This file documents awk, a program that you can use to select particular records in a file and perform operations upon them.
Copyright © 1989, 1991, 1992, 1993, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2007 Free Software Foundation, Inc.
This is Edition 3 of GAWK: Effective AWK Programming: A User's Guide for GNU Awk, for the 3.1.6 (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”.
getline
getline with No Arguments
getline into a Variable
getline from a File
getline into a Variable from a File
getline from a Pipe
getline into a Variable from a Pipe
getline from a Coprocess
getline into a Variable from a Coprocess
getline
getline Variants
delete Statement
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
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.
In addition, gawk provides facilities that make it easy to:
This Web page 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 Web page, 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.
1 part egrep | 1 part snobol
| |
2 parts ed | 3 parts C
|
Blend all parts well usinglexandyacc. Document minimally and release.After eight years, add another part
egrepand 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, Jürgen 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.
See Contributors, for a complete list of those who made important contributions to gawk.
The awk language has evolved over the years. Full details are provided in Language History. The language described in this Web page 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.2
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 Web page, chances are good that you have gawk!)
Throughout this Web page, 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.
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 Web page 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 Web page 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.3 Finally, any gawk features that are not in the POSIX standard for awk are noted.
This Web page has the difficult task of being both a tutorial and a reference. If you are a novice, feel free to skip over details that seem too complex. You should also ignore the many cross-references; they are for the expert user and for the online Info version of the document.
There are subsections labelled as Advanced Notes scattered throughout the Web page. 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 Web page 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 Library Functions, and in Sample Programs, should be of interest.
Getting Started, provides the essentials you need to know to begin using awk.
Regexp, introduces regular expressions in general, and in particular the flavors supported by POSIX awk and gawk.
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.
Printing,
describes how awk programs can produce output with
print and printf.
Expressions, describes expressions, which are the basic building blocks for getting most things done in a program.
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.
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.
Functions, describes the built-in functions awk and gawk provide, as well as how to define your own functions.
Internationalization, describes special features in gawk for translating program messages into different languages at runtime.
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.
Invoking Gawk, describes how to run gawk, the meaning of its command-line options, and how it finds awk program source files.
Library Functions, and Sample Programs, provide many sample awk programs. Reading them allows you to see awk solving real problems.
Language History, describes how the awk language has evolved since first release to present. It also describes how gawk has acquired features over time.
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.
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.
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 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.
Copying, and GNU Free Documentation License, present the licenses that cover the gawk source code and this Web page, respectively.
This Web page 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. Because of this, the typographical conventions are slightly different than in other books you may have read.
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
In the text, command names appear in this font, while code segments
appear in the same font and quoted, ‘like this’. Some things are
emphasized like this, and if a point needs to be made
strongly, it is done like this. The first occurrence of
a new term is usually its definition and appears in the same
font as the previous occurrence of “definition” in this sentence.
file names are indicated like this: /path/to/ourfile.
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 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 Web page 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.
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 GNU4 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 in this Web page for your reference (see 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. This Web page may also be read from their web site.
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.5 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 Web page you are reading is actually free—at least, the information in it is free to anyone. The machine-readable source code for the Web page comes with gawk; anyone may take this Web page to a copying machine and make as many copies as they like. (Take a moment to check the Free Documentation License in GNU Free Documentation License.)
Although you could just print it out yourself, bound books are much easier to read and use. Furthermore, the proceeds from sales of this book go back to the FSF to help fund development of more free software.
The Web page 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 Array Sorting, as well as Bitwise Functions, Internationalization, and also Advanced Features, and 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 Web page, please report it! See Bugs, for information on submitting problem reports electronically, or write to me in care of the publisher.
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.
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 Web page 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 Web page 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, Jürgen 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 Web page 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
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. See 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 }
...
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 section discusses both mechanisms, along with several variations of each.
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.
Very Simple, later in this chapter, presents several short, self-contained programs.
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.6
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
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 (see 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.
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 systems7 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 awk8 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.
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]
(see 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.
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 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