples in this Info file or from other sources often need
minor changes.  They _are_ minor though, and all `awk' programs should
run correctly.

Here are a couple of trivial tests:

     $ gawk -- "BEGIN {print ""Hello, World!""}"
     $ gawk -"W" version
     ! could also be -"W version" or "-W version"

Note that uppercase and mixed-case text must be quoted.

The VMS port of `gawk' includes a `DCL'-style interface in addition to
the original shell-style interface (see the help entry for details).
One side effect of dual command-line parsing is that if there is only a
single parameter (as in the quoted string program above), the command
becomes ambiguous.  To work around this, the normally optional `--'
flag is required to force Unix style rather than `DCL' parsing.  If any
other dash-type options (or multiple parameters such as data files to
process) are present, there is no ambiguity and `--' can be omitted.

The default search path, when looking for `awk' program files specified
by the `-f' option, is `"SYS$DISK:[],AWK_LIBRARY:"'.  The logical name
`AWKPATH' can be used to override this default.  The format of
`AWKPATH' is a comma-separated list of directory specifications.  When
defining it, the value should be quoted so that it retains a single
translation and not a multitranslation `RMS' searchlist.


File: gawk.info,  Node: VMS POSIX,  Prev: VMS Running,  Up: VMS Installation

B.3.4.4 Building and Using `gawk' on VMS POSIX
..............................................

Ignore the instructions above, although `vms/gawk.hlp' should still be
made available in a help library.  The source tree should be unpacked
into a container file subsystem rather than into the ordinary VMS
filesystem.  Make sure that the two scripts, `configure' and
`vms/posix-cc.sh', are executable; use `chmod +x' on them if necessary.
Then execute the following two commands:

     psx> CC=vms/posix-cc.sh configure
     psx> make CC=c89 gawk

The first command constructs files `config.h' and `Makefile' out of
templates, using a script to make the C compiler fit `configure''s
expectations.  The second command compiles and links `gawk' using the C
compiler directly; ignore any warnings from `make' about being unable
to redefine `CC'.  `configure' takes a very long time to execute, but
at least it provides incremental feedback as it runs.

This has been tested with VAX/VMS V6.2, VMS POSIX V2.0, and DEC C V5.2.

Once built, `gawk' works like any other shell utility.  Unlike the
normal VMS port of `gawk', no special command-line manipulation is
needed in the VMS POSIX environment.


File: gawk.info,  Node: Unsupported,  Next: Bugs,  Prev: Non-Unix Installation,  Up: Installation

B.4 Unsupported Operating System Ports
======================================

This sections describes systems for which the `gawk' port is no longer
supported.

* Menu:

* Atari Installation::          Installing `gawk' on the Atari ST.
* Tandem Installation::         Installing `gawk' on a Tandem.


File: gawk.info,  Node: Atari Installation,  Next: Tandem Installation,  Up: Unsupported

B.4.1 Installing `gawk' on the Atari ST
---------------------------------------

The Atari port is no longer supported.  It is included for those who
might want to use it but it is no longer being actively maintained.

There are no substantial differences when installing `gawk' on various
Atari models.  Compiled `gawk' executables do not require a large
amount of memory with most `awk' programs, and should run on all
Motorola processor-based models (called further ST, even if that is not
exactly right).

In order to use `gawk', you need to have a shell, either text or
graphics, that does not map all the characters of a command line to
uppercase.  Maintaining case distinction in option flags is very
important (*note Options::).  These days this is the default and it may
only be a problem for some very old machines.  If your system does not
preserve the case of option flags, you need to upgrade your tools.
Support for I/O redirection is necessary to make it easy to import
`awk' programs from other environments.  Pipes are nice to have but not
vital.

* Menu:

* Atari Compiling::             Compiling `gawk' on Atari.
* Atari Using::                 Running `gawk' on Atari.


File: gawk.info,  Node: Atari Compiling,  Next: Atari Using,  Up: Atari Installation

B.4.1.1 Compiling `gawk' on the Atari ST
........................................

A proper compilation of `gawk' sources when `sizeof(int)' differs from
`sizeof(void *)' requires an ISO C compiler. An initial port was done
with `gcc'.  You may actually prefer executables where `int's are four
bytes wide but the other variant works as well.

You may need quite a bit of memory when trying to recompile the `gawk'
sources, as some source files (`regex.c' in particular) are quite big.
If you run out of memory compiling such a file, try reducing the
optimization level for this particular file, which may help.

With a reasonable shell (`bash' will do), you have a pretty good chance
that the `configure' utility will succeed, and in particular if you run
GNU/Linux, MiNT or a similar operating system.  Otherwise sample
versions of `config.h' and `Makefile.st' are given in the `atari'
subdirectory and can be edited and copied to the corresponding files in
the main source directory.  Even if `configure' produces something, it
might be advisable to compare its results with the sample versions and
possibly make adjustments.

Some `gawk' source code fragments depend on a preprocessor define
`atarist'.  This basically assumes the TOS environment with `gcc'.
Modify these sections as appropriate if they are not right for your
environment.  Also see the remarks about `AWKPATH' and `envsep' in
*Note Atari Using::.

As shipped, the sample `config.h' claims that the `system' function is
missing from the libraries, which is not true, and an alternative
implementation of this function is provided in
`unsupported/atari/system.c'.  Depending upon your particular
combination of shell and operating system, you might want to change the
file to indicate that `system' is available.


File: gawk.info,  Node: Atari Using,  Prev: Atari Compiling,  Up: Atari Installation

B.4.1.2 Running `gawk' on the Atari ST
......................................

An executable version of `gawk' should be placed, as usual, anywhere in
your `PATH' where your shell can find it.

While executing, the Atari version of `gawk' creates a number of
temporary files.  When using `gcc' libraries for TOS, `gawk' looks for
either of the environment variables, `TEMP' or `TMPDIR', in that order.
If either one is found, its value is assumed to be a directory for
temporary files.  This directory must exist, and if you can spare the
memory, it is a good idea to put it on a RAM drive.  If neither `TEMP'
nor `TMPDIR' are found, then `gawk' uses the current directory for its
temporary files.

The ST version of `gawk' searches for its program files, as described in
*Note AWKPATH Variable::.  The default value for the `AWKPATH' variable
is taken from `DEFPATH' defined in `Makefile'. The sample `gcc'/TOS
`Makefile' for the ST in the distribution sets `DEFPATH' to
`".,c:\lib\awk,c:\gnu\lib\awk"'.  The search path can be modified by
explicitly setting `AWKPATH' to whatever you want.  Note that colons
cannot be used on the ST to separate elements in the `AWKPATH'
variable, since they have another reserved meaning.  Instead, you must
use a comma to separate elements in the path.  When recompiling, the
separating character can be modified by initializing the `envsep'
variable in `unsupported/atari/gawkmisc.atr' to another value.

Although `awk' allows great flexibility in doing I/O redirections from
within a program, this facility should be used with care on the ST
running under TOS.  In some circumstances, the OS routines for
file-handle pool processing lose track of certain events, causing the
computer to crash and requiring a reboot.  Often a warm reboot is
sufficient.  Fortunately, this happens infrequently and in rather
esoteric situations.  In particular, avoid having one part of an `awk'
program using `print' statements explicitly redirected to
`/dev/stdout', while other `print' statements use the default standard
output, and a calling shell has redirected standard output to a file.

When `gawk' is compiled with the ST version of `gcc' and its usual
libraries, it accepts both `/' and `\' as path separators.  While this
is convenient, it should be remembered that this removes one
technically valid character (`/') from your file name.  It may also
create problems for external programs called via the `system' function,
which may not support this convention.  Whenever it is possible that a
file created by `gawk' will be used by some other program, use only
backslashes.  Also remember that in `awk', backslashes in strings have
to be doubled in order to get literal backslashes (*note Escape
Sequences::).


File: gawk.info,  Node: Tandem Installation,  Prev: Atari Installation,  Up: Unsupported

B.4.2 Installing `gawk' on a Tandem
-----------------------------------

The Tandem port is only minimally supported.  The port's contributor no
longer has access to a Tandem system.

The Tandem port was done on a Cyclone machine running D20.  The port is
pretty clean and all facilities seem to work except for the I/O piping
facilities (*note Getline/Pipe::, *Note Getline/Variable/Pipe::, and
*Note Redirection::), which is just too foreign a concept for Tandem.

To build a Tandem executable from source, download all of the files so
that the file names on the Tandem box conform to the restrictions of
D20.  For example, `array.c' becomes `ARRAYC', and `awk.h' becomes
`AWKH'.  The totally Tandem-specific files are in the `tandem'
"subvolume" (`unsupported/tandem' in the `gawk' distribution) and
should be copied to the main source directory before building `gawk'.

The file `compit' can then be used to compile and bind an executable.
Alas, there is no `configure' or `make'.

Usage is the same as for Unix, except that D20 requires all `{' and `}'
characters to be escaped with `~' on the command line (but _not_ in
script files). Also, the standard Tandem syntax for `/in filename,out
filename/' must be used instead of the usual Unix `<' and `>' for file
redirection.  (Redirection options on `getline', `print' etc., are
supported.)

The `-mr VAL' option (*note Options::) has been "stolen" to enable
Tandem users to process fixed-length records with no "end-of-line"
character. That is, `-mr 74' tells `gawk' to read the input file as
fixed 74-byte records.


File: gawk.info,  Node: Bugs,  Next: Other Versions,  Prev: Unsupported,  Up: Installation

B.5 Reporting Problems and Bugs
===============================

     There is nothing more dangerous than a bored archeologist.
     The Hitchhiker's Guide to the Galaxy

If you have problems with `gawk' or think that you have found a bug,
please report it to the developers; we cannot promise to do anything
but we might well want to fix it.

Before reporting a bug, make sure you have actually found a real bug.
Carefully reread the documentation and see if it really says you can do
what you're trying to do.  If it's not clear whether you should be able
to do something or not, report that too; it's a bug in the
documentation!

Before reporting a bug or trying to fix it yourself, try to isolate it
to the smallest possible `awk' program and input data file that
reproduces the problem.  Then send us the program and data file, some
idea of what kind of Unix system you're using, the compiler you used to
compile `gawk', and the exact results `gawk' gave you.  Also say what
you expected to occur; this helps us decide whether the problem is
really in the documentation.

Once you have a precise problem, send email to <bug-gawk@gnu.org>.

Please include the version number of `gawk' you are using.  You can get
this information with the command `gawk --version'.  Using this address
automatically sends a carbon copy of your mail to me.  If necessary, I
can be reached directly at <arnold@gnu.org>.  The bug reporting address
is preferred since the email list is archived at the GNU Project.  _All
email should be in English, since that is my native language._

*Caution:* Do _not_ try to report bugs in `gawk' by posting to the
Usenet/Internet newsgroup `comp.lang.awk'.  While the `gawk' developers
do occasionally read this newsgroup, there is no guarantee that we will
see your posting.  The steps described above are the official
recognized ways for reporting bugs.

Non-bug suggestions are always welcome as well.  If you have questions
about things that are unclear in the documentation or are just obscure
features, ask me; I will try to help you out, although I may not have
the time to fix the problem.  You can send me electronic mail at the
Internet address noted previously.

If you find bugs in one of the non-Unix ports of `gawk', please send an
electronic mail message to the person who maintains that port.  They
are named in the following list, as well as in the `README' file in the
`gawk' distribution.  Information in the `README' file should be
considered authoritative if it conflicts with this Info file.

The people maintaining the non-Unix ports of `gawk' are as follows:

Amiga        Fred Fish, <fnf@ninemoons.com>.
BeOS         Martin Brown, <mc@whoever.com>.
MS-DOS       Scott Deifik, <scottd@amgen.com> and Darrel
             Hankerson, <hankedr@mail.auburn.edu>.
MS-Windows   Juan Grigera, <juan@biophnet.unlp.edu.ar>.
OS/2         The Unix for OS/2 team,
             <gawk-maintainer@unixos2.org>.
Tandem       Stephen Davies, <scldad@sdc.com.au>.
VMS          Pat Rankin, <rankin@pactechdata.com>.

If your bug is also reproducible under Unix, please send a copy of your
report to the <bug-gawk@gnu.org> email list as well.


File: gawk.info,  Node: Other Versions,  Prev: Bugs,  Up: Installation

B.6 Other Freely Available `awk' Implementations
================================================

     It's kind of fun to put comments like this in your awk code.
     `// Do C++ comments work? answer: yes! of course'
     Michael Brennan

There are three other freely available `awk' implementations.  This
minor node briefly describes where to get them:

Unix `awk'
     Brian Kernighan has made his implementation of `awk' freely
     available.  You can retrieve this version via the World Wide Web
     from his home page.(1) It is available in several archive formats:

    Shell archive
          `http://cm.bell-labs.com/who/bwk/awk.shar'

    Compressed `tar' file
          `http://cm.bell-labs.com/who/bwk/awk.tar.gz'

    Zip file
          `http://cm.bell-labs.com/who/bwk/awk.zip'

     This version requires an ISO C (1990 standard) compiler; the C
     compiler from GCC (the GNU Compiler Collection) works quite nicely.

     *Note BTL::, for a list of extensions in this `awk' that are not
     in POSIX `awk'.

`mawk'
     Michael Brennan has written an independent implementation of `awk',
     called `mawk'.  It is available under the GPL (*note Copying::),
     just as `gawk' is.

     You can get it via anonymous `ftp' to the host `ftp.whidbey.net'.
     Change directory to `/pub/brennan'.  Use "binary" or "image" mode,
     and retrieve `mawk1.3.3.tar.gz' (or the latest version that is
     there).

     `gunzip' may be used to decompress this file. Installation is
     similar to `gawk''s (*note Unix Installation::).

     `mawk' has the following extensions that are not in POSIX `awk':

        * The `fflush' built-in function for flushing buffered output
          (*note I/O Functions::).

        * The `**' and `**=' operators (*note Arithmetic Ops:: and also
          see *Note Assignment Ops::).

        * The use of `func' as an abbreviation for `function' (*note
          Definition Syntax::).

        * The `\x' escape sequence (*note Escape Sequences::).

        * The `/dev/stdout', and `/dev/stderr' special files (*note
          Special Files::).  Use `"-"' instead of `"/dev/stdin"' with
          `mawk'.

        * The ability for `FS' and for the third argument to `split' to
          be null strings (*note Single Character Fields::).

        * The ability to delete all of an array at once with `delete
          ARRAY' (*note Delete::).

        * The ability for `RS' to be a regexp (*note Records::).

        * The `BINMODE' special variable for non-Unix operating systems
          (*note PC Using::).

     The next version of `mawk' will support `nextfile'.

`awka'
     Written by Andrew Sumner, `awka' translates `awk' programs into C,
     compiles them, and links them with a library of functions that
     provides the core `awk' functionality.  It also has a number of
     extensions.

     The `awk' translator is released under the GPL, and the library is
     under the LGPL.

     To get `awka', go to `http://awka.sourceforge.net'.  You can reach
     Andrew Sumner at <andrew@zbcom.net>.

`pawk'
     Nelson H.F. Beebe at the University of Utah has modified the Bell
     Labs `awk' to provide timing and profiling information.  It is
     different from `pgawk' (*note Profiling::), in that it uses
     CPU-based profiling, not line-count profiling.  You may find it at
     either `ftp://ftp.math.utah.edu/pub/pawk/pawk-20020210.tar.gz' or
     `http://www.math.utah.edu/pub/pawk/pawk-20020210.tar.gz'.


---------- Footnotes ----------

(1) `http://cm.bell-labs.com/who/bwk'


File: gawk.info,  Node: Notes,  Next: Basic Concepts,  Prev: Installation,  Up: Top

Appendix C Implementation Notes
*******************************

This appendix contains information mainly of interest to implementors
and maintainers of `gawk'.  Everything in it applies specifically to
`gawk' and not to other implementations.

* Menu:

* Compatibility Mode::          How to disable certain `gawk'
                                extensions.
* Additions::                   Making Additions To `gawk'.
* Dynamic Extensions::          Adding new built-in functions to
                                `gawk'.
* Future Extensions::           New features that may be implemented one day.


File: gawk.info,  Node: Compatibility Mode,  Next: Additions,  Up: Notes

C.1 Downward Compatibility and Debugging
========================================

*Note POSIX/GNU::, for a summary of the GNU extensions to the `awk'
language and program.  All of these features can be turned off by
invoking `gawk' with the `--traditional' option or with the `--posix'
option.

If `gawk' is compiled for debugging with `-DDEBUG', then there is one
more option available on the command line:

`-W parsedebug'
`--parsedebug'
     Prints out the parse stack information as the program is being
     parsed.

This option is intended only for serious `gawk' developers and not for
the casual user.  It probably has not even been compiled into your
version of `gawk', since it slows down execution.


File: gawk.info,  Node: Additions,  Next: Dynamic Extensions,  Prev: Compatibility Mode,  Up: Notes

C.2 Making Additions to `gawk'
==============================

If you find that you want to enhance `gawk' in a significant fashion,
you are perfectly free to do so.  That is the point of having free
software; the source code is available and you are free to change it as
you want (*note Copying::).

This minor node discusses the ways you might want to change `gawk' as
well as any considerations you should bear in mind.

* Menu:

* Adding Code::                 Adding code to the main body of
                                `gawk'.
* New Ports::                   Porting `gawk' to a new operating
                                system.


File: gawk.info,  Node: Adding Code,  Next: New Ports,  Up: Additions

C.2.1 Adding New Features
-------------------------

You are free to add any new features you like to `gawk'.  However, if
you want your changes to be incorporated into the `gawk' distribution,
there are several steps that you need to take in order to make it
possible for me to include your changes:

  1. Before building the new feature into `gawk' itself, consider
     writing it as an extension module (*note Dynamic Extensions::).
     If that's not possible, continue with the rest of the steps in
     this list.

  2. Get the latest version.  It is much easier for me to integrate
     changes if they are relative to the most recent distributed
     version of `gawk'.  If your version of `gawk' is very old, I may
     not be able to integrate them at all.  (*Note Getting::, for
     information on getting the latest version of `gawk'.)

  3. See *note (Version)Top:: standards, GNU Coding Standards.  This
     document describes how GNU software should be written. If you
     haven't read it, please do so, preferably _before_ starting to
     modify `gawk'.  (The `GNU Coding Standards' are available from the
     GNU Project's `ftp' site, at
     `ftp://ftp.gnu.org/gnu/GNUinfo/standards.text'.  An HTML version,
     suitable for reading with a WWW browser, is available at
     `http://www.gnu.org/prep/standards_toc.html'.  Texinfo, Info, and
     DVI versions are also available.)

  4. Use the `gawk' coding style.  The C code for `gawk' follows the
     instructions in the `GNU Coding Standards', with minor exceptions.
     The code is formatted using the traditional "K&R" style,
     particularly as regards to the placement of braces and the use of
     tabs.  In brief, the coding rules for `gawk' are as follows:

        * Use ANSI/ISO style (prototype) function headers when defining
          functions.

        * Put the name of the function at the beginning of its own line.

        * Put the return type of the function, even if it is `int', on
          the line above the line with the name and arguments of the
          function.

        * Put spaces around parentheses used in control structures
          (`if', `while', `for', `do', `switch', and `return').

        * Do not put spaces in front of parentheses used in function
          calls.

        * Put spaces around all C operators and after commas in
          function calls.

        * Do not use the comma operator to produce multiple side
          effects, except in `for' loop initialization and increment
          parts, and in macro bodies.

        * Use real tabs for indenting, not spaces.

        * Use the "K&R" brace layout style.

        * Use comparisons against `NULL' and `'\0'' in the conditions of
          `if', `while', and `for' statements, as well as in the `case's
          of `switch' statements, instead of just the plain pointer or
          character value.

        * Use the `TRUE', `FALSE' and `NULL' symbolic constants and the
          character constant `'\0'' where appropriate, instead of `1'
          and `0'.

        * Use the `ISALPHA', `ISDIGIT', etc. macros, instead of the
          traditional lowercase versions; these macros are better
          behaved for non-ASCII character sets.

        * Provide one-line descriptive comments for each function.

        * Do not use `#elif'. Many older Unix C compilers cannot handle
          it.

        * Do not use the `alloca' function for allocating memory off
          the stack.  Its use causes more portability trouble than is
          worth the minor benefit of not having to free the storage.
          Instead, use `malloc' and `free'.

          NOTE: If I have to reformat your code to follow the coding
          style used in `gawk', I may not bother to integrate your
          changes at all.

  5. Be prepared to sign the appropriate paperwork.  In order for the
     FSF to distribute your changes, you must either place those
     changes in the public domain and submit a signed statement to that
     effect, or assign the copyright in your changes to the FSF.  Both
     of these actions are easy to do and _many_ people have done so
     already. If you have questions, please contact me (*note Bugs::),
     or <gnu@gnu.org>.

  6. Update the documentation.  Along with your new code, please supply
     new sections and/or chapters for this Info file.  If at all
     possible, please use real Texinfo, instead of just supplying
     unformatted ASCII text (although even that is better than no
     documentation at all).  Conventions to be followed in `GAWK:
     Effective AWK Programming' are provided after the `@bye' at the
     end of the Texinfo source file.  If possible, please update the
     `man' page as well.

     You will also have to sign paperwork for your documentation
     changes.

  7. Submit changes as context diffs or unified diffs.  Use `diff -c -r
     -N' or `diff -u -r -N' to compare the original `gawk' source tree
     with your version.  (I find context diffs to be more readable but
     unified diffs are more compact.)  I recommend using the GNU
     version of `diff'.  Send the output produced by either run of
     `diff' to me when you submit your changes.  (*Note Bugs::, for the
     electronic mail information.)

     Using this format makes it easy for me to apply your changes to the
     master version of the `gawk' source code (using `patch').  If I
     have to apply the changes manually, using a text editor, I may not
     do so, particularly if there are lots of changes.

  8. Include an entry for the `ChangeLog' file with your submission.
     This helps further minimize the amount of work I have to do,
     making it easier for me to accept patches.

Although this sounds like a lot of work, please remember that while you
may write the new code, I have to maintain it and support it. If it
isn't possible for me to do that with a minimum of extra work, then I
probably will not.


File: gawk.info,  Node: New Ports,  Prev: Adding Code,  Up: Additions

C.2.2 Porting `gawk' to a New Operating System
----------------------------------------------

If you want to port `gawk' to a new operating system, there are several
steps:

  1. Follow the guidelines in *Note Adding Code::, concerning coding
     style, submission of diffs, and so on.

  2. When doing a port, bear in mind that your code must coexist
     peacefully with the rest of `gawk' and the other ports. Avoid
     gratuitous changes to the system-independent parts of the code. If
     at all possible, avoid sprinkling `#ifdef's just for your port
     throughout the code.

     If the changes needed for a particular system affect too much of
     the code, I probably will not accept them.  In such a case, you
     can, of course, distribute your changes on your own, as long as
     you comply with the GPL (*note Copying::).

  3. A number of the files that come with `gawk' are maintained by other
     people at the Free Software Foundation.  Thus, you should not
     change them unless it is for a very good reason; i.e., changes are
     not out of the question, but changes to these files are
     scrutinized extra carefully.  The files are `getopt.h', `getopt.c',
     `getopt1.c', `regex.h', `regex.c', `dfa.h', `dfa.c', `install-sh',
     and `mkinstalldirs'.

  4. Be willing to continue to maintain the port.  Non-Unix operating
     systems are supported by volunteers who maintain the code needed
     to compile and run `gawk' on their systems. If noone volunteers to
     maintain a port, it becomes unsupported and it may be necessary to
     remove it from the distribution.

  5. Supply an appropriate `gawkmisc.???' file.  Each port has its own
     `gawkmisc.???' that implements certain operating system specific
     functions. This is cleaner than a plethora of `#ifdef's scattered
     throughout the code.  The `gawkmisc.c' in the main source
     directory includes the appropriate `gawkmisc.???' file from each
     subdirectory.  Be sure to update it as well.

     Each port's `gawkmisc.???' file has a suffix reminiscent of the
     machine or operating system for the port--for example,
     `pc/gawkmisc.pc' and `vms/gawkmisc.vms'. The use of separate
     suffixes, instead of plain `gawkmisc.c', makes it possible to move
     files from a port's subdirectory into the main subdirectory,
     without accidentally destroying the real `gawkmisc.c' file.
     (Currently, this is only an issue for the PC operating system
     ports.)

  6. Supply a `Makefile' as well as any other C source and header files
     that are necessary for your operating system.  All your code
     should be in a separate subdirectory, with a name that is the same
     as, or reminiscent of, either your operating system or the
     computer system.  If possible, try to structure things so that it
     is not necessary to move files out of the subdirectory into the
     main source directory.  If that is not possible, then be sure to
     avoid using names for your files that duplicate the names of files
     in the main source directory.

  7. Update the documentation.  Please write a section (or sections)
     for this Info file describing the installation and compilation
     steps needed to compile and/or install `gawk' for your system.

  8. Be prepared to sign the appropriate paperwork.  In order for the
     FSF to distribute your code, you must either place your code in
     the public domain and submit a signed statement to that effect, or
     assign the copyright in your code to the FSF.  Both of these
     actions are easy to do and _many_ people have done so already. If
     you have questions, please contact me, or <gnu@gnu.org>.

Following these steps makes it much easier to integrate your changes
into `gawk' and have them coexist happily with other operating systems'
code that is already there.

In the code that you supply and maintain, feel free to use a coding
style and brace layout that suits your taste.


File: gawk.info,  Node: Dynamic Extensions,  Next: Future Extensions,  Prev: Additions,  Up: Notes

C.3 Adding New Built-in Functions to `gawk'
===========================================

     Danger Will Robinson!  Danger!!
     Warning! Warning!
     The Robot

Beginning with `gawk' 3.1, it is possible to add new built-in functions
to `gawk' using dynamically loaded libraries. This facility is
available on systems (such as GNU/Linux) that support the `dlopen' and
`dlsym' functions.  This minor node describes how to write and use
dynamically loaded extensions for `gawk'.  Experience with programming
in C or C++ is necessary when reading this minor node.

*Caution:* The facilities described in this minor node are very much
subject to change in a future `gawk' release.  Be aware that you may
have to re-do everything, perhaps from scratch, at some future time.

*Caution:* If you have written your own dynamic extensions, be sure to
recompile them for each new `gawk' release.  There is no guarantee of
binary compatibility between different releases, no will there ever be
such a guarantee.

* Menu:

* Internals::                   A brief look at some `gawk' internals.
* Sample Library::              A example of new functions.


File: gawk.info,  Node: Internals,  Next: Sample Library,  Up: Dynamic Extensions

C.3.1 A Minimal Introduction to `gawk' Internals
------------------------------------------------

The truth is that `gawk' was not designed for simple extensibility.
The facilities for adding functions using shared libraries work, but
are something of a "bag on the side."  Thus, this tour is brief and
simplistic; would-be `gawk' hackers are encouraged to spend some time
reading the source code before trying to write extensions based on the
material presented here.  Of particular note are the files `awk.h',
`builtin.c', and `eval.c'.  Reading `awkgram.y' in order to see how the
parse tree is built would also be of use.

With the disclaimers out of the way, the following types, structure
members, functions, and macros are declared in `awk.h' and are of use
when writing extensions.  The next minor node shows how they are used:

`AWKNUM'
     An `AWKNUM' is the internal type of `awk' floating-point numbers.
     Typically, it is a C `double'.

`NODE'
     Just about everything is done using objects of type `NODE'.  These
     contain both strings and numbers, as well as variables and arrays.

`AWKNUM force_number(NODE *n)'
     This macro forces a value to be numeric. It returns the actual
     numeric value contained in the node.  It may end up calling an
     internal `gawk' function.

`void force_string(NODE *n)'
     This macro guarantees that a `NODE''s string value is current.  It
     may end up calling an internal `gawk' function.  It also
     guarantees that the string is zero-terminated.

`size_t get_curfunc_arg_count(void)'
     This function returns the actual number of parameters passed to
     the current function.  Inside the code of an extension this can be
     used to determine the maximum index which is safe to use with
     `stack_ptr'.  If this value is greater than `tree->param_cnt', the
     function was called incorrectly from the `awk' program.

     *Caution:* This function is new as of `gawk' 3.1.4.

`n->param_cnt'
     Inside an extension function, this is the maximum number of
     expected parameters, as set by the `make_builtin' function.

`n->stptr'
`n->stlen'
     The data and length of a `NODE''s string value, respectively.  The
     string is _not_ guaranteed to be zero-terminated.  If you need to
     pass the string value to a C library function, save the value in
     `n->stptr[n->stlen]', assign `'\0'' to it, call the routine, and
     then restore the value.

`n->type'
     The type of the `NODE'. This is a C `enum'. Values should be
     either `Node_var' or `Node_var_array' for function parameters.

`n->vname'
     The "variable name" of a node.  This is not of much use inside
     externally written extensions.

`void assoc_clear(NODE *n)'
     Clears the associative array pointed to by `n'.  Make sure that
     `n->type == Node_var_array' first.

`NODE **assoc_lookup(NODE *symbol, NODE *subs, int reference)'
     Finds, and installs if necessary, array elements.  `symbol' is the
     array, `subs' is the subscript.  This is usually a value created
     with `tmp_string' (see below).  `reference' should be `TRUE' if it
     is an error to use the value before it is created. Typically,
     `FALSE' is the correct value to use from extension functions.

`NODE *make_string(char *s, size_t len)'
     Take a C string and turn it into a pointer to a `NODE' that can be
     stored appropriately.  This is permanent storage; understanding of
     `gawk' memory management is helpful.

`NODE *make_number(AWKNUM val)'
     Take an `AWKNUM' and turn it into a pointer to a `NODE' that can
     be stored appropriately.  This is permanent storage; understanding
     of `gawk' memory management is helpful.

`NODE *tmp_string(char *s, size_t len);'
     Take a C string and turn it into a pointer to a `NODE' that can be
     stored appropriately.  This is temporary storage; understanding of
     `gawk' memory management is helpful.

`NODE *tmp_number(AWKNUM val)'
     Take an `AWKNUM' and turn it into a pointer to a `NODE' that can
     be stored appropriately.  This is temporary storage; understanding
     of `gawk' memory management is helpful.

`NODE *dupnode(NODE *n)'
     Duplicate a node.  In most cases, this increments an internal
     reference count instead of actually duplicating the entire `NODE';
     understanding of `gawk' memory management is helpful.

`void free_temp(NODE *n)'
     This macro releases the memory associated with a `NODE' allocated
     with `tmp_string' or `tmp_number'.  Understanding of `gawk' memory
     management is helpful.

`void make_builtin(char *name, NODE *(*func)(NODE *), int count)'
     Register a C function pointed to by `func' as new built-in
     function `name'. `name' is a regular C string. `count' is the
     maximum number of arguments that the function takes.  The function
     should be written in the following manner:

          /* do_xxx --- do xxx function for gawk */

          NODE *
          do_xxx(NODE *tree)
          {
              ...
          }

`NODE *get_argument(NODE *tree, int i)'
     This function is called from within a C extension function to get
     the `i'-th argument from the function call.  The first argument is
     argument zero.

`NODE *get_actual_argument(NODE *tree, unsigned int i,'
`                          int optional, int wantarray);'
     This function retrieves a particular argument `i'.  `wantarray' is
     `TRUE' if the argument should be an array, `FALSE' otherwise. If
     `optional' is `TRUE', the argument need not have been supplied.
     If it wasn't, the return value is `NULL'.  It is a fatal error if
     `optional' is `TRUE' but the argument was not provided.

     *Caution:* This function is new as of `gawk' 3.1.4.

`get_scalar_argument(t, i, opt)'
     This is a convenience macro that calls `get_actual_argument'.

     *Caution:* This macro is new as of `gawk' 3.1.4.

`get_array_argument(t, i, opt)'
     This is a convenience macro that calls `get_actual_argument'.

     *Caution:* This macro is new as of `gawk' 3.1.4.

`void set_value(NODE *tree)'
     This function is called from within a C extension function to set
     the return value from the extension function.  This value is what
     the `awk' program sees as the return value from the new `awk'
     function.

`void update_ERRNO(void)'
     This function is called from within a C extension function to set
     the value of `gawk''s `ERRNO' variable, based on the current value
     of the C `errno' variable.  It is provided as a convenience.

`void update_ERRNO_saved(int errno_saved)'
     This function is called from within a C extension function to set
     the value of `gawk''s `ERRNO' variable, based on the saved value
     of the C `errno' variable provided as the argument.  It is
     provided as a convenience.

     *Caution:* This function is new as of `gawk' 3.1.5.

`void register_deferred_variable(const char *name, NODE *(*load_func)(void))'
     This function is called to register a function to be called when a
     reference to an undefined variable with the given name is
     encountered.  The callback function will never be called if the
     variable exists already, so, unless the calling code is running at
     program startup, it should first check whether a variable of the
     given name already exists.  The argument function must return a
     pointer to a NODE containing the newly created variable.  This
     function is used to implement the builtin `ENVIRON' and `PROCINFO'
     variables, so you can refer to them for examples.

     *Caution:* This function is new as of `gawk' 3.1.5.

`void register_open_hook(void *(*open_func)(IOBUF *))'
     This function is called to register a function to be called
     whenever a new data file is opened, leading to the creation of an
     `IOBUF' structure in `iop_alloc'.  After creating the new `IOBUF',
     `iop_alloc' will call (in reverse order of registration, so the
     last function registered is called first) each open hook until one
     returns non-NULL.  If any hook returns a non-NULL value, that
     value is assigned to the `IOBUF''s `opaque' field (which will
     presumably point to a structure containing additional state
     associated with the input processing), and no further open hooks
     are called.

     The function called will most likely want to set the `IOBUF'
     `get_record' method to indicate that future input records should
     be retrieved by calling that method instead of using the standard
     `gawk' input processing.

     And the function will also probably want to set the `IOBUF'
     `close_func' method to be called when the file is closed to clean
     up any state associated with the input.

     Finally, hook functions should be prepared to receive an `IOBUF'
     structure where the `fd' field is set to `INVALID_HANDLE', meaning
     that `gawk' was not able to open the file itself. In this case,
     the hook function must be able to successfully open the file and
     place a valid file descriptor there.

     Currently, for example, the hook function facility is used to
     implement the XML parser shared library extension.  For more info,
     please look in `awk.h' and in `io.c'.

     *Caution:* This function is new as of `gawk' 3.1.5.

An argument that is supposed to be an array needs to be handled with
some extra code, in case the array being passed in is actually from a
function parameter.

In versions of `gawk' up to and including 3.1.2, the following
boilerplate code shows how to do this:

     NODE *the_arg;

     the_arg = get_argument(tree, 2); /* assume need 3rd arg, 0-based */

     /* if a parameter, get it off the stack */
     if (the_arg->type == Node_param_list)
         the_arg = stack_ptr[the_arg->param_cnt];

     /* parameter referenced an array, get it */
     if (the_arg->type == Node_array_ref)
         the_arg = the_arg->orig_array;

     /* check type */
     if (the_arg->type != Node_var && the_arg->type != Node_var_array)
         fatal("newfunc: third argument is not an array");

     /* force it to be an array, if necessary, clear it */
     the_arg->type = Node_var_array;
     assoc_clear(the_arg);

For versions 3.1.3 and later, the internals changed.  In particular,
the interface was actually _simplified_ drastically.  The following
boilerplate code now suffices:

     NODE *the_arg;

     the_arg = get_argument(tree, 2); /* assume need 3rd arg, 0-based */

     /* force it to be an array: */
     the_arg = get_array(the_arg);

     /* if necessary, clear it: */
     assoc_clear(the_arg);

As of version 3.1.4, the internals improved again, and became even
simpler:

     NODE *the_arg;

     the_arg = get_array_argument(tree, 2, FALSE); /* assume need 3rd arg, 0-based */

Again, you should spend time studying the `gawk' internals; don't just
blindly copy this code.


File: gawk.info,  Node: Sample Library,  Prev: Internals,  Up: Dynamic Extensions

C.3.2 Directory and File Operation Built-ins
--------------------------------------------

Two useful functions that are not in `awk' are `chdir' (so that an
`awk' program can change its directory) and `stat' (so that an `awk'
program can gather information about a file).  This minor node
implements these functions for `gawk' in an external extension library.

* Menu:

* Internal File Description::   What the new functions will do.
* Internal File Ops::           The code for internal file operations.
* Using Internal File Ops::     How to use an external extension.


File: gawk.info,  Node: Internal File Description,  Next: Internal File Ops,  Up: Sample Library

C.3.2.1 Using `chdir' and `stat'
................................

This minor node shows how to use the new functions at the `awk' level
once they've been integrated into the running `gawk' interpreter.
Using `chdir' is very straightforward. It takes one argument, the new
directory to change to:

     ...
     newdir = "/home/arnold/funstuff"
     ret = chdir(newdir)
     if (ret < 0) {
         printf("could not change to %s: %s\n",
                        newdir, ERRNO) > "/dev/stderr"
         exit 1
     }
     ...

The return value is negative if the `chdir' failed, and `ERRNO' (*note
Built-in Variables::) is set to a string indicating the error.

Using `stat' is a bit more complicated.  The C `stat' function fills in
a structure that has a fair amount of information.  The right way to
model this in `awk' is to fill in an associative array with the
appropriate information:

     file = "/home/arnold/.profile"
     fdata[1] = "x"    # force `fdata' to be an array
     ret = stat(file, fdata)
     if (ret < 0) {
         printf("could not stat %s: %s\n",
                  file, ERRNO) > "/dev/stderr"
         exit 1
     }
     printf("size of %s is %d bytes\n", file, fdata["size"])

The `stat' function always clears the data array, even if the `stat'
fails.  It fills in the following elements:

`"name"'
     The name of the file that was `stat''ed.

`"dev"'
`"ino"'
     The file's device and inode numbers, respectively.

`"mode"'
     The file's mode, as a numeric value. This includes both the file's
     type and its permissions.

`"nlink"'
     The number of hard links (directory entries) the file has.

`"uid"'
`"gid"'
     The numeric user and group ID numbers of the file's owner.

`"size"'
     The size in bytes of the file.

`"blocks"'
     The number of disk blocks the file actually occupies. This may not
     be a function of the file's size if the file has holes.

`"atime"'
`"mtime"'
`"ctime"'
     The file's last access, modification, and inode update times,
     respectively.  These are numeric timestamps, suitable for
     formatting with `strftime' (*note Built-in::).

`"pmode"'
     The file's "printable mode."  This is a string representation of
     the file's type and permissions, such as what is produced by `ls
     -l'--for example, `"drwxr-xr-x"'.

`"type"'
     A printable string representation of the file's type.  The value
     is one of the following:

    `"blockdev"'
    `"chardev"'
          The file is a block or character device ("special file").

    `"directory"'
          The file is a directory.

    `"fifo"'
          The file is a named-pipe (also known as a FIFO).

    `"file"'
          The file is just a regular file.

    `"socket"'
          The file is an `AF_UNIX' ("Unix domain") socket in the
          filesystem.

    `"symlink"'
          The file is a symbolic link.

Several additional elements may be present depending upon the operating
system and the type of the file.  You can test for them in your `awk'
program by using the `in' operator (*note Reference to Elements::):

`"blksize"'
     The preferred block size for I/O to the file. This field is not
     present on all POSIX-like systems in the C `stat' structure.

`"linkval"'
     If the file is a symbolic link, this element is the name of the
     file the link points to (i.e., the value of the link).

`"rdev"'
`"major"'
`"minor"'
     If the file is a block or character device file, then these values
     represent the numeric device number and the major and minor
     components of that number, respectively.


File: gawk.info,  Node: Internal File Ops,  Next: Using Internal File Ops,  Prev: Internal File Description,  Up: Sample Library

C.3.2.2 C Code for `chdir' and `stat'
.....................................

Here is the C code for these extensions.  They were written for
GNU/Linux.  The code needs some more work for complete portability to
other POSIX-compliant systems:(1)

     #include "awk.h"

     #include <sys/sysmacros.h>

     /*  do_chdir --- provide dynamically loaded
                      chdir() builtin for gawk */

     static NODE *
     do_chdir(tree)
     NODE *tree;
     {
         NODE *newdir;
         int ret = -1;

         if (do_lint && get_curfunc_arg_count() != 1)
             lintwarn("chdir: called with incorrect number of arguments");

         newdir = get_scalar_argument(tree, 0);

The file includes the `"awk.h"' header file for definitions for the
`gawk' internals.  It includes `<sys/sysmacros.h>' for access to the
`major' and `minor' macros.

By convention, for an `awk' function `foo', the function that
implements it is called `do_foo'.  The function should take a `NODE *'
argument, usually called `tree', that represents the argument list to
the function.  The `newdir' variable represents the new directory to
change to, retrieved with `get_argument'.  Note that the first argument
is numbered zero.

This code actually accomplishes the `chdir'. It first forces the
argument to be a string and passes the string value to the `chdir'
system call. If the `chdir' fails, `ERRNO' is updated.  The result of
`force_string' has to be freed with `free_temp':

         (void) force_string(newdir);
         ret = chdir(newdir->stptr);
         if (ret < 0)
             update_ERRNO();
         free_temp(newdir);

Finally, the function returns the return value to the `awk' level,
using `set_value'. Then it must return a value from the call to the new
built-in (this value ignored by the interpreter):

         /* Set the return value */
         set_value(tmp_number((AWKNUM) ret));

         /* Just to make the interpreter happy */
         return tmp_number((AWKNUM) 0);
     }

The `stat' built-in is more involved.  First comes a function that
turns a numeric mode into a printable representation (e.g., 644 becomes
`-rw-r--r--'). This is omitted here for brevity:

     /* format_mode --- turn a stat mode field
                        into something readable */

     static char *
     format_mode(fmode)
     unsigned long fmode;
     {
         ...
     }

Next comes the actual `do_stat' function itself.  First come the
variable declarations and argument checking:

     /* do_stat --- provide a stat() function for gawk */

     static NODE *
     do_stat(tree)
     NODE *tree;
     {
         NODE *file, *array;
         struct stat sbuf;
         int ret;
         NODE **aptr;
         char *pmode;    /* printable mode */
         char *type = "unknown";


         if (do_lint && get_curfunc_arg_count() > 2)
             lintwarn("stat: called with too many arguments");

Then comes the actual work. First, we get the arguments.  Then, we
always clear the array.  To get the file information, we use `lstat',
in case the file is a symbolic link.  If there's an error, we set
`ERRNO' and return:

         /* directory is first arg, array to hold results is second */
         file = get_scalar_argument(tree, 0, FALSE);
         array = get_array_argument(tree, 1, FALSE);

         /* empty out the array */
         assoc_clear(array);

         /* lstat the file, if error, set ERRNO and return */
         (void) force_string(file);
         ret = lstat(file->stptr, & sbuf);
         if (ret < 0) {
             update_ERRNO();

             set_value(tmp_number((AWKNUM) ret));

             free_temp(file);
             return tmp_number((AWKNUM) 0);
         }

Now comes the tedious part: filling in the array.  Only a few of the
calls are shown here, since they all follow the same pattern:

         /* fill in the array */
         aptr = assoc_lookup(array, tmp_string("name", 4), FALSE);
         *aptr = dupnode(file);

         aptr = assoc_lookup(array, tmp_string("mode", 4), FALSE);
         *aptr = make_number((AWKNUM) sbuf.st_mode);

         aptr = assoc_lookup(array, tmp_string("pmode", 5), FALSE);
         pmode = format_mode(sbuf.st_mode);
         *aptr = make_string(pmode, strlen(pmode));

When done, we free the temporary value containing the file name, set
the return value, and return:

         free_temp(file);

         /* Set the return value */
         set_value(tmp_number((AWKNUM) ret));

         /* Just to make the interpreter happy */
         return tmp_number((AWKNUM) 0);
     }

Finally, it's necessary to provide the "glue" that loads the new
function(s) into `gawk'.  By convention, each library has a routine
named `dlload' that does the job:

     /* dlload --- load new builtins in this library */

     NODE *
     dlload(tree, dl)
     NODE *tree;
     void *dl;
     {
         make_builtin("chdir", do_chdir, 1);
         make_builtin("stat", do_stat, 2);
         return tmp_number((AWKNUM) 0);
     }

And that's it!  As an exercise, consider adding functions to implement
system calls such as `chown', `chmod', and `umask'.

---------- Footnotes ----------

(1) This version is edited slightly for presentation.  The complete
version can be found in `extension/filefuncs.c' in the `gawk'
distribution.


File: gawk.info,  Node: Using Internal File Ops,  Prev: Internal File Ops,  Up: Sample Library

C.3.2.3 Integrating the Extensions
..................................

Now that the code is written, it must be possible to add it at runtime
to the running `gawk' interpreter.  First, the code must be compiled.
Assuming that the functions are in a file named `filefuncs.c', and IDIR
is the location of the `gawk' include files, the following steps create
a GNU/Linux shared library:

     $ gcc -shared -DHAVE_CONFIG_H -c -O -g -IIDIR filefuncs.c
     $ ld -o filefuncs.so -shared filefuncs.o

Once the library exists, it is loaded by calling the `extension'
built-in function.  This function takes two arguments: the name of the
library to load and the name of a function to call when the library is
first loaded. This function adds the new functions to `gawk'.  It
returns the value returned by the initialization function within the
shared library:

     # file testff.awk
     BEGIN {
         extension("./filefuncs.so", "dlload")

         chdir(".")  # no-op

         data[1] = 1 # force `data' to be an array
         print "Info for testff.awk"
         ret = stat("testff.awk", data)
         print "ret =", ret
         for (i in data)
             printf "data[\"%s\"] = %s\n", i, data[i]
         print "testff.awk modified:",
             strftime("%m %d %y %H:%M:%S", data["mtime"])
     }

Here are the results of running the program:

     $ gawk -f testff.awk
     -| Info for testff.awk
     -| ret = 0
     -| data["blksize"] = 4096
     -| data["mtime"] = 932361936
     -| data["mode"] = 33188
     -| data["type"] = file
     -| data["dev"] = 2065
     -| data["gid"] = 10
     -| data["ino"] = 878597
     -| data["ctime"] = 971431797
     -| data["blocks"] = 2
     -| data["nlink"] = 1
     -| data["name"] = testff.awk
     -| data["atime"] = 971608519
     -| data["pmode"] = -rw-r--r--
     -| data["size"] = 607
     -| data["uid"] = 2076
     -| testff.awk modified: 07 19 99 08:25:36


File: gawk.info,  Node: Future Extensions,  Prev: Dynamic Extensions,  Up: Notes

C.4 Probable Future Extensions
==============================

     AWK is a language similar to PERL, only considerably more elegant.
     Arnold Robbins

     Hey!
     Larry Wall

This minor node briefly lists extensions and possible improvements that
indicate the directions we are currently considering for `gawk'.  The
file `FUTURES' in the `gawk' distribution lists these extensions as
well.

Following is a list of probable future changes visible at the `awk'
language level:

Loadable module interface
     It is not clear that the `awk'-level interface to the modules
     facility is as good as it should be.  The interface needs to be
     redesigned, particularly taking namespace issues into account, as
     well as possibly including issues such as library search path order
     and versioning.

`RECLEN' variable for fixed-length records
     Along with `FIELDWIDTHS', this would speed up the processing of
     fixed-length records.  `PROCINFO["RS"]' would be `"RS"' or
     `"RECLEN"', depending upon which kind of record processing is in
     effect.

Additional `printf' specifiers
     The 1999 ISO C standard added a number of additional `printf'
     format specifiers.  These should be evaluated for possible
     inclusion in `gawk'.

Databases
     It may be possible to map a GDBM/NDBM/SDBM file into an `awk'
     array.

More `lint' warnings
     There are more things that could be checked for portability.

Following is a list of probable improvements that will make `gawk''s
source code easier to work with:

Loadable module mechanics
     The current extension mechanism works (*note Dynamic Extensions::),
     but is rather primitive. It requires a fair amount of manual work
     to create and integrate a loadable module.  Nor is the current
     mechanism as portable as might be desired.  The GNU `libtool'
     package provides a number of features that would make using
     loadable modules much easier.  `gawk' should be changed to use
     `libtool'.

Loadable module internals
     The API to its internals that `gawk' "exports" should be revised.
     Too many things are needlessly exposed.  A new API should be
     designed and implemented to make module writing easier.

Better array subscript management
     `gawk''s management of array subscript storage could use revamping,
     so that using the same value to index multiple arrays only stores
     one copy of the index value.

Integrating the DBUG library
     Integrating Fred Fish's DBUG library would be helpful during
     development, but it's a lot of work to do.

Following is a list of probable improvements that will make `gawk'
perform better:

Compilation of `awk' programs
     `gawk' uses a Bison (YACC-like) parser to convert the script given
     it into a syntax tree; the syntax tree is then executed by a
     simple recursive evaluator.  This method incurs a lot of overhead,
     since the recursive evaluator performs many procedure calls to do
     even the simplest things.

     It should be possible for `gawk' to convert the script's parse tree
     into a C program which the user would then compile, using the
     normal C compiler and a special `gawk' library to provide all the
     needed functions (regexps, fields, associative arrays, type
     coercion, and so on).

     An easier possibility might be for an intermediate phase of `gawk'
     to convert the parse tree into a linear byte code form like the
     one used in GNU Emacs Lisp.  The recursive evaluator would then be
     replaced by a straight line byte code interpreter that would be
     intermediate in speed between running a compiled program and doing
     what `gawk' does now.

Finally, the programs in the test suite could use documenting in this
Info file.

*Note Additions::, if you are interested in tackling any of these
projects.


File: gawk.info,  Node: Basic Concepts,  Next: Glossary,  Prev: Notes,  Up: Top

Appendix D Basic Programming Concepts
*************************************

This major node attempts to define some of the basic concepts and terms
that are used throughout the rest of this Info file.  As this Info file
is specifically about `awk', and not about computer programming in
general, the coverage here is by necessity fairly cursory and
simplistic.  (If you need more background, there are many other
introductory texts that you should refer to instead.)

* Menu:

* Basic High Level::            The high level view.
* Basic Data Typing::           A very quick intro to data types.
* Floating Point Issues::       Stuff to know about floating-point numbers.


File: gawk.info,  Node: Basic High Level,  Next: Basic Data Typing,  Up: Basic Concepts

D.1 What a Program Does
=======================

At the most basic level, the job of a program is to process some input
data and produce results.

                       _______
     +------+         /       \         +---------+
     | Data | -----> < Program > -----> | Results |
     +------+         \_______/         +---------+

The "program" in the figure can be either a compiled program(1) (such
as `ls'), or it may be "interpreted".  In the latter case, a
machine-executable program such as `awk' reads your program, and then
uses the instructions in your program to process the data.

When you write a program, it usually consists of the following, very
basic set of steps:

                                   ______
     +----------------+           / More \  No       +----------+
     | Initialization | -------> <  Data  > -------> | Clean Up |
     +----------------+    ^      \   ?  /           +----------+
                           |       +--+-+
                           |          | Yes
                           |          |
                           |          V
                           |     +---------+
                           +-----+ Process |
                                 +---------+

Initialization
     These are the things you do before actually starting to process
     data, such as checking arguments, initializing any data you need
     to work with, and so on.  This step corresponds to `awk''s `BEGIN'
     rule (*note BEGIN/END::).

     If you were baking a cake, this might consist of laying out all the
     mixing bowls and the baking pan, and making sure you have all the
     ingredients that you need.

Processing
     This is where the actual work is done.  Your program reads data,
     one logical chunk at a time, and processes it as appropriate.

     In most programming languages, you have to manually manage the
     reading of data, checking to see if there is more each time you
     read a chunk.  `awk''s pattern-action paradigm (*note Getting
     Started::) handles the mechanics of this for you.

     In baking a cake, the processing corresponds to the actual labor:
     breaking eggs, mixing the flour, water, and other ingredients, and
     then putting the cake into the oven.

Clean Up
     Once you've processed all the data, you may have things you need to
     do before exiting.  This step corresponds to `awk''s `END' rule
     (*note BEGIN/END::).

     After the cake comes out of the oven, you still have to wrap it in
     plastic wrap to keep anyone from tasting it, as well as wash the
     mixing bowls and utensils.

An "algorithm" is a detailed set of instructions necessary to accomplish
a task, or process data.  It is much the same as a recipe for baking a
cake.  Programs implement algorithms.  Often, it is up to you to design
the algorithm and implement it, simultaneously.

The "logical chunks" we talked about previously are called "records",
similar to the records a company keeps on employees, a school keeps for
students, or a doctor keeps for patients.  Each record has many
component parts, such as first and last names, date of birth, address,
and so on.  The component parts are referred to as the "fields" of the
record.

The act of reading data is termed "input", and that of generating
results, not too surprisingly, is termed "output".  They are often
referred to together as "input/output," and even more often, as "I/O"
for short.  (You will also see "input" and "output" used as verbs.)

`awk' manages the reading of data for you, as well as the breaking it
up into records and fields.  Your program's job is to tell `awk' what
to with the data.  You do this by describing "patterns" in the data to
look for, and "actions" to execute when those patterns are seen.  This
"data-driven" nature of `awk' programs usually makes them both easier
to write and easier to read.

---------- Footnotes ----------

(1) Compiled programs are typically written in lower-level languages
such as C, C++, Fortran, or Ada, and then translated, or "compiled",
into a form that the computer can execute directly.


File: gawk.info,  Node: Basic Data Typing,  Next: Floating Point Issues,  Prev: Basic High Level,  Up: Basic Concepts

D.2 Data Values in a Computer
=============================

In a program, you keep track of information and values in things called
"variables".  A variable is just a name for a given value, such as
`first_name', `last_name', `address', and so on.  `awk' has several
predefined variables, and it has special names to refer to the current
input record and the fields of the record.  You may also group multiple
associated values under one name, as an array.

Data, particularly in `awk', consists of either numeric values, such as
42 or 3.1415927, or string values.  String values are essentially
anything that's not a number, such as a name.  Strings are sometimes
referred to as "character data", since they store the individual
characters that comprise them.  Individual variables, as well as
numeric and string variables, are referred to as "scalar" values.
Groups of values, such as arrays, are not scalars.

Within computers, there are two kinds of numeric values: "integers" and
"floating-point".  In school, integer values were referred to as
"whole" numbers--that is, numbers without any fractional part, such as
1, 42, or -17.  The advantage to integer numbers is that they represent
values exactly.  The disadvantage is that their range is limited.  On
most modern systems, this range is -2,147,483,648 to 2,147,483,647.

Integer values come in two flavors: "signed" and "unsigned".  Signed
values may be negative or positive, with the range of values just
described.  Unsigned values are always positive.  On most modern
systems, the range is from 0 to 4,294,967,295.

Floating-point numbers represent what are called "real" numbers; i.e.,
those that do have a fractional part, such as 3.1415927.  The advantage
to floating-point numbers is that they can represent a much larger
range of values.  The disadvantage is that there are numbers that they
cannot represent exactly.  `awk' uses "double-precision" floating-point
numbers, which can hold more digits than "single-precision"
floating-point numbers.  Floating-point issues are discussed more fully
in *Note Floating Point Issues::.

At the very lowest level, computers store values as groups of binary
digits, or "bits".  Modern computers group bits into groups of eight,
called "bytes".  Advanced applications sometimes have to manipulate
bits directly, and `gawk' provides functions for doing so.

While you are probably used to the idea of a number without a value
(i.e., zero), it takes a bit more getting used to the idea of
zero-length character data.  Nevertheless, such a thing exists.  It is
called the "null string".  The null string is character data that has
no value.  In other words, it is empty.  It is written in `awk' programs
like this: `""'.

Humans are used to working in decimal; i.e., base 10.  In base 10,
numbers go from 0 to 9, and then "roll over" into the next column.
(Remember grade school? 42 is 4 times 10 plus 2.)

There are other number bases though.  Computers commonly use base 2 or
"binary", base 8 or "octal", and base 16 or "hexadecimal".  In binary,
each column represents two times the value in the column to its right.
Each column may contain either a 0 or a 1.  Thus, binary 1010
represents 1 times 8, plus 0 times 4, plus 1 times 2, plus 0 times 1,
or decimal 10.  Octal and hexadecimal are discussed more in *Note
Nondecimal-numbers::.

Programs are written in programming languages.  Hundreds, if not
thousands, of programming languages exist.  One of the most popular is
the C programming language.  The C language had a very strong influence
on the design of the `awk' language.

There have been several versions of C.  The first is often referred to
as "K&R" C, after the initials of Brian Kernighan and Dennis Ritchie,
the authors of the first book on C.  (Dennis Ritchie created the
language, and Brian Kernighan was one of the creators of `awk'.)

In the mid-1980s, an effort began to produce an international standard
for C.  This work culminated in 1989, with the production of the ANSI
standard for C.  This standard became an ISO standard in 1990.  Where
it makes sense, POSIX `awk' is compatible with 1990 ISO C.

In 1999, a revised ISO C standard was approved and released.  Future
versions of `gawk' will be as compatible as possible with this standard.


File: gawk.info,  Node: Floating Point Issues,  Prev: Basic Data Typing,  Up: Basic Concepts

D.3 Floating-Point Number Caveats
=================================

As mentioned earlier, floating-point numbers represent what are called
"real" numbers, i.e., those that have a fractional part.  `awk' uses
double-precision floating-point numbers to represent all numeric
values.  This minor node describes some of the issues involved in using
floating-point numbers.

There is a very nice paper on floating-point arithmetic by David
Goldberg, "What Every Computer Scientist Should Know About
Floating-point Arithmetic," `ACM Computing Surveys' *23*, 1 (1991-03),
5-48.(1) This is worth reading if you are interested in the details,
but it does require a background in computer science.

Internally, `awk' keeps both the numeric value (double-precision
floating-point) and the string value for a variable.  Separately, `awk'
keeps track of what type the variable has (*note Typing and
Comparison::), which plays a role in how variables are used in
comparisons.

It is important to note that the string value for a number may not
reflect the full value (all the digits) that the numeric value actually
contains.  The following program (`values.awk') illustrates this:

     {
        $1 = $2 + $3
        # see it for what it is
        printf("$1 = %.12g\n", $1)
        # use CONVFMT
        a = "<" $1 ">"
        print "a =", a
        # use OFMT
        print "$1 =", $1
     }

This program shows the full value of the sum of `$2' and `$3' using
`printf', and then prints the string values obtained from both
automatic conversion (via `CONVFMT') and from printing (via `OFMT').

Here is what happens when the program is run:

     $ echo 2 3.654321 1.2345678 | awk -f values.awk
     -| $1 = 4.8888888
     -| a = <4.88889>
     -| $1 = 4.88889

This makes it clear that the full numeric value is different from what
the default string representations show.

`CONVFMT''s default value is `"%.6g"', which yields a value with at
least six significant digits.  For some applications, you might want to
change it to specify more precision.  On most modern machines, most of
the time, 17 digits is enough to capture a floating-point number's
value exactly.(2)

Unlike numbers in the abstract sense (such as what you studied in high
school or college math), numbers stored in computers are limited in
certain ways.  They cannot represent an infinite number of digits, nor
can they always represent things exactly.  In particular,
floating-point numbers cannot always represent values exactly.  Here is
an example:

     $ awk '{ printf("%010d\n", $1 * 100) }'
     515.79
     -| 0000051579
     515.80
     -| 0000051579
     515.81
     -| 0000051580
     515.82
     -| 0000051582
     Ctrl-d

This shows that some values can be represented exactly, whereas others
are only approximated.  This is not a "bug" in `awk', but simply an
artifact of how computers represent numbers.

Another peculiarity of floating-point numbers on modern systems is that
they often have more than one representation for the number zero!  In
particular, it is possible to represent "minus zero" as well as
regular, or "positive" zero.

This example shows that negative and positive zero are distinct values
when stored internally, but that they are in fact equal to each other,
as well as to "regular" zero:

     $ gawk 'BEGIN { mz = -0 ; pz = 0
     > printf "-0 = %g, +0 = %g, (-0 == +0) -> %d\n", mz, pz, mz == pz
     > printf "mz == 0 -> %d, pz == 0 -> %d\n", mz == 0, pz == 0
     > }'
     -| -0 = -0, +0 = 0, (-0 == +0) -> 1
     -| mz == 0 -> 1, pz == 0 -> 1

It helps to keep this in mind should you process numeric data that
contains negative zero values; the fact that the zero is negative is
noted and can affect comparisons.

---------- Footnotes ----------

(1) `http://www.validlab.com/goldberg/paper.ps'.

(2) Pathological cases can require up to 752 digits (!), but we doubt
that you need to worry about this.


File: gawk.info,  Node: Glossary,  Next: Copying,  Prev: Basic Concepts,  Up: Top

Glossary
********

Action
     A series of `awk' statements attached to a rule.  If the rule's
     pattern matches an input record, `awk' executes the rule's action.
     Actions are always enclosed in curly braces.  (*Note Action
     Overview::.)

Amazing `awk' Assembler
     Henry Spencer at the University of Toronto wrote a retargetable
     assembler completely as `sed' and `awk' scripts.  It is thousands
     of lines long, including machine descriptions for several eight-bit
     microcomputers.  It is a good example of a program that would have
     been better written in another language.  You can get it from
     `ftp://ftp.freefriends.org/arnold/Awkstuff/aaa.tgz'.

Amazingly Workable Formatter (`awf')
     Henry Spencer at the University of Toronto wrote a formatter that
     accepts a large subset of the `nroff -ms' and `nroff -man'
     formatting commands, using `awk' and `sh'.  It is available over
     the Internet from
     `ftp://ftp.freefriends.org/arnold/Awkstuff/awf.tgz'.

Anchor
     The regexp metacharacters `^' and `$', which force the match to
     the beginning or end of the string, respectively.

ANSI
     The American National Standards Institute.  This organization
     produces many standards, among them the standards for the C and
     C++ programming languages.  These standards often become
     international standards as well. See also "ISO."

Array
     A grouping of multiple values under the same name.  Most languages
     just provide sequential arrays.  `awk' provides associative arrays.

Assertion
     A statement in a program that a condition is true at this point in
     the program.  Useful for reasoning about how a program is supposed
     to behave.

Assignment
     An `awk' expression that changes the value of some `awk' variable
     or data object.  An object that you can assign to is called an
     "lvalue".  The assigned values are called "rvalues".  *Note
     Assignment Ops::.

Associative Array
     Arrays in which the indices may be numbers or strings, not just
     sequential integers in a fixed range.

`awk' Language
     The language in which `awk' programs are written.

`awk' Program
     An `awk' program consists of a series of "patterns" and "actions",
     collectively known as "rules".  For each input record given to the
     program, the program's rules are all processed in turn.  `awk'
     programs may also contain function definitions.

`awk' Script
     Another name for an `awk' program.

Bash
     The GNU version of the standard shell (the Bourne-Again SHell).
     See also "Bourne Shell."

BBS
     See "Bulletin Board System."

Bit
     Short for "Binary Digit."  All values in computer memory
     ultimately reduce to binary digits: values that are either zero or
     one.  Groups of bits may be interpreted differently--as integers,
     floating-point numbers, character data, addresses of other memory
     objects, or other data.  `awk' lets you work with floating-point
     numbers and strings.  `gawk' lets you manipulate bit values with
     the built-in functions described in *Note Bitwise Functions::.

     Computers are often defined by how many bits they use to represent
     integer values.  Typical systems are 32-bit systems, but 64-bit
     systems are becoming increasingly popular, and 16-bit systems are
     waning in popularity.

Boolean Expression
     Named after the English mathematician Boole. See also "Logical
     Expression."

Bourne Shell
     The standard shell (`/bin/sh') on Unix and Unix-like systems,
     originally written by Steven R. Bourne.  Many shells (`bash',
     `ksh', `pdksh', `zsh') are generally upwardly compatible with the
     Bourne shell.

Built-in Function
     The `awk' language provides built-in functions that perform various
     numerical, I/O-related, and string computations.  Examples are
     `sqrt' (for the square root of a number) and `substr' (for a
     substring of a string).  `gawk' provides functions for timestamp
     management, bit manipulation, and runtime string translation.
     (*Note Built-in::.)

Built-in Variable
     `ARGC', `ARGV', `CONVFMT', `ENVIRON', `FILENAME', `FNR', `FS',
     `NF', `NR', `OFMT', `OFS', `ORS', `RLENGTH', `RSTART', `RS', and
     `SUBSEP' are the variables that have special meaning to `awk'.  In
     addition, `ARGIND', `BINMODE', `ERRNO', `FIELDWIDTHS',
     `IGNORECASE', `LINT', `PROCINFO', `RT', and `TEXTDOMAIN' are the
     variables that have special meaning to `gawk'.  Changing some of
     them affects `awk''s running environment.  (*Note Built-in
     Variables::.)

Braces
     See "Curly Braces."

Bulletin Board System
     A computer system allowing users to log in and read and/or leave
     messages for other users of the system, much like leaving paper
     notes on a bulletin board.

C
     The system programming language that most GNU software is written
     in.  The `awk' programming language has C-like syntax, and this
     Info file points out similarities between `awk' and C when
     appropriate.

     In general, `gawk' attempts to be as similar to the 1990 version
     of ISO C as makes sense.  Future versions of `gawk' may adopt
     features from the newer 1999 standard, as appropriate.

C++
     A popular object-oriented programming language derived from C.

Character Set
     The set of numeric codes used by a computer system to represent the
     characters (letters, numbers, punctuation, etc.) of a particular
     country or place. The most common character set in use today is
     ASCII (American Standard Code for Information Interchange).  Many
     European countries use an extension of ASCII known as ISO-8859-1
     (ISO Latin-1).

CHEM
     A preprocessor for `pic' that reads descriptions of molecules and
     produces `pic' input for drawing them.  It was written in `awk' by
     Brian Kernighan and Jon Bentley, and is available from
     `http://cm.bell-labs.com/netlib/typesetting/chem.gz'.

Coprocess
     A subordinate program with which two-way communications is
     possible.

Compiler
     A program that translates human-readable source code into
     machine-executable object code.  The object code is then executed
     directly by the computer.  See also "Interpreter."

Compound Statement
     A series of `awk' statements, enclosed in curly braces.  Compound
     statements may be nested.  (*Note Statements::.)

Concatenation
     Concatenating two strings means sticking them together, one after
     another, producing a new string.  For example, the string `foo'
     concatenated with the string `bar' gives the string `foobar'.
     (*Note Concatenation::.)

Conditional Expression
     An expression using the `?:' ternary operator, such as `EXPR1 ?
     EXPR2 : EXPR3'.  The expression EXPR1 is evaluated; if the result
     is true, the value of the whole expression is the value of EXPR2;
     otherwise the value is EXPR3.  In either case, only one of EXPR2
     and EXPR3 is evaluated. (*Note Conditional Exp::.)

Comparison Expression
     A relation that is either true or false, such as `(a < b)'.
     Comparison expressions are used in `if', `while', `do', and `for'
     statements, and in patterns to select which input records to
     process.  (*Note Typing and Comparison::.)

Curly Braces
     The characters `{' and `}'.  Curly braces are used in `awk' for
     delimiting actions, compound statements, and function bodies.

Dark Corner
     An area in the language where specifications often were (or still
     are) not clear, leading to unexpected or undesirable behavior.
     Such areas are marked in this Info file with "(d.c.)" in the text
     and are indexed under the heading "dark corner."

Data Driven
     A description of `awk' programs, where you specify the data you
     are interested in processing, and what to do when that data is
     seen.

Data Objects
     These are numbers and strings of characters.  Numbers are
     converted into strings and vice versa, as needed.  (*Note
     Conversion::.)

Deadlock
     The situation in which two communicating processes are each waiting
     for the other to perform an action.

Double-Precision
     An internal representation of numbers that can have fractional
     parts.  Double-precision numbers keep track of more digits than do
     single-precision numbers, but operations on them are sometimes
     more expensive.  This is the way `awk' stores numeric values.  It
     is the C type `double'.

Dynamic Regular Expression
     A dynamic regular expression is a regular expression written as an
     ordinary expression.  It could be a string constant, such as
     `"foo"', but it may also be an expression whose value can vary.
     (*Note Computed Regexps::.)

Environment
     A collection of strings, of the form NAME`='VAL, that each program
     has available to it. Users generally place values into the
     environment in order to provide information to various programs.
     Typical examples are the environment variables `HOME' and `PATH'.

Empty String
     See "Null String."

Epoch
     The date used as the "beginning of time" for timestamps.  Time
     values in Unix systems are represented as seconds since the epoch,
     with library functions available for converting these values into
     standard date and time formats.

     The epoch on Unix and POSIX systems is 1970-01-01 00:00:00 UTC.
     See also "GMT" and "UTC."

Escape Sequences
     A special sequence of characters used for describing nonprinting
     characters, such as `\n' for newline or `\033' for the ASCII ESC
     (Escape) character. (*Note Escape Sequences::.)

FDL
     See "Free Documentation License."

Field
     When `awk' reads an input record, it splits the record into pieces
     separated by whitespace (or by a separator regexp that you can
     change by setting the built-in variable `FS').  Such pieces are
     called fields.  If the pieces are of fixed length, you can use the
     built-in variable `FIELDWIDTHS' to describe their lengths.  (*Note
     Field Separators::, and *Note Constant Size::.)

Flag
     A variable whose truth value indicates the existence or
     nonexistence of some condition.

Floating-Point Number
     Often referred to in mathematical terms as a "rational" or real
     number, this is just a number that can have a fractional part.
     See also "Double-Precision" and "Single-Precision."

Format
     Format strings are used to control the appearance of output in the
     `strftime' and `sprintf' functions, and are used in the `printf'
     statement as well.  Also, data conversions from numbers to strings
     are controlled by the format string contained in the built-in
     variable `CONVFMT'. (*Note Control Letters::.)

Free Documentation License
     This document describes the terms under which this Info file is
     published and may be copied. (*Note GNU Free Documentation
     License::.)

Function
     A specialized group of statements used to encapsulate general or
     program-specific tasks.  `awk' has a number of built-in functions,
     and also allows you to define your own.  (*Note Functions::.)

FSF
     See "Free Software Foundation."

Free Software Foundation
     A nonprofit organization dedicated to the production and
     distribution of freely distributable software.  It was founded by
     Richard M. Stallman, the author of the original Emacs editor.  GNU
     Emacs is the most widely used version of Emacs today.

`gawk'
     The GNU implementation of `awk'.

General Public License
     This document describes the terms under which `gawk' and its source
     code may be distributed. (*Note Copying::.)

GMT
     "Greenwich Mean Time."  This is the old term for UTC.  It is the
     time of day used as the epoch for Unix and POSIX systems.  See
     also "Epoch" and "UTC."

GNU
     "GNU's not Unix".  An on-going project of the Free Software
     Foundation to create a complete, freely distributable,
     POSIX-compliant computing environment.

GNU/Linux
     A variant of the GNU system using the Linux kernel, instead of the
     Free Software Foundation's Hurd kernel.  Linux is a stable,
     efficient, full-featured clone of Unix that has been ported to a
     variety of architectures.  It is most popular on PC-class systems,
     but runs well on a variety of other systems too.  The Linux kernel
     source code is available under the terms of the GNU General Public
     License, which is perhaps its most important aspect.

GPL
     See "General Public License."

Hexadecimal
     Base 16 notation, where the digits are `0'-`9' and `A'-`F', with
     `A' representing 10, `B' representing 11, and so on, up to `F' for
     15.  Hexadecimal numbers are written in C using a leading `0x', to
     indicate their base.  Thus, `0x12' is 18 (1 times 16 plus 2).

I/O
     Abbreviation for "Input/Output," the act of moving data into and/or
     out of a running program.

Input Record
     A single chunk of data that is read in by `awk'.  Usually, an
     `awk' input record consists of one line of text.  (*Note
     Records::.)

Integer
     A whole number, i.e., a number that does not have a fractional
     part.

Internationalization
     The process of writing or modifying a program so that it can use
     multiple languages without requiring further source code changes.

Interpreter
     A program that reads human-readable source code directly, and uses
     the instructions in it to process data and produce results.  `awk'
     is typically (but not always) implemented as an interpreter.  See
     also "Compiler."

Interval Expression
     A component of a regular expression that lets you specify repeated
     matches of some part of the regexp.  Interval expressions were not
     traditionally available in `awk' programs.

ISO
     The International Standards Organization.  This organization
     produces international standards for many things, including
     programming languages, such as C and C++.  In the computer arena,
     important standards like those for C, C++, and POSIX become both
     American national and ISO international standards simultaneously.
     This Info file refers to Standard C as "ISO C" throughout.

Keyword
     In the `awk' language, a keyword is a word that has special
     meaning.  Keywords are reserved and may not be used as variable
     names.

     `gawk''s keywords are: `BEGIN', `END', `if', `else', `while',
     `do...while', `for', `for...in', `break', `continue', `delete',
     `next', `nextfile', `function', `func', and `exit'.

Lesser General Public License
     This document describes the terms under which binary library
     archives or shared objects, and their source code may be
     distributed.

Linux
     See "GNU/Linux."

LGPL
     See "Lesser General Public License."

Localization
     The process of providing the data necessary for an
     internationalized program to work in a particular language.

Logical Expression
     An expression using the operators for logic, AND, OR, and NOT,
     written `&&', `||', and `!' in `awk'. Often called Boolean
     expressions, after the mathematician who pioneered this kind of
     mathematical logic.

Lvalue
     An expression that can appear on the left side of an assignment
     operator.  In most languages, lvalues can be variables or array
     elements.  In `awk', a field designator can also be used as an
     lvalue.

Matching
     The act of testing a string against a regular expression.  If the
     regexp describes the contents of the string, it is said to "match"
     it.

Metacharacters
     Characters used within a regexp that do not stand for themselves.
     Instead, they denote regular expression operations, such as
     repetition, grouping, or alternation.

Null String
     A string with no characters in it.  It is represented explicitly in
     `awk' programs by placing two double quote characters next to each
     other (`""').  It can appear in input data by having two successive
     occurrences of the field separator appear next to each other.

Number
     A numeric-valued data object.  Modern `awk' implementations use
     double-precision floating-point to represent numbers.  Very old
     `awk' implementations use single-precision floating-point.

Octal
     Base-eight notation, where the digits are `0'-`7'.  Octal numbers
     are written in C using a leading `0', to indicate their base.
     Thus, `013' is 11 (one times 8 plus 3).

P1003.2
     See "POSIX."

Pattern
     Patterns tell `awk' which input records are interesting to which
     rules.

     A pattern is an arbitrary conditional expression against which
     input is tested.  If the condition is satisfied, the pattern is
     said to "match" the input record.  A typical pattern might compare
     the input record against a regular expression. (*Note Pattern
     Overview::.)

POSIX
     The name for a series of standards that specify a Portable
     Operating System interface.  The "IX" denotes the Unix heritage of
     these standards.  The main standard of interest for `awk' users is
     `IEEE Standard for Information Technology, Standard 1003.2-1992,
     Portable Operating System Interface (POSIX) Part 2: Shell and
     Utilities'.  Informally, this standard is often referred to as
     simply "P1003.2."

Precedence
     The order in which operations are performed when operators are used
     without explicit parentheses.

Private
     Variables and/or functions that are meant for use exclusively by
     library functions and not for the main `awk' program. Special care
     must be taken when naming such variables and functions.  (*Note
     Library Names::.)

Range (of input lines)
     A sequence of consecutive lines from the input file(s).  A pattern
     can specify ranges of input lines for `awk' to process or it can
     specify single lines. (*Note Pattern Overview::.)

Recursion
     When a function calls itself, either directly or indirectly.  If
     this isn't clear, refer to the entry for "recursion."

Redirection
     Redirection means performing input from something other than the
     standard input stream, or performing output to something other
     than the standard output stream.

     You can redirect the output of the `print' and `printf' statements
     to a file or a system command, using the `>', `>>', `|', and `|&'
     operators.  You can redirect input to the `getline' statement using
     the `<', `|', and `|&' operators.  (*Note Redirection::, and *Note
     Getline::.)

Regexp
     Short for "regular expression".  A regexp is a pattern that
     denotes a set of strings, possibly an infinite set.  For example,
     the regexp `R.*xp' matches any string starting with the letter `R'
     and ending with the letters `xp'.  In `awk', regexps are used in
     patterns and in conditional expressions.  Regexps may contain
     escape sequences. (*Note Regexp::.)

Regular Expression
     See "regexp."

Regular Expression Constant
     A regular expression constant is a regular expression written
     within slashes, such as `/foo/'.  This regular expression is chosen
     when you write the `awk' program and cannot be changed during its
     execution. (*Note Regexp Usage::.)

Rule
     A segment of an `awk' program that specifies how to process single
     input records.  A rule consists of a "pattern" and an "action".
     `awk' reads an input record; then, for each rule, if the input
     record satisfies the rule's pattern, `awk' executes the rule's
     action.  Otherwise, the rule does nothing for that input record.

Rvalue
     A value that can appear on the right side of an assignment
     operator.  In `awk', essentially every expression has a value.
     These values are rvalues.

Scalar
     A single value, be it a number or a string.  Regular variables are
     scalars; arrays and functions are not.

Search Path
     In `gawk', a list of directories to search for `awk' program
     source files.  In the shell, a list of directories to search for
     executable programs.

Seed
     The initial value, or starting point, for a sequence of random
     numbers.

`sed'
     See "Stream Editor."

Shell
     The command interpreter for Unix and POSIX-compliant systems.  The
     shell works both interactively, and as a programming language for
     batch files, or shell scripts.

Short-Circuit
     The nature of the `awk' logical operators `&&' and `||'.  If the
     value of the entire expression is determinable from evaluating just
     the lefthand side of these operators, the righthand side is not
     evaluated.  (*Note Boolean Ops::.)

Side Effect
     A side effect occurs when an expression has an effect aside from
     merely producing a value.  Assignment expressions, increment and
     decrement expressions, and function calls have side effects.
     (*Note Assignment Ops::.)

Single-Precision
     An internal representation of numbers that can have fractional
     parts.  Single-precision numbers keep track of fewer digits than
     do double-precision numbers, but operations on them are sometimes
     less expensive in terms of CPU time.  This is the type used by
     some very old versions of `awk' to store numeric values.  It is
     the C type `float'.

Space
     The character generated by hitting the space bar on the keyboard.

Special File
     A file name interpreted internally by `gawk', instead of being
     handed directly to the underlying operating system--for example,
     `/dev/stderr'.  (*Note Special Files::.)

Stream Editor
     A program that reads records from an input stream and processes
     them one or more at a time.  This is in contrast with batch
     programs, which may expect to read their input files in entirety
     before starting to do anything, as well as with interactive
     programs which require input from the user.

String
     A datum consisting of a sequence of characters, such as `I am a
     string'.  Constant strings are written with double quotes in the
     `awk' language and may contain escape sequences.  (*Note Escape
     Sequences::.)

Tab
     The character generated by hitting the `TAB' key on the keyboard.
     It usually expands to up to eight spaces upon output.

Text Domain
     A unique name that identifies an application.  Used for grouping
     messages that are translated at runtime into the local language.

Timestamp
     A value in the "seconds since the epoch" format used by Unix and
     POSIX systems.  Used for the `gawk' functions `mktime',
     `strftime', and `systime'.  See also "Epoch" and "UTC."

Unix
     A computer operating system originally developed in the early
     1970's at AT&T Bell Laboratories.  It initially became popular in
     universities around the world and later moved into commercial
     environments as a software development system and network server
     system. There are many commercial versions of Unix, as well as
     several work-alike systems whose source code is freely available
     (such as GNU/Linux, NetBSD, FreeBSD, and OpenBSD).

UTC
     The accepted abbreviation for "Universal Coordinated Time."  This
     is standard time in Greenwich, England, which is used as a
     reference time for day and date calculations.  See also "Epoch"
     and "GMT."

Whitespace
     A sequence of space, TAB, or newline characters occurring inside
     an input record or a string.


File: gawk.info,  Node: Copying,  Next: GNU Free Documentation License,  Prev: Glossary,  Up: Top

GNU General Public License
**************************

                         Version 2, June 1991
     Copyright (C) 1989, 1991 Free Software Foundation, Inc.
     51 Franklin Street, Fifth Floor, Boston, MA 02111, USA

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

Preamble
========

The licenses for most software are designed to take away your freedom
to share and change it.  By contrast, the GNU General Public License is
intended to guarantee your freedom to share and change free
software--to make sure the software is free for all its users.  This
General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to
using it.  (Some other Free Software Foundation software is covered by
the GNU Library General Public License instead.)  You can apply it to
your programs, too.

When we speak of free software, we are referring to freedom, not price.
Our General Public Licenses are designed to make sure that you have
the freedom to distribute copies of free software (and charge for this
service if you wish), that you receive source code or can get it if you
want it, that you can change the software or use pieces of it in new
free programs; and that you know you can do these things.

To protect your rights, we need to make restrictions that forbid anyone
to deny you these rights or to ask you to surrender the rights.  These
restrictions translate to certain responsibilities for you if you
distribute copies of the software, or if you modify it.

For example, if you distribute copies of such a program, whether gratis
or for a fee, you must give the recipients all the rights that you
have.  You must make sure that they, too, receive or can get the source
code.  And you must show them these terms so they know their rights.

We protect your rights with two steps: (1) copyright the software, and
(2) offer you this license which gives you legal permission to copy,
distribute and/or modify the software.

Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software.  If the software is modified by someone else and passed on, we
want its recipients to know that what they have is not the original, so
that any problems introduced by others will not reflect on the original
authors' reputations.

Finally, any free program is threatened constantly by software patents.
We wish to avoid the danger that redistributors of a free program will
individually obtain patent licenses, in effect making the program
proprietary.  To prevent this, we have made it clear that any patent
must be licensed for everyone's free use or not licensed at all.

The precise terms and conditions for copying, distribution and
modification follow.

    TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
  0. This License applies to any program or other work which contains a
     notice placed by the copyright holder saying it may be distributed
     under the terms of this General Public License.  The "Program",
     below, refers to any such program or work, and a "work based on
     the Program" means either the Program or any derivative work under
     copyright law: that is to say, a work containing the Program or a
     portion of it, either verbatim or with modifications and/or
     translated into another language.  (Hereinafter, translation is
     included without limitation in the term "modification".)  Each
     licensee is addressed as "you".

     Activities other than copying, distribution and modification are
     not covered by this License; they are outside its scope.  The act
     of running the Program is not restricted, and the output from the
     Program is covered only if its contents constitute a work based on
     the Program (independent of having been made by running the
     Program).  Whether that is true depends on what the Program does.

  1. You may copy and distribute verbatim copies of the Program's
     source code as you receive it, in any medium, provided that you
     conspicuously and appropriately publish on each copy an appropriate
     copyright notice and disclaimer of warranty; keep intact all the
     notices that refer to this License and to the absence of any
     warranty; and give any other recipients of the Program a copy of
     this License along with the Program.

     You may charge a fee for the physical act of transferring a copy,
     and you may at your option offer warranty protection in exchange
     for a fee.

  2. You may modify your copy or copies of the Program or any portion
     of it, thus forming a work based on the Program, and copy and
     distribute such modifications or work under the terms of Section 1
     above, provided that you also meet all of these conditions:

       a. You must cause the modified files to carry prominent notices
          stating that you changed the files and the date of any change.

       b. You must cause any work that you distribute or publish, that
          in whole or in part contains or is derived from the Program
          or any part thereof, to be licensed as a whole at no charge
          to all third parties under the terms of this License.

       c. If the modified program normally reads commands interactively
          when run, you must cause it, when started running for such
          interactive use in the most ordinary way, to print or display
          an announcement including an appropriate copyright notice and
          a notice that there is no warranty (or else, saying that you
          provide a warranty) and that users may redistribute the
          program under these conditions, and telling the user how to
          view a copy of this License.  (Exception: if the Program
          itself is interactive but does not normally print such an
          announcement, your work based on the Program is not required
          to print an announcement.)

     These requirements apply to the modified work as a whole.  If
     identifiable sections of that work are not derived from the
     Program, and can be reasonably considered independent and separate
     works in themselves, then this License, and its terms, do not
     apply to those sections when you distribute them as separate
     works.  But when you distribute the same sections as part of a
     whole which is a work based on the Program, the distribution of
     the whole must be on the terms of this License, whose permissions
     for other licensees extend to the entire whole, and thus to each
     and every part regardless of who wrote it.

     Thus, it is not the intent of this section to claim rights or
     contest your rights to work written entirely by you; rather, the
     intent is to exercise the right to control the distribution of
     derivative or collective works based on the Program.

     In addition, mere aggregation of another work not based on the
     Program with the Program (or with a work based on the Program) on
     a volume of a storage or distribution medium does not bring the
     other work under the scope of this License.

  3. You may copy and distribute the Program (or a work based on it,
     under Section 2) in object code or executable form under the terms
     of Sections 1 and 2 above provided that you also do one of the
     following:

       a. Accompany it with the complete corresponding machine-readable
          source code, which must be distributed under the terms of
          Sections 1 and 2 above on a medium customarily used for
          software interchange; or,

       b. Accompany it with a written offer, valid for at least three
          years, to give any third party, for a charge no more than your
          cost of physically performing source distribution, a complete
          machine-readable copy of the corresponding source code, to be
          distributed under the terms of Sections 1 and 2 above on a
          medium customarily used for software interchange; or,

       c. Accompany it with the information you received as to the offer
          to distribute corresponding source code.  (This alternative is
          allowed only for noncommercial distribution and only if you
          received the program in object code or executable form with
          such an offer, in accord with Subsection b above.)

     The source code for a work means the preferred form of the work for
     making modifications to it.  For an executable work, complete
     source code means all the source code for all modules it contains,
     plus any associated interface definition files, plus the scripts
     used to control compilation and installation of the executable.
     However, as a special exception, the source code distributed need
     not include anything that is normally distributed (in either
     source or binary form) with the major components (compiler,
     kernel, and so on) of the operating system on which the executable
     runs, unless that component itself accompanies the executable.

     If distribution of executable or object code is made by offering
     access to copy from a designated place, then offering equivalent
     access to copy the source code from the same place counts as
     distribution of the source code, even though third parties are not
     compelled to copy the source along with the object code.

  4. You may not copy, modify, sublicense, or distribute the Program
     except as expressly provided under this License.  Any attempt
     otherwise to copy, modify, sublicense or distribute the Program is
     void, and will automatically terminate your rights under this
     License.  However, parties who have received copies, or rights,
     from you under this License will not have their licenses
     terminated so long as such parties remain in full compliance.

  5. You are not required to accept this License, since you have not
     signed it.  However, nothing else grants you permission to modify
     or distribute the Program or its derivative works.  These actions
     are prohibited by law if you do not accept this License.
     Therefore, by modifying or distributing the Program (or any work
     based on the Program), you indicate your acceptance of this
     License to do so, and all its terms and conditions for copying,
     distributing or modifying the Program or works based on it.

  6. Each time you redistribute the Program (or any work based on the
     Program), the recipient automatically receives a license from the
     original licensor to copy, distribute or modify the Program
     subject to these terms and conditions.  You may not impose any
     further restrictions on the recipients' exercise of the rights
     granted herein.  You are not responsible for enforcing compliance
     by third parties to this License.

  7. If, as a consequence of a court judgment or allegation of patent
     infringement or for any other reason (not limited to patent
     issues), conditions are imposed on you (whether by court order,
     agreement or otherwise) that contradict the conditions of this
     License, they do not excuse you from the conditions of this
     License.  If you cannot distribute so as to satisfy simultaneously
     your obligations under this License and any other pertinent
     obligations, then as a consequence you may not distribute the
     Program at all.  For example, if a patent license would not permit
     royalty-free redistribution of the Program by all those who
     receive copies directly or indirectly through you, then the only
     way you could satisfy both it and this License would be to refrain
     entirely from distribution of the Program.

     If any portion of this section is held invalid or unenforceable
     under any particular circumstance, the balance of the section is
     intended to apply and the section as a whole is intended to apply
     in other circumstances.

     It is not the purpose of this section to induce you to infringe any
     patents or other property right claims or to contest validity of
     any such claims; this section has the sole purpose of protecting
     the integrity of the free software distribution system, which is
     implemented by public license practices.  Many people have made
     generous contributions to the wide range of software distributed
     through that system in reliance on consistent application of that
     system; it is up to the author/donor to decide if he or she is
     willing to distribute software through any other system and a
     licensee cannot impose that choice.

     This section is intended to make thoroughly clear what is believed
     to be a consequence of the rest of this License.

  8. If the distribution and/or use of the Program is restricted in
     certain countries either by patents or by copyrighted interfaces,
     the original copyright holder who places the Program under this
     License may add an explicit geographical distribution limitation
     excluding those countries, so that distribution is permitted only
     in or among countries not thus excluded.  In such case, this
     License incorporates the limitation as if written in the body of
     this License.

  9. The Free Software Foundation may publish revised and/or new
     versions of the General Public License from time to time.  Such
     new versions will be similar in spirit to the present version, but
     may differ in detail to address new problems or concerns.

     Each version is given a distinguishing version number.  If the
     Program specifies a version number of this License which applies
     to it and "any later version", you have the option of following
     the terms and conditions either of that version or of any later
     version published by the Free Software Foundation.  If the Program
     does not specify a version number of this License, you may choose
     any version ever published by the Free Software Foundation.

 10. If you wish to incorporate parts of the Program into other free
     programs whose distribution conditions are different, write to the
     author to ask for permission.  For software which is copyrighted
     by the Free Software Foundation, write to the Free Software
     Foundation; we sometimes make exceptions for this.  Our decision
     will be guided by the two goals of preserving the free status of
     all derivatives of our free software and of promoting the sharing
     and reuse of software generally.

                                NO WARRANTY

 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO
     WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE
     LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
     HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT
     WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT
     NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
     FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS TO THE
     QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
     PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY
     SERVICING, REPAIR OR CORRECTION.

 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
     WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY
     MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE
     LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL,
     INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR
     INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
     DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU
     OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY
     OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN
     ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

                      END OF TERMS AND CONDITIONS

How to Apply These Terms to Your New Programs
=============================================

If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.

To do so, attach the following notices to the program.  It is safest to
attach them to the start of each source file to most effectively convey
the exclusion of warranty; and each file should have at least the
"copyright" line and a pointer to where the full notice is found.

     ONE LINE TO GIVE THE PROGRAM'S NAME AND AN IDEA OF WHAT IT DOES.
     Copyright (C) YEAR  NAME OF AUTHOR

     This program is free software; you can redistribute it and/or
     modify it under the terms of the GNU General Public License
     as published by the Free Software Foundation; either version 2
     of the License, or (at your option) any later version.

     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with this program; if not, write to the Free Software
     Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02111, USA.

Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this
when it starts in an interactive mode:

     Gnomovision version 69, Copyright (C) YEAR NAME OF AUTHOR
     Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
     type `show w'.  This is free software, and you are welcome
     to redistribute it under certain conditions; type `show c'
     for details.

The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License.  Of course, the
commands you use may be called something other than `show w' and `show
c'; they could even be mouse-clicks or menu items--whatever suits your
program.

You should also get your employer (if you work as a programmer) or your
school, if any, to sign a "copyright disclaimer" for the program, if
necessary.  Here is a sample; alter the names:

     Yoyodyne, Inc., hereby disclaims all copyright
     interest in the program `Gnomovision'
     (which makes passes at compilers) written
     by James Hacker.

     SIGNATURE OF TY COON, 1 April 1989
     Ty Coon, President of Vice

This General Public License does not permit incorporating your program
into proprietary programs.  If your program is a subroutine library,
you may consider it more useful to permit linking proprietary
applications with the library.  If this is what you want to do, use the
GNU Lesser General Public License instead of this License.


File: gawk.info,  Node: GNU Free Documentation License,  Next: Index,  Prev: Copying,  Up: Top

GNU Free Documentation License
******************************

                      Version 1.2, November 2002
     Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
     51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

  0. PREAMBLE

     The purpose of this License is to make a manual, textbook, or other
     functional and useful document "free" in the sense of freedom: to
     assure everyone the effective freedom to copy and redistribute it,
     with or without modifying it, either commercially or
     noncommercially.  Secondarily, this License preserves for the
     author and publisher a way to get credit for their work, while not
     being considered responsible for modifications made by others.

     This License is a kind of "copyleft", which means that derivative
     works of the document must themselves be free in the same sense.
     It complements the GNU General Public License, which is a copyleft
     license designed for free software.

     We have designed this License in order to use it for manuals for
     free software, because free software needs free documentation: a
     free program should come with manuals providing the same freedoms
     that the software does.  But this License is not limited to
     software manuals; it can be used for any textual work, regardless
     of subject matter or whether it is published as a printed book.
     We recommend this License principally for works whose purpose is
     instruction or reference.

  1. APPLICABILITY AND DEFINITIONS

     This License applies to any manual or other work, in any medium,
     that contains a notice placed by the copyright holder saying it
     can be distributed under the terms of this License.  Such a notice
     grants a world-wide, royalty-free license, unlimited in duration,
     to use that work under the conditions stated herein.  The
     "Document", below, refers to any such manual or work.  Any member
     of the public is a licensee, and is addressed as "you".  You
     accept the license if you copy, modify or distribute the work in a
     way requiring permission under copyright law.

     A "Modified Version" of the Document means any work containing the
     Document or a portion of it, either copied verbatim, or with
     modifications and/or translated into another language.

     A "Secondary Section" is a named appendix or a front-matter section
     of the Document that deals exclusively with the relationship of the
     publishers or authors of the Document to the Document's overall
     subject (or to related matters) and contains nothing that could
     fall directly within that overall subject.  (Thus, if the Document
     is in part a textbook of mathematics, a Secondary Section may not
     explain any mathematics.)  The relationship could be a matter of
     historical connection with the subject or with related matters, or
     of legal, commercial, philosophical, ethical or political position
     regarding them.

     The "Invariant Sections" are certain Secondary Sections whose
     titles are designated, as being those of Invariant Sections, in
     the notice that says that the Document is released under this
     License.  If a section does not fit the above definition of
     Secondary then it is not allowed to be designated as Invariant.
     The Document may contain zero Invariant Sections.  If the Document
     does not identify any Invariant Sections then there are none.

     The "Cover Texts" are certain short passages of text that are
     listed, as Front-Cover Texts or Back-Cover Texts, in the notice
     that says that the Document is released under this License.  A
     Front-Cover Text may be at most 5 words, and a Back-Cover Text may
     be at most 25 words.

     A "Transparent" copy of the Document means a machine-readable copy,
     represented in a format whose specification is available to the
     general public, that is suitable for revising the document
     straightforwardly with generic text editors or (for images
     composed of pixels) generic paint programs or (for drawings) some
     widely available drawing editor, and that is suitable for input to
     text formatters or for automatic translation to a variety of
     formats suitable for input to text formatters.  A copy made in an
     otherwise Transparent file format whose markup, or absence of
     markup, has been arranged to thwart or discourage subsequent
     modification by readers is not Transparent.  An image format is
     not Transparent if used for any substantial amount of text.  A
     copy that is not "Transparent" is called "Opaque".

     Examples of suitable formats for Transparent copies include plain
     ASCII without markup, Texinfo input format, LaTeX input format,
     SGML or XML using a publicly available DTD, and
     standard-conforming simple HTML, PostScript or PDF designed for
     human modification.  Examples of transparent image formats include
     PNG, XCF and JPG.  Opaque formats include proprietary formats that
     can be read and edited only by proprietary word processors, SGML or
     XML for which the DTD and/or processing tools are not generally
     available, and the machine-generated HTML, PostScript or PDF
     produced by some word processors for output purposes only.

     The "Title Page" means, for a printed book, the title page itself,
     plus such following pages as are needed to hold, legibly, the
     material this License requires to appear in the title page.  For
     works in formats which do not have any title page as such, "Title
     Page" means the text near the most prominent appearance of the
     work's title, preceding the beginning of the body of the text.

     A section "Entitled XYZ" means a named subunit of the Document
     whose title either is precisely XYZ or contains XYZ in parentheses
     following text that translates XYZ in another language.  (Here XYZ
     stands for a specific section name mentioned below, such as
     "Acknowledgements", "Dedications", "Endorsements", or "History".)
     To "Preserve the Title" of such a section when you modify the
     Document means that it remains a section "Entitled XYZ" according
     to this definition.

     The Document may include Warranty Disclaimers next to the notice
     which states that this License applies to the Document.  These
     Warranty Disclaimers are considered to be included by reference in
     this License, but only as regards disclaiming warranties: any other
     implication that these Warranty Disclaimers may have is void and
     has no effect on the meaning of this License.

  2. VERBATIM COPYING

     You may copy and distribute the Document in any medium, either
     commercially or noncommercially, provided that this License, the
     copyright notices, and the license notice saying this License
     applies to the Document are reproduced in all copies, and that you
     add no other conditions whatsoever to those of this License.  You
     may not use technical measures to obstruct or control the reading
     or further copying of the copies you make or distribute.  However,
     you may accept compensation in exchange for copies.  If you
     distribute a large enough number of copies you must also follow
     the conditions in section 3.

     You may also lend copies, under the same conditions stated above,
     and you may publicly display copies.

  3. COPYING IN QUANTITY

     If you publish printed copies (or copies in media that commonly
     have printed covers) of the Document, numbering more than 100, and
     the Document's license notice requires Cover Texts, you must
     enclose the copies in covers that carry, clearly and legibly, all
     these Cover Texts: Front-Cover Texts on the front cover, and
     Back-Cover Texts on the back cover.  Both covers must also clearly
     and legibly identify you as the publisher of these copies.  The
     front cover must present the full title with all words of the
     title equally prominent and visible.  You may add other material
     on the covers in addition.  Copying with changes limited to the
     covers, as long as they preserve the title of the Document and
     satisfy these conditions, can be treated as verbatim copying in
     other respects.

     If the required texts for either cover are too voluminous to fit
     legibly, you should put the first ones listed (as many as fit
     reasonably) on the actual cover, and continue the rest onto
     adjacent pages.

     If you publish or distribute Opaque copies of the Document
     numbering more than 100, you must either include a
     machine-readable Transparent copy along with each Opaque copy, or
     state in or with each Opaque copy a computer-network location from
     which the general network-using public has access to download
     using public-standard network protocols a complete Transparent
     copy of the Document, free of added material.  If you use the
     latter option, you must take reasonably prudent steps, when you
     begin distribution of Opaque copies in quantity, to ensure that
     this Transparent copy will remain thus accessible at the stated
     location until at least one year after the last time you
     distribute an Opaque copy (directly or through your agents or
     retailers) of that edition to the public.

     It is requested, but not required, that you contact the authors of
     the Document well before redistributing any large number of
     copies, to give them a chance to provide you with an updated
     version of the Document.

  4. MODIFICATIONS

     You may copy and distribute a Modified Version of the Document
     under the conditions of sections 2 and 3 above, provided that you
     release the Modified Version under precisely this License, with
     the Modified Version filling the role of the Document, thus
     licensing distribution and modification of the Modified Version to
     whoever possesses a copy of it.  In addition, you must do these
     things in the Modified Version:

       A. Use in the Title Page (and on the covers, if any) a title
          distinct from that of the Document, and from those of
          previous versions (which should, if there were any, be listed
          in the History section of the Document).  You may use the
          same title as a previous version if the original publisher of
          that version gives permission.

       B. List on the Title Page, as authors, one or more persons or
          entities responsible for authorship of the modifications in
          the Modified Version, together with at least five of the
          principal authors of the Document (all of its principal
          authors, if it has fewer than five), unless they release you
          from this requirement.

       C. State on the Title page the name of the publisher of the
          Modified Version, as the publisher.

       D. Preserve all the copyright notices of the Document.

       E. Add an appropriate copyright notice for your modifications
          adjacent to the other copyright notices.

       F. Include, immediately after the copyright notices, a license
          notice giving the public permission to use the Modified
          Version under the terms of this License, in the form shown in
          the Addendum below.

       G. Preserve in that license notice the full lists of Invariant
          Sections and required Cover Texts given in the Document's
          license notice.

       H. Include an unaltered copy of this License.

       I. Preserve the section Entitled "History", Preserve its Title,
          and add to it an item stating at least the title, year, new
          authors, and publisher of the Modified Version as given on
          the Title Page.  If there is no section Entitled "History" in
          the Document, create one stating the title, year, authors,
          and publisher of the Document as given on its Title Page,
          then add an item describing the Modified Version as stated in
          the previous sentence.

       J. Preserve the network location, if any, given in the Document
          for public access to a Transparent copy of the Document, and
          likewise the network locations given in the Document for
          previous versions it was based on.  These may be placed in
          the "History" section.  You may omit a network location for a
          work that was published at least four years before the
          Document itself, or if the original publisher of the version
          it refers to gives permission.

       K. For any section Entitled "Acknowledgements" or "Dedications",
          Preserve the Title of the section, and preserve in the
          section all the substance and tone of each of the contributor
          acknowledgements and/or dedications given therein.

       L. Preserve all the Invariant Sections of the Document,
          unaltered in their text and in their titles.  Section numbers
          or the equivalent are not considered part of the section
          titles.

       M. Delete any section Entitled "Endorsements".  Such a section
          may not be included in the Modified Version.

       N. Do not retitle any existing section to be Entitled
          "Endorsements" or to conflict in title with any Invariant
          Section.

       O. Preserve any Warranty Disclaimers.

     If the Modified Version includes new front-matter sections or
     appendices that qualify as Secondary Sections and contain no
     material copied from the Document, you may at your option
     designate some or all of these sections as invariant.  To do this,
     add their titles to the list of Invariant Sections in the Modified
     Version's license notice.  These titles must be distinct from any
     other section titles.

     You may add a section Entitled "Endorsements", provided it contains
     nothing but endorsements of your Modified Version by various
     parties--for example, statements of peer review or that the text
     has been approved by an organization as the authoritative
     definition of a standard.

     You may add a passage of up to five words as a Front-Cover Text,
     and a passage of up to 25 words as a Back-Cover Text, to the end
     of the list of Cover Texts in the Modified Version.  Only one
     passage of Front-Cover Text and one of Back-Cover Text may be
     added by (or through arrangements made by) any one entity.  If the
     Document already includes a cover text for the same cover,
     previously added by you or by arrangement made by the same entity
     you are acting on behalf of, you may not add another; but you may
     replace the old one, on explicit permission from the previous
     publisher that added the old one.

     The author(s) and publisher(s) of the Document do not by this
     License give permission to use their names for publicity for or to
     assert or imply endorsement of any Modified Version.

  5. COMBINING DOCUMENTS

     You may combine the Document with other documents released under
     this License, under the terms defined in section 4 above for
     modified versions, provided that you include in the combination
     all of the Invariant Sections of all of the original documents,
     unmodified, and list them all as Invariant Sections of your
     combined work in its license notice, and that you preserve all
     their Warranty Disclaimers.

     The combined work need only contain one copy of this License, and
     multiple identical Invariant Sections may be replaced with a single
     copy.  If there are multiple Invariant Sections with the same name
     but different contents, make the title of each such section unique
     by adding at the end of it, in parentheses, the name of the
     original author or publisher of that section if known, or else a
     unique number.  Make the same adjustment to the section titles in
     the list of Invariant Sections in the license notice of the
     combined work.

     In the combination, you must combine any sections Entitled
     "History" in the various original documents, forming one section
     Entitled "History"; likewise combine any sections Entitled
     "Acknowledgements", and any sections Entitled "Dedications".  You
     must delete all sections Entitled "Endorsements."

  6. COLLECTIONS OF DOCUMENTS

     You may make a collection consisting of the Document and other
     documents released under this License, and replace the individual
     copies of this License in the various documents with a single copy
     that is included in the collection, provided that you follow the
     rules of this License for verbatim copying of each of the
     documents in all other respects.

     You may extract a single document from such a collection, and
     distribute it individually under this License, provided you insert
     a copy of this License into the extracted document, and follow
     this License in all other respects regarding verbatim copying of
     that document.

  7. AGGREGATION WITH INDEPENDENT WORKS

     A compilation of the Document or its derivatives with other
     separate and independent documents or works, in or on a volume of
     a storage or distribution medium, is called an "aggregate" if the
     copyright resulting from the compilation is not used to limit the
     legal rights of the compilation's users beyond what the individual
     works permit.  When the Document is included an aggregate, this
     License does not apply to the other works in the aggregate which
     are not themselves derivative works of the Document.

     If the Cover Text requirement of section 3 is applicable to these
     copies of the Document, then if the Document is less than one half
     of the entire aggregate, the Document's Cover Texts may be placed
     on covers that bracket the Document within the aggregate, or the
     electronic equivalent of covers if the Document is in electronic
     form.  Otherwise they must appear on printed covers that bracket
     the whole aggregate.

  8. TRANSLATION

     Translation is considered a kind of modification, so you may
     distribute translations of the Document under the terms of section
     4.  Replacing Invariant Sections with translations requires special
     permission from their copyright holders, but you may include
     translations of some or all Invariant Sections in addition to the
     original versions of these Invariant Sections.  You may include a
     translation of this License, and all the license notices in the
     Document, and any Warrany Disclaimers, provided that you also
     include the original English version of this License and the
     original versions of those notices and disclaimers.  In case of a
     disagreement between the translation and the original version of
     this License or a notice or disclaimer, the original version will
     prevail.

     If a section in the Document is Entitled "Acknowledgements",
     "Dedications", or "History", the requirement (section 4) to
     Preserve its Title (section 1) will typically require changing the
     actual title.

  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided for under this License.  Any other
     attempt to copy, modify, sublicense or distribute the Document is
     void, and will automatically terminate your rights under this
     License.  However, parties who have received copies, or rights,
     from you under this License will not have their licenses
     terminated so long as such parties remain in full compliance.

 10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
     the GNU Free Documentation License from time to time.  Such new
     versions will be similar in spirit to the present version, but may
     differ in detail to address new problems or concerns.  See
     `http://www.gnu.org/copyleft/'.

     Each version of the License is given a distinguishing version
     number.  If the Document specifies that a particular numbered
     version of this License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that specified version or of any later version that has been
     published (not as a draft) by the Free Software Foundation.  If
     the Document does not specify a version number of this License,
     you may choose any version ever published (not as a draft) by the
     Free Software Foundation.

ADDENDUM: How to use this License for your documents
====================================================

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
       A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the "with...Texts." line with this:

         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.


File: gawk.info,  Node: Index,  Prev: GNU Free Documentation License,  Up: Top

Index
*****

* Menu:

* ! (exclamation point), !  operator:    Boolean Ops.       (line  6524)
* ! (exclamation point), ! operator <1>: Egrep Program.     (line 14679)
* ! (exclamation point), ! operator:     Precedence.        (line  6698)
* ! (exclamation point), != operator <1>: Precedence.       (line  6711)
* ! (exclamation point), != operator:    Typing and Comparison.
                                                            (line  6342)
* ! (exclamation point), !~ operator <1>: Expression Patterns.
                                                            (line  6851)
* ! (exclamation point), !~ operator <2>: Precedence.       (line  6727)
* ! (exclamation point), !~ operator <3>: Typing and Comparison.
                                                            (line  6342)
* ! (exclamation point), !~ operator <4>: Regexp Constants. (line  5532)
* ! (exclamation point), !~ operator <5>: Computed Regexps. (line  2656)
* ! (exclamation point), !~ operator <6>: Case-sensitivity. (line  2569)
* ! (exclamation point), !~ operator:    Regexp Usage.      (line  1989)
* ! operator <1>:                        Egrep Program.     (line 14687)
* ! operator:                            Ranges.            (line  6955)
* " (double quote) <1>:                  Quoting.           (line  1376)
* " (double quote):                      Read Terminal.     (line  1165)
* " (double quote), regexp constants:    Computed Regexps.  (line  2677)
* # (number sign), #! (executable scripts): Executable Scripts.
                                                            (line  1233)
* # (number sign), #! (executable scripts), portability issues with: Executable Scripts.
                                                            (line  1233)
* # (number sign), commenting:           Comments.          (line  1296)
* $ (dollar sign):                       Regexp Operators.  (line  2210)
* $ (dollar sign), $ field operator <1>: Precedence.        (line  6689)
* $ (dollar sign), $ field operator:     Fields.            (line  3027)
* $ (dollar sign), incrementing fields and arrays: Increment Ops.
                                                            (line  6184)
* $ field operator:                      Fields.            (line  3027)
* % (percent sign), % operator:          Precedence.        (line  6701)
* % (percent sign), %= operator <1>:     Precedence.        (line  6742)
* % (percent sign), %= operator:         Assignment Ops.    (line  6111)
* & (ampersand), && operator <1>:        Precedence.        (line  6733)
* & (ampersand), && operator:            Boolean Ops.       (line  6514)
* & (ampersand), gsub/gensub/sub functions and: Gory Details.
                                                            (line  9642)
* ' (single quote) <1>:                  Quoting.           (line  1370)
* ' (single quote) <2>:                  Long.              (line  1223)
* ' (single quote):                      One-shot.          (line  1126)
* ' (single quote), vs. apostrophe:      Comments.          (line  1317)
* ' (single quote), with double quotes:  Quoting.           (line  1392)
* () (parentheses):                      Regexp Operators.  (line  2253)
* () (parentheses), pgawk program:       Profiling.         (line 11877)
* * (asterisk), * operator, as multiplication operator: Precedence.
                                                            (line  6701)
* * (asterisk), * operator, as regexp operator: Regexp Operators.
                                                            (line  2261)
* * (asterisk), * operator, null strings, matching: Gory Details.
                                                            (line  9796)
* * (asterisk), ** operator <1>:         Options.           (line 12191)
* * (asterisk), ** operator <2>:         Precedence.        (line  6695)
* * (asterisk), ** operator:             Arithmetic Ops.    (line  5898)
* * (asterisk), **= operator <1>:        Options.           (line 12191)
* * (asterisk), **= operator <2>:        Precedence.        (line  6742)
* * (asterisk), **= operator:            Assignment Ops.    (line  6111)
* * (asterisk), *= operator <1>:         Precedence.        (line  6742)
* * (asterisk), *= operator:             Assignment Ops.    (line  6111)
* + (plus sign):                         Regexp Operators.  (line  2276)
* + (plus sign), + operator:             Precedence.        (line  6698)
* + (plus sign), ++ operator <1>:        Precedence.        (line  6692)
* + (plus sign), ++ operator:            Increment Ops.     (line  6194)
* + (plus sign), += operator <1>:        Precedence.        (line  6742)
* + (plus sign), += operator:            Assignment Ops.    (line  6064)
* + (plus sign), decrement/increment operators: Increment Ops.
                                                            (line  6165)
* , (comma), in range patterns:          Ranges.            (line  6913)
* - (hyphen), - operator:                Precedence.        (line  6698)
* - (hyphen), -- (decrement/increment) operator: Precedence.
                                                            (line  6692)
* - (hyphen), -- operator:               Increment Ops.     (line  6202)
* - (hyphen), -= operator <1>:           Precedence.        (line  6742)
* - (hyphen), -= operator:               Assignment Ops.    (line  6111)
* - (hyphen), filenames beginning with:  Options.           (line 12073)
* - (hyphen), in character lists:        Character Lists.   (line  2364)
* --assign option:                       Options.           (line 12036)
* --compat option:                       Options.           (line 12085)
* --copyleft option:                     Options.           (line 12098)
* --copyright option:                    Options.           (line 12093)
* --disable-lint configuration option:   Additional Configuration Options.
                                                            (line 17477)
* --disable-nls configuration option:    Additional Configuration Options.
                                                            (line 17492)
* --dump-variables option <1>:           Library Names.     (line 12580)
* --dump-variables option:               Options.           (line 12101)
* --enable-portals configuration option <1>: Additional Configuration Options.
                                                            (line 17469)
* --enable-portals configuration option: Portal Files.      (line 11725)
* --enable-switch configuration option:  Additional Configuration Options.
                                                            (line 17473)
* --exec option:                         Options.           (line 12117)
* --field-separator option:              Options.           (line 12027)
* --file option:                         Options.           (line 12031)
* --gen-po option <1>:                   Options.           (line 12136)
* --gen-po option:                       String Extraction. (line 11177)
* --help option:                         Options.           (line 12145)
* --lint option <1>:                     Options.           (line 12150)
* --lint option:                         Command Line.      (line 12002)
* --lint-old option:                     Options.           (line 12162)
* --non-decimal-data option <1>:         Options.           (line 12167)
* --non-decimal-data option:             Nondecimal Data.   (line 11480)
* --non-decimal-data option, strtonum function and: Nondecimal Data.
                                                            (line 11510)
* --posix option:                        Options.           (line 12175)
* --posix option, --traditional option and: Options.        (line 12202)
* --profile option <1>:                  Options.           (line 12208)
* --profile option:                      Profiling.         (line 11749)
* --re-interval option:                  Options.           (line 12220)
* --source option:                       Options.           (line 12227)
* --traditional option:                  Options.           (line 12085)
* --traditional option, --posix option and: Options.        (line 12202)
* --usage option:                        Options.           (line 12145)
* --version option:                      Options.           (line 12235)
* -f option:                             Options.           (line 12031)
* -F option <1>:                         Options.           (line 12027)
* -F option:                             Command Line Field Separator.
                                                            (line  3427)
* -f option:                             Long.              (line  1202)
* -F option, -Ft sets FS to TAB:         Options.           (line 12243)
* -f option, on command line:            Options.           (line 12248)
* -F option, troubleshooting:            Known Bugs.        (line 12454)
* -mf/-mr options:                       Options.           (line 12051)
* -v option:                             Options.           (line 12036)
* -v option, variables, assigning:       Assignment Options.
                                                            (line  5677)
* -W option:                             Options.           (line 12061)
* . (period):                            Regexp Operators.  (line  2218)
* .mo files:                             Explaining gettext.
                                                            (line 10954)
* .mo files, converting from .po:        I18N Example.      (line 11400)
* .mo files, specifying directory of <1>: Programmer i18n.  (line 11090)
* .mo files, specifying directory of:    Explaining gettext.
                                                            (line 10966)
* .po files <1>:                         Translator i18n.   (line 11156)
* .po files:                             Explaining gettext.
                                                            (line 10951)
* .po files, converting to .mo:          I18N Example.      (line 11400)
* / (forward slash):                     Regexp.            (line  1949)
* / (forward slash), / operator:         Precedence.        (line  6701)
* / (forward slash), /= operator <1>:    Precedence.        (line  6742)
* / (forward slash), /= operator:        Assignment Ops.    (line  6111)
* / (forward slash), /= operator, vs. /=.../ regexp constant: Assignment Ops.
                                                            (line  6137)
* / (forward slash), patterns and:       Expression Patterns.
                                                            (line  6851)
* /= operator vs. /=.../ regexp constant: Assignment Ops.   (line  6137)
* /dev/... special files (gawk):         Special FD.        (line  5054)
* /inet/ files (gawk):                   TCP/IP Networking. (line 11658)
* /p files (gawk):                       Portal Files.      (line 11725)
* ; (semicolon):                         Statements/Lines.  (line  1853)
* ; (semicolon), AWKPATH variable and:   PC Using.          (line 17858)
* ; (semicolon), separating statements in actions <1>: Statements.
                                                            (line  7228)
* ; (semicolon), separating statements in actions: Action Overview.
                                                            (line  7178)
* < (left angle bracket), < operator <1>: Precedence.       (line  6711)
* < (left angle bracket), < operator:    Typing and Comparison.
                                                            (line  6342)
* < (left angle bracket), < operator (I/O): Getline/File.   (line  3979)
* < (left angle bracket), <= operator <1>: Precedence.      (line  6711)
* < (left angle bracket), <= operator:   Typing and Comparison.
                                                            (line  6342)
* = (equals sign), = operator:           Assignment Ops.    (line  5989)
* = (equals sign), == operator <1>:      Precedence.        (line  6711)
* = (equals sign), == operator:          Typing and Comparison.
                                                            (line  6342)
* > (right angle bracket), > operator <1>: Precedence.      (line  6711)
* > (right angle bracket), > operator:   Typing and Comparison.
                                                            (line  6342)
* > (right angle bracket), > operator (I/O): Redirection.   (line  4864)
* > (right angle bracket), >= operator <1>: Precedence.     (line  6711)
* > (right angle bracket), >= operator:  Typing and Comparison.
                                                            (line  6342)
* > (right angle bracket), >> operator (I/O) <1>: Precedence.
                                                            (line  6711)
* > (right angle bracket), >> operator (I/O): Redirection.  (line  4892)
* ? (question mark) <1>:                 GNU Regexp Operators.
                                                            (line  2506)
* ? (question mark):                     Regexp Operators.  (line  2285)
* ? (question mark), ?: operator:        Precedence.        (line  6739)
* [] (square brackets):                  Regexp Operators.  (line  2230)
* \ (backslash) <1>:                     Regexp Operators.  (line  2193)
* \ (backslash) <2>:                     Quoting.           (line  1370)
* \ (backslash) <3>:                     Comments.          (line  1339)
* \ (backslash):                         Read Terminal.     (line  1165)
* \ (backslash), \" escape sequence:     Escape Sequences.  (line  2108)
* \ (backslash), \' operator (gawk):     GNU Regexp Operators.
                                                            (line  2503)
* \ (backslash), \/ escape sequence:     Escape Sequences.  (line  2101)
* \ (backslash), \< operator (gawk):     GNU Regexp Operators.
                                                            (line  2477)
* \ (backslash), \> operator (gawk):     GNU Regexp Operators.
                                                            (line  2481)
* \ (backslash), \` operator (gawk):     GNU Regexp Operators.
                                                            (line  2501)
* \ (backslash), \a escape sequence:     Escape Sequences.  (line  2066)
* \ (backslash), \b escape sequence:     Escape Sequences.  (line  2070)
* \ (backslash), \B operator (gawk):     GNU Regexp Operators.
                                                            (line  2490)
* \ (backslash), \f escape sequence:     Escape Sequences.  (line  2073)
* \ (backslash), \n escape sequence:     Escape Sequences.  (line  2076)
* \ (backslash), \NNN escape sequence:   Escape Sequences.  (line  2088)
* \ (backslash), \r escape sequence:     Escape Sequences.  (line  2079)
* \ (backslash), \t escape sequence:     Escape Sequences.  (line  2082)
* \ (backslash), \v escape sequence:     Escape Sequences.  (line  2085)
* \ (backslash), \W operator (gawk):     GNU Regexp Operators.
                                                            (line  2473)
* \ (backslash), \w operator (gawk):     GNU Regexp Operators.
                                                            (line  2468)
* \ (backslash), \x escape sequence:     Escape Sequences.  (line  2093)
* \ (backslash), \y operator (gawk):     GNU Regexp Operators.
                                                            (line  2485)
* \ (backslash), as field separators:    Command Line Field Separator.
                                                            (line  3448)
* \ (backslash), continuing lines and <1>: Egrep Program.   (line 14737)
* \ (backslash), continuing lines and:   Statements/Lines.  (line  1783)
* \ (backslash), continuing lines and, comments and: Statements/Lines.
                                                            (line  1838)
* \ (backslash), continuing lines and, in csh <1>: Statements/Lines.
                                                            (line  1807)
* \ (backslash), continuing lines and, in csh: More Complex.
                                                            (line  1708)
* \ (backslash), gsub/gensub/sub functions and: Gory Details.
                                                            (line  9642)
* \ (backslash), in character lists:     Character Lists.   (line  2364)
* \ (backslash), in escape sequences:    Escape Sequences.  (line  2038)
* \ (backslash), in escape sequences, POSIX and: Escape Sequences.
                                                            (line  2145)
* \ (backslash), regexp constants:       Computed Regexps.  (line  2677)
* ^ (caret) <1>:                         GNU Regexp Operators.
                                                            (line  2506)
* ^ (caret):                             Regexp Operators.  (line  2197)
* ^ (caret), ^ operator <1>:             Options.           (line 12191)
* ^ (caret), ^ operator:                 Precedence.        (line  6695)
* ^ (caret), ^= operator <1>:            Options.           (line 12191)
* ^ (caret), ^= operator <2>:            Precedence.        (line  6742)
* ^ (caret), ^= operator:                Assignment Ops.    (line  6111)
* ^ (caret), in character lists:         Character Lists.   (line  2364)
* _ (underscore), _ C macro:             Explaining gettext.
                                                            (line 10983)
* _ (underscore), in names of private variables: Library Names.
                                                            (line 12564)
* _ (underscore), translatable string:   Programmer i18n.   (line 11112)
* _gr_init user-defined function:        Group Functions.   (line 14042)
* _pw_init user-defined function:        Passwd Functions.  (line 13828)
* accessing fields:                      Fields.            (line  3014)
* account information <1>:               Group Functions.   (line 13968)
* account information:                   Passwd Functions.  (line 13753)
* actions:                               Action Overview.   (line  7165)
* actions, control statements in:        Statements.        (line  7224)
* actions, default:                      Very Simple.       (line  1559)
* actions, empty:                        Very Simple.       (line  1564)
* adding, features to gawk:              Adding Code.       (line 18547)
* adding, fields:                        Changing Fields.   (line  3177)
* adding, functions to gawk:             Dynamic Extensions.
                                                            (line 18765)
* advanced features, buffering:          I/O Functions.     (line  9904)
* advanced features, close function:     Close Files And Pipes.
                                                            (line  5323)
* advanced features, constants, values of: Nondecimal-numbers.
                                                            (line  5518)
* advanced features, data files as single record: Records.  (line  2979)
* advanced features, fixed-width data:   Constant Size.     (line  3605)
* advanced features, FNR/NR variables:   Auto-set.          (line  8148)
* advanced features, gawk:               Advanced Features. (line 11449)
* advanced features, gawk, BSD portals:  Portal Files.      (line 11725)
* advanced features, gawk, network programming: TCP/IP Networking.
                                                            (line 11658)
* advanced features, gawk, nondecimal input data: Nondecimal Data.
                                                            (line 11480)
* advanced features, gawk, processes, communicating with: Two-way I/O.
                                                            (line 11539)
* advanced features, network connections, See Also networks, connections: Advanced Features.
                                                            (line 11449)
* advanced features, null strings, matching: Gory Details.  (line  9796)
* advanced features, operators, precedence: Increment Ops.  (line  6215)
* advanced features, piping into sh:     Redirection.       (line  4981)
* advanced features, regexp constants:   Assignment Ops.    (line  6137)
* Aho, Alfred <1>:                       Contributors.      (line 17062)
* Aho, Alfred:                           History.           (line   640)
* alarm clock example program:           Alarm Program.     (line 15480)
* alarm.awk program:                     Alarm Program.     (line 15498)
* algorithms:                            Basic High Level.  (line 19603)
* Alpha (DEC):                           Manual History.    (line   886)
* amazing awk assembler (aaa):           Glossary.          (line 19837)
* amazingly workable formatter (awf):    Glossary.          (line 19845)
* ambiguity, syntactic: /= operator vs. /=.../ regexp constant: Assignment Ops.
                                                            (line  6137)
* amiga:                                 Amiga Installation.
                                                            (line 17569)
* ampersand (&), && operator:            Boolean Ops.       (line  6514)
* ampersand (&), &&operator:             Precedence.        (line  6733)
* ampersand (&), gsub/gensub/sub functions and: Gory Details.
                                                            (line  9642)
* AND bitwise operation:                 Bitwise Functions. (line 10314)
* and Boolean-logic operator:            Boolean Ops.       (line  6463)
* and function (gawk):                   Bitwise Functions. (line 10347)
* ANSI:                                  Glossary.          (line 19856)
* archeologists:                         Bugs.              (line 18314)
* ARGC/ARGV variables <1>:               ARGC and ARGV.     (line  8180)
* ARGC/ARGV variables:                   Auto-set.          (line  7972)
* ARGC/ARGV variables, command-line arguments: Other Arguments.
                                                            (line 12311)
* ARGC/ARGV variables, portability and:  Executable Scripts.
                                                            (line  1270)
* ARGIND variable:                       Auto-set.          (line  8001)
* ARGIND variable, command-line arguments: Other Arguments. (line 12311)
* arguments, command-line <1>:           Other Arguments.   (line 12305)
* arguments, command-line <2>:           ARGC and ARGV.     (line  8180)
* arguments, command-line:               Auto-set.          (line  7972)
* arguments, command-line, invoking awk: Command Line.      (line 11988)
* arguments, in function calls:          Function Calls.    (line  6603)
* arguments, processing:                 Getopt Function.   (line 13460)
* arguments, retrieving:                 Internals.         (line 18907)
* arithmetic operators:                  Arithmetic Ops.    (line  5823)
* arrays:                                Arrays.            (line  8276)
* arrays, as parameters to functions:    Function Caveats.  (line 10716)
* arrays, associative:                   Array Intro.       (line  8356)
* arrays, associative, clearing:         Internals.         (line 18852)
* arrays, associative, library functions and: Library Names.
                                                            (line 12592)
* arrays, deleting entire contents:      Delete.            (line  8618)
* arrays, elements, assigning:           Assigning Elements.
                                                            (line  8460)
* arrays, elements, deleting:            Delete.            (line  8585)
* arrays, elements, installing:          Internals.         (line 18856)
* arrays, elements, order of:            Scanning an Array. (line  8571)
* arrays, elements, referencing:         Reference to Elements.
                                                            (line  8413)
* arrays, elements, retrieving number of: String Functions. (line  9176)
* arrays, for statement and:             Scanning an Array. (line  8544)
* arrays, IGNORECASE variable and:       Array Intro.       (line  8398)
* arrays, indexing:                      Array Intro.       (line  8356)
* arrays, merging into strings:          Join Function.     (line 13067)
* arrays, multidimensional:              Multi-dimensional. (line  8754)
* arrays, multidimensional, scanning:    Multi-scanning.    (line  8840)
* arrays, names of:                      Arrays.            (line  8287)
* arrays, scanning:                      Scanning an Array. (line  8530)
* arrays, sorting:                       Array Sorting.     (line  8875)
* arrays, sorting, IGNORECASE variable and: Array Sorting.  (line  8953)
* arrays, sparse:                        Array Intro.       (line  8377)
* arrays, subscripts:                    Numeric Array Subscripts.
                                                            (line  8656)
* arrays, subscripts, uninitialized variables as: Uninitialized Subscripts.
                                                            (line  8707)
* artificial intelligence, gawk and:     Distribution contents.
                                                            (line 17294)
* ASCII:                                 Ordinal Functions. (line 13014)
* asort function (gawk) <1>:             String Functions.  (line  9176)
* asort function (gawk):                 Array Sorting.     (line  8875)
* asort function (gawk), arrays, sorting: Array Sorting.    (line  8875)
* asorti function (gawk):                String Functions.  (line  9205)
* assert function (C library):           Assert Function.   (line 12815)
* assert user-defined function:          Assert Function.   (line 12837)
* assertions:                            Assert Function.   (line 12815)
* assignment operators:                  Assignment Ops.    (line  5989)
* assignment operators, evaluation order: Assignment Ops.   (line  6093)
* assignment operators, lvalues/rvalues: Assignment Ops.    (line  6014)
* assignments as filenames:              Ignoring Assigns.  (line 13418)
* assoc_clear internal function:         Internals.         (line 18852)
* assoc_lookup internal function:        Internals.         (line 18856)
* associative arrays:                    Array Intro.       (line  8356)
* asterisk (*), * operator, as multiplication operator: Precedence.
                                                            (line  6701)
* asterisk (*), * operator, as regexp operator: Regexp Operators.
                                                            (line  2261)
* asterisk (*), * operator, null strings, matching: Gory Details.
                                                            (line  9796)
* asterisk (*), ** operator <1>:         Options.           (line 12191)
* asterisk (*), ** operator <2>:         Precedence.        (line  6695)
* asterisk (*), ** operator:             Arithmetic Ops.    (line  5898)
* asterisk (*), **= operator <1>:        Options.           (line 12191)
* asterisk (*), **= operator <2>:        Precedence.        (line  6742)
* asterisk (*), **= operator:            Assignment Ops.    (line  6111)
* asterisk (*), *= operator <1>:         Precedence.        (line  6742)
* asterisk (*), *= operator:             Assignment Ops.    (line  6111)
* atan2 function:                        Numeric Functions. (line  9082)
* atari:                                 Atari Installation.
                                                            (line 18161)
* awf (amazingly workable formatter) program: Glossary.     (line 19845)
* awk language, POSIX version:           Assignment Ops.    (line  6122)
* awk programs <1>:                      Two Rules.         (line  1647)
* awk programs <2>:                      Executable Scripts.
                                                            (line  1233)
* awk programs:                          Getting Started.   (line  1038)
* awk programs, complex:                 When.              (line  1923)
* awk programs, documenting <1>:         Library Names.     (line 12541)
* awk programs, documenting:             Comments.          (line  1296)
* awk programs, examples of:             Sample Programs.   (line 14200)
* awk programs, execution of:            Next Statement.    (line  7645)
* awk programs, internationalizing <1>:  Programmer i18n.   (line 11051)
* awk programs, internationalizing:      I18N Functions.    (line 10436)
* awk programs, lengthy:                 Long.              (line  1196)
* awk programs, lengthy, assertions:     Assert Function.   (line 12815)
* awk programs, location of:             Options.           (line 12031)
* awk programs, one-line examples:       Very Simple.       (line  1570)
* awk programs, profiling:               Profiling.         (line 11740)
* awk programs, profiling, enabling:     Options.           (line 12208)
* awk programs, running <1>:             Long.              (line  1196)
* awk programs, running:                 Running gawk.      (line  1084)
* awk programs, running, from shell scripts: One-shot.      (line  1133)
* awk programs, running, without input files: Read Terminal.
                                                            (line  1157)
* awk programs, shell variables in:      Using Shell Variables.
                                                            (line  7114)
* awk, function of:                      Getting Started.   (line  1032)
* awk, gawk and <1>:                     This Manual.       (line   718)
* awk, gawk and:                         Preface.           (line   569)
* awk, history of:                       History.           (line   640)
* awk, implementation issues, pipes:     Redirection.       (line  4973)
* awk, implementations:                  Other Versions.    (line 18383)
* awk, implementations, limits:          Getline Notes.     (line  4193)
* awk, invoking:                         Command Line.      (line 11988)
* awk, new vs. old:                      Names.             (line   677)
* awk, new vs. old, OFMT variable:       Conversion.        (line  5767)
* awk, POSIX and:                        Preface.           (line   569)
* awk, POSIX and, See Also POSIX awk:    Preface.           (line   569)
* awk, regexp constants and:             Typing and Comparison.
                                                            (line  6442)
* awk, See Also gawk:                    Preface.           (line   582)
* awk, terms describing:                 This Manual.       (line   711)
* awk, uses for <1>:                     When.              (line  1899)
* awk, uses for <2>:                     Getting Started.   (line  1038)
* awk, uses for:                         Preface.           (line   569)
* awk, versions of <1>:                  V7/SVR3.1.         (line 16665)
* awk, versions of:                      Names.             (line   681)
* awk, versions of, changes between SVR3.1 and SVR4: SVR4.  (line 16724)
* awk, versions of, changes between SVR4 and POSIX awk: POSIX.
                                                            (line 16765)
* awk, versions of, changes between V7 and SVR3.1: V7/SVR3.1.
                                                            (line 16665)
* awk, versions of, See Also Bell Laboratories awk: BTL.    (line 16809)
* awk.h file (internal):                 Internals.         (line 18801)
* awka compiler for awk:                 Other Versions.    (line 18453)
* AWKNUM internal type:                  Internals.         (line 18805)
* AWKPATH environment variable <1>:      PC Using.          (line 17858)
* AWKPATH environment variable:          AWKPATH Variable.  (line 12361)
* awkprof.out file:                      Profiling.         (line 11744)
* awksed.awk program:                    Simple Sed.        (line 16189)
* awkvars.out file:                      Options.           (line 12101)
* backslash (\) <1>:                     Regexp Operators.  (line  2193)
* backslash (\) <2>:                     Quoting.           (line  1370)
* backslash (\) <3>:                     Comments.          (line  1339)
* backslash (\):                         Read Terminal.     (line  1165)
* backslash (\), \" escape sequence:     Escape Sequences.  (line  2108)
* backslash (\), \' operator (gawk):     GNU Regexp Operators.
                                                            (line  2503)
* backslash (\), \/ escape sequence:     Escape Sequences.  (line  2101)
* backslash (\), \< operator (gawk):     GNU Regexp Operators.
                                                            (line  2477)
* backslash (\), \> operator (gawk):     GNU Regexp Operators.
                                                            (line  2481)
* backslash (\), \` operator (gawk):     GNU Regexp Operators.
                                                            (line  2501)
* backslash (\), \a escape sequence:     Escape Sequences.  (line  2066)
* backslash (\), \b escape sequence:     Escape Sequences.  (line  2070)
* backslash (\), \B operator (gawk):     GNU Regexp Operators.
                                                            (line  2490)
* backslash (\), \f escape sequence:     Escape Sequences.  (line  2073)
* backslash (\), \n escape sequence:     Escape Sequences.  (line  2076)
* backslash (\), \NNN escape sequence:   Escape Sequences.  (line  2088)
* backslash (\), \r escape sequence:     Escape Sequences.  (line  2079)
* backslash (\), \t escape sequence:     Escape Sequences.  (line  2082)
* backslash (\), \v escape sequence:     Escape Sequences.  (line  2085)
* backslash (\), \W operator (gawk):     GNU Regexp Operators.
                                                            (line  2473)
* backslash (\), \w operator (gawk):     GNU Regexp Operators.
                                                            (line  2468)
* backslash (\), \x escape sequence:     Escape Sequences.  (line  2093)
* backslash (\), \y operator (gawk):     GNU Regexp Operators.
                                                            (line  2485)
* backslash (\), as field separators:    Command Line Field Separator.
                                                            (line  3448)
* backslash (\), continuing lines and <1>: Egrep Program.   (line 14737)
* backslash (\), continuing lines and:   Statements/Lines.  (line  1783)
* backslash (\), continuing lines and, comments and: Statements/Lines.
                                                            (line  1838)
* backslash (\), continuing lines and, in csh <1>: Statements/Lines.
                                                            (line  1807)
* backslash (\), continuing lines and, in csh: More Complex.
                                                            (line  1708)
* backslash (\), gsub/gensub/sub functions and: Gory Details.
                                                            (line  9642)
* backslash (\), in character lists:     Character Lists.   (line  2364)
* backslash (\), in escape sequences:    Escape Sequences.  (line  2038)
* backslash (\), in escape sequences, POSIX and: Escape Sequences.
                                                            (line  2145)
* backslash (\), regexp constants:       Computed Regexps.  (line  2677)
* BBS-list file:                         Sample Data Files. (line  1461)
* Beebe, Nelson:                         Acknowledgments.   (line   995)
* Beebe, Nelson H.F.:                    Other Versions.    (line 18465)
* BEGIN pattern <1>:                     BEGIN/END.         (line  6980)
* BEGIN pattern <2>:                     Field Separators.  (line  3300)
* BEGIN pattern:                         Records.           (line  2839)
* BEGIN pattern, assert user-defined function and: Assert Function.
                                                            (line 12891)
* BEGIN pattern, Boolean patterns and:   Expression Patterns.
                                                            (line  6900)
* BEGIN pattern, exit statement and:     Exit Statement.    (line  7743)
* BEGIN pattern, getline and:            Getline Notes.     (line  4198)
* BEGIN pattern, headings, adding:       Print Examples.    (line  4350)
* BEGIN pattern, next/nextfile statements and <1>: Next Statement.
                                                            (line  7668)
* BEGIN pattern, next/nextfile statements and: I/O And BEGIN/END.
                                                            (line  7088)
* BEGIN pattern, OFS/ORS variables, assigning values to: Output Separators.
                                                            (line  4407)
* BEGIN pattern, operators and:          Using BEGIN/END.   (line  7010)
* BEGIN pattern, pgawk program:          Profiling.         (line 11802)
* BEGIN pattern, print statement and:    I/O And BEGIN/END. (line  7068)
* BEGIN pattern, pwcat program:          Passwd Functions.  (line 13862)
* BEGIN pattern, running awk programs and: Cut Program.     (line 14331)
* BEGIN pattern, TEXTDOMAIN variable and: Programmer i18n.  (line 11103)
* beginfile user-defined function:       Filetrans Function.
                                                            (line 13265)
* Bell Laboratories awk extensions:      BTL.               (line 16809)
* Benzinger, Michael:                    Contributors.      (line 17135)
* BeOS:                                  BeOS Installation. (line 17602)
* Berry, Karl:                           Acknowledgments.   (line   972)
* binary input/output:                   User-modified.     (line  7817)
* bindtextdomain function (C library):   Explaining gettext.
                                                            (line 10962)
* bindtextdomain function (gawk) <1>:    Programmer i18n.   (line 11090)
* bindtextdomain function (gawk):        I18N Functions.    (line 10456)
* bindtextdomain function (gawk), portability and: I18N Portability.
                                                            (line 11306)
* BINMODE variable <1>:                  PC Using.          (line 17887)
* BINMODE variable:                      User-modified.     (line  7817)
* bits2str user-defined function:        Bitwise Functions. (line 10368)
* bitwise, complement:                   Bitwise Functions. (line 10333)
* bitwise, operations:                   Bitwise Functions. (line 10314)
* bitwise, shift:                        Bitwise Functions. (line 10340)
* body, in actions:                      Statements.        (line  7228)
* body, in loops:                        While Statement.   (line  7307)
* Boolean expressions:                   Boolean Ops.       (line  6463)
* Boolean expressions, as patterns:      Expression Patterns.
                                                            (line  6868)
* Boolean operators, See Boolean expressions: Boolean Ops.  (line  6463)
* Bourne shell, quoting rules for:       Quoting.           (line  1357)
* braces ({}), actions and:              Action Overview.   (line  7178)
* braces ({}), pgawk program:            Profiling.         (line 11873)
* braces ({}), statements, grouping:     Statements.        (line  7228)
* bracket expressions, See character lists: Regexp Operators.
                                                            (line  2230)
* break statement:                       Break Statement.   (line  7525)
* Brennan, Michael <1>:                  Other Versions.    (line 18383)
* Brennan, Michael <2>:                  Simple Sed.        (line 16189)
* Brennan, Michael <3>:                  Two-way I/O.       (line 11522)
* Brennan, Michael:                      Delete.            (line  8630)
* Broder, Alan J.:                       Contributors.      (line 17126)
* Brown, Martin <1>:                     Bugs.              (line 18364)
* Brown, Martin <2>:                     Contributors.      (line 17121)
* Brown, Martin:                         Acknowledgments.   (line   995)
* BSD portals:                           Portal Files.      (line 11725)
* BSD-based operating systems:           Glossary.          (line 20404)
* Buening, Andreas <1>:                  Contributors.      (line 17130)
* Buening, Andreas:                      Acknowledgments.   (line   995)
* buffering, input/output <1>:           Two-way I/O.       (line 11587)
* buffering, input/output:               I/O Functions.     (line  9936)
* buffering, interactive vs. noninteractive: I/O Functions. (line  9904)
* buffers, flushing:                     I/O Functions.     (line  9838)
* buffers, operators for:                GNU Regexp Operators.
                                                            (line  2495)
* bug reports, email address, bug-gawk@gnu.org: Bugs.       (line 18335)
* bug-gawk@gnu.org bug reporting address: Bugs.             (line 18335)
* built-in functions:                    Functions.         (line  8964)
* built-in functions, evaluation order:  Calling Built-in.  (line  9031)
* built-in variables:                    Built-in Variables.
                                                            (line  7787)
* built-in variables, -v option, setting with: Options.     (line 12044)
* built-in variables, conveying information: Auto-set.      (line  7967)
* built-in variables, user-modifiable:   User-modified.     (line  7813)
* call by reference:                     Function Caveats.  (line 10716)
* call by value:                         Function Caveats.  (line 10687)
* caret (^) <1>:                         GNU Regexp Operators.
                                                            (line  2506)
* caret (^):                             Regexp Operators.  (line  2197)
* caret (^), ^ operator <1>:             Options.           (line 12191)
* caret (^), ^ operator:                 Precedence.        (line  6695)
* caret (^), ^= operator <1>:            Options.           (line 12191)
* caret (^), ^= operator <2>:            Precedence.        (line  6742)
* caret (^), ^= operator:                Assignment Ops.    (line  6111)
* caret (^), in character lists:         Character Lists.   (line  2364)
* case keyword:                          Switch Statement.  (line  7464)
* case sensitivity, array indices and:   Array Intro.       (line  8398)
* case sensitivity, converting case:     String Functions.  (line  9611)
* case sensitivity, example programs:    Library Functions. (line 12506)
* case sensitivity, gawk:                Case-sensitivity.  (line  2569)
* case sensitivity, regexps and <1>:     User-modified.     (line  7875)
* case sensitivity, regexps and:         Case-sensitivity.  (line  2549)
* case sensitivity, string comparisons and: User-modified.  (line  7875)
* CGI, awk scripts for:                  Options.           (line 12117)
* character encodings:                   Ordinal Functions. (line 13014)
* character lists <1>:                   Character Lists.   (line  2353)
* character lists:                       Regexp Operators.  (line  2230)
* character lists, character classes:    Character Lists.   (line  2377)
* character lists, collating elements:   Character Lists.   (line  2430)
* character lists, collating symbols:    Character Lists.   (line  2437)
* character lists, complemented:         Regexp Operators.  (line  2237)
* character lists, equivalence classes:  Character Lists.   (line  2443)
* character lists, non-ASCII:            Character Lists.   (line  2430)
* character lists, range expressions:    Character Lists.   (line  2353)
* character sets:                        Ordinal Functions. (line 13014)
* character sets (machine character encodings): Glossary.   (line 19963)
* character sets, See Also character lists: Regexp Operators.
                                                            (line  2230)
* characters, counting:                  Wc Program.        (line 15264)
* characters, transliterating:           Translate Program. (line 15601)
* characters, values of as numbers:      Ordinal Functions. (line 12976)
* Chassell, Robert J.:                   Acknowledgments.   (line   972)
* chdir function, implementing in gawk:  Sample Library.    (line 19054)
* chem utility:                          Glossary.          (line 19971)
* chr user-defined function:             Ordinal Functions. (line 12986)
* Cliff random numbers:                  Cliff Random Function.
                                                            (line 12945)
* cliff_rand user-defined function:      Cliff Random Function.
                                                            (line 12950)
* close function <1>:                    I/O Functions.     (line  9819)
* close function <2>:                    Close Files And Pipes.
                                                            (line  5211)
* close function <3>:                    Getline/Pipe.      (line  4069)
* close function:                        Getline/Variable/File.
                                                            (line  4036)
* close function, return values:         Close Files And Pipes.
                                                            (line  5323)
* close function, two-way pipes and:     Two-way I/O.       (line 11594)
* Close, Diane <1>:                      Contributors.      (line 17071)
* Close, Diane:                          Manual History.    (line   898)
* close_func input method:               Internals.         (line 18964)
* collating elements:                    Character Lists.   (line  2430)
* collating symbols:                     Character Lists.   (line  2437)
* columns, aligning:                     Print Examples.    (line  4377)
* columns, cutting:                      Cut Program.       (line 14271)
* comma (,), in range patterns:          Ranges.            (line  6913)
* command line, arguments <1>:           Other Arguments.   (line 12305)
* command line, arguments <2>:           ARGC and ARGV.     (line  8180)
* command line, arguments:               Auto-set.          (line  7972)
* command line, formats:                 Running gawk.      (line  1090)
* command line, FS on, setting:          Command Line Field Separator.
                                                            (line  3427)
* command line, invoking awk from:       Command Line.      (line 11988)
* command line, options <1>:             Options.           (line 12012)
* command line, options <2>:             Command Line Field Separator.
                                                            (line  3427)
* command line, options:                 Long.              (line  1202)
* command line, options, end of:         Options.           (line 12068)
* command line, variables, assigning on: Assignment Options.
                                                            (line  5671)
* command-line options, processing:      Getopt Function.   (line 13460)
* command-line options, string extraction: String Extraction.
                                                            (line 11177)
* commenting:                            Comments.          (line  1296)
* commenting, backslash continuation and: Statements/Lines. (line  1838)
* comp.lang.awk newsgroup:               Bugs.              (line 18344)
* comparison expressions:                Typing and Comparison.
                                                            (line  6277)
* comparison expressions, as patterns:   Expression Patterns.
                                                            (line  6841)
* comparison expressions, string vs. regexp: Typing and Comparison.
                                                            (line  6419)
* compatibility mode (gawk), extensions: POSIX/GNU.         (line 16852)
* compatibility mode (gawk), file names: Special Caveats.   (line  5167)
* compatibility mode (gawk), hexadecimal numbers: Nondecimal-numbers.
                                                            (line  5511)
* compatibility mode (gawk), octal numbers: Nondecimal-numbers.
                                                            (line  5511)
* compatibility mode (gawk), specifying: Options.           (line 12085)
* compiled programs <1>:                 Glossary.          (line 19981)
* compiled programs:                     Basic High Level.  (line 19551)
* compl function (gawk):                 Bitwise Functions. (line 10351)
* complement, bitwise:                   Bitwise Functions. (line 10333)
* compound statements, control statements and: Statements.  (line  7228)
* concatenating:                         Concatenation.     (line  5911)
* conditional expressions:               Conditional Exp.   (line  6553)
* configuration option, --disable-lint:  Additional Configuration Options.
                                                            (line 17477)
* configuration option, --disable-nls:   Additional Configuration Options.
                                                            (line 17492)
* configuration option, --enable-portals: Additional Configuration Options.
                                                            (line 17469)
* configuration option, --enable-switch: Additional Configuration Options.
                                                            (line 17473)
* configuration options, gawk:           Additional Configuration Options.
                                                            (line 17466)
* constants, nondecimal:                 Nondecimal Data.   (line 11480)
* constants, types of:                   Constants.         (line  5405)
* continue statement:                    Continue Statement.
                                                            (line  7582)
* control statements:                    Statements.        (line  7224)
* converting, case:                      String Functions.  (line  9611)
* converting, dates to timestamps:       Time Functions.    (line 10050)
* converting, during subscripting:       Numeric Array Subscripts.
                                                            (line  8681)
* converting, numbers:                   Conversion.        (line  5719)
* converting, numbers, to strings:       Bitwise Functions. (line 10407)
* converting, strings to numbers:        Conversion.        (line  5719)
* CONVFMT variable <1>:                  User-modified.     (line  7833)
* CONVFMT variable:                      Conversion.        (line  5742)
* CONVFMT variable, array subscripts and: Numeric Array Subscripts.
                                                            (line  8656)
* coprocesses <1>:                       Two-way I/O.       (line 11560)
* coprocesses:                           Redirection.       (line  4944)
* coprocesses, closing:                  Close Files And Pipes.
                                                            (line  5199)
* coprocesses, getline from:             Getline/Coprocess. (line  4137)
* cos function:                          Numeric Functions. (line  9079)
* counting:                              Wc Program.        (line 15264)
* csh utility:                           Statements/Lines.  (line  1807)
* csh utility, backslash continuation and: More Complex.    (line  1708)
* csh utility, POSIXLY_CORRECT environment variable: Options.
                                                            (line 12286)
* csh utility, |& operator, comparison with: Two-way I/O.   (line 11560)
* ctime user-defined function:           Function Example.  (line 10649)
* currency symbols, localization:        Explaining gettext.
                                                            (line 11014)
* custom.h file:                         Configuration Philosophy.
                                                            (line 17530)
* cut utility:                           Cut Program.       (line 14271)
* cut.awk program:                       Cut Program.       (line 14309)
* d.c., See dark corner:                 Conventions.       (line   850)
* dark corner <1>:                       Glossary.          (line 20013)
* dark corner <2>:                       Truth Values.      (line  6264)
* dark corner <3>:                       Assignment Ops.    (line  6137)
* dark corner <4>:                       Format Modifiers.  (line  4667)
* dark corner:                           Conventions.       (line   850)
* dark corner, array subscripts:         Uninitialized Subscripts.
                                                            (line  8743)
* dark corner, break statement:          Break Statement.   (line  7566)
* dark corner, close function:           Close Files And Pipes.
                                                            (line  5323)
* dark corner, command-line arguments:   Assignment Options.
                                                            (line  5708)
* dark corner, continue statement:       Continue Statement.
                                                            (line  7619)
* dark corner, CONVFMT variable:         Conversion.        (line  5753)
* dark corner, escape sequences:         Other Arguments.   (line 12330)
* dark corner, escape sequences, for metacharacters: Escape Sequences.
                                                            (line  2168)
* dark corner, exit statement:           Exit Statement.    (line  7760)
* dark corner, field separators:         Field Splitting Summary.
                                                            (line  3555)
* dark corner, FILENAME variable <1>:    Auto-set.          (line  8049)
* dark corner, FILENAME variable:        Getline Notes.     (line  4198)
* dark corner, FNR/NR variables:         Auto-set.          (line  8148)
* dark corner, format-control characters: Control Letters.  (line  4601)
* dark corner, FS as null string:        Single Character Fields.
                                                            (line  3415)
* dark corner, input files:              Records.           (line  2908)
* dark corner, invoking awk:             Command Line.      (line 11998)
* dark corner, multiline records:        Multiple Line.     (line  3734)
* dark corner, NF variable, decrementing: Changing Fields.  (line  3231)
* dark corner, OFMT variable:            OFMT.              (line  4455)
* dark corner, regexp constants:         Using Constant Regexps.
                                                            (line  5544)
* dark corner, regexp constants, /= operator and: Assignment Ops.
                                                            (line  6137)
* dark corner, regexp constants, as arguments to user-defined functions: Using Constant Regexps.
                                                            (line  5582)
* dark corner, split function:           String Functions.  (line  9378)
* dark corner, strings, storing:         Records.           (line  2995)
* data, fixed-width:                     Constant Size.     (line  3605)
* data-driven languages:                 Basic High Level.  (line 19620)
* database, group, reading:              Group Functions.   (line 13968)
* database, users, reading:              Passwd Functions.  (line 13743)
* date utility, GNU:                     Time Functions.    (line  9998)
* date utility, POSIX:                   Time Functions.    (line 10245)
* dates, converting to timestamps:       Time Functions.    (line 10050)
* dates, information related to, localization: Explaining gettext.
                                                            (line 11026)
* Davies, Stephen <1>:                   Bugs.              (line 18369)
* Davies, Stephen:                       Contributors.      (line 17118)
* dcgettext function (gawk) <1>:         Programmer i18n.   (line 11064)
* dcgettext function (gawk):             I18N Functions.    (line 10442)
* dcgettext function (gawk), portability and: I18N Portability.
                                                            (line 11306)
* dcngettext function (gawk) <1>:        Programmer i18n.   (line 11080)
* dcngettext function (gawk):            I18N Functions.    (line 10448)
* dcngettext function (gawk), portability and: I18N Portability.
                                                            (line 11306)
* deadlocks:                             Two-way I/O.       (line 11587)
* debugging gawk:                        Known Bugs.        (line 12454)
* debugging gawk, bug reports:           Bugs.              (line 18317)
* decrement operators:                   Increment Ops.     (line  6189)
* default keyword:                       Switch Statement.  (line  7464)
* Deifik, Scott <1>:                     Bugs.              (line 18365)
* Deifik, Scott <2>:                     Contributors.      (line 17102)
* Deifik, Scott:                         Acknowledgments.   (line   995)
* delete statement:                      Delete.            (line  8585)
* deleting elements in arrays:           Delete.            (line  8585)
* deleting entire arrays:                Delete.            (line  8618)
* differences between gawk and awk:      String Functions.  (line  9246)
* differences in awk and gawk, ARGC/ARGV variables: ARGC and ARGV.
                                                            (line  8259)
* differences in awk and gawk, ARGIND variable: Auto-set.   (line  8001)
* differences in awk and gawk, array elements, deleting: Delete.
                                                            (line  8618)
* differences in awk and gawk, AWKPATH environment variable: AWKPATH Variable.
                                                            (line 12361)
* differences in awk and gawk, BEGIN/END patterns: I/O And BEGIN/END.
                                                            (line  7068)
* differences in awk and gawk, BINMODE variable <1>: PC Using.
                                                            (line 17887)
* differences in awk and gawk, BINMODE variable: User-modified.
                                                            (line  7828)
* differences in awk and gawk, close function: Close Files And Pipes.
                                                            (line  5274)
* differences in awk and gawk, ERRNO variable: Auto-set.    (line  8033)
* differences in awk and gawk, error messages: Special FD.  (line  5028)
* differences in awk and gawk, FIELDWIDTHS variable: User-modified.
                                                            (line  7840)
* differences in awk and gawk, function arguments (gawk): Calling Built-in.
                                                            (line  9017)
* differences in awk and gawk, getline command: Getline.    (line  3856)
* differences in awk and gawk, IGNORECASE variable: User-modified.
                                                            (line  7875)
* differences in awk and gawk, implementation limitations <1>: Redirection.
                                                            (line  4973)
* differences in awk and gawk, implementation limitations: Getline Notes.
                                                            (line  4193)
* differences in awk and gawk, input/output operators <1>: Redirection.
                                                            (line  4944)
* differences in awk and gawk, input/output operators: Getline/Coprocess.
                                                            (line  4137)
* differences in awk and gawk, line continuations: Conditional Exp.
                                                            (line  6581)
* differences in awk and gawk, LINT variable: User-modified.
                                                            (line  7890)
* differences in awk and gawk, match function: String Functions.
                                                            (line  9309)
* differences in awk and gawk, next/nextfile statements: Nextfile Statement.
                                                            (line  7684)
* differences in awk and gawk, print/printf statements: Format Modifiers.
                                                            (line  4621)
* differences in awk and gawk, PROCINFO array: Auto-set.    (line  8080)
* differences in awk and gawk, record separators: Records.  (line  2921)
* differences in awk and gawk, regexp constants: Using Constant Regexps.
                                                            (line  5582)
* differences in awk and gawk, regular expressions: Case-sensitivity.
                                                            (line  2569)
* differences in awk and gawk, RS/RT variables: Records.    (line  2971)
* differences in awk and gawk, RT variable: Auto-set.       (line  8137)
* differences in awk and gawk, single-character fields: Single Character Fields.
                                                            (line  3401)
* differences in awk and gawk, split function: String Functions.
                                                            (line  9367)
* differences in awk and gawk, strings:  Scalar Constants.  (line  5439)
* differences in awk and gawk, strings, storing: Records.   (line  2991)
* differences in awk and gawk, strtonum function (gawk): String Functions.
                                                            (line  9405)
* differences in awk and gawk, TEXTDOMAIN variable: User-modified.
                                                            (line  7945)
* differences in awk and gawk, trunc-mod operation: Arithmetic Ops.
                                                            (line  5883)
* directories, changing:                 Sample Library.    (line 19054)
* directories, searching <1>:            Igawk Program.     (line 16601)
* directories, searching:                AWKPATH Variable.  (line 12361)
* division:                              Arithmetic Ops.    (line  5861)
* do-while statement <1>:                Do Statement.      (line  7346)
* do-while statement:                    Regexp Usage.      (line  1989)
* documentation, of awk programs:        Library Names.     (line 12541)
* documentation, online:                 Manual History.    (line   870)
* documents, searching:                  Dupword Program.   (line 15429)
* dollar sign ($):                       Regexp Operators.  (line  2210)
* dollar sign ($), $ field operator <1>: Precedence.        (line  6689)
* dollar sign ($), $ field operator:     Fields.            (line  3027)
* dollar sign ($), incrementing fields and arrays: Increment Ops.
                                                            (line  6184)
* double quote (") <1>:                  Quoting.           (line  1376)
* double quote ("):                      Read Terminal.     (line  1165)
* double quote ("), regexp constants:    Computed Regexps.  (line  2677)
* double-precision floating-point:       Basic Data Typing. (line 19666)
* Drepper, Ulrich:                       Acknowledgments.   (line   991)
* dupnode internal function:             Internals.         (line 18883)
* dupword.awk program:                   Dupword Program.   (line 15454)
* EBCDIC:                                Ordinal Functions. (line 13014)
* egrep utility <1>:                     Egrep Program.     (line 14525)
* egrep utility:                         Character Lists.   (line  2371)
* egrep.awk program:                     Egrep Program.     (line 14573)
* elements in arrays:                    Reference to Elements.
                                                            (line  8413)
* elements in arrays, assigning:         Assigning Elements.
                                                            (line  8460)
* elements in arrays, deleting:          Delete.            (line  8585)
* elements in arrays, order of:          Scanning an Array. (line  8571)
* elements in arrays, scanning:          Scanning an Array. (line  8530)
* email address for bug reports, bug-gawk@gnu.org: Bugs.    (line 18335)
* EMISTERED:                             TCP/IP Networking. (line 11658)
* empty pattern:                         Empty.             (line  7101)
* empty strings, See null strings:       Regexp Field Splitting.
                                                            (line  3379)
* END pattern:                           BEGIN/END.         (line  6980)
* END pattern, assert user-defined function and: Assert Function.
                                                            (line 12883)
* END pattern, backslash continuation and: Egrep Program.   (line 14737)
* END pattern, Boolean patterns and:     Expression Patterns.
                                                            (line  6900)
* END pattern, exit statement and:       Exit Statement.    (line  7743)
* END pattern, next/nextfile statements and <1>: Next Statement.
                                                            (line  7668)
* END pattern, next/nextfile statements and: I/O And BEGIN/END.
                                                            (line  7088)
* END pattern, operators and:            Using BEGIN/END.   (line  7010)
* END pattern, pgawk program:            Profiling.         (line 11802)
* END pattern, print statement and:      I/O And BEGIN/END. (line  7068)
* endfile user-defined function:         Filetrans Function.
                                                            (line 13265)
* endgrent function (C library):         Group Functions.   (line 14175)
* endgrent user-defined function:        Group Functions.   (line 14178)
* endpwent function (C library):         Passwd Functions.  (line 13929)
* endpwent user-defined function:        Passwd Functions.  (line 13932)
* ENVIRON variable <1>:                  Internals.         (line 18951)
* ENVIRON variable:                      Auto-set.          (line  8021)
* environment variables:                 Auto-set.          (line  8021)
* epoch, definition of:                  Glossary.          (line 20055)
* equals sign (=), = operator:           Assignment Ops.    (line  5989)
* equals sign (=), == operator <1>:      Precedence.        (line  6711)
* equals sign (=), == operator:          Typing and Comparison.
                                                            (line  6342)
* EREs (Extended Regular Expressions):   Character Lists.   (line  2371)
* ERRNO variable <1>:                    Internals.         (line 18938)
* ERRNO variable <2>:                    Auto-set.          (line  8033)
* ERRNO variable:                        Getline.           (line  3856)
* error handling:                        Special FD.        (line  5028)
* error handling, ERRNO variable and:    Auto-set.          (line  8033)
* error output:                          Special FD.        (line  5019)
* escape processing, gsub/gensub/sub functions: Gory Details.
                                                            (line  9642)
* escape sequences:                      Escape Sequences.  (line  2038)
* escape sequences, unrecognized:        Options.           (line 12179)
* evaluation order:                      Increment Ops.     (line  6215)
* evaluation order, concatenation:       Concatenation.     (line  5943)
* evaluation order, functions:           Calling Built-in.  (line  9031)
* examining fields:                      Fields.            (line  3014)
* exclamation point (!), ! operator <1>: Egrep Program.     (line 14679)
* exclamation point (!), ! operator <2>: Precedence.        (line  6698)
* exclamation point (!), ! operator:     Boolean Ops.       (line  6524)
* exclamation point (!), != operator <1>: Precedence.       (line  6711)
* exclamation point (!), != operator:    Typing and Comparison.
                                                            (line  6342)
* exclamation point (!), !~ operator <1>: Expression Patterns.
                                                            (line  6851)
* exclamation point (!), !~ operator <2>: Precedence.       (line  6727)
* exclamation point (!), !~ operator <3>: Typing and Comparison.
                                                            (line  6342)
* exclamation point (!), !~ operator <4>: Regexp Constants. (line  5532)
* exclamation point (!), !~ operator <5>: Computed Regexps. (line  2656)
* exclamation point (!), !~ operator <6>: Case-sensitivity. (line  2569)
* exclamation point (!), !~ operator:    Regexp Usage.      (line  1989)
* exit statement:                        Exit Statement.    (line  7737)
* exp function:                          Numeric Functions. (line  9067)
* expand utility:                        Very Simple.       (line  1594)
* expressions:                           Expressions.       (line  5362)
* expressions, as patterns:              Expression Patterns.
                                                            (line  6833)
* expressions, assignment:               Assignment Ops.    (line  5989)
* expressions, Boolean:                  Boolean Ops.       (line  6463)
* expressions, comparison:               Typing and Comparison.
                                                            (line  6277)
* expressions, conditional:              Conditional Exp.   (line  6553)
* expressions, matching, See comparison expressions: Typing and Comparison.
                                                            (line  6277)
* expressions, selecting:                Conditional Exp.   (line  6553)
* Extended Regular Expressions (EREs):   Character Lists.   (line  2371)
* extension function (gawk):             Using Internal File Ops.
                                                            (line 19373)
* extensions, Bell Laboratories awk:     BTL.               (line 16809)
* extensions, in gawk, not in POSIX awk: POSIX/GNU.         (line 16852)
* extensions, mawk:                      Other Versions.    (line 18423)
* extract.awk program:                   Extract Program.   (line 16050)
* extraction, of marked strings (internationalization): String Extraction.
                                                            (line 11177)
* false, logical:                        Truth Values.      (line  6246)
* FDL (Free Documentation License):      GNU Free Documentation License.
                                                            (line 20789)
* features, adding to gawk:              Adding Code.       (line 18547)
* features, advanced, See advanced features: Obsolete.      (line 12421)
* features, deprecated:                  Obsolete.          (line 12421)
* features, undocumented:                Undocumented.      (line 12443)
* Fenlason, Jay <1>:                     Contributors.      (line 17069)
* Fenlason, Jay:                         History.           (line   653)
* fflush function:                       I/O Functions.     (line  9834)
* fflush function, unsupported:          Options.           (line 12199)
* field numbers:                         Nonconstant Fields.
                                                            (line  3085)
* field operator $:                      Fields.            (line  3027)
* field operators, dollar sign as:       Fields.            (line  3027)
* field separators <1>:                  User-modified.     (line  7850)
* field separators:                      Field Separators.  (line  3271)
* field separators, choice of:           Field Separators.  (line  3306)
* field separators, FIELDWIDTHS variable and: User-modified.
                                                            (line  7840)
* field separators, in multiline records: Multiple Line.    (line  3740)
* field separators, on command line:     Command Line Field Separator.
                                                            (line  3427)
* field separators, POSIX and <1>:       Field Splitting Summary.
                                                            (line  3549)
* field separators, POSIX and:           Fields.            (line  3014)
* field separators, regular expressions as <1>: Regexp Field Splitting.
                                                            (line  3343)
* field separators, regular expressions as: Field Separators.
                                                            (line  3306)
* field separators, See Also OFS:        Changing Fields.   (line  3188)
* field separators, spaces as:           Cut Program.       (line 14371)
* fields <1>:                            Basic High Level.  (line 19608)
* fields <2>:                            Fields.            (line  3014)
* fields:                                Reading Files.     (line  2788)
* fields, adding:                        Changing Fields.   (line  3177)
* fields, changing contents of:          Changing Fields.   (line  3130)
* fields, cutting:                       Cut Program.       (line 14271)
* fields, examining:                     Fields.            (line  3014)
* fields, number of:                     Fields.            (line  3041)
* fields, numbers:                       Nonconstant Fields.
                                                            (line  3085)
* fields, printing:                      Print Examples.    (line  4329)
* fields, separating:                    Field Separators.  (line  3271)
* fields, single-character:              Single Character Fields.
                                                            (line  3401)
* FIELDWIDTHS variable <1>:              User-modified.     (line  7840)
* FIELDWIDTHS variable:                  Constant Size.     (line  3618)
* file descriptors:                      Special FD.        (line  5019)
* file names, distinguishing:            Auto-set.          (line  8013)
* file names, in compatibility mode:     Special Caveats.   (line  5167)
* file names, standard streams in gawk:  Special FD.        (line  5054)
* FILENAME variable <1>:                 Auto-set.          (line  8049)
* FILENAME variable:                     Reading Files.     (line  2780)
* FILENAME variable, getline, setting with: Getline Notes.  (line  4198)
* filenames, assignments as:             Ignoring Assigns.  (line 13418)
* files, .mo:                            Explaining gettext.
                                                            (line 10954)
* files, .mo, converting from .po:       I18N Example.      (line 11400)
* files, .mo, specifying directory of <1>: Programmer i18n. (line 11090)
* files, .mo, specifying directory of:   Explaining gettext.
                                                            (line 10966)
* files, .po <1>:                        Translator i18n.   (line 11156)
* files, .po:                            Explaining gettext.
                                                            (line 10951)
* files, .po, converting to .mo:         I18N Example.      (line 11400)
* files, /dev/... special files:         Special FD.        (line  5054)
* files, /inet/ (gawk):                  TCP/IP Networking. (line 11658)
* files, /p (gawk):                      Portal Files.      (line 11725)
* files, as single records:              Records.           (line  3000)
* files, awk programs in:                Long.              (line  1196)
* files, awkprof.out:                    Profiling.         (line 11744)
* files, awkvars.out:                    Options.           (line 12101)
* files, closing:                        I/O Functions.     (line  9819)
* files, descriptors, See file descriptors: Special FD.     (line  5019)
* files, for process information:        Special Process.   (line  5086)
* files, group:                          Group Functions.   (line 13968)
* files, information about, retrieving:  Sample Library.    (line 19054)
* files, initialization and cleanup:     Filetrans Function.
                                                            (line 13211)
* files, input, See input files:         Read Terminal.     (line  1157)
* files, log, timestamps in:             Time Functions.    (line  9987)
* files, managing:                       Data File Management.
                                                            (line 13194)
* files, managing, data file boundaries: Filetrans Function.
                                                            (line 13211)
* files, message object:                 Explaining gettext.
                                                            (line 10954)
* files, message object, converting from portable object files: I18N Example.
                                                            (line 11400)
* files, message object, specifying directory of <1>: Programmer i18n.
                                                            (line 11090)
* files, message object, specifying directory of: Explaining gettext.
                                                            (line 10966)
* files, multiple passes over:           Other Arguments.   (line 12348)
* files, multiple, duplicating output into: Tee Program.    (line 14964)
* files, output, See output files:       Close Files And Pipes.
                                                            (line  5199)
* files, password:                       Passwd Functions.  (line 13753)
* files, portable object <1>:            Translator i18n.   (line 11156)
* files, portable object:                Explaining gettext.
                                                            (line 10951)
* files, portable object, converting to message object files: I18N Example.
                                                            (line 11400)
* files, portable object, generating:    Options.           (line 12136)
* files, portal:                         Portal Files.      (line 11725)
* files, processing, ARGIND variable and: Auto-set.         (line  8008)
* files, reading:                        Rewind Function.   (line 13292)
* files, reading, multiline records:     Multiple Line.     (line  3705)
* files, searching for regular expressions: Egrep Program.  (line 14525)
* files, skipping:                       File Checking.     (line 13334)
* files, source, search path for:        Igawk Program.     (line 16601)
* files, splitting:                      Split Program.     (line 14862)
* files, Texinfo, extracting programs from: Extract Program.
                                                            (line 15979)
* Fish, Fred <1>:                        Bugs.              (line 18364)
* Fish, Fred:                            Contributors.      (line 17100)
* fixed-width data:                      Constant Size.     (line  3605)
* flag variables <1>:                    Tee Program.       (line 14978)
* flag variables:                        Boolean Ops.       (line  6524)
* floating-point:                        Floating Point Issues.
                                                            (line 19776)
* floating-point, numbers:               Basic Data Typing. (line 19654)
* floating-point, numbers, AWKNUM internal type: Internals. (line 18805)
* FNR variable <1>:                      Auto-set.          (line  8059)
* FNR variable:                          Records.           (line  2817)
* FNR variable, changing:                Auto-set.          (line  8148)
* for statement:                         For Statement.     (line  7382)
* for statement, in arrays:              Scanning an Array. (line  8544)
* force_number internal function:        Internals.         (line 18813)
* force_string internal function:        Internals.         (line 18818)
* format specifiers, mixing regular with positional specifiers: Printf Ordering.
                                                            (line 11254)
* format specifiers, printf statement:   Control Letters.   (line  4527)
* format specifiers, strftime function (gawk): Time Functions.
                                                            (line 10063)
* format strings:                        Basic Printf.      (line  4495)
* formats, numeric output:               OFMT.              (line  4434)
* formatting output:                     Printf.            (line  4465)
* forward slash (/):                     Regexp.            (line  1949)
* forward slash (/), / operator:         Precedence.        (line  6701)
* forward slash (/), /= operator <1>:    Precedence.        (line  6742)
* forward slash (/), /= operator:        Assignment Ops.    (line  6111)
* forward slash (/), /= operator, vs. /=.../ regexp constant: Assignment Ops.
                                                            (line  6137)
* forward slash (/), patterns and:       Expression Patterns.
                                                            (line  6851)
* Free Documentation License (FDL):      GNU Free Documentation License.
                                                            (line 20789)
* Free Software Foundation (FSF) <1>:    Glossary.          (line 20109)
* Free Software Foundation (FSF) <2>:    Getting.           (line 17193)
* Free Software Foundation (FSF):        Manual History.    (line   865)
* free_temp internal macro:              Internals.         (line 18888)
* FreeBSD:                               Glossary.          (line 20404)
* FS variable <1>:                       User-modified.     (line  7850)
* FS variable:                           Field Separators.  (line  3271)
* FS variable, --field-separator option and: Options.       (line 12027)
* FS variable, as null string:           Single Character Fields.
                                                            (line  3415)
* FS variable, as TAB character:         Options.           (line 12195)
* FS variable, changing value of <1>:    Known Bugs.        (line 12454)
* FS variable, changing value of:        Field Separators.  (line  3290)
* FS variable, running awk programs and: Cut Program.       (line 14331)
* FS variable, setting from command line: Command Line Field Separator.
                                                            (line  3427)
* FSF (Free Software Foundation) <1>:    Glossary.          (line 20109)
* FSF (Free Software Foundation) <2>:    Getting.           (line 17193)
* FSF (Free Software Foundation):        Manual History.    (line   865)
* function calls:                        Function Calls.    (line  6593)
* functions, arrays as parameters to:    Function Caveats.  (line 10716)
* functions, built-in <1>:               Functions.         (line  8964)
* functions, built-in:                   Function Calls.    (line  6597)
* functions, built-in, adding to gawk:   Dynamic Extensions.
                                                            (line 18765)
* functions, built-in, evaluation order: Calling Built-in.  (line  9031)
* functions, defining:                   Definition Syntax. (line 10492)
* functions, library:                    Library Functions. (line 12469)
* functions, library, assertions:        Assert Function.   (line 12815)
* functions, library, associative arrays and: Library Names.
                                                            (line 12592)
* functions, library, C library:         Getopt Function.   (line 13460)
* functions, library, character values as numbers: Ordinal Functions.
                                                            (line 12976)
* functions, library, Cliff random numbers: Cliff Random Function.
                                                            (line 12945)
* functions, library, command-line options: Getopt Function.
                                                            (line 13460)
* functions, library, example program for using: Igawk Program.
                                                            (line 16250)
* functions, library, group database, reading: Group Functions.
                                                            (line 13968)
* functions, library, managing data files: Data File Management.
                                                            (line 13194)
* functions, library, managing time:     Gettimeofday Function.
                                                            (line 13112)
* functions, library, merging arrays into strings: Join Function.
                                                            (line 13067)
* functions, library, nextfile statement: Nextfile Function.
                                                            (line 12645)
* functions, library, rounding numbers:  Round Function.    (line 12900)
* functions, library, user database, reading: Passwd Functions.
                                                            (line 13743)
* functions, names of <1>:               Definition Syntax. (line 10506)
* functions, names of:                   Arrays.            (line  8287)
* functions, recursive:                  Definition Syntax. (line 10554)
* functions, return values, setting:     Internals.         (line 18932)
* functions, string-translation:         I18N Functions.    (line 10436)
* functions, undefined:                  Function Caveats.  (line 10740)
* functions, user-defined:               User-defined.      (line 10472)
* functions, user-defined, calling:      Function Caveats.  (line 10667)
* functions, user-defined, counts:       Profiling.         (line 11868)
* functions, user-defined, library of:   Library Functions. (line 12469)
* functions, user-defined, next/nextfile statements and <1>: Nextfile Statement.
                                                            (line  7717)
* functions, user-defined, next/nextfile statements and: Next Statement.
                                                            (line  7668)
* G-d:                                   Acknowledgments.   (line  1012)
* Garfinkle, Scott:                      Contributors.      (line 17087)
* gawk, awk and <1>:                     This Manual.       (line   718)
* gawk, awk and:                         Preface.           (line   569)
* gawk, bitwise operations in:           Bitwise Functions. (line 10347)
* gawk, break statement in:              Break Statement.   (line  7566)
* gawk, built-in variables and:          Built-in Variables.
                                                            (line  7795)
* gawk, character classes and:           Character Lists.   (line  2451)
* gawk, coding style in:                 Adding Code.       (line 18573)
* gawk, command-line options:            GNU Regexp Operators.
                                                            (line  2517)
* gawk, comparison operators and:        Typing and Comparison.
                                                            (line  6390)
* gawk, configuring:                     Configuration Philosophy.
                                                            (line 17507)
* gawk, configuring, options:            Additional Configuration Options.
                                                            (line 17466)
* gawk, continue statement in:           Continue Statement.
                                                            (line  7619)
* gawk, debugging:                       Known Bugs.        (line 12454)
* gawk, distribution:                    Distribution contents.
                                                            (line 17253)
* gawk, escape sequences:                Escape Sequences.  (line  2157)
* gawk, extensions, disabling:           Options.           (line 12175)
* gawk, features, adding:                Adding Code.       (line 18547)
* gawk, features, advanced:              Advanced Features. (line 11449)
* gawk, fflush function in:              I/O Functions.     (line  9854)
* gawk, field separators and:            User-modified.     (line  7870)
* gawk, FIELDWIDTHS variable in:         User-modified.     (line  7846)
* gawk, file names in:                   Special Files.     (line  5002)
* gawk, format-control characters:       Control Letters.   (line  4601)
* gawk, function arguments and:          Calling Built-in.  (line  9017)
* gawk, functions, adding:               Dynamic Extensions.
                                                            (line 18765)
* gawk, hexadecimal numbers and:         Nondecimal-numbers.
                                                            (line  5493)
* gawk, IGNORECASE variable in:          User-modified.     (line  7886)
* gawk, implementation issues:           Notes.             (line 18484)
* gawk, implementation issues, debugging: Compatibility Mode.
                                                            (line 18503)
* gawk, implementation issues, downward compatibility: Compatibility Mode.
                                                            (line 18503)
* gawk, implementation issues, limits:   Getline Notes.     (line  4193)
* gawk, implementation issues, pipes:    Redirection.       (line  4973)
* gawk, installing:                      Installation.      (line 17151)
* gawk, internals:                       Internals.         (line 18792)
* gawk, internationalization and, See internationalization: Internationalization.
                                                            (line 10883)
* gawk, interpreter, adding code to <1>: Future Extensions. (line 19505)
* gawk, interpreter, adding code to:     Using Internal File Ops.
                                                            (line 19364)
* gawk, interval expressions and:        Regexp Operators.  (line  2313)
* gawk, line continuation in:            Conditional Exp.   (line  6581)
* gawk, LINT variable in:                User-modified.     (line  7899)
* gawk, list of contributors to:         Contributors.      (line 17056)
* gawk, MS-DOS version of:               PC Using.          (line 17858)
* gawk, newlines in:                     Statements/Lines.  (line  1776)
* gawk, next file statement in:          Nextfile Statement.
                                                            (line  7724)
* gawk, nextfile statement in <1>:       Nextfile Function. (line 12645)
* gawk, nextfile statement in:           Nextfile Statement.
                                                            (line  7724)
* gawk, octal numbers and:               Nondecimal-numbers.
                                                            (line  5493)
* gawk, OS/2 version of:                 PC Using.          (line 17858)
* gawk, regexp constants and:            Using Constant Regexps.
                                                            (line  5566)
* gawk, regular expressions, case sensitivity: Case-sensitivity.
                                                            (line  2569)
* gawk, regular expressions, operators:  GNU Regexp Operators.
                                                            (line  2461)
* gawk, regular expressions, precedence: Regexp Operators.  (line  2329)
* gawk, See Also awk:                    Preface.           (line   582)
* gawk, source code, obtaining:          Getting.           (line 17189)
* gawk, splitting fields and:            Constant Size.     (line  3682)
* gawk, string-translation functions:    I18N Functions.    (line 10436)
* gawk, timestamps:                      Time Functions.    (line  9987)
* gawk, uses for:                        Preface.           (line   582)
* gawk, versions of, information about, printing: Options.  (line 12235)
* gawk, word-boundary operator:          GNU Regexp Operators.
                                                            (line  2510)
* General Public License (GPL):          Glossary.          (line 20118)
* General Public License, See GPL:       Manual History.    (line   870)
* gensub function (gawk) <1>:            String Functions.  (line  9519)
* gensub function (gawk):                Using Constant Regexps.
                                                            (line  5582)
* gensub function (gawk), escape processing: Gory Details.  (line  9642)
* get_actual_argument internal function: Internals.         (line 18912)
* get_argument internal function:        Internals.         (line 18907)
* get_array_argument internal macro:     Internals.         (line 18927)
* get_curfunc_arg_count internal function: Internals.       (line 18823)
* get_record input method:               Internals.         (line 18964)
* get_scalar_argument internal macro:    Internals.         (line 18922)
* getgrent function (C library):         Group Functions.   (line 13968)
* getgrent user-defined function:        Group Functions.   (line 13968)
* getgrgid function (C library):         Group Functions.   (line 14142)
* getgrgid user-defined function:        Group Functions.   (line 14145)
* getgrnam function (C library):         Group Functions.   (line 14130)
* getgrnam user-defined function:        Group Functions.   (line 14134)
* getgruser function (C library):        Group Functions.   (line 14153)
* getgruser function, user-defined:      Group Functions.   (line 14156)
* getline command:                       Reading Files.     (line  2794)
* getline command, _gr_init user-defined function: Group Functions.
                                                            (line 14042)
* getline command, _pw_init function:    Passwd Functions.  (line 13873)
* getline command, coprocesses, using from <1>: Close Files And Pipes.
                                                            (line  5199)
* getline command, coprocesses, using from: Getline/Coprocess.
                                                            (line  4137)
* getline command, deadlock and:         Two-way I/O.       (line 11587)
* getline command, explicit input with:  Getline.           (line  3843)
* getline command, FILENAME variable and: Getline Notes.    (line  4198)
* getline command, return values:        Getline.           (line  3856)
* getline command, variants:             Getline Summary.   (line  4219)
* getopt function (C library):           Getopt Function.   (line 13469)
* getopt user-defined function:          Getopt Function.   (line 13559)
* getpwent function (C library):         Passwd Functions.  (line 13753)
* getpwent user-defined function:        Passwd Functions.  (line 13753)
* getpwnam function (C library):         Passwd Functions.  (line 13893)
* getpwnam user-defined function:        Passwd Functions.  (line 13897)
* getpwuid function (C library):         Passwd Functions.  (line 13905)
* getpwuid user-defined function:        Passwd Functions.  (line 13909)
* getservbyname function (C library):    TCP/IP Networking. (line 11686)
* gettext function (C library):          Explaining gettext.
                                                            (line 10975)
* gettext library:                       Explaining gettext.
                                                            (line 10921)
* gettext library, locale categories:    Explaining gettext.
                                                            (line 10993)
* gettimeofday user-defined function:    Gettimeofday Function.
                                                            (line 13122)
* GNITS mailing list:                    Acknowledgments.   (line   991)
* GNU awk, See gawk:                     Preface.           (line   595)
* GNU Free Documentation License:        GNU Free Documentation License.
                                                            (line 20789)
* GNU General Public License:            Glossary.          (line 20118)
* GNU Lesser General Public License:     Glossary.          (line 20195)
* GNU long options <1>:                  Options.           (line 12012)
* GNU long options:                      Command Line.      (line 11995)
* GNU long options, printing list of:    Options.           (line 12145)
* GNU Project <1>:                       Glossary.          (line 20127)
* GNU Project:                           Manual History.    (line   870)
* GNU/Linux <1>:                         Glossary.          (line 20404)
* GNU/Linux <2>:                         Atari Compiling.   (line 18198)
* GNU/Linux <3>:                         I18N Example.      (line 11393)
* GNU/Linux:                             Manual History.    (line   886)
* GPL (General Public License) <1>:      Glossary.          (line 20118)
* GPL (General Public License):          Manual History.    (line   870)
* GPL (General Public License), printing: Options.          (line 12093)
* grcat program:                         Group Functions.   (line 13977)
* Grigera, Juan <1>:                     Bugs.              (line 18366)
* Grigera, Juan:                         Contributors.      (line 17104)
* group database, reading:               Group Functions.   (line 13968)
* group file:                            Group Functions.   (line 13968)
* groups, information about:             Group Functions.   (line 13968)
* gsub function <1>:                     String Functions.  (line  9503)
* gsub function:                         Using Constant Regexps.
                                                            (line  5582)
* gsub function, arguments of:           String Functions.  (line  9483)
* gsub function, escape processing:      Gory Details.      (line  9642)
* Hankerson, Darrel <1>:                 Bugs.              (line 18365)
* Hankerson, Darrel <2>:                 Contributors.      (line 17106)
* Hankerson, Darrel:                     Acknowledgments.   (line   995)
* Hartholz, Elaine:                      Acknowledgments.   (line   977)
* Hartholz, Marshall:                    Acknowledgments.   (line   977)
* Hasegawa, Isamu <1>:                   Contributors.      (line 17132)
* Hasegawa, Isamu:                       Acknowledgments.   (line   995)
* hexadecimal numbers:                   Nondecimal-numbers.
                                                            (line  5457)
* hexadecimal values, enabling interpretation of: Options.  (line 12167)
* histsort.awk program:                  History Sorting.   (line 15953)
* Hughes, Phil:                          Acknowledgments.   (line   982)
* HUP signal:                            Profiling.         (line 11943)
* hyphen (-), - operator:                Precedence.        (line  6698)
* hyphen (-), -- (decrement/increment) operators: Precedence.
                                                            (line  6692)
* hyphen (-), -- operator:               Increment Ops.     (line  6202)
* hyphen (-), -= operator <1>:           Precedence.        (line  6742)
* hyphen (-), -= operator:               Assignment Ops.    (line  6111)
* hyphen (-), filenames beginning with:  Options.           (line 12073)
* hyphen (-), in character lists:        Character Lists.   (line  2364)
* id utility:                            Id Program.        (line 14755)
* id.awk program:                        Id Program.        (line 14779)
* if statement <1>:                      If Statement.      (line  7260)
* if statement:                          Regexp Usage.      (line  1989)
* if statement, actions, changing:       Ranges.            (line  6932)
* igawk.sh program:                      Igawk Program.     (line 16362)
* IGNORECASE variable <1>:               User-modified.     (line  7875)
* IGNORECASE variable:                   Case-sensitivity.  (line  2569)
* IGNORECASE variable, array sorting and: Array Sorting.    (line  8953)
* IGNORECASE variable, array subscripts and: Array Intro.   (line  8398)
* IGNORECASE variable, in example programs: Library Functions.
                                                            (line 12506)
* implementation issues, gawk:           Notes.             (line 18484)
* implementation issues, gawk, debugging: Compatibility Mode.
                                                            (line 18503)
* implementation issues, gawk, limits <1>: Redirection.     (line  4973)
* implementation issues, gawk, limits:   Getline Notes.     (line  4193)
* in operator <1>:                       Id Program.        (line 14842)
* in operator <2>:                       For Statement.     (line  7449)
* in operator <3>:                       Precedence.        (line  6730)
* in operator:                           Typing and Comparison.
                                                            (line  6342)
* in operator, arrays and <1>:           Scanning an Array. (line  8541)
* in operator, arrays and:               Reference to Elements.
                                                            (line  8432)
* increment operators:                   Increment Ops.     (line  6160)
* index function:                        String Functions.  (line  9218)
* indexing arrays:                       Array Intro.       (line  8356)
* initialization, automatic:             More Complex.      (line  1731)
* input files:                           Reading Files.     (line  2780)
* input files, closing:                  Close Files And Pipes.
                                                            (line  5199)
* input files, counting elements in:     Wc Program.        (line 15264)
* input files, examples:                 Sample Data Files. (line  1461)
* input files, reading:                  Reading Files.     (line  2780)
* input files, running awk without:      Read Terminal.     (line  1146)
* input files, skipping:                 Nextfile Function. (line 12645)
* input files, variable assignments and: Other Arguments.   (line 12318)
* input pipeline:                        Getline/Pipe.      (line  4051)
* input redirection:                     Getline/File.      (line  3979)
* input, data, nondecimal:               Nondecimal Data.   (line 11480)
* input, explicit:                       Getline.           (line  3843)
* input, files, See input files:         Multiple Line.     (line  3705)
* input, multiline records:              Multiple Line.     (line  3705)
* input, splitting into records:         Records.           (line  2817)
* input, standard <1>:                   Special FD.        (line  5019)
* input, standard:                       Read Terminal.     (line  1146)
* input/output, binary:                  User-modified.     (line  7817)
* input/output, from BEGIN and END:      I/O And BEGIN/END. (line  7058)
* input/output, two-way:                 Two-way I/O.       (line 11560)
* insomnia, cure for:                    Alarm Program.     (line 15477)
* installation, amiga:                   Amiga Installation.
                                                            (line 17569)
* installation, atari:                   Atari Installation.
                                                            (line 18161)
* installation, beos:                    BeOS Installation. (line 17602)
* installation, tandem:                  Tandem Installation.
                                                            (line 18278)
* installation, vms:                     VMS Installation.  (line 17981)
* installing gawk:                       Installation.      (line 17151)
* int function:                          Numeric Functions. (line  9056)
* INT signal (MS-DOS):                   Profiling.         (line 11946)
* integers:                              Basic Data Typing. (line 19654)
* integers, unsigned:                    Basic Data Typing. (line 19661)
* interacting with other programs:       I/O Functions.     (line  9872)
* internationalization <1>:              I18N and L10N.     (line 10906)
* internationalization:                  I18N Functions.    (line 10436)
* internationalization, localization <1>: Internationalization.
                                                            (line 10883)
* internationalization, localization:    User-modified.     (line  7945)
* internationalization, localization, character classes: Character Lists.
                                                            (line  2451)
* internationalization, localization, gawk and: Internationalization.
                                                            (line 10883)
* internationalization, localization, locale categories: Explaining gettext.
                                                            (line 10993)
* internationalization, localization, marked strings: Programmer i18n.
                                                            (line 11059)
* internationalization, localization, portability and: I18N Portability.
                                                            (line 11280)
* internationalizing a program:          Explaining gettext.
                                                            (line 10921)
* interpreted programs <1>:              Glossary.          (line 20167)
* interpreted programs:                  Basic High Level.  (line 19551)
* interval expressions:                  Regexp Operators.  (line  2290)
* inventory-shipped file:                Sample Data Files. (line  1487)
* IOBUF internal structure:              Internals.         (line 18964)
* iop_alloc internal function:           Internals.         (line 18964)
* ISO:                                   Glossary.          (line 20178)
* ISO 8859-1:                            Glossary.          (line 19963)
* ISO Latin-1:                           Glossary.          (line 19963)
* Jacobs, Andrew:                        Passwd Functions.  (line 13813)
* Jaegermann, Michal <1>:                Contributors.      (line 17095)
* Jaegermann, Michal:                    Acknowledgments.   (line   995)
* Jedi knights:                          Undocumented.      (line 12443)
* join user-defined function:            Join Function.     (line 13079)
* Kahrs, Ju"rgen <1>:                    Contributors.      (line 17114)
* Kahrs, Ju"rgen:                        Acknowledgments.   (line   995)
* Kenobi, Obi-Wan:                       Undocumented.      (line 12443)
* Kernighan, Brian <1>:                  Basic Data Typing. (line 19704)
* Kernighan, Brian <2>:                  Other Versions.    (line 18390)
* Kernighan, Brian <3>:                  Contributors.      (line 17062)
* Kernighan, Brian <4>:                  BTL.               (line 16809)
* Kernighan, Brian <5>:                  Concatenation.     (line  5908)
* Kernighan, Brian <6>:                  Acknowledgments.   (line  1002)
* Kernighan, Brian <7>:                  Conventions.       (line   846)
* Kernighan, Brian:                      History.           (line   640)
* kill command, dynamic profiling:       Profiling.         (line 11921)
* Knights, jedi:                         Undocumented.      (line 12443)
* Kwok, Conrad:                          Contributors.      (line 17087)
* labels.awk program:                    Labels Program.    (line 15765)
* languages, data-driven:                Basic High Level.  (line 19620)
* LC_ALL locale category:                Explaining gettext.
                                                            (line 11031)
* LC_COLLATE locale category:            Explaining gettext.
                                                            (line 11004)
* LC_CTYPE locale category:              Explaining gettext.
                                                            (line 11008)
* LC_MESSAGES locale category:           Explaining gettext.
                                                            (line 10998)
* LC_MESSAGES locale category, bindtextdomain function (gawk): Programmer i18n.
                                                            (line 11131)
* LC_MONETARY locale category:           Explaining gettext.
                                                            (line 11014)
* LC_NUMERIC locale category:            Explaining gettext.
                                                            (line 11018)
* LC_RESPONSE locale category:           Explaining gettext.
                                                            (line 11022)
* LC_TIME locale category:               Explaining gettext.
                                                            (line 11026)
* left angle bracket (<), < operator <1>: Precedence.       (line  6711)
* left angle bracket (<), < operator:    Typing and Comparison.
                                                            (line  6342)
* left angle bracket (<), < operator (I/O): Getline/File.   (line  3979)
* left angle bracket (<), <= operator <1>: Precedence.      (line  6711)
* left angle bracket (<), <= operator:   Typing and Comparison.
                                                            (line  6342)
* left shift, bitwise:                   Bitwise Functions. (line 10340)
* leftmost longest match:                Multiple Line.     (line  3725)
* length function:                       String Functions.  (line  9229)
* Lesser General Public License (LGPL):  Glossary.          (line 20195)
* LGPL (Lesser General Public License):  Glossary.          (line 20195)
* libraries of awk functions:            Library Functions. (line 12469)
* libraries of awk functions, assertions: Assert Function.  (line 12815)
* libraries of awk functions, associative arrays and: Library Names.
                                                            (line 12592)
* libraries of awk functions, character values as numbers: Ordinal Functions.
                                                            (line 12976)
* libraries of awk functions, command-line options: Getopt Function.
                                                            (line 13460)
* libraries of awk functions, example program for using: Igawk Program.
                                                            (line 16250)
* libraries of awk functions, group database, reading: Group Functions.
                                                            (line 13968)
* libraries of awk functions, managing, data files: Data File Management.
                                                            (line 13194)
* libraries of awk functions, managing, time: Gettimeofday Function.
                                                            (line 13112)
* libraries of awk functions, merging arrays into strings: Join Function.
                                                            (line 13067)
* libraries of awk functions, nextfile statement: Nextfile Function.
                                                            (line 12645)
* libraries of awk functions, rounding numbers: Round Function.
                                                            (line 12900)
* libraries of awk functions, user database, reading: Passwd Functions.
                                                            (line 13743)
* line breaks:                           Statements/Lines.  (line  1770)
* line continuations:                    Boolean Ops.       (line  6519)
* line continuations, gawk:              Conditional Exp.   (line  6581)
* line continuations, in print statement: Print Examples.   (line  4383)
* line continuations, with C shell:      More Complex.      (line  1723)
* lines, blank, printing:                Print.             (line  4300)
* lines, counting:                       Wc Program.        (line 15264)
* lines, duplicate, removing:            History Sorting.   (line 15934)
* lines, matching ranges of:             Ranges.            (line  6913)
* lines, skipping between markers:       Ranges.            (line  6950)
* lint checking:                         User-modified.     (line  7890)
* lint checking, array elements:         Delete.            (line  8613)
* lint checking, array subscripts:       Uninitialized Subscripts.
                                                            (line  8743)
* lint checking, empty programs:         Command Line.      (line 11998)
* lint checking, issuing warnings:       Options.           (line 12150)
* lint checking, POSIXLY_CORRECT environment variable: Options.
                                                            (line 12273)
* lint checking, undefined functions:    Function Caveats.  (line 10757)
* LINT variable:                         User-modified.     (line  7890)
* Linux <1>:                             Glossary.          (line 20404)
* Linux <2>:                             Atari Compiling.   (line 18198)
* Linux <3>:                             I18N Example.      (line 11393)
* Linux:                                 Manual History.    (line   886)
* locale categories:                     Explaining gettext.
                                                            (line 10993)
* localization:                          I18N and L10N.     (line 10906)
* localization, See internationalization, localization: I18N and L10N.
                                                            (line 10906)
* log files, timestamps in:              Time Functions.    (line  9987)
* log function:                          Numeric Functions. (line  9072)
* logical false/true:                    Truth Values.      (line  6246)
* logical operators, See Boolean expressions: Boolean Ops.  (line  6463)
* login information:                     Passwd Functions.  (line 13753)
* long options:                          Command Line.      (line 11995)
* loops:                                 While Statement.   (line  7299)
* loops, continue statements and:        For Statement.     (line  7438)
* loops, count for header:               Profiling.         (line 11862)
* loops, exiting:                        Break Statement.   (line  7525)
* loops, See Also while statement:       While Statement.   (line  7299)
* Lost In Space:                         Dynamic Extensions.
                                                            (line 18761)
* ls utility:                            More Complex.      (line  1708)
* lshift function (gawk):                Bitwise Functions. (line 10353)
* lvalues/rvalues:                       Assignment Ops.    (line  6014)
* mailing labels, printing:              Labels Program.    (line 15723)
* mailing list, GNITS:                   Acknowledgments.   (line   991)
* make_builtin internal function:        Internals.         (line 18893)
* make_number internal function:         Internals.         (line 18868)
* make_string internal function:         Internals.         (line 18863)
* mark parity:                           Ordinal Functions. (line 13014)
* marked string extraction (internationalization): String Extraction.
                                                            (line 11177)
* marked strings, extracting:            String Extraction. (line 11177)
* Marx, Groucho:                         Increment Ops.     (line  6215)
* match function:                        String Functions.  (line  9256)
* match function, RSTART/RLENGTH variables: String Functions.
                                                            (line  9273)
* matching, expressions, See comparison expressions: Typing and Comparison.
                                                            (line  6277)
* matching, leftmost longest:            Multiple Line.     (line  3725)
* matching, null strings:                Gory Details.      (line  9796)
* mawk program:                          Other Versions.    (line 18410)
* McPhee, Patrick:                       Contributors.      (line 17138)
* memory, releasing:                     Internals.         (line 18888)
* memory, setting limits:                Options.           (line 12051)
* message object files:                  Explaining gettext.
                                                            (line 10954)
* message object files, converting from portable object files: I18N Example.
                                                            (line 11400)
* message object files, specifying directory of <1>: Programmer i18n.
                                                            (line 11090)
* message object files, specifying directory of: Explaining gettext.
                                                            (line 10966)
* metacharacters, escape sequences for:  Escape Sequences.  (line  2164)
* mktime function (gawk):                Time Functions.    (line 10011)
* modifiers, in format specifiers:       Format Modifiers.  (line  4614)
* monetary information, localization:    Explaining gettext.
                                                            (line 11014)
* msgfmt utility:                        I18N Example.      (line 11400)
* names, arrays/variables <1>:           Library Names.     (line 12541)
* names, arrays/variables:               Arrays.            (line  8287)
* names, functions <1>:                  Library Names.     (line 12541)
* names, functions:                      Definition Syntax. (line 10506)
* namespace issues <1>:                  Library Names.     (line 12541)
* namespace issues:                      Arrays.            (line  8287)
* namespace issues, functions:           Definition Syntax. (line 10506)
* nawk utility:                          Names.             (line   688)
* negative zero:                         Floating Point Issues.
                                                            (line 19798)
* NetBSD:                                Glossary.          (line 20404)
* networks, programming:                 TCP/IP Networking. (line 11658)
* networks, support for:                 Special Network.   (line  5145)
* newlines <1>:                          Options.           (line 12182)
* newlines <2>:                          Boolean Ops.       (line  6524)
* newlines:                              Statements/Lines.  (line  1770)
* newlines, as field separators:         Field Separators.  (line  3320)
* newlines, as record separators:        Records.           (line  2831)
* newlines, in dynamic regexps:          Computed Regexps.  (line  2708)
* newlines, in regexp constants:         Computed Regexps.  (line  2718)
* newlines, printing:                    Print Examples.    (line  4320)
* newlines, separating statements in actions <1>: Statements.
                                                            (line  7228)
* newlines, separating statements in actions: Action Overview.
                                                            (line  7178)
* next file statement:                   POSIX/GNU.         (line 17001)
* next file statement, deprecated:       Obsolete.          (line 12426)
* next file statement, in gawk:          Nextfile Statement.
                                                            (line  7724)
* next statement <1>:                    Next Statement.    (line  7635)
* next statement:                        Boolean Ops.       (line  6541)
* next statement, BEGIN/END patterns and: I/O And BEGIN/END.
                                                            (line  7088)
* next statement, user-defined functions and: Next Statement.
                                                            (line  7668)
* nextfile statement:                    Nextfile Statement.
                                                            (line  7684)
* nextfile statement, BEGIN/END patterns and: I/O And BEGIN/END.
                                                            (line  7088)
* nextfile statement, implementing:      Nextfile Function. (line 12645)
* nextfile statement, in gawk:           Nextfile Statement.
                                                            (line  7724)
* nextfile statement, next file statement and: Obsolete.    (line 12426)
* nextfile statement, user-defined functions and: Nextfile Statement.
                                                            (line  7717)
* nextfile user-defined function:        Nextfile Function. (line 12677)
* NF variable <1>:                       Auto-set.          (line  8064)
* NF variable:                           Fields.            (line  3041)
* NF variable, decrementing:             Changing Fields.   (line  3231)
* noassign.awk program:                  Ignoring Assigns.  (line 13427)
* NODE internal type:                    Internals.         (line 18809)
* nodes, duplicating:                    Internals.         (line 18883)
* not Boolean-logic operator:            Boolean Ops.       (line  6463)
* NR variable <1>:                       Auto-set.          (line  8075)
* NR variable:                           Records.           (line  2817)
* NR variable, changing:                 Auto-set.          (line  8148)
* null strings <1>:                      Basic Data Typing. (line 19680)
* null strings <2>:                      Truth Values.      (line  6246)
* null strings <3>:                      Regexp Field Splitting.
                                                            (line  3379)
* null strings:                          Records.           (line  2912)
* null strings, array elements and:      Delete.            (line  8606)
* null strings, as array subscripts:     Uninitialized Subscripts.
                                                            (line  8743)
* null strings, converting numbers to strings: Conversion.  (line  5734)
* null strings, matching:                Gory Details.      (line  9796)
* null strings, quoting and:             Quoting.           (line  1401)
* number sign (#), #! (executable scripts): Executable Scripts.
                                                            (line  1233)
* number sign (#), #! (executable scripts), portability issues with: Executable Scripts.
                                                            (line  1233)
* number sign (#), commenting:           Comments.          (line  1296)
* numbers:                               Internals.         (line 18868)
* numbers, as array subscripts:          Numeric Array Subscripts.
                                                            (line  8656)
* numbers, as values of characters:      Ordinal Functions. (line 12976)
* numbers, Cliff random:                 Cliff Random Function.
                                                            (line 12945)
* numbers, converting:                   Conversion.        (line  5719)
* numbers, converting, to strings <1>:   Bitwise Functions. (line 10407)
* numbers, converting, to strings:       User-modified.     (line  7833)
* numbers, floating-point:               Basic Data Typing. (line 19654)
* numbers, floating-point, AWKNUM internal type: Internals. (line 18805)
* numbers, hexadecimal:                  Nondecimal-numbers.
                                                            (line  5457)
* numbers, NODE internal type:           Internals.         (line 18809)
* numbers, octal:                        Nondecimal-numbers.
                                                            (line  5457)
* numbers, random:                       Numeric Functions. (line  9115)
* numbers, rounding:                     Round Function.    (line 12900)
* numeric, constants:                    Scalar Constants.  (line  5425)
* numeric, output format:                OFMT.              (line  4434)
* numeric, strings:                      Typing and Comparison.
                                                            (line  6281)
* numeric, values:                       Internals.         (line 18813)
* oawk utility:                          Names.             (line   688)
* obsolete features:                     Obsolete.          (line 12421)
* octal numbers:                         Nondecimal-numbers.
                                                            (line  5457)
* octal values, enabling interpretation of: Options.        (line 12167)
* OFMT variable <1>:                     User-modified.     (line  7907)
* OFMT variable <2>:                     Conversion.        (line  5767)
* OFMT variable:                         OFMT.              (line  4443)
* OFMT variable, POSIX awk and:          OFMT.              (line  4455)
* OFS variable <1>:                      User-modified.     (line  7916)
* OFS variable <2>:                      Output Separators. (line  4393)
* OFS variable:                          Changing Fields.   (line  3188)
* OpenBSD:                               Glossary.          (line 20404)
* operating systems, BSD-based <1>:      Portal Files.      (line 11725)
* operating systems, BSD-based:          Manual History.    (line   886)
* operating systems, PC, gawk on:        PC Using.          (line 17853)
* operating systems, PC, gawk on, installing: PC Installation.
                                                            (line 17634)
* operating systems, porting gawk to:    New Ports.         (line 18680)
* operating systems, See Also GNU/Linux, PC operating systems, Unix: Installation.
                                                            (line 17151)
* operations, bitwise:                   Bitwise Functions. (line 10314)
* operators, arithmetic:                 Arithmetic Ops.    (line  5823)
* operators, assignment:                 Assignment Ops.    (line  5989)
* operators, assignment, evaluation order: Assignment Ops.  (line  6093)
* operators, Boolean, See Boolean expressions: Boolean Ops. (line  6463)
* operators, decrement/increment:        Increment Ops.     (line  6160)
* operators, GNU-specific:               GNU Regexp Operators.
                                                            (line  2461)
* operators, input/output <1>:           Precedence.        (line  6711)
* operators, input/output <2>:           Redirection.       (line  4864)
* operators, input/output <3>:           Getline/Coprocess. (line  4137)
* operators, input/output <4>:           Getline/Pipe.      (line  4051)
* operators, input/output:               Getline/File.      (line  3979)
* operators, logical, See Boolean expressions: Boolean Ops. (line  6463)
* operators, precedence <1>:             Precedence.        (line  6657)
* operators, precedence:                 Increment Ops.     (line  6215)
* operators, relational, See operators, comparison: Typing and Comparison.
                                                            (line  6277)
* operators, short-circuit:              Boolean Ops.       (line  6514)
* operators, string:                     Concatenation.     (line  5911)
* operators, string-matching:            Regexp Usage.      (line  1989)
* operators, string-matching, for buffers: GNU Regexp Operators.
                                                            (line  2495)
* operators, word-boundary (gawk):       GNU Regexp Operators.
                                                            (line  2510)
* options, command-line <1>:             Options.           (line 12012)
* options, command-line <2>:             Command Line Field Separator.
                                                            (line  3427)
* options, command-line:                 Long.              (line  1202)
* options, command-line, end of:         Options.           (line 12068)
* options, command-line, invoking awk:   Command Line.      (line 11988)
* options, command-line, processing:     Getopt Function.   (line 13460)
* options, deprecated:                   Obsolete.          (line 12421)
* options, long <1>:                     Options.           (line 12012)
* options, long:                         Command Line.      (line 11995)
* options, printing list of:             Options.           (line 12145)
* OR bitwise operation:                  Bitwise Functions. (line 10314)
* or Boolean-logic operator:             Boolean Ops.       (line  6463)
* or function (gawk):                    Bitwise Functions. (line 10347)
* ord user-defined function:             Ordinal Functions. (line 12986)
* order of evaluation, concatenation:    Concatenation.     (line  5943)
* ORS variable <1>:                      User-modified.     (line  7921)
* ORS variable:                          Output Separators. (line  4407)
* output field separator, See OFS variable: Changing Fields.
                                                            (line  3188)
* output record separator, See ORS variable: Output Separators.
                                                            (line  4407)
* output redirection:                    Redirection.       (line  4851)
* output, buffering:                     I/O Functions.     (line  9838)
* output, duplicating into files:        Tee Program.       (line 14964)
* output, files, closing:                Close Files And Pipes.
                                                            (line  5199)
* output, format specifier, OFMT:        OFMT.              (line  4443)
* output, formatted:                     Printf.            (line  4465)
* output, pipes:                         Redirection.       (line  4899)
* output, printing, See printing:        Printing.          (line  4249)
* output, records:                       Output Separators. (line  4407)
* output, standard:                      Special FD.        (line  5019)
* P1003.2 POSIX standard:                Glossary.          (line 20248)
* param_cnt internal variable:           Internals.         (line 18832)
* parameters, number of:                 Internals.         (line 18832)
* parentheses ():                        Regexp Operators.  (line  2253)
* parentheses (), pgawk program:         Profiling.         (line 11877)
* password file:                         Passwd Functions.  (line 13753)
* patterns:                              Patterns and Actions.
                                                            (line  6755)
* patterns, comparison expressions as:   Expression Patterns.
                                                            (line  6841)
* patterns, counts:                      Profiling.         (line 11849)
* patterns, default:                     Very Simple.       (line  1559)
* patterns, empty:                       Empty.             (line  7101)
* patterns, expressions as:              Regexp Patterns.   (line  6819)
* patterns, ranges in:                   Ranges.            (line  6913)
* patterns, regexp constants as:         Expression Patterns.
                                                            (line  6863)
* patterns, types of:                    Pattern Overview.  (line  6788)
* pawk profiling Bell Labs awk:          Other Versions.    (line 18465)
* PC operating systems, gawk on:         PC Using.          (line 17853)
* PC operating systems, gawk on, installing: PC Installation.
                                                            (line 17634)
* percent sign (%), % operator:          Precedence.        (line  6701)
* percent sign (%), %= operator <1>:     Precedence.        (line  6742)
* percent sign (%), %= operator:         Assignment Ops.    (line  6111)
* period (.):                            Regexp Operators.  (line  2218)
* PERL:                                  Future Extensions. (line 19424)
* Peters, Arno:                          Contributors.      (line 17123)
* Peterson, Hal:                         Contributors.      (line 17090)
* pgawk program:                         Profiling.         (line 11740)
* pgawk program, awkprof.out file:       Profiling.         (line 11744)
* pgawk program, dynamic profiling:      Profiling.         (line 11913)
* pipes, closing:                        Close Files And Pipes.
                                                            (line  5199)
* pipes, input:                          Getline/Pipe.      (line  4051)
* pipes, output:                         Redirection.       (line  4899)
* plus sign (+):                         Regexp Operators.  (line  2276)
* plus sign (+), + operator:             Precedence.        (line  6698)
* plus sign (+), ++ operator <1>:        Precedence.        (line  6692)
* plus sign (+), ++ operator:            Increment Ops.     (line  6194)
* plus sign (+), += operator <1>:        Precedence.        (line  6742)
* plus sign (+), += operator:            Assignment Ops.    (line  6064)
* plus sign (+), decrement/increment operators: Increment Ops.
                                                            (line  6165)
* portability:                           Escape Sequences.  (line  2126)
* portability, #! (executable scripts):  Executable Scripts.
                                                            (line  1261)
* portability, ** operator and:          Arithmetic Ops.    (line  5898)
* portability, **= operator and:         Assignment Ops.    (line  6131)
* portability, ARGV variable:            Executable Scripts.
                                                            (line  1270)
* portability, backslash continuation and: Statements/Lines.
                                                            (line  1793)
* portability, backslash in escape sequences: Escape Sequences.
                                                            (line  2145)
* portability, close function and:       Close Files And Pipes.
                                                            (line  5274)
* portability, data files as single record: Records.        (line  2979)
* portability, deleting array elements:  Delete.            (line  8630)
* portability, example programs:         Library Functions. (line 12494)
* portability, fflush function and:      I/O Functions.     (line  9838)
* portability, functions, defining:      Definition Syntax. (line 10574)
* portability, gawk:                     New Ports.         (line 18680)
* portability, gettext library and:      Explaining gettext.
                                                            (line 10925)
* portability, internationalization and: I18N Portability.  (line 11280)
* portability, length function:          String Functions.  (line  9238)
* portability, new awk vs. old awk:      Conversion.        (line  5767)
* portability, next statement in user-defined functions: Function Caveats.
                                                            (line 10760)
* portability, NF variable, decrementing: Changing Fields.  (line  3239)
* portability, operators:                Increment Ops.     (line  6215)
* portability, operators, not in POSIX awk: Precedence.     (line  6746)
* portability, POSIXLY_CORRECT environment variable: Options.
                                                            (line 12291)
* portability, substr function:          String Functions.  (line  9601)
* portable object files <1>:             Translator i18n.   (line 11156)
* portable object files:                 Explaining gettext.
                                                            (line 10951)
* portable object files, converting to message object files: I18N Example.
                                                            (line 11400)
* portable object files, generating:     Options.           (line 12136)
* portal files:                          Portal Files.      (line 11725)
* porting gawk:                          New Ports.         (line 18680)
* positional specifiers, printf statement <1>: Printf Ordering.
                                                            (line 11203)
* positional specifiers, printf statement: Format Modifiers.
                                                            (line  4621)
* positional specifiers, printf statement, mixing with regular formats: Printf Ordering.
                                                            (line 11254)
* positive zero:                         Floating Point Issues.
                                                            (line 19798)
* POSIX awk <1>:                         Assignment Ops.    (line  6122)
* POSIX awk:                             This Manual.       (line   718)
* POSIX awk, **= operator and:           Assignment Ops.    (line  6131)
* POSIX awk, < operator and:             Getline/File.      (line  3999)
* POSIX awk, arithmetic operators and:   Arithmetic Ops.    (line  5853)
* POSIX awk, backslashes in string constants: Escape Sequences.
                                                            (line  2145)
* POSIX awk, BEGIN/END patterns:         I/O And BEGIN/END. (line  7068)
* POSIX awk, break statement and:        Break Statement.   (line  7566)
* POSIX awk, changes in awk versions:    POSIX.             (line 16765)
* POSIX awk, character lists and:        Character Lists.   (line  2371)
* POSIX awk, character lists and, character classes: Character Lists.
                                                            (line  2377)
* POSIX awk, continue statement and:     Continue Statement.
                                                            (line  7619)
* POSIX awk, CONVFMT variable and:       User-modified.     (line  7833)
* POSIX awk, date utility and:           Time Functions.    (line 10245)
* POSIX awk, field separators and <1>:   Field Splitting Summary.
                                                            (line  3549)
* POSIX awk, field separators and:       Fields.            (line  3014)
* POSIX awk, FS variable and:            User-modified.     (line  7859)
* POSIX awk, function keyword in:        Definition Syntax. (line 10559)
* POSIX awk, functions and, gsub/sub:    Gory Details.      (line  9689)
* POSIX awk, functions and, length:      String Functions.  (line  9238)
* POSIX awk, GNU long options and:       Options.           (line 12021)
* POSIX awk, interval expressions in:    Regexp Operators.  (line  2309)
* POSIX awk, next/nextfile statements and: Next Statement.  (line  7668)
* POSIX awk, numeric strings and:        Typing and Comparison.
                                                            (line  6281)
* POSIX awk, OFMT variable and <1>:      Conversion.        (line  5767)
* POSIX awk, OFMT variable and:          OFMT.              (line  4455)
* POSIX awk, period (.), using:          Regexp Operators.  (line  2225)
* POSIX awk, printf format strings and:  Format Modifiers.  (line  4767)
* POSIX awk, regular expressions and:    Regexp Operators.  (line  2329)
* POSIX awk, timestamps and:             Time Functions.    (line  9987)
* POSIX awk, | I/O operator and:         Getline/Pipe.      (line  4097)
* POSIX mode:                            Options.           (line 12175)
* POSIX, awk and:                        Preface.           (line   569)
* POSIX, gawk extensions not included in: POSIX/GNU.        (line 16852)
* POSIX, programs, implementing in awk:  Clones.            (line 14243)
* POSIXLY_CORRECT environment variable:  Options.           (line 12273)
* precedence <1>:                        Precedence.        (line  6657)
* precedence:                            Increment Ops.     (line  6215)
* precedence, regexp operators:          Regexp Operators.  (line  2324)
* print statement:                       Printing.          (line  4259)
* print statement, BEGIN/END patterns and: I/O And BEGIN/END.
                                                            (line  7068)
* print statement, commas, omitting:     Print Examples.    (line  4338)
* print statement, I/O operators in:     Precedence.        (line  6718)
* print statement, line continuations and: Print Examples.  (line  4383)
* print statement, OFMT variable and:    User-modified.     (line  7916)
* print statement, See Also redirection, of output: Redirection.
                                                            (line  4859)
* print statement, sprintf function and: Round Function.    (line 12900)
* printf statement <1>:                  Printf.            (line  4465)
* printf statement:                      Printing.          (line  4259)
* printf statement, columns, aligning:   Print Examples.    (line  4377)
* printf statement, format-control characters: Control Letters.
                                                            (line  4527)
* printf statement, I/O operators in:    Precedence.        (line  6718)
* printf statement, modifiers:           Format Modifiers.  (line  4614)
* printf statement, positional specifiers <1>: Printf Ordering.
                                                            (line 11203)
* printf statement, positional specifiers: Format Modifiers.
                                                            (line  4621)
* printf statement, positional specifiers, mixing with regular formats: Printf Ordering.
                                                            (line 11254)
* printf statement, See Also redirection, of output: Redirection.
                                                            (line  4859)
* printf statement, sprintf function and: Round Function.   (line 12900)
* printf statement, syntax of:           Basic Printf.      (line  4486)
* printing:                              Printing.          (line  4249)
* printing, list of options:             Options.           (line 12145)
* printing, mailing labels:              Labels Program.    (line 15723)
* printing, unduplicated lines of text:  Uniq Program.      (line 15048)
* printing, user information:            Id Program.        (line 14755)
* private variables:                     Library Names.     (line 12546)
* process information, files for:        Special Process.   (line  5086)
* processes, two-way communications with: Two-way I/O.      (line 11539)
* processing data:                       Basic High Level.  (line 19543)
* PROCINFO array <1>:                    Group Functions.   (line 13968)
* PROCINFO array <2>:                    Passwd Functions.  (line 13743)
* PROCINFO array <3>:                    Auto-set.          (line  8080)
* PROCINFO array:                        Special Caveats.   (line  5170)
* PROCINFO variable:                     Internals.         (line 18951)
* profiling awk programs:                Profiling.         (line 11740)
* profiling awk programs, dynamically:   Profiling.         (line 11913)
* profiling gawk, See pgawk program:     Profiling.         (line 11740)
* program, definition of:                Getting Started.   (line  1047)
* programmers, attractiveness of:        Two-way I/O.       (line 11522)
* programming conventions, --non-decimal-data option: Nondecimal Data.
                                                            (line 11510)
* programming conventions, ARGC/ARGV variables: Auto-set.   (line  7992)
* programming conventions, exit statement: Exit Statement.  (line  7767)
* programming conventions, function parameters: Return Statement.
                                                            (line 10803)
* programming conventions, functions, calling: Calling Built-in.
                                                            (line  9011)
* programming conventions, functions, writing: Definition Syntax.
                                                            (line 10536)
* programming conventions, gawk internals: Internal File Ops.
                                                            (line 19220)
* programming conventions, nextfile statement: Nextfile Function.
                                                            (line 12659)
* programming conventions, private variable names: Library Names.
                                                            (line 12558)
* programming language, recipe for:      History.           (line   630)
* programming languages, data-driven vs. procedural: Getting Started.
                                                            (line  1038)
* programming, basic steps:              Basic High Level.  (line 19556)
* programming, concepts:                 Basic Concepts.    (line 19524)
* pwcat program:                         Passwd Functions.  (line 13760)
* question mark (?) <1>:                 GNU Regexp Operators.
                                                            (line  2506)
* question mark (?):                     Regexp Operators.  (line  2285)
* question mark (?), ?: operator:        Precedence.        (line  6739)
* QUIT signal (MS-DOS):                  Profiling.         (line 11946)
* quoting <1>:                           Comments.          (line  1317)
* quoting <2>:                           Long.              (line  1216)
* quoting:                               Read Terminal.     (line  1165)
* quoting, rules for:                    Quoting.           (line  1349)
* quoting, tricks for:                   Quoting.           (line  1410)
* Rakitzis, Byron:                       History Sorting.   (line 15953)
* rand function:                         Numeric Functions. (line  9085)
* random numbers, Cliff:                 Cliff Random Function.
                                                            (line 12945)
* random numbers, rand/srand functions:  Numeric Functions. (line  9085)
* random numbers, seed of:               Numeric Functions. (line  9115)
* range expressions:                     Character Lists.   (line  2353)
* range patterns:                        Ranges.            (line  6913)
* Rankin, Pat <1>:                       Bugs.              (line 18371)
* Rankin, Pat <2>:                       Contributors.      (line 17085)
* Rankin, Pat <3>:                       Assignment Ops.    (line  6082)
* Rankin, Pat:                           Acknowledgments.   (line   995)
* raw sockets:                           TCP/IP Networking. (line 11682)
* readable data files, checking:         File Checking.     (line 13334)
* readable.awk program:                  File Checking.     (line 13339)
* recipe for a programming language:     History.           (line   630)
* record separators <1>:                 User-modified.     (line  7926)
* record separators:                     Records.           (line  2825)
* record separators, changing:           Records.           (line  2891)
* record separators, regular expressions as: Records.       (line  2921)
* record separators, with multiline records: Multiple Line. (line  3709)
* records <1>:                           Basic High Level.  (line 19608)
* records:                               Reading Files.     (line  2788)
* records, multiline:                    Multiple Line.     (line  3705)
* records, printing:                     Print.             (line  4300)
* records, splitting input into:         Records.           (line  2817)
* records, terminating:                  Records.           (line  2921)
* records, treating files as:            Records.           (line  3000)
* recursive functions:                   Definition Syntax. (line 10554)
* redirection of input:                  Getline/File.      (line  3979)
* redirection of output:                 Redirection.       (line  4851)
* reference counting, sorting arrays:    Array Sorting.     (line  8946)
* regexp constants <1>:                  Typing and Comparison.
                                                            (line  6442)
* regexp constants <2>:                  Regexp Constants.  (line  5532)
* regexp constants:                      Regexp Usage.      (line  2028)
* regexp constants, /=.../, /= operator and: Assignment Ops.
                                                            (line  6137)
* regexp constants, as patterns:         Expression Patterns.
                                                            (line  6863)
* regexp constants, in gawk:             Using Constant Regexps.
                                                            (line  5566)
* regexp constants, slashes vs. quotes:  Computed Regexps.  (line  2677)
* regexp constants, vs. string constants: Computed Regexps. (line  2687)
* regexp, See regular expressions:       Regexp.            (line  1945)
* register_deferred_variable internal function: Internals.  (line 18951)
* register_open_hook internal function:  Internals.         (line 18964)
* regular expressions:                   Regexp.            (line  1945)
* regular expressions as field separators: Field Separators.
                                                            (line  3306)
* regular expressions, anchors in:       Regexp Operators.  (line  2197)
* regular expressions, as field separators: Regexp Field Splitting.
                                                            (line  3343)
* regular expressions, as patterns <1>:  Regexp Patterns.   (line  6819)
* regular expressions, as patterns:      Regexp Usage.      (line  1976)
* regular expressions, as record separators: Records.       (line  2921)
* regular expressions, case sensitivity <1>: User-modified. (line  7875)
* regular expressions, case sensitivity: Case-sensitivity.  (line  2549)
* regular expressions, computed:         Computed Regexps.  (line  2656)
* regular expressions, constants, See regexp constants: Regexp Usage.
                                                            (line  2028)
* regular expressions, dynamic:          Computed Regexps.  (line  2656)
* regular expressions, dynamic, with embedded newlines: Computed Regexps.
                                                            (line  2708)
* regular expressions, gawk, command-line options: GNU Regexp Operators.
                                                            (line  2517)
* regular expressions, interval expressions and: Options.   (line 12220)
* regular expressions, leftmost longest match: Leftmost Longest.
                                                            (line  2626)
* regular expressions, operators <1>:    Regexp Operators.  (line  2181)
* regular expressions, operators:        Regexp Usage.      (line  1989)
* regular expressions, operators, for buffers: GNU Regexp Operators.
                                                            (line  2495)
* regular expressions, operators, for words: GNU Regexp Operators.
                                                            (line  2461)
* regular expressions, operators, gawk:  GNU Regexp Operators.
                                                            (line  2461)
* regular expressions, operators, precedence of: Regexp Operators.
                                                            (line  2324)
* regular expressions, searching for:    Egrep Program.     (line 14525)
* relational operators, See comparison operators: Typing and Comparison.
                                                            (line  6277)
* return statement, user-defined functions: Return Statement.
                                                            (line 10770)
* return values, close function:         Close Files And Pipes.
                                                            (line  5323)
* rev user-defined function:             Function Example.  (line 10629)
* rewind user-defined function:          Rewind Function.   (line 13302)
* right angle bracket (>), > operator <1>: Precedence.      (line  6711)
* right angle bracket (>), > operator:   Typing and Comparison.
                                                            (line  6342)
* right angle bracket (>), > operator (I/O): Redirection.   (line  4864)
* right angle bracket (>), >= operator <1>: Precedence.     (line  6711)
* right angle bracket (>), >= operator:  Typing and Comparison.
                                                            (line  6342)
* right angle bracket (>), >> operator (I/O) <1>: Precedence.
                                                            (line  6711)
* right angle bracket (>), >> operator (I/O): Redirection.  (line  4892)
* right shift, bitwise:                  Bitwise Functions. (line 10340)
* Ritchie, Dennis:                       Basic Data Typing. (line 19704)
* RLENGTH variable:                      Auto-set.          (line  8124)
* RLENGTH variable, match function and:  String Functions.  (line  9273)
* Robbins, Arnold <1>:                   Future Extensions. (line 19424)
* Robbins, Arnold <2>:                   Bugs.              (line 18337)
* Robbins, Arnold <3>:                   Contributors.      (line 17141)
* Robbins, Arnold <4>:                   Alarm Program.     (line 15477)
* Robbins, Arnold <5>:                   Passwd Functions.  (line 13813)
* Robbins, Arnold <6>:                   Getline/Pipe.      (line  4081)
* Robbins, Arnold:                       Command Line Field Separator.
                                                            (line  3501)
* Robbins, Bill:                         Getline/Pipe.      (line  4081)
* Robbins, Harry:                        Acknowledgments.   (line  1012)
* Robbins, Jean:                         Acknowledgments.   (line  1012)
* Robbins, Miriam <1>:                   Passwd Functions.  (line 13813)
* Robbins, Miriam <2>:                   Getline/Pipe.      (line  4081)
* Robbins, Miriam:                       Acknowledgments.   (line  1012)
* Robinson, Will:                        Dynamic Extensions.
                                                            (line 18761)
* robot, the:                            Dynamic Extensions.
                                                            (line 18761)
* Rommel, Kai Uwe <1>:                   Contributors.      (line 17092)
* Rommel, Kai Uwe:                       Acknowledgments.   (line   995)
* round user-defined function:           Round Function.    (line 12910)
* rounding:                              Round Function.    (line 12900)
* rounding numbers:                      Round Function.    (line 12900)
* RS variable <1>:                       User-modified.     (line  7926)
* RS variable:                           Records.           (line  2831)
* RS variable, multiline records and:    Multiple Line.     (line  3716)
* rshift function (gawk):                Bitwise Functions. (line 10354)
* RSTART variable:                       Auto-set.          (line  8130)
* RSTART variable, match function and:   String Functions.  (line  9273)
* RT variable <1>:                       Auto-set.          (line  8137)
* RT variable <2>:                       Multiple Line.     (line  3828)
* RT variable:                           Records.           (line  2921)
* Rubin, Paul <1>:                       Contributors.      (line 17066)
* Rubin, Paul:                           History.           (line   653)
* rule, definition of:                   Getting Started.   (line  1047)
* rvalues/lvalues:                       Assignment Ops.    (line  6014)
* scalar values:                         Basic Data Typing. (line 19646)
* Schreiber, Bert:                       Acknowledgments.   (line   977)
* Schreiber, Rita:                       Acknowledgments.   (line   977)
* search paths <1>:                      VMS Running.       (line 18102)
* search paths:                          PC Using.          (line 17858)
* search paths, for source files <1>:    VMS Running.       (line 18102)
* search paths, for source files <2>:    Igawk Program.     (line 16601)
* search paths, for source files:        AWKPATH Variable.  (line 12361)
* searching:                             String Functions.  (line  9218)
* searching, files for regular expressions: Egrep Program.  (line 14525)
* searching, for words:                  Dupword Program.   (line 15429)
* sed utility <1>:                       Glossary.          (line 19837)
* sed utility <2>:                       Simple Sed.        (line 16170)
* sed utility:                           Field Splitting Summary.
                                                            (line  3555)
* semicolon (;):                         Statements/Lines.  (line  1853)
* semicolon (;), AWKPATH variable and:   PC Using.          (line 17858)
* semicolon (;), separating statements in actions <1>: Statements.
                                                            (line  7228)
* semicolon (;), separating statements in actions: Action Overview.
                                                            (line  7178)
* separators, field:                     User-modified.     (line  7850)
* separators, field, FIELDWIDTHS variable and: User-modified.
                                                            (line  7840)
* separators, field, POSIX and:          Fields.            (line  3014)
* separators, for records:               Records.           (line  2825)
* separators, for records, regular expressions as: Records. (line  2921)
* separators, for statements in actions: Action Overview.   (line  7178)
* separators, record:                    User-modified.     (line  7926)
* separators, subscript:                 User-modified.     (line  7939)
* set_value internal function:           Internals.         (line 18932)
* shells, piping commands into:          Redirection.       (line  4981)
* shells, quoting:                       Using Shell Variables.
                                                            (line  7120)
* shells, quoting, rules for:            Quoting.           (line  1357)
* shells, scripts:                       One-shot.          (line  1133)
* shells, variables:                     Using Shell Variables.
                                                            (line  7114)
* shift, bitwise:                        Bitwise Functions. (line 10340)
* short-circuit operators:               Boolean Ops.       (line  6514)
* side effects <1>:                      Increment Ops.     (line  6165)
* side effects:                          Concatenation.     (line  5943)
* side effects, array indexing:          Reference to Elements.
                                                            (line  8437)
* side effects, asort function:          Array Sorting.     (line  8894)
* side effects, assignment expressions:  Assignment Ops.    (line  6005)
* side effects, Boolean operators:       Boolean Ops.       (line  6487)
* side effects, conditional expressions: Conditional Exp.   (line  6569)
* side effects, decrement/increment operators: Increment Ops.
                                                            (line  6165)
* side effects, FILENAME variable:       Getline Notes.     (line  4198)
* side effects, function calls:          Function Calls.    (line  6635)
* side effects, statements:              Action Overview.   (line  7191)
* signals, HUP/SIGHUP:                   Profiling.         (line 11943)
* signals, INT/SIGINT (MS-DOS):          Profiling.         (line 11946)
* signals, QUIT/SIGQUIT (MS-DOS):        Profiling.         (line 11946)
* signals, USR1/SIGUSR1:                 Profiling.         (line 11921)
* sin function:                          Numeric Functions. (line  9076)
* single quote (') <1>:                  Quoting.           (line  1370)
* single quote (') <2>:                  Long.              (line  1223)
* single quote ('):                      One-shot.          (line  1126)
* single quote ('), vs. apostrophe:      Comments.          (line  1317)
* single quote ('), with double quotes:  Quoting.           (line  1392)
* single-character fields:               Single Character Fields.
                                                            (line  3401)
* single-precision floating-point:       Basic Data Typing. (line 19666)
* Skywalker, Luke:                       Undocumented.      (line 12443)
* sleep utility:                         Alarm Program.     (line 15572)
* sockets:                               TCP/IP Networking. (line 11682)
* sort function, arrays, sorting:        Array Sorting.     (line  8875)
* sort utility:                          Word Sorting.      (line 15876)
* sort utility, coprocesses and:         Two-way I/O.       (line 11600)
* sorting characters in different languages: Explaining gettext.
                                                            (line 11004)
* source code, awka:                     Other Versions.    (line 18453)
* source code, Bell Laboratories awk:    Other Versions.    (line 18390)
* source code, gawk:                     Gawk Distribution. (line 17174)
* source code, mawk:                     Other Versions.    (line 18410)
* source code, mixing:                   Options.           (line 12227)
* source files, search path for:         Igawk Program.     (line 16601)
* sparse arrays:                         Array Intro.       (line  8377)
* Spencer, Henry:                        Glossary.          (line 19837)
* split function:                        String Functions.  (line  9344)
* split function, array elements, deleting: Delete.         (line  8635)
* split utility:                         Split Program.     (line 14862)
* split.awk program:                     Split Program.     (line 14886)
* sprintf function <1>:                  String Functions.  (line  9397)
* sprintf function:                      OFMT.              (line  4443)
* sprintf function, OFMT variable and:   User-modified.     (line  7916)
* sprintf function, print/printf statements and: Round Function.
                                                            (line 12900)
* sqrt function:                         Numeric Functions. (line  9063)
* square brackets ([]):                  Regexp Operators.  (line  2230)
* srand function:                        Numeric Functions. (line  9125)
* Stallman, Richard <1>:                 Glossary.          (line 20109)
* Stallman, Richard <2>:                 Contributors.      (line 17074)
* Stallman, Richard <3>:                 Acknowledgments.   (line   960)
* Stallman, Richard:                     Manual History.    (line   865)
* standard input <1>:                    Special FD.        (line  5019)
* standard input:                        Read Terminal.     (line  1146)
* standard output:                       Special FD.        (line  5019)
* stat function, implementing in gawk:   Sample Library.    (line 19054)
* statements, compound, control statements and: Statements. (line  7228)
* statements, control, in actions:       Statements.        (line  7224)
* statements, multiple:                  Statements/Lines.  (line  1853)
* stlen internal variable:               Internals.         (line 18836)
* stptr internal variable:               Internals.         (line 18836)
* stream editors <1>:                    Simple Sed.        (line 16170)
* stream editors:                        Field Splitting Summary.
                                                            (line  3555)
* strftime function (gawk):              Time Functions.    (line 10034)
* string constants:                      Scalar Constants.  (line  5434)
* string constants, vs. regexp constants: Computed Regexps. (line  2687)
* string extraction (internationalization): String Extraction.
                                                            (line 11177)
* string operators:                      Concatenation.     (line  5911)
* string-matching operators:             Regexp Usage.      (line  1989)
* strings:                               Internals.         (line 18863)
* strings, converting:                   Conversion.        (line  5719)
* strings, converting, numbers to <1>:   Bitwise Functions. (line 10407)
* strings, converting, numbers to:       User-modified.     (line  7833)
* strings, empty, See null strings:      Records.           (line  2912)
* strings, extracting:                   String Extraction. (line 11177)
* strings, for localization:             Programmer i18n.   (line 11059)
* strings, length of:                    Scalar Constants.  (line  5439)
* strings, merging arrays into:          Join Function.     (line 13067)
* strings, NODE internal type:           Internals.         (line 18809)
* strings, null:                         Regexp Field Splitting.
                                                            (line  3379)
* strings, numeric:                      Typing and Comparison.
                                                            (line  6281)
* strings, splitting:                    String Functions.  (line  9358)
* strtonum function (gawk):              String Functions.  (line  9405)
* strtonum function (gawk), --non-decimal-data option and: Nondecimal Data.
                                                            (line 11510)
* sub function <1>:                      String Functions.  (line  9426)
* sub function:                          Using Constant Regexps.
                                                            (line  5582)
* sub function, arguments of:            String Functions.  (line  9483)
* sub function, escape processing:       Gory Details.      (line  9642)
* subscript separators:                  User-modified.     (line  7939)
* subscripts in arrays, multidimensional: Multi-dimensional.
                                                            (line  8754)
* subscripts in arrays, multidimensional, scanning: Multi-scanning.
                                                            (line  8840)
* subscripts in arrays, numbers as:      Numeric Array Subscripts.
                                                            (line  8656)
* subscripts in arrays, uninitialized variables as: Uninitialized Subscripts.
                                                            (line  8707)
* SUBSEP variable:                       User-modified.     (line  7939)
* SUBSEP variable, multidimensional arrays: Multi-dimensional.
                                                            (line  8760)
* substr function:                       String Functions.  (line  9570)
* Sumner, Andrew:                        Other Versions.    (line 18453)
* switch statement:                      Switch Statement.  (line  7464)
* syntactic ambiguity: /= operator vs. /=.../ regexp constant: Assignment Ops.
                                                            (line  6137)
* system function:                       I/O Functions.     (line  9872)
* systime function (gawk):               Time Functions.    (line 10005)
* tandem:                                Tandem Installation.
                                                            (line 18278)
* Tcl:                                   Library Names.     (line 12592)
* TCP/IP:                                TCP/IP Networking. (line 11658)
* TCP/IP, support for:                   Special Network.   (line  5145)
* tee utility:                           Tee Program.       (line 14964)
* tee.awk program:                       Tee Program.       (line 14984)
* terminating records:                   Records.           (line  2921)
* testbits.awk program:                  Bitwise Functions. (line 10368)
* Texinfo <1>:                           Adding Code.       (line 18640)
* Texinfo <2>:                           Distribution contents.
                                                            (line 17315)
* Texinfo <3>:                           Extract Program.   (line 15985)
* Texinfo <4>:                           Dupword Program.   (line 15440)
* Texinfo <5>:                           Library Functions. (line 12485)
* Texinfo <6>:                           Sample Data Files. (line  1521)
* Texinfo:                               Conventions.       (line   819)
* Texinfo, chapter beginnings in files:  Regexp Operators.  (line  2197)
* Texinfo, extracting programs from source files: Extract Program.
                                                            (line 15979)
* text, printing:                        Print.             (line  4300)
* text, printing, unduplicated lines of: Uniq Program.      (line 15048)
* textdomain function (C library):       Explaining gettext.
                                                            (line 10942)
* TEXTDOMAIN variable <1>:               Programmer i18n.   (line 11054)
* TEXTDOMAIN variable:                   User-modified.     (line  7945)
* TEXTDOMAIN variable, BEGIN pattern and: Programmer i18n.  (line 11103)
* TEXTDOMAIN variable, portability and:  I18N Portability.  (line 11294)
* tilde (~), ~ operator <1>:             Expression Patterns.
                                                            (line  6851)
* tilde (~), ~ operator <2>:             Precedence.        (line  6727)
* tilde (~), ~ operator <3>:             Typing and Comparison.
                                                            (line  6342)
* tilde (~), ~ operator <4>:             Regexp Constants.  (line  5532)
* tilde (~), ~ operator <5>:             Computed Regexps.  (line  2656)
* tilde (~), ~ operator <6>:             Case-sensitivity.  (line  2569)
* tilde (~), ~ operator:                 Regexp Usage.      (line  1989)
* time, alarm clock example program:     Alarm Program.     (line 15480)
* time, localization and:                Explaining gettext.
                                                            (line 11026)
* time, managing:                        Gettimeofday Function.
                                                            (line 13112)
* time, retrieving:                      Time Functions.    (line  9998)
* timestamps:                            Time Functions.    (line  9987)
* timestamps, converting dates to:       Time Functions.    (line 10050)
* timestamps, formatted:                 Gettimeofday Function.
                                                            (line 13112)
* tmp_number internal function:          Internals.         (line 18878)
* tmp_string internal function:          Internals.         (line 18873)
* tolower function:                      String Functions.  (line  9612)
* toupper function:                      String Functions.  (line  9618)
* tr utility:                            Translate Program. (line 15601)
* translate.awk program:                 Translate Program. (line 15649)
* troubleshooting, --non-decimal-data option: Options.      (line 12170)
* troubleshooting, -F option:            Known Bugs.        (line 12454)
* troubleshooting, == operator:          Typing and Comparison.
                                                            (line  6377)
* troubleshooting, awk uses FS not IFS:  Field Separators.  (line  3285)
* troubleshooting, backslash before nonspecial character: Escape Sequences.
                                                            (line  2145)
* troubleshooting, division:             Arithmetic Ops.    (line  5861)
* troubleshooting, fatal errors, field widths, specifying: Constant Size.
                                                            (line  3618)
* troubleshooting, fatal errors, printf format strings: Format Modifiers.
                                                            (line  4767)
* troubleshooting, fflush function:      I/O Functions.     (line  9860)
* troubleshooting, function call syntax: Function Calls.    (line  6615)
* troubleshooting, gawk <1>:             Compatibility Mode.
                                                            (line 18503)
* troubleshooting, gawk:                 Known Bugs.        (line 12454)
* troubleshooting, gawk, bug reports:    Bugs.              (line 18317)
* troubleshooting, gawk, fatal errors, function arguments: Calling Built-in.
                                                            (line  9017)
* troubleshooting, getline function:     File Checking.     (line 13352)
* troubleshooting, gsub/sub functions:   String Functions.  (line  9493)
* troubleshooting, match function:       String Functions.  (line  9339)
* troubleshooting, print statement, omitting commas: Print Examples.
                                                            (line  4338)
* troubleshooting, printing:             Redirection.       (line  4959)
* troubleshooting, quotes with file names: Special FD.      (line  5076)
* troubleshooting, readable data files:  File Checking.     (line 13334)
* troubleshooting, regexp constants vs. string constants: Computed Regexps.
                                                            (line  2687)
* troubleshooting, string concatenation: Concatenation.     (line  5929)
* troubleshooting, substr function:      String Functions.  (line  9588)
* troubleshooting, system function:      I/O Functions.     (line  9896)
* troubleshooting, typographical errors, global variables: Options.
                                                            (line 12107)
* true, logical:                         Truth Values.      (line  6246)
* Trueman, David <1>:                    Contributors.      (line 17081)
* Trueman, David <2>:                    Acknowledgments.   (line   986)
* Trueman, David:                        History.           (line   653)
* trunc-mod operation:                   Arithmetic Ops.    (line  5883)
* truth values:                          Truth Values.      (line  6246)
* type conversion:                       Conversion.        (line  5734)
* type internal variable:                Internals.         (line 18844)
* undefined functions:                   Function Caveats.  (line 10740)
* underscore (_), _ C macro:             Explaining gettext.
                                                            (line 10983)
* underscore (_), in names of private variables: Library Names.
                                                            (line 12564)
* underscore (_), translatable string:   Programmer i18n.   (line 11112)
* undocumented features:                 Undocumented.      (line 12443)
* uninitialized variables, as array subscripts: Uninitialized Subscripts.
                                                            (line  8707)
* uniq utility:                          Uniq Program.      (line 15048)
* uniq.awk program:                      Uniq Program.      (line 15107)
* Unix:                                  Glossary.          (line 20404)
* Unix awk, backslashes in escape sequences: Escape Sequences.
                                                            (line  2157)
* Unix awk, close function and:          Close Files And Pipes.
                                                            (line  5323)
* Unix awk, password files, field separators and: Command Line Field Separator.
                                                            (line  3493)
* Unix, awk scripts and:                 Executable Scripts.
                                                            (line  1233)
* unsigned integers:                     Basic Data Typing. (line 19661)
* update_ERRNO internal function:        Internals.         (line 18938)
* update_ERRNO_saved internal function:  Internals.         (line 18943)
* user database, reading:                Passwd Functions.  (line 13743)
* user-defined, functions:               User-defined.      (line 10472)
* user-defined, functions, counts:       Profiling.         (line 11868)
* user-defined, variables:               Variables.         (line  5621)
* user-modifiable variables:             User-modified.     (line  7813)
* users, information about, printing:    Id Program.        (line 14755)
* users, information about, retrieving:  Passwd Functions.  (line 13753)
* USR1 signal:                           Profiling.         (line 11921)
* values, numeric:                       Basic Data Typing. (line 19646)
* values, string:                        Basic Data Typing. (line 19646)
* variable typing:                       Typing and Comparison.
                                                            (line  6277)
* variables <1>:                         Basic Data Typing. (line 19639)
* variables:                             Other Features.    (line  1879)
* variables, assigning on command line:  Assignment Options.
                                                            (line  5671)
* variables, built-in <1>:               Built-in Variables.
                                                            (line  7787)
* variables, built-in:                   Using Variables.   (line  5650)
* variables, built-in, -v option, setting with: Options.    (line 12044)
* variables, built-in, conveying information: Auto-set.     (line  7967)
* variables, flag:                       Boolean Ops.       (line  6524)
* variables, getline command into, using <1>: Getline/Variable/Coprocess.
                                                            (line  4167)
* variables, getline command into, using <2>: Getline/Variable/Pipe.
                                                            (line  4110)
* variables, getline command into, using <3>: Getline/Variable/File.
                                                            (line  4012)
* variables, getline command into, using: Getline/Variable. (line  3938)
* variables, global, for library functions: Library Names.  (line 12546)
* variables, global, printing list of:   Options.           (line 12101)
* variables, initializing:               Using Variables.   (line  5650)
* variables, names of:                   Arrays.            (line  8287)
* variables, private:                    Library Names.     (line 12546)
* variables, setting:                    Options.           (line 12036)
* variables, shadowing:                  Definition Syntax. (line 10542)
* variables, types of:                   Assignment Ops.    (line  6022)
* variables, types of, comparison expressions and: Typing and Comparison.
                                                            (line  6277)
* variables, uninitialized, as array subscripts: Uninitialized Subscripts.
                                                            (line  8707)
* variables, user-defined:               Variables.         (line  5621)
* vertical bar (|):                      Regexp Operators.  (line  2243)
* vertical bar (|), | operator (I/O) <1>: Precedence.       (line  6711)
* vertical bar (|), | operator (I/O):    Getline/Pipe.      (line  4051)
* vertical bar (|), |& I/O operator (I/O): Two-way I/O.     (line 11560)
* vertical bar (|), |& operator (I/O) <1>: Precedence.      (line  6711)
* vertical bar (|), |& operator (I/O):   Getline/Coprocess. (line  4137)
* vertical bar (|), |& operator (I/O), two-way communications: Portal Files.
                                                            (line 11729)
* vertical bar (|), || operator <1>:     Precedence.        (line  6736)
* vertical bar (|), || operator:         Boolean Ops.       (line  6514)
* vname internal variable:               Internals.         (line 18848)
* w utility:                             Constant Size.     (line  3618)
* Wall, Larry:                           Future Extensions. (line 19424)
* warnings, issuing:                     Options.           (line 12150)
* wc utility:                            Wc Program.        (line 15264)
* wc.awk program:                        Wc Program.        (line 15303)
* Weinberger, Peter <1>:                 Contributors.      (line 17062)
* Weinberger, Peter:                     History.           (line   640)
* while statement <1>:                   While Statement.   (line  7299)
* while statement:                       Regexp Usage.      (line  1989)
* whitespace, as field separators:       Field Separators.  (line  3320)
* whitespace, functions, calling:        Calling Built-in.  (line  9011)
* whitespace, newlines as:               Options.           (line 12182)
* Williams, Kent:                        Contributors.      (line 17087)
* Woods, John:                           Contributors.      (line 17078)
* word boundaries, matching:             GNU Regexp Operators.
                                                            (line  2485)
* word, regexp definition of:            GNU Regexp Operators.
                                                            (line  2461)
* word-boundary operator (gawk):         GNU Regexp Operators.
                                                            (line  2510)
* wordfreq.awk program:                  Word Sorting.      (line 15882)
* words, counting:                       Wc Program.        (line 15264)
* words, duplicate, searching for:       Dupword Program.   (line 15429)
* words, usage counts, generating:       Word Sorting.      (line 15828)
* xgettext utility:                      String Extraction. (line 11184)
* XML:                                   Internals.         (line 18964)
* XOR bitwise operation:                 Bitwise Functions. (line 10314)
* xor function (gawk):                   Bitwise Functions. (line 10349)
* Zaretskii, Eli:                        Acknowledgments.   (line   995)
* zero, negative vs. positive:           Floating Point Issues.
                                                            (line 19798)
* zerofile.awk program:                  Empty Files.       (line 13377)
* Zoulas, Christos:                      Contributors.      (line 17111)
* {} (braces), actions and:              Action Overview.   (line  7178)
* {} (braces), pgawk program:            Profiling.         (line 11873)
* {} (braces), statements, grouping:     Statements.        (line  7228)
* | (vertical bar):                      Regexp Operators.  (line  2243)
* | (vertical bar), | operator (I/O) <1>: Precedence.       (line  6711)
* | (vertical bar), | operator (I/O) <2>: Redirection.      (line  4899)
* | (vertical bar), | operator (I/O):    Getline/Pipe.      (line  4051)
* | (vertical bar), |& operator (I/O) <1>: Two-way I/O.     (line 11560)
* | (vertical bar), |& operator (I/O) <2>: Precedence.      (line  6711)
* | (vertical bar), |& operator (I/O) <3>: Redirection.     (line  4944)
* | (vertical bar), |& operator (I/O):   Getline/Coprocess. (line  4137)
* | (vertical bar), |& operator (I/O), pipes, closing: Close Files And Pipes.
                                                            (line  5310)
* | (vertical bar), |& operator (I/O), two-way communications: Portal Files.
                                                            (line 11729)
* | (vertical bar), || operator <1>:     Precedence.        (line  6736)
* | (vertical bar), || operator:         Boolean Ops.       (line  6514)
* ~ (tilde), ~ operator <1>:             Expression Patterns.
                                                            (line  6851)
* ~ (tilde), ~ operator <2>:             Precedence.        (line  6727)
* ~ (tilde), ~ operator <3>:             Typing and Comparison.
                                                            (line  6342)
* ~ (tilde), ~ operator <4>:             Regexp Constants.  (line  5532)
* ~ (tilde), ~ operator <5>:             Computed Regexps.  (line  2656)
* ~ (tilde), ~ operator:                 Case-sensitivity.  (line  2569)



Tag Table:
Node: Top1326
Node: Foreword26895
Node: Preface31216
Ref: Preface-Footnote-134077
Node: History34306
Node: Names36509
Ref: Names-Footnote-137969
Node: This Manual38038
Ref: This Manual-Footnote-142723
Node: Conventions42820
Node: Manual History44682
Ref: Manual History-Footnote-148102
Ref: Manual History-Footnote-248140
Node: How To Contribute48211
Node: Acknowledgments48809
Node: Getting Started52576
Node: Running gawk54940
Node: One-shot56120
Node: Read Terminal57336
Ref: Read Terminal-Footnote-158982
Node: Long59150
Node: Executable Scripts60520
Ref: Executable Scripts-Footnote-162404
Ref: Executable Scripts-Footnote-262552
Node: Comments63000
Node: Quoting65353
Node: Sample Data Files69833
Node: Very Simple72853
Node: Two Rules77443
Node: More Complex79581
Ref: More Complex-Footnote-182489
Ref: More Complex-Footnote-282934
Node: Statements/Lines83014
Ref: Statements/Lines-Footnote-187372
Node: Other Features87634
Node: When88480
Ref: When-Footnote-190706
Node: Regexp90784
Node: Regexp Usage92235
Node: Escape Sequences94272
Node: Regexp Operators99988
Ref: Regexp Operators-Footnote-1107077
Ref: Regexp Operators-Footnote-2107221
Node: Character Lists107316
Ref: table-char-classes109260
Node: GNU Regexp Operators112784
Node: Case-sensitivity116355
Ref: Case-sensitivity-Footnote-1119505
Node: Leftmost Longest119737
Node: Computed Regexps120919
Node: Locales124282
Node: Reading Files126302
Node: Records128053
Ref: Records-Footnote-1136555
Node: Fields136589
Ref: Fields-Footnote-1139601
Node: Nonconstant Fields139684
Node: Changing Fields141876
Node: Field Separators147122
Node: Regexp Field Splitting150591
Node: Single Character Fields153047
Node: Command Line Field Separator154096
Node: Field Splitting Summary157513
Ref: Field Splitting Summary-Footnote-1160691
Node: Constant Size160789
Node: Multiple Line165245
Ref: Multiple Line-Footnote-1170908
Node: Getline171084
Node: Plain Getline173143
Node: Getline/Variable175185
Node: Getline/File176323
Node: Getline/Variable/File177641
Node: Getline/Pipe179188
Node: Getline/Variable/Pipe181244
Node: Getline/Coprocess182345
Node: Getline/Variable/Coprocess183576
Node: Getline Notes184284
Node: Getline Summary185927
Ref: table-getline-variants186211
Node: Printing187376
Node: Print189005
Node: Print Examples190325
Node: Output Separators193105
Node: OFMT194857
Node: Printf196209
Node: Basic Printf197128
Node: Control Letters198655
Node: Format Modifiers201875
Node: Printf Examples207914
Node: Redirection210613
Node: Special Files217175
Node: Special FD217809
Node: Special Process220823
Node: Special Network223055
Node: Special Caveats223894
Ref: Special Caveats-Footnote-1225089
Node: Close Files And Pipes225469
Ref: Close Files And Pipes-Footnote-1232348
Ref: Close Files And Pipes-Footnote-2232493
Node: Expressions232638
Node: Constants234824
Node: Scalar Constants235502
Ref: Scalar Constants-Footnote-1236351
Node: Nondecimal-numbers236530
Node: Regexp Constants239572
Node: Using Constant Regexps240045
Node: Variables243122
Node: Using Variables243778
Node: Assignment Options245279
Node: Conversion247153
Ref: Conversion-Footnote-1251902
Node: Arithmetic Ops252008
Node: Concatenation254503
Node: Assignment Ops257187
Ref: table-assign-ops262136
Node: Increment Ops264040
Node: Truth Values267515
Node: Typing and Comparison268562
Ref: table-relational-ops271609
Ref: Typing and Comparison-Footnote-1275850
Node: Boolean Ops275992
Node: Conditional Exp279998
Node: Function Calls281729
Node: Precedence284612
Node: Patterns and Actions288033
Node: Pattern Overview289084
Node: Regexp Patterns290518
Node: Expression Patterns291061
Node: Ranges294593
Node: BEGIN/END297667
Node: Using BEGIN/END298417
Ref: Using BEGIN/END-Footnote-1301135
Node: I/O And BEGIN/END301246
Node: Empty303503
Node: Using Shell Variables303811
Node: Action Overview306082
Node: Statements308434
Node: If Statement310287
Node: While Statement311783
Node: Do Statement313812
Node: For Statement314958
Node: Switch Statement318074
Node: Break Statement320338
Node: Continue Statement322386
Node: Next Statement324284
Node: Nextfile Statement326552
Node: Exit Statement329128
Node: Built-in Variables331183
Node: User-modified332275
Ref: User-modified-Footnote-1339515
Node: Auto-set339574
Ref: Auto-set-Footnote-1347911
Node: ARGC and ARGV348113
Node: Arrays351807
Node: Array Intro353709
Node: Reference to Elements357883
Node: Assigning Elements359738
Node: Array Example360205
Node: Scanning an Array361921
Node: Delete364182
Ref: Delete-Footnote-1366534
Node: Numeric Array Subscripts366588
Node: Uninitialized Subscripts368766
Node: Multi-dimensional370357
Node: Multi-scanning373353
Node: Array Sorting374962
Node: Functions378599
Node: Built-in379331
Node: Calling Built-in380301
Node: Numeric Functions382256
Ref: Numeric Functions-Footnote-1385995
Ref: Numeric Functions-Footnote-2386318
Node: String Functions386584
Ref: String Functions-Footnote-1406443
Ref: String Functions-Footnote-2406569
Ref: String Functions-Footnote-3406813
Node: Gory Details406897
Ref: table-sub-escapes408523
Ref: table-sub-posix-92409858
Ref: table-sub-proposed411197
Ref: table-posix-2001-sub412550
Ref: table-gensub-escapes413887
Ref: Gory Details-Footnote-1415070
Node: I/O Functions415118
Ref: I/O Functions-Footnote-1421680
Node: Time Functions421768
Ref: Time Functions-Footnote-1432452
Ref: Time Functions-Footnote-2432517
Ref: Time Functions-Footnote-3432672
Ref: Time Functions-Footnote-4432780
Ref: Time Functions-Footnote-5432902
Ref: Time Functions-Footnote-6433126
Node: Bitwise Functions433385
Ref: table-bitwise-ops433960
Ref: Bitwise Functions-Footnote-1438182
Node: I18N Functions438363
Node: User-defined440086
Node: Definition Syntax440867
Node: Function Example445193
Node: Function Caveats447758
Node: Return Statement451662
Node: Dynamic Typing454301
Node: Internationalization455035
Node: I18N and L10N456451
Node: Explaining gettext457135
Ref: Explaining gettext-Footnote-1462023
Ref: Explaining gettext-Footnote-2462259
Node: Programmer i18n462425
Node: Translator i18n466642
Node: String Extraction467429
Ref: String Extraction-Footnote-1468373
Node: Printf Ordering468496
Ref: Printf Ordering-Footnote-1471248
Node: I18N Portability471309
Ref: I18N Portability-Footnote-1473733
Node: I18N Example473793
Ref: I18N Example-Footnote-1476385
Node: Gawk I18N476454
Node: Advanced Features477033
Node: Nondecimal Data478427
Node: Two-way I/O479977
Ref: Two-way I/O-Footnote-1485426
Node: TCP/IP Networking485500
Node: Portal Files487911
Node: Profiling488552
Node: Invoking Gawk496068
Node: Command Line497245
Node: Options498024
Ref: Options-Footnote-1510187
Node: Other Arguments510209
Node: AWKPATH Variable512869
Ref: AWKPATH Variable-Footnote-1515626
Node: Obsolete515883
Node: Undocumented516877
Node: Known Bugs517136
Node: Library Functions517738
Ref: Library Functions-Footnote-1520692
Node: Library Names520860
Ref: Library Names-Footnote-1524307
Ref: Library Names-Footnote-2524523
Node: General Functions524606
Node: Nextfile Function525665
Node: Strtonum Function530004
Node: Assert Function532926
Node: Round Function536212
Node: Cliff Random Function537719
Ref: Cliff Random Function-Footnote-1538702
Node: Ordinal Functions538770
Ref: Ordinal Functions-Footnote-1541818
Node: Join Function542031
Ref: Join Function-Footnote-1543782
Node: Gettimeofday Function543979
Node: Data File Management547676
Node: Filetrans Function548308
Node: Rewind Function551716
Node: File Checking553153
Node: Empty Files554201
Node: Ignoring Assigns556408
Node: Getopt Function557944
Ref: Getopt Function-Footnote-1568908
Node: Passwd Functions569106
Ref: Passwd Functions-Footnote-1577714
Node: Group Functions577799
Node: Sample Programs585738
Node: Running Examples586412
Node: Clones587134
Node: Cut Program588260
Node: Egrep Program597933
Ref: Egrep Program-Footnote-1605635
Node: Id Program605742
Node: Split Program609332
Node: Tee Program612780
Node: Uniq Program615442
Node: Wc Program622780
Ref: Wc Program-Footnote-1626994
Node: Miscellaneous Programs627187
Node: Dupword Program628183
Node: Alarm Program630205
Node: Translate Program634730
Ref: Translate Program-Footnote-1638949
Ref: Translate Program-Footnote-2639183
Node: Labels Program639314
Ref: Labels Program-Footnote-1642587
Node: Word Sorting642668
Node: History Sorting646931
Node: Extract Program648757
Node: Simple Sed656078
Node: Igawk Program659112
Ref: Igawk Program-Footnote-1673741
Ref: Igawk Program-Footnote-2673939
Node: Language History674074
Node: V7/SVR3.1675458
Node: SVR4677538
Node: POSIX678977
Node: BTL680484
Node: POSIX/GNU682006
Node: Contributors689379
Node: Installation692822
Node: Gawk Distribution693793
Node: Getting694277
Node: Extracting695508
Node: Distribution contents696890
Node: Unix Installation701971
Node: Quick Installation702562
Node: Additional Configuration Options704253
Node: Configuration Philosophy706001
Node: Non-Unix Installation708349
Node: Amiga Installation708936
Node: BeOS Installation710023
Node: PC Installation711164
Node: PC Binary Installation712391
Node: PC Compiling714222
Node: PC Dynamic718742
Node: PC Using721088
Node: Cygwin725682
Ref: Cygwin-Footnote-1726674
Node: VMS Installation726703
Node: VMS Compilation727231
Node: VMS Installation Details728802
Node: VMS Running730426
Node: VMS POSIX732015
Node: Unsupported733286
Node: Atari Installation733689
Node: Atari Compiling734972
Node: Atari Using736844
Node: Tandem Installation739677
Node: Bugs741342
Node: Other Versions744605
Ref: Other Versions-Footnote-1748206
Node: Notes748245
Node: Compatibility Mode748937
Node: Additions749725
Node: Adding Code750472
Node: New Ports756519
Node: Dynamic Extensions760574
Node: Internals761821
Node: Sample Library772806
Node: Internal File Description773465
Node: Internal File Ops777146
Ref: Internal File Ops-Footnote-1782436
Node: Using Internal File Ops782581
Node: Future Extensions784598
Node: Basic Concepts788534
Node: Basic High Level789291
Ref: Basic High Level-Footnote-1793302
Node: Basic Data Typing793493
Node: Floating Point Issues797895
Ref: Floating Point Issues-Footnote-1801748
Ref: Floating Point Issues-Footnote-2801798
Node: Glossary801904
Node: Copying825513
Node: GNU Free Documentation License844649
Node: Index867040

End Tag Table
