bashref.texi

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@setfilename bashref.info
@settitle Bash Reference Manual
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@include version.texi

@copying
This text is a brief description of the features that are present in
the Bash shell (version @value{VERSION}, @value{UPDATED}).

This is Edition @value{EDITION}, last updated @value{UPDATED},
of @cite{The GNU Bash Reference Manual},
for @code{Bash}, Version @value{VERSION}.

Copyright @copyright{} 1988--2011 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.

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover texts being ``A GNU Manual'',
and with the Back-Cover Texts as in (a) below.  A copy of the license is
included in the section entitled ``GNU Free Documentation License''.

(a) The FSF's Back-Cover Text is: You are free to copy and modify
this GNU manual.  Buying copies from GNU Press supports the FSF in
developing GNU and promoting software freedom.''

@end quotation
@end copying

@defcodeindex bt
@defcodeindex rw
@set BashFeatures

@dircategory Basics
@direntry
* Bash: (bash).                     The GNU Bourne-Again SHell.
@end direntry

@finalout

@titlepage
@title Bash Reference Manual
@subtitle Reference Documentation for Bash
@subtitle Edition @value{EDITION}, for @code{Bash} Version @value{VERSION}.
@subtitle @value{UPDATED-MONTH}
@author Chet Ramey, Case Western Reserve University
@author Brian Fox, Free Software Foundation

@page
@vskip 0pt plus 1filll
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@sp 1
Published by the Free Software Foundation @*
59 Temple Place, Suite 330, @*
Boston, MA 02111-1307 @*
USA @*

@end titlepage

@contents

@ifnottex
@node Top, Introduction, (dir), (dir)
@top Bash Features

This text is a brief description of the features that are present in
the Bash shell (version @value{VERSION}, @value{UPDATED}).

This is Edition @value{EDITION}, last updated @value{UPDATED},
of @cite{The GNU Bash Reference Manual},
for @code{Bash}, Version @value{VERSION}.

Bash contains features that appear in other popular shells, and some
features that only appear in Bash.  Some of the shells that Bash has
borrowed concepts from are the Bourne Shell (@file{sh}), the Korn Shell
(@file{ksh}), and the C-shell (@file{csh} and its successor,
@file{tcsh}). The following menu breaks the features up into
categories based upon which one of these other shells inspired the
feature.

This manual is meant as a brief introduction to features found in
Bash.  The Bash manual page should be used as the definitive
reference on shell behavior.

@menu
* Introduction::		An introduction to the shell.
* Definitions::			Some definitions used in the rest of this
				manual.
* Basic Shell Features::	The shell "building blocks".
* Shell Builtin Commands::	Commands that are a part of the shell.
* Shell Variables::		Variables used or set by Bash.
* Bash Features::		Features found only in Bash.
* Job Control::			What job control is and how Bash allows you
				to use it.
* Command Line Editing::	Chapter describing the command line
				editing features.
* Using History Interactively::	Command History Expansion
* Installing Bash::		How to build and install Bash on your system.
* Reporting Bugs::		How to report bugs in Bash.
* Major Differences From The Bourne Shell::	A terse list of the differences
						between Bash and historical
						versions of /bin/sh.
* GNU Free Documentation License::	Copying and sharing this documentation.
* Indexes::			Various indexes for this manual.
@end menu
@end ifnottex

@node Introduction
@chapter Introduction
@menu
* What is Bash?::		A short description of Bash.
* What is a shell?::		A brief introduction to shells.
@end menu

@node What is Bash?
@section What is Bash?

Bash is the shell, or command language interpreter,
for the @sc{gnu} operating system.
The name is an acronym for the @samp{Bourne-Again SHell},
a pun on Stephen Bourne, the author of the direct ancestor of
the current Unix shell @code{sh}, 
which appeared in the Seventh Edition Bell Labs Research version
of Unix.

Bash is largely compatible with @code{sh} and incorporates useful
features from the Korn shell @code{ksh} and the C shell @code{csh}.
It is intended to be a conformant implementation of the @sc{ieee}
@sc{posix} Shell and Tools portion of the @sc{ieee} @sc{posix}
specification (@sc{ieee} Standard 1003.1).
It offers functional improvements over @code{sh} for both interactive and
programming use.

While the @sc{gnu} operating system provides other shells, including
a version of @code{csh}, Bash is the default shell.
Like other @sc{gnu} software, Bash is quite portable.  It currently runs
on nearly every version of Unix and a few other operating systems @minus{}
independently-supported ports exist for @sc{ms-dos}, @sc{os/2},
and Windows platforms.

@node What is a shell?
@section What is a shell?

At its base, a shell is simply a macro processor that executes
commands.  The term macro processor means functionality where text
and symbols are expanded to create larger expressions.

A Unix shell is both a command interpreter and a programming
language.  As a command interpreter, the shell provides the user
interface to the rich set of @sc{gnu} utilities.  The programming
language features allow these utilities to be combined.
Files containing commands can be created, and become
commands themselves.  These new commands have the same status as
system commands in directories such as @file{/bin}, allowing users
or groups to establish custom environments to automate their common
tasks.

Shells may be used interactively or non-interactively.  In
interactive mode, they accept input typed from the keyboard.
When executing non-interactively, shells execute commands read
from a file.

A shell allows execution of @sc{gnu} commands, both synchronously and
asynchronously.
The shell waits for synchronous commands to complete before accepting
more input; asynchronous commands continue to execute in parallel
with the shell while it reads and executes additional commands.
The @dfn{redirection} constructs permit
fine-grained control of the input and output of those commands.
Moreover, the shell allows control over the contents of commands'
environments.

Shells also provide a small set of built-in
commands (@dfn{builtins}) implementing functionality impossible
or inconvenient to obtain via separate utilities.
For example, @code{cd}, @code{break}, @code{continue}, and
@code{exec}) cannot be implemented outside of the shell because
they directly manipulate the shell itself.
The @code{history}, @code{getopts}, @code{kill}, or @code{pwd}
builtins, among others, could be implemented in separate utilities,
but they are more convenient to use as builtin commands.
All of the shell builtins are described in
subsequent sections.

While executing commands is essential, most of the power (and
complexity) of shells is due to their embedded programming
languages.  Like any high-level language, the shell provides
variables, flow control constructs, quoting, and functions. 

Shells offer features geared specifically for
interactive use rather than to augment the programming language. 
These interactive features include job control, command line
editing, command history and aliases.  Each of these features is
described in this manual.

@node Definitions
@chapter Definitions
These definitions are used throughout the remainder of this manual.

@table @code

@item POSIX
@cindex POSIX
A family of open system standards based on Unix.  Bash
is primarily concerned with the Shell and Utilities portion of the
@sc{posix} 1003.1 standard. 

@item blank
A space or tab character.

@item builtin
@cindex builtin
A command that is implemented internally by the shell itself, rather
than by an executable program somewhere in the file system.

@item control operator
@cindex control operator
A @code{token} that performs a control function.  It is a @code{newline}
or one of the following:
@samp{||}, @samp{&&}, @samp{&}, @samp{;}, @samp{;;},
@samp{|}, @samp{|&}, @samp{(}, or @samp{)}.

@item exit status
@cindex exit status
The value returned by a command to its caller.  The value is restricted
to eight bits, so the maximum value is 255.

@item field
@cindex field
A unit of text that is the result of one of the shell expansions.  After
expansion, when executing a command, the resulting fields are used as
the command name and arguments.

@item filename
@cindex filename
A string of characters used to identify a file.

@item job
@cindex job
A set of processes comprising a pipeline, and any processes descended
from it, that are all in the same process group.

@item job control
@cindex job control
A mechanism by which users can selectively stop (suspend) and restart
(resume) execution of processes.

@item metacharacter
@cindex metacharacter
A character that, when unquoted, separates words.  A metacharacter is
a @code{blank} or one of the following characters:
@samp{|}, @samp{&}, @samp{;}, @samp{(}, @samp{)}, @samp{<}, or
@samp{>}.

@item name
@cindex name
@cindex identifier
A @code{word} consisting solely of letters, numbers, and underscores,
and beginning with a letter or underscore.  @code{Name}s are used as
shell variable and function names.
Also referred to as an @code{identifier}.

@item operator
@cindex operator, shell
A @code{control operator} or a @code{redirection operator}.
@xref{Redirections}, for a list of redirection operators.
Operators contain at least one unquoted @code{metacharacter}.

@item process group
@cindex process group
A collection of related processes each having the same process
group @sc{id}.

@item process group ID
@cindex process group ID
A unique identifier that represents a @code{process group}
during its lifetime.

@item reserved word
@cindex reserved word
A @code{word} that has a special meaning to the shell.  Most reserved
words introduce shell flow control constructs, such as @code{for} and
@code{while}.

@item return status
@cindex return status
A synonym for @code{exit status}.

@item signal
@cindex signal
A mechanism by which a process may be notified by the kernel
of an event occurring in the system.

@item special builtin
@cindex special builtin
A shell builtin command that has been classified as special by the
@sc{posix} standard.

@item token
@cindex token
A sequence of characters considered a single unit by the shell.
It is either a @code{word} or an @code{operator}.

@item word
@cindex word
A sequence of characters treated as a unit by the shell.
Words may not include unquoted @code{metacharacters}.
@end table

@node Basic Shell Features
@chapter Basic Shell Features
@cindex Bourne shell

Bash is an acronym for @samp{Bourne-Again SHell}.
The Bourne shell is
the traditional Unix shell originally written by Stephen Bourne.
All of the Bourne shell builtin commands are available in Bash,
The rules for evaluation and quoting are taken from the @sc{posix}
specification for the `standard' Unix shell.

This chapter briefly summarizes the shell's `building blocks':
commands, control structures, shell functions, shell @i{parameters},
shell expansions,
@i{redirections}, which are a way to direct input and output from
and to named files, and how the shell executes commands.

@menu
* Shell Syntax::		What your input means to the shell.
* Shell Commands::		The types of commands you can use.
* Shell Functions::		Grouping commands by name.
* Shell Parameters::		How the shell stores values.
* Shell Expansions::		How Bash expands parameters and the various
				expansions available.
* Redirections::		A way to control where input and output go.
* Executing Commands::		What happens when you run a command.
* Shell Scripts::		Executing files of shell commands.
@end menu

@node Shell Syntax
@section Shell Syntax
@menu
* Shell Operation::	The basic operation of the shell.
* Quoting::		How to remove the special meaning from characters.