gawk.texi

早期freebsd实现

\input texinfo   @c -*-texinfo-*-
@c %**start of header (This is for running Texinfo on a region.)
@setfilename gawk.info
@settitle The GAWK Manual
@c @smallbook
@c %**end of header (This is for running Texinfo on a region.)

@ifinfo
@synindex fn cp
@synindex vr cp
@end ifinfo
@iftex
@syncodeindex fn cp
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@c If "finalout" is commented out, the printed output will show
@c black boxes that mark lines that are too long.  Thus, it is
@c unwise to comment it out when running a master in case there are
@c overfulls which are deemed okay.

@iftex
@finalout
@end iftex

@c ===> NOTE! <==
@c Determine the edition number in *four* places by hand:
@c   1. First ifinfo section  2. title page  3. copyright page 4. top node
@c To find the locations, search for !!set

@ifinfo
This file documents @code{awk}, a program that you can use to select
particular records in a file and perform operations upon them.

This is Edition 0.15 of @cite{The GAWK Manual}, @*
for the 2.15 version of the GNU implementation @*
of AWK.

Copyright (C) 1989, 1991, 1992, 1993 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

@ignore
Permission is granted to process this file through TeX and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).

@end ignore
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the Foundation.
@end ifinfo

@setchapternewpage odd

@c !!set edition, date, version
@titlepage
@title The GAWK Manual
@subtitle Edition 0.15
@subtitle April 1993
@author Diane Barlow Close
@author Arnold D. Robbins
@author Paul H. Rubin
@author Richard Stallman

@c Include the Distribution inside the titlepage environment so
@c that headings are turned off.  Headings on and off do not work.

@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1989, 1991, 1992, 1993 Free Software Foundation, Inc.
@sp 2
        
@c !!set edition, date, version
This is Edition 0.15 of @cite{The GAWK Manual}, @*
for the 2.15 version of the GNU implementation @*
of AWK.

@sp 2
Published by the Free Software Foundation @*
675 Massachusetts Avenue @*
Cambridge, MA 02139 USA @*
Printed copies are available for $20 each.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the Foundation.
@end titlepage

@ifinfo
@node Top, Preface, (dir), (dir)
@comment  node-name,  next,  previous,  up
@top General Introduction
@c Preface or Licensing nodes should come right after the Top
@c node, in `unnumbered' sections, then the chapter, `What is gawk'.

This file documents @code{awk}, a program that you can use to select
particular records in a file and perform operations upon them.

@c !!set edition, date, version
This is Edition 0.15 of @cite{The GAWK Manual}, @*
for the 2.15 version of the GNU implementation @*
of AWK.

@end ifinfo

@menu
* Preface::                     What you can do with @code{awk}; brief history
                                and acknowledgements.
* Copying::                     Your right to copy and distribute @code{gawk}.
* This Manual::                 Using this manual. 
                                Includes sample input files that you can use.
* Getting Started::             A basic introduction to using @code{awk}.
                                How to run an @code{awk} program.  
                                Command line syntax.
* Reading Files::               How to read files and manipulate fields.
* Printing::                    How to print using @code{awk}.  Describes the
                                @code{print} and @code{printf} statements.  
                                Also describes redirection of output.
* One-liners::                  Short, sample @code{awk} programs.
* Patterns::                    The various types of patterns 
                                explained in detail.
* Actions::                     The various types of actions are
                                introduced here.  Describes
                                expressions and the various operators in
                                detail.  Also describes comparison expressions.
* Expressions::                 Expressions are the basic building
                                blocks of statements.
* Statements::                  The various control statements are 
                                described in detail.
* Arrays::                      The description and use of arrays.  
                                Also includes array-oriented control 
                                statements.
* Built-in::                    The built-in functions are summarized here.
* User-defined::                User-defined functions are described in detail.
* Built-in Variables::          Built-in Variables
* Command Line::                How to run @code{gawk}.
* Language History::            The evolution of the @code{awk} language.
* Installation::                Installing @code{gawk} under 
                                various operating systems.
* Gawk Summary::                @code{gawk} Options and Language Summary.
* Sample Program::              A sample @code{awk} program with a 
                                complete explanation.
* Bugs::                        Reporting Problems and Bugs.
* Notes::                       Something about the 
                                implementation of @code{gawk}.
* Glossary::                    An explanation of some unfamiliar terms.
* Index::                       
@end menu

@node Preface, Copying, Top, Top
@comment  node-name,  next,  previous,  up
@unnumbered Preface

@iftex
@cindex what is @code{awk}
@end iftex
If you are like many computer users, you would frequently like to make
changes in various text files wherever certain patterns appear, or
extract data from parts of certain lines while discarding the rest.  To
write a program to do this in a language such as C or Pascal is a
time-consuming inconvenience that may take many lines of code.  The job
may be easier with @code{awk}.

The @code{awk} utility interprets a special-purpose programming language
that makes it possible to handle simple data-reformatting jobs easily
with just a few lines of code.

The GNU implementation of @code{awk} is called @code{gawk}; it is fully
upward compatible with the System V Release 4 version of
@code{awk}.  @code{gawk} is also upward compatible with the @sc{posix}
(draft) specification of the @code{awk} language.  This means that all
properly written @code{awk} programs should work with @code{gawk}.
Thus, we usually don't distinguish between @code{gawk} and other @code{awk}
implementations in this manual.@refill

@cindex uses of @code{awk}
This manual teaches you what @code{awk} does and how you can use
@code{awk} effectively.  You should already be familiar with basic
system commands such as @code{ls}.  Using @code{awk} you can: @refill

@itemize @bullet
@item
manage small, personal databases

@item
generate reports

@item
validate data
@item
produce indexes, and perform other document preparation tasks

@item
even experiment with algorithms that can be adapted later to other computer
languages
@end itemize

@iftex
This manual has the difficult task of being both tutorial and 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 on-line Info version of the manual.
@end iftex

@menu
* History::                     The history of @code{gawk} and
                                @code{awk}.  Acknowledgements.
@end menu

@node History,  , Preface, Preface
@comment  node-name,  next,  previous,  up
@unnumberedsec History of @code{awk} and @code{gawk}

@cindex acronym
@cindex history of @code{awk}
The name @code{awk} comes from the initials of its designers: Alfred V.
Aho, Peter J. Weinberger, and Brian W. Kernighan.  The original version of
@code{awk} was written in 1977.  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 generally available with System V Release 3.1.
The version in System V Release 4 added some new features and also cleaned
up the behavior in some of the ``dark corners'' of the language.
The specification for @code{awk} in the @sc{posix} Command Language
and Utilities standard further clarified the language based on feedback
from both the @code{gawk} designers, and the original @code{awk}
designers.@refill

The GNU implementation, @code{gawk}, was written in 1986 by Paul Rubin
and Jay Fenlason, with advice from Richard Stallman.  John Woods
contributed parts of the code as well.  In 1988 and 1989, David Trueman, with
help from Arnold Robbins, thoroughly reworked @code{gawk} for compatibility
with the newer @code{awk}.  Current development (1992) focuses on bug fixes,
performance improvements, and standards compliance.

We need to thank many people for their assistance in producing this
manual.  Jay Fenlason contributed many ideas and sample programs.  Richard
Mlynarik and Robert J. Chassell gave helpful comments on early drafts of this
manual.  The paper @cite{A Supplemental Document for @code{awk}} by John W.
Pierce of the Chemistry Department at UC San Diego, pinpointed several
issues relevant both to @code{awk} implementation and to this manual, that
would otherwise have escaped us.  David Trueman, Pat Rankin, and Michal
Jaegermann also contributed sections of the manual.@refill

The following people provided many helpful comments on this edition of
the manual: Rick Adams, Michael Brennan, Rich Burridge, Diane Close,
Christopher (``Topher'') Eliot, Michael Lijewski, Pat Rankin, Miriam Robbins,
and Michal Jaegermann.  Robert J. Chassell provided much valuable advice on
the use of Texinfo.

Finally, we would like to thank Brian Kernighan of Bell Labs for invaluable
assistance during the testing and debugging of @code{gawk}, and for
help in clarifying numerous points about the language.@refill

@node Copying, This Manual, Preface, Top
@unnumbered GNU GENERAL PUBLIC LICENSE
@center Version 2, June 1991

@display
Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc.
675 Mass Ave, Cambridge, MA 02139, USA

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
@end display

@c fakenode --- for prepinfo
@unnumberedsec 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