gawk: This Manual
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 how to write programs in 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,
it notes any 'gawk' features that are not in the POSIX standard for
'awk'.
There are sidebars 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 "sidebar."
Most of the time, the examples use complete 'awk' programs. Some of
the more advanced minor nodes show only the part of the 'awk' program
that illustrates the concept being described.
Although 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 
Library Functions, and
in Sample Programs, should be of interest.
This Info file is split into several parts, as follows:
* Part I describes the 'awk' language and the 'gawk' program in
detail. It starts with the basics, and continues through all of
the features of 'awk'. It contains the following chapters:
- Getting Started, provides the essentials you need to
know to begin using 'awk'.
- Invoking Gawk, describes how to run 'gawk', the
meaning of its command-line options, and how it finds 'awk'
program source files.
- 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. Network I/O is also briefly introduced 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 predefined variables 'awk' and
'gawk' use.
- Arrays, covers 'awk''s one-and-only data structure:
the associative array. Deleting array elements and whole
arrays is described, as well as sorting arrays in 'gawk'. The
major node also describes how 'gawk' provides arrays of
arrays.
- Functions, describes the built-in functions 'awk' and
'gawk' provide, as well as how to define your own functions.
It also discusses how 'gawk' lets you call functions
indirectly.
* Part II shows how to use 'awk' and 'gawk' for problem solving.
There is lots of code here for you to read and learn from. This
part contains the following chapters:
- Library Functions, provides a number of functions
meant to be used from main 'awk' programs.
- Sample Programs, provides many sample 'awk' programs.
Reading these two chapters allows you to see 'awk' solving real
problems.
* Part III focuses on features specific to 'gawk'. It contains the
following chapters:
- Advanced Features, describes a number of advanced
features. Of particular note are the abilities to control the
order of array traversal, have two-way communications with
another process, perform TCP/IP networking, and profile your
'awk' programs.
- Internationalization, describes special features for
translating program messages into different languages at
runtime.
- Debugger, describes the 'gawk' debugger.
- Arbitrary Precision Arithmetic, describes advanced
arithmetic facilities.
- Dynamic Extensions, describes how to add new variables
and functions to 'gawk' by writing extensions in C or C++.
* Part IV provides the appendices, the Glossary, and two licenses
that cover the 'gawk' source code and this Info file, respectively.
It contains the following appendices:
- Language History, describes how the 'awk' language has
evolved since its first release to the present. It also
describes how 'gawk' has acquired features over time.
- Installation, describes how to get 'gawk', how to
compile it on POSIX-compatible systems, and how to compile and
use it on different non-POSIX systems. It also describes how
to report bugs in 'gawk' and where to get other freely
available 'awk' implementations.
- Notes, describes how to disable 'gawk''s extensions,
as well as how to contribute new code to 'gawk', 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.
The Glossary, defines most, if not all, of the
significant terms used throughout the Info file. 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 Info file, respectively.
---------- Footnotes ----------
(1) All such differences appear in the index under the entry
"differences in 'awk' and 'gawk'."
Info Catalog
gawk: Names
gawk: Preface
gawk: Conventions