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This is Info file bashref.info, produced by Makeinfo version 1.67 from
the input file /usr/homes/chet/src/bash/bash-2.01.1/doc/bashref.texi.
INFO-DIR-SECTION Utilities
START-INFO-DIR-ENTRY
* Bash: (bash). GNU Bourne-Again SHell
END-INFO-DIR-ENTRY
This text is a brief description of the features that are present in
the Bash shell.
This is Edition 2.0, last updated 19 May 1997,
of `The GNU Bash Reference Manual',
for `Bash', Version 2.01.
Copyright (C) 1991, 1993, 1996 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.
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.

File: bashref.info, Node: Top, Next: Introduction, Prev: (dir), Up: (dir)
Bash Features
*************
This text is a brief description of the features that are present in
the Bash shell.
This is Edition 2.0, last updated 19 May 1997, of `The GNU Bash
Reference Manual', for `Bash', Version 2.01.
Copyright (C) 1991, 1993, 1996 Free Software Foundation, Inc.
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 (`sh'), the Korn Shell
(`ksh'), and the C-shell (`csh' and its successor, `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".
* Bourne Shell Features:: Features similar to those found in the
Bourne shell.
* Csh Features:: Features originally found in the
Berkeley C-Shell.
* Korn Shell Features:: Features originally found in the Korn
Shell.
* Bash Features:: Features found only in Bash.
* Job Control:: A chapter describing what job control is
and how Bash allows you to use it.
* Using History Interactively:: Chapter dealing with history expansion
rules.
* Command Line Editing:: Chapter describing the command line
editing features.
* Installing Bash:: How to build and install Bash on your system.
* Reporting Bugs:: How to report bugs in Bash.
* Builtin Index:: Index of Bash builtin commands.
* Reserved Word Index:: Index of Bash reserved words.
* Variable Index:: Quick reference helps you find the
variable you want.
* Function Index:: Index of bindable Readline functions.
* Concept Index:: General index for concepts described in
this manual.

File: bashref.info, Node: Introduction, Next: Definitions, Prev: Top, Up: Top
Introduction
************
* Menu:
* What is Bash?:: A short description of Bash.
* What is a shell?:: A brief introduction to shells.

File: bashref.info, Node: What is Bash?, Next: What is a shell?, Up: Introduction
What is Bash?
=============
Bash is the shell, or command language interpreter, that will appear
in the GNU operating system. The name is an acronym for the
`Bourne-Again SHell', a pun on Steve Bourne, the author of the direct
ancestor of the current Unix shell `/bin/sh', which appeared in the
Seventh Edition Bell Labs Research version of Unix.
Bash is an `sh'-compatible shell that incorporates useful features
from the Korn shell `ksh' and the C shell `csh'. It is ultimately
intended to be a conformant implementation of the IEEE POSIX Shell and
Tools specification (IEEE Working Group 1003.2). It offers functional
improvements over `sh' for both interactive and programming use.
While the GNU operating system will include a version of `csh', Bash
will be the default shell. Like other GNU software, Bash is quite
portable. It currently runs on nearly every version of Unix and a few
other operating systems - independently-supported ports exist for OS/2
and Windows NT.

File: bashref.info, Node: What is a shell?, Prev: What is Bash?, Up: Introduction
What is a shell?
================
At its base, a shell is simply a macro processor that executes
commands. A Unix shell is both a command interpreter, which provides
the user interface to the rich set of Unix utilities, and a programming
language, allowing these utilitites to be combined. The shell reads
commands either from a terminal or a file. Files containing commands
can be created, and become commands themselves. These new commands
have the same status as system commands in directories like `/bin',
allowing users or groups to establish custom environments.
A shell allows execution of Unix commands, both synchronously and
asynchronously. The "redirection" constructs permit fine-grained
control of the input and output of those commands, and the shell allows
control over the contents of their environment. Unix shells also
provide a small set of built-in commands ("builtins") implementing
functionality impossible (e.g., `cd', `break', `continue', and `exec'),
or inconvenient (`history', `getopts', `kill', or `pwd', for example)
to obtain via separate utilities. Shells may be used interactively or
non-interactively: they accept input typed from the keyboard or from a
file. 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 have begun offering features geared specifically for
interactive use rather than to augment the programming language. These
interactive features include job control, command line editing, history
and aliases. Each of these features is described in this manual.

File: bashref.info, Node: Definitions, Next: Basic Shell Features, Prev: Introduction, Up: Top
Definitions
***********
These definitions are used throughout the remainder of this manual.
`POSIX'
A family of open system standards based on Unix. Bash is
concerned with POSIX 1003.2, the Shell and Tools Standard.
`blank'
A space or tab character.
`builtin'
A command that is implemented internally by the shell itself,
rather than by an executable program somewhere in the file system.
`control operator'
A `word' that performs a control function. It is a `newline' or
one of the following: `||', `&&', `&', `;', `;;', `|', `(', or `)'.
`exit status'
The value returned by a command to its caller.
`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.
`filename'
A string of characters used to identify a file.
`job'
A set of processes comprising a pipeline, and any processes
descended from it, that are all in the same process group.
`job control'
A mechanism by which users can selectively stop (suspend) and
restart (resume) execution of processes.
`metacharacter'
A character that, when unquoted, separates words. A metacharacter
is a `blank' or one of the following characters: `|', `&', `;',
`(', `)', `<', or `>'.
`name'
A `word' consisting solely of letters, numbers, and underscores,
and beginning with a letter or underscore. `Name's are used as
shell variable and function names. Also referred to as an
`identifier'.
`operator'
A `control operator' or a `redirection operator'. *Note
Redirections::, for a list of redirection operators.
`process group'
A collection of related processes each having the same process
group ID.
`process group ID'
A unique identifer that represents a `process group' during its
lifetime.
`reserved word'
A `word' that has a special meaning to the shell. Most reserved
words introduce shell flow control constructs, such as `for' and
`while'.
`return status'
A synonym for `exit status'.
`signal'
A mechanism by which a process may be notified by the kernal of an
event occurring in the system.
`special builtin'
A shell builtin command that has been classified as special by the
POSIX.2 standard.
`token'
A sequence of characters considered a single unit by the shell.
It is either a `word' or an `operator'.
`word'
A `token' that is not an `operator'.

File: bashref.info, Node: Basic Shell Features, Next: Bourne Shell Features, Prev: Definitions, Up: Top
Basic Shell Features
********************
Bash is an acronym for `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, and the
rules for evaluation and quoting are taken from the POSIX 1003.2
specification for the `standard' Unix shell.
This chapter briefly summarizes the shell's "building blocks":
commands, control structures, shell functions, shell parameters, shell
expansions, 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.
* Simple Commands:: The most common type of command.
* Pipelines:: Connecting the input and output of several
commands.
* Lists:: How to execute commands sequentially.
* Looping Constructs:: Shell commands for iterative action.
* Conditional Constructs:: Shell commands for conditional execution.
* Command Grouping:: Ways to group commands.
* Shell Functions:: Grouping commands by name.
* Shell Parameters:: Special shell variables.
* Shell Expansions:: How Bash expands variables 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.

File: bashref.info, Node: Shell Syntax, Next: Simple Commands, Up: Basic Shell Features
Shell Syntax
============
* Menu:
* Shell Operation:: The basic operation of the shell.
* Quoting:: How to remove the special meaning from characters.
* Comments:: How to specify comments.

File: bashref.info, Node: Shell Operation, Next: Quoting, Up: Shell Syntax
Shell Operation
---------------
The following is a brief description of the shell's operation when it
reads and executes a command. Basically, the shell does the following:
1. Reads its input from a file (*note Shell Scripts::.), from a string
supplied as an argument to the `-c' invocation option (*note
Invoking Bash::.), or from the user's terminal.
2. Breaks the input into words and operators, obeying the quoting
rules described in *Note Quoting::. Tokens are separated by
`metacharacters'. Alias expansion is performed by this step
(*note Aliases::.).
3. Parses the tokens into simple and compound commands.
4. Performs the various shell expansions (*note Shell Expansions::.),
breaking the expanded tokens into lists of filenames (*note
Filename Expansion::.) and commands and arguments.
5. Performs any necessary redirections (*note Redirections::.) and
removes the redirection operators and their operands from the
argument list.
6. Executes the command (*note Executing Commands::.).
7. Optionally waits for the command to complete and collects its exit
status.

File: bashref.info, Node: Quoting, Next: Comments, Prev: Shell Operation, Up: Shell Syntax
Quoting
-------
* Menu:
* Escape Character:: How to remove the special meaning from a single
character.
* Single Quotes:: How to inhibit all interpretation of a sequence
of characters.
* Double Quotes:: How to suppress most of the interpretation of a
sequence of characters.
* ANSI-C Quoting:: How to expand ANSI-C sequences in quoted strings.
* Locale Translation:: How to translate strings into different languages.
Quoting is used to remove the special meaning of certain characters
or words to the shell. Quoting can be used to disable special
treatment for special characters, to prevent reserved words from being
recognized as such, and to prevent parameter expansion.
Each of the shell `metacharacters' (*note Definitions::.) has
special meaning to the shell and must be quoted if they are to
represent themselves. There are three quoting mechanisms: the ESCAPE
CHARACTER, single quotes, and double quotes.

File: bashref.info, Node: Escape Character, Next: Single Quotes, Up: Quoting
Escape Character
................
A non-quoted backslash `\' is the Bash escape character. It
preserves the literal value of the next character that follows, with
the exception of `newline'. If a `\newline' pair appears, and the
backslash is not quoted, the `\newline' is treated as a line
continuation (that is, it is effectively ignored).

File: bashref.info, Node: Single Quotes, Next: Double Quotes, Prev: Escape Character, Up: Quoting
Single Quotes
.............
Enclosing characters in single quotes preserves the literal value of
each character within the quotes. A single quote may not occur between
single quotes, even when preceded by a backslash.

File: bashref.info, Node: Double Quotes, Next: ANSI-C Quoting, Prev: Single Quotes, Up: Quoting
Double Quotes
.............
Enclosing characters in double quotes preserves the literal value of
all characters within the quotes, with the exception of `$', ``', and
`\'. The characters `$' and ``' retain their special meaning within
double quotes. The backslash retains its special meaning only when
followed by one of the following characters: `$', ``', `"', `\', or
`newline'. A double quote may be quoted within double quotes by
preceding it with a backslash.
The special parameters `*' and `@' have special meaning when in
double quotes (*note Shell Parameter Expansion::.).

File: bashref.info, Node: ANSI-C Quoting, Next: Locale Translation, Prev: Double Quotes, Up: Quoting
ANSI-C Quoting
..............
Words of the form `$'STRING'' are treated specially. The word
expands to STRING, with backslash-escaped characters replaced as
specifed by the ANSI C standard. Backslash escape sequences, if
present, are decoded as follows:
`\a'
alert (bell)
`\b'
backspace
`\e'
an escape character (not ANSI C)
`\f'
form feed
`\n'
newline
`\r'
carriage return
`\t'
horizontal tab
`\v'
vertical tab
`\\'
backslash
`\NNN'
the character whose `ASCII' code is NNN in octal
The result is single-quoted, as if the dollar sign had not been present.

File: bashref.info, Node: Locale Translation, Prev: ANSI-C Quoting, Up: Quoting
Locale-Specific Translation
...........................
A double-quoted string preceded by a dollar sign (`$') will cause
the string to be translated according to the current locale. If the
current locale is `C' or `POSIX', the dollar sign is ignored. If the
string is translated and replaced, the replacement is double-quoted.

File: bashref.info, Node: Comments, Prev: Quoting, Up: Shell Syntax
Comments
--------
In a non-interactive shell, or an interactive shell in which the
`interactive_comments' option to the `shopt' builtin is enabled (*note
Bash Builtins::.), a word beginning with `#' causes that word and all
remaining characters on that line to be ignored. An interactive shell
without the `interactive_comments' option enabled does not allow
comments. The `interactive_comments' option is on by default in
interactive shells.

File: bashref.info, Node: Simple Commands, Next: Pipelines, Prev: Shell Syntax, Up: Basic Shell Features
Simple Commands
===============
A simple command is the kind of command you'll encounter most often.
It's just a sequence of words separated by `blank's, terminated by one
of the shell control operators (*note Definitions::.). The first word
generally specifies a command to be executed.
The return status (*note Exit Status::.) of a simple command is its
exit status as provided by the POSIX.1 `waitpid' function, or 128+N if
the command was terminated by signal N.

File: bashref.info, Node: Pipelines, Next: Lists, Prev: Simple Commands, Up: Basic Shell Features
Pipelines
=========
A `pipeline' is a sequence of simple commands separated by `|'.
The format for a pipeline is
[`time' [`-p']] [`!'] COMMAND1 [`|' COMMAND2 ...]
The output of each command in the pipeline is connected to the input of
the next command. That is, each command reads the previous command's
output.
The reserved word `time' causes timing statistics to be printed for
the pipeline once it finishes. The `-p' option changes the output
format to that specified by POSIX. The `TIMEFORMAT' variable may be
set to a format string that specifies how the timing information should
be displayed. *Note Bash Variables::, for a description of the
available formats.
Each command in a pipeline is executed in its own subshell. The exit
status of a pipeline is the exit status of the last command in the
pipeline. If the reserved word `!' precedes the pipeline, the exit
status is the logical NOT of the exit status of the last command.

File: bashref.info, Node: Lists, Next: Looping Constructs, Prev: Pipelines, Up: Basic Shell Features
Lists of Commands
=================
A `list' is a sequence of one or more pipelines separated by one of
the operators `;', `&', `&&', or `||', and optionally terminated by one
of `;', `&', or a `newline'.
Of these list operators, `&&' and `||' have equal precedence,
followed by `;' and `&', which have equal precedence.
If a command is terminated by the control operator `&', the shell
executes the command in the BACKGROUND in a subshell. The shell does
not wait for the command to finish, and the return status is 0 (true).
Commands separated by a `;' are executed sequentially; the shell waits
for each command to terminate in turn. The return status is the exit
status of the last command executed.
The control operators `&&' and `||' denote AND lists and OR lists,
respectively. An AND list has the form
COMMAND && COMMAND2
COMMAND2 is executed if, and only if, COMMAND returns an exit status of
zero.
An OR list has the form
COMMAND || COMMAND2
COMMAND2 is executed if and only if COMMAND returns a non-zero exit
status.
The return status of AND and OR lists is the exit status of the last
command executed in the list.

File: bashref.info, Node: Looping Constructs, Next: Conditional Constructs, Prev: Lists, Up: Basic Shell Features
Looping Constructs
==================
Note that wherever you see a `;' in the description of a command's
syntax, it may be replaced indiscriminately with one or more newlines.
Bash supports the following looping constructs.
`until'
The syntax of the `until' command is:
until TEST-COMMANDS; do CONSEQUENT-COMMANDS; done
Execute CONSEQUENT-COMMANDS as long as the final command in
TEST-COMMANDS has an exit status which is not zero.
`while'
The syntax of the `while' command is:
while TEST-COMMANDS; do CONSEQUENT-COMMANDS; done
Execute CONSEQUENT-COMMANDS as long as the final command in
TEST-COMMANDS has an exit status of zero.
`for'
The syntax of the `for' command is:
for NAME [in WORDS ...]; do COMMANDS; done
Execute COMMANDS for each member in WORDS, with NAME bound to the
current member. If `in WORDS' is not present, `in "$@"' is
assumed.
The `break' and `continue' builtins (*note Bourne Shell Builtins::.)
may be used to control loop execution.

File: bashref.info, Node: Conditional Constructs, Next: Command Grouping, Prev: Looping Constructs, Up: Basic Shell Features
Conditional Constructs
======================
`if'
The syntax of the `if' command is:
if TEST-COMMANDS; then
CONSEQUENT-COMMANDS;
[elif MORE-TEST-COMMANDS; then
MORE-CONSEQUENTS;]
[else ALTERNATE-CONSEQUENTS;]
fi
Execute CONSEQUENT-COMMANDS only if the final command in
TEST-COMMANDS has an exit status of zero. Otherwise, each `elif'
list is executed in turn, and if its exit status is zero, the
corresponding MORE-CONSEQUENTS is executed and the command
completes. If `else ALTERNATE-CONSEQUENTS' is present, and the
final command in the final `if' or `elif' clause has a non-zero
exit status, then execute ALTERNATE-CONSEQUENTS.
`case'
The syntax of the `case' command is:
`case WORD in [ ( PATTERN [| PATTERN]...) COMMANDS ;;]... esac'
Selectively execute COMMANDS based upon WORD matching PATTERN.
The `|' is used to separate multiple patterns.
Here is an example using `case' in a script that could be used to
describe one interesting feature of an animal:
echo -n "Enter the name of an animal: "
read ANIMAL
echo -n "The $ANIMAL has "
case $ANIMAL in
horse | dog | cat) echo -n "four";;
man | kangaroo ) echo -n "two";;
*) echo -n "an unknown number of";;
esac
echo " legs."
`((...))'
(( EXPRESSION ))
The EXPRESSION is evaluated according to the rules described below
(*note Arithmetic Evaluation::.). If the value of the expression
is non-zero, the return status is 0; otherwise the return status
is 1. This is exactly equivalent to
let "EXPRESSION"
The `select' construct, which allows users to choose from a list of
items presented as a menu, is also available. *Note Korn Shell
Constructs::, for a full description of `select'.

File: bashref.info, Node: Command Grouping, Next: Shell Functions, Prev: Conditional Constructs, Up: Basic Shell Features
Grouping Commands
=================
Bash provides two ways to group a list of commands to be executed as
a unit. When commands are grouped, redirections may be applied to the
entire command list. For example, the output of all the commands in
the list may be redirected to a single stream.
`()'
( LIST )
Placing a list of commands between parentheses causes a subshell
to be created, and each of the commands to be executed in that
subshell. Since the LIST is executed in a subshell, variable
assignments do not remain in effect after the subshell completes.
`{}'
{ LIST; }
Placing a list of commands between curly braces causes the list to
be executed in the current shell context. No subshell is created.
The semicolon following LIST is required.
In addition to the creation of a subshell, there is a subtle
difference between these two constructs due to historical reasons. The
braces are `reserved words', so they must be separated from the LIST by
`blank's. The parentheses are `operators', and are recognized as
separate tokens by the shell even if they are not separated from the
LIST by whitespace.
The exit status of both of these constructs is the exit status of
LIST.

File: bashref.info, Node: Shell Functions, Next: Shell Parameters, Prev: Command Grouping, Up: Basic Shell Features
Shell Functions
===============
Shell functions are a way to group commands for later execution
using a single name for the group. They are executed just like a
"regular" command. Shell functions are executed in the current shell
context; no new process is created to interpret them.
Functions are declared using this syntax:
[ `function' ] NAME () { COMMAND-LIST; }
This defines a shell function named NAME. The reserved word
`function' is optional. The BODY of the function is the COMMAND-LIST
between { and }. This list is executed whenever NAME is specified as
the name of a command. The exit status of a function is the exit
status of the last command executed in the body.
When a function is executed, the arguments to the function become
the positional parameters during its execution (*note Positional
Parameters::.). The special parameter `#' that expands to the number of
positional parameters is updated to reflect the change. Positional
parameter `0' is unchanged.
If the builtin command `return' is executed in a function, the
function completes and execution resumes with the next command after
the function call. When a function completes, the values of the
positional parameters and the special parameter `#' are restored to the
values they had prior to function execution. If a numeric argument is
given to `return', that is the function return status.
Variables local to the function may be declared with the `local'
builtin. These variables are visible only to the function and the
commands it invokes.
Functions may be recursive. No limit is placed on the number of
recursive calls.

File: bashref.info, Node: Shell Parameters, Next: Shell Expansions, Prev: Shell Functions, Up: Basic Shell Features
Shell Parameters
================
* Menu:
* Positional Parameters:: The shell's command-line arguments.
* Special Parameters:: Parameters with special meanings.
A PARAMETER is an entity that stores values. It can be a `name', a
number, or one of the special characters listed below. For the shell's
purposes, a VARIABLE is a parameter denoted by a `name'.
A parameter is set if it has been assigned a value. The null string
is a valid value. Once a variable is set, it may be unset only by using
the `unset' builtin command.
A variable may be assigned to by a statement of the form
NAME=[VALUE]
If VALUE is not given, the variable is assigned the null string. All
VALUEs undergo tilde expansion, parameter and variable expansion,
command substitution, arithmetic expansion, and quote removal (detailed
below). If the variable has its `-i' attribute set (see the
description of the `declare' builtin in *Note Bash Builtins::), then
VALUE is subject to arithmetic expansion even if the `$((...))' syntax
does not appear (*note Arithmetic Expansion::.). Word splitting is not
performed, with the exception of `"$@"' as explained below. Filename
expansion is not performed.

File: bashref.info, Node: Positional Parameters, Next: Special Parameters, Up: Shell Parameters
Positional Parameters
---------------------
A POSITIONAL PARAMETER is a parameter denoted by one or more digits,
other than the single digit `0'. Positional parameters are assigned
from the shell's arguments when it is invoked, and may be reassigned
using the `set' builtin command. Positional parameters may not be
assigned to with assignment statements. The positional parameters are
temporarily replaced when a shell function is executed (*note Shell
Functions::.).
When a positional parameter consisting of more than a single digit
is expanded, it must be enclosed in braces.

File: bashref.info, Node: Special Parameters, Prev: Positional Parameters, Up: Shell Parameters
Special Parameters
------------------
The shell treats several parameters specially. These parameters may
only be referenced; assignment to them is not allowed.
`*'
Expands to the positional parameters, starting from one. When the
expansion occurs within double quotes, it expands to a single word
with the value of each parameter separated by the first character
of the `IFS' special variable. That is, `"$*"' is equivalent to
`"$1C$2C..."', where C is the first character of the value of the
`IFS' variable. If `IFS' is unset, the parameters are separated
by spaces. If `IFS' is null, the parameters are joined without
intervening separators.
`@'
Expands to the positional parameters, starting from one. When the
expansion occurs within double quotes, each parameter expands as a
separate word. That is, `"$@"' is equivalent to `"$1" "$2" ...'.
When there are no positional parameters, `"$@"' and `$@' expand to
nothing (i.e., they are removed).
`#'
Expands to the number of positional parameters in decimal.
`?'
Expands to the exit status of the most recently executed foreground
pipeline.
`-'
Expands to the current option flags as specified upon invocation,
by the `set' builtin command, or those set by the shell itself
(such as the `-i' option).
`$'
Expands to the process ID of the shell. In a `()' subshell, it
expands to the process ID of the current shell, not the subshell.
`!'
Expands to the process ID of the most recently executed background
(asynchronous) command.
`0'
Expands to the name of the shell or shell script. This is set at
shell initialization. If Bash is invoked with a file of commands,
`$0' is set to the name of that file. If Bash is started with the
`-c' option, then `$0' is set to the first argument after the
string to be executed, if one is present. Otherwise, it is set to
the filename used to invoke Bash, as given by argument zero.
`_'
At shell startup, set to the absolute filename of the shell or
shell script being executed as passed in the argument list.
Subsequently, expands to the last argument to the previous command,
after expansion. Also set to the full filename of each command
executed and placed in the environment exported to that command.
When checking mail, this parameter holds the name of the mail file.

File: bashref.info, Node: Shell Expansions, Next: Redirections, Prev: Shell Parameters, Up: Basic Shell Features
Shell Expansions
================
Expansion is performed on the command line after it has been split
into `token's. There are seven kinds of expansion performed:
* brace expansion
* tilde expansion
* parameter and variable expansion
* command substitution
* arithmetic expansion
* word splitting
* filename expansion
* Menu:
* Shell Parameter Expansion:: How Bash expands variables to their values.
* Command Substitution:: Using the output of a command as an argument.
* Process Substitution:: A way to write and read to and from a
command.
* Word Splitting:: How the results of expansion are split into separate
arguments.
* Filename Expansion:: A shorthand for specifying filenames matching patterns.
* Quote Removal:: How and when quote characters are removed from
words.
Brace expansion, tilde expansion, and arithmetic expansion are
described in other sections. For brace expansion, see *Note Brace
Expansion::; for tilde expansion, see *Note Tilde Expansion::; and for
arithmetic expansion, see *Note Arithmetic Expansion::.
The order of expansions is: brace expansion, tilde expansion,
parameter, variable, and arithmetic expansion and command substitution
(done in a left-to-right fashion), word splitting, and filename
expansion.
On systems that can support it, there is an additional expansion
available: PROCESS SUBSTITUTION. This is performed at the same time as
parameter, variable, and arithemtic expansion and command substitution.
Only brace expansion, word splitting, and filename expansion can
change the number of words of the expansion; other expansions expand a
single word to a single word. The only exceptions to this are the
expansions of `"$@"' (*note Special Parameters::.) and `"${NAME[@]}"'
(*note Arrays::.).
After all expansions, `quote removal' (*note Quote Removal::.) is
performed.

File: bashref.info, Node: Shell Parameter Expansion, Next: Command Substitution, Up: Shell Expansions
Shell Parameter Expansion
-------------------------
The `$' character introduces parameter expansion, command
substitution, or arithmetic expansion. The parameter name or symbol to
be expanded may be enclosed in braces, which are optional but serve to
protect the variable to be expanded from characters immediately
following it which could be interpreted as part of the name.
The basic form of parameter expansion is ${PARAMETER}. The value of
PARAMETER is substituted. The braces are required when PARAMETER is a
positional parameter with more than one digit, or when PARAMETER is
followed by a character that is not to be interpreted as part of its
name.
If the first character of PARAMETER is an exclamation point, a level
of variable indirection is introduced. Bash uses the value of the
variable formed from the rest of PARAMETER as the name of the variable;
this variable is then expanded and that value is used in the rest of
the substitution, rather than the value of PARAMETER itself. This is
known as `indirect expansion'.
In each of the cases below, WORD is subject to tilde expansion,
parameter expansion, command substitution, and arithmetic expansion.
When not performing substring expansion, Bash tests for a parameter
that is unset or null; omitting the colon results in a test only for a
parameter that is unset.
`${PARAMETER:-WORD}'
If PARAMETER is unset or null, the expansion of WORD is
substituted. Otherwise, the value of PARAMETER is substituted.
`${PARAMETER:=WORD}'
If PARAMETER is unset or null, the expansion of WORD is assigned
to PARAMETER. The value of PARAMETER is then substituted.
Positional parameters and special parameters may not be assigned
to in this way.
`${PARAMETER:?WORD}'
If PARAMETER is null or unset, the expansion of WORD (or a message
to that effect if WORD is not present) is written to the standard
error and the shell, if it is not interactive, exits. Otherwise,
the value of PARAMETER is substituted.
`${PARAMETER:+WORD}'
If PARAMETER is null or unset, nothing is substituted, otherwise
the expansion of WORD is substituted.
`${PARAMETER:OFFSET}'
`${PARAMETER:OFFSET:LENGTH}'
Expands to up to LENGTH characters of PARAMETER, starting at
OFFSET. If LENGTH is omitted, expands to the substring of
PARAMETER, starting at the character specified by OFFSET. LENGTH
and OFFSET are arithmetic expressions (*note Arithmetic
Evaluation::.). This is referred to as Substring Expansion.
LENGTH must evaluate to a number greater than or equal to zero.
If OFFSET evaluates to a number less than zero, the value is used
as an offset from the end of the value of PARAMETER. If PARAMETER
is `@', the result is LENGTH positional parameters beginning at
OFFSET. If PARAMETER is an array name indexed by `@' or `*', the
result is the LENGTH members of the array beginning with
${PARAMETER[OFFSET]}. Substring indexing is zero-based unless the
positional parameters are used, in which case the indexing starts
at 1.
`${#PARAMETER}'
The length in characters of the value of PARAMETER is substituted.
If PARAMETER is `*' or `@', the length substituted is the number
of positional parameters. If PARAMETER is an array name
subscripted by `*' or `@', the length substituted is the number of
elements in the array.
`${PARAMETER#WORD}'
`${PARAMETER##WORD}'
The WORD is expanded to produce a pattern just as in filename
expansion (*note Filename Expansion::.). If the pattern matches
the beginning of the value of PARAMETER, then the expansion is the
value of PARAMETER with the shortest matching pattern (the `#'
case) or the longest matching pattern (the `##' case) deleted. If
PARAMETER is `@' or `*', the pattern removal operation is applied
to each positional parameter in turn, and the expansion is the
resultant list. If PARAMETER is an array variable subscripted with
`@' or `*', the pattern removal operation is applied to each
member of the array in turn, and the expansion is the resultant
list.
`${PARAMETER%WORD}'
`${PARAMETER%%WORD}'
The WORD is expanded to produce a pattern just as in filename
expansion. If the pattern matches a trailing portion of the value
of PARAMETER, then the expansion is the value of PARAMETER with
the shortest matching pattern (the `%' case) or the longest
matching pattern (the `%%' case) deleted. If PARAMETER is `@' or
`*', the pattern removal operation is applied to each positional
parameter in turn, and the expansion is the resultant list. If
PARAMETER is an array variable subscripted with `@' or `*', the
pattern removal operation is applied to each member of the array
in turn, and the expansion is the resultant list.
`${PARAMETER/PATTERN/STRING}'
`${PARAMETER//PATTERN/STRING}'
The PATTERN is expanded to produce a pattern just as in filename
expansion. PARAMETER is expanded and the longest match of PATTERN
against its value is replaced with STRING. In the first form,
only the first match is replaced. The second form causes all
matches of PATTERN to be replaced with STRING. If PATTERN begins
with `#', it must match at the beginning of STRING. If PATTERN
begins with `%', it must match at the end of STRING. If STRING is
null, matches of PATTERN are deleted and the `/' following PATTERN
may be omitted. If PARAMETER is `@' or `*', the substitution
operation is applied to each positional parameter in turn, and the
expansion is the resultant list. If PARAMETER is an array
variable subscripted with `@' or `*', the substitution operation
is applied to each member of the array in turn, and the expansion
is the resultant list.

File: bashref.info, Node: Command Substitution, Next: Process Substitution, Prev: Shell Parameter Expansion, Up: Shell Expansions
Command Substitution
--------------------
Command substitution allows the output of a command to replace the
command name. There are two forms:
$(COMMAND)
or
`COMMAND`
Bash performs the expansion by executing COMMAND and replacing the
command substitution with the standard output of the command, with any
trailing newlines deleted.
When the old-style backquote form of substitution is used, backslash
retains its literal meaning except when followed by `$', ``', or `\'.
When using the `$(COMMAND)' form, all characters between the
parentheses make up the command; none are treated specially.
Command substitutions may be nested. To nest when using the old
form, escape the inner backquotes with backslashes.
If the substitution appears within double quotes, word splitting and
filename expansion are not performed on the results.

File: bashref.info, Node: Process Substitution, Next: Word Splitting, Prev: Command Substitution, Up: Shell Expansions
Process Substitution
--------------------
Process substitution is supported on systems that support named
pipes (FIFOs) or the `/dev/fd' method of naming open files. It takes
the form of
<(LIST)
or
>(LIST)
The process LIST is run with its input or output connected to a FIFO or
some file in `/dev/fd'. The name of this file is passed as an argument
to the current command as the result of the expansion. If the
`>(LIST)' form is used, writing to the file will provide input for
LIST. If the `<(LIST)' form is used, the file passed as an argument
should be read to obtain the output of LIST.
On systems that support it, process substitution is performed
simultaneously with parameter and variable expansion, command
substitution, and arithmetic expansion.

File: bashref.info, Node: Word Splitting, Next: Filename Expansion, Prev: Process Substitution, Up: Shell Expansions
Word Splitting
--------------
The shell scans the results of parameter expansion, command
substitution, and arithmetic expansion that did not occur within double
quotes for word splitting.
The shell treats each character of `$IFS' as a delimiter, and splits
the results of the other expansions into words on these characters. If
`IFS' is unset, or its value is exactly `<space><tab><newline>', the
default, then any sequence of `IFS' characters serves to delimit words.
If `IFS' has a value other than the default, then sequences of the
whitespace characters `space' and `tab' are ignored at the beginning
and end of the word, as long as the whitespace character is in the
value of `IFS' (an `IFS' whitespace character). Any character in `IFS'
that is not `IFS' whitespace, along with any adjacent `IFS' whitespace
characters, delimits a field. A sequence of `IFS' whitespace
characters is also treated as a delimiter. If the value of `IFS' is
null, no word splitting occurs.
Explicit null arguments (`""' or `''') are retained. Unquoted
implicit null arguments, resulting from the expansion of PARAMETERs
that have no values, are removed. If a parameter with no value is
expanded within double quotes, a null argument results and is retained.
Note that if no expansion occurs, no splitting is performed.

File: bashref.info, Node: Filename Expansion, Next: Quote Removal, Prev: Word Splitting, Up: Shell Expansions
Filename Expansion
------------------
After word splitting, unless the `-f' option has been set (*note The
Set Builtin::.), Bash scans each word for the characters `*', `?', and
`['. If one of these characters appears, then the word is regarded as
a PATTERN, and replaced with an alphabetically sorted list of file
names matching the pattern. If no matching file names are found, and
the shell option `nullglob' is disabled, the word is left unchanged. If
the option is set, and no matches are found, the word is removed. When
a pattern is used for filename generation, the character `.' at the
start of a filename or immediately following a slash must be matched
explicitly, unless the shell option `dotglob' is set. The slash
character must always be matched explicitly. In other cases, the `.'
character is not treated specially. See the description of `shopt' in
*Note Bash Builtins::, for a description of the `nullglob' and
`dotglob' options.
The `GLOBIGNORE' shell variable may be used to restrict the set of
filenames matching a PATTERN. If `GLOBIGNORE' is set, each matching
filename that also matches one of the patterns in `GLOBIGNORE' is
removed from the list of matches. The filenames `.' and `..' are
always ignored, even when `GLOBIGNORE'. is set. However, setting
`GLOBIGNORE' has the effect of enabling the `dotglob' shell option, so
all other filenames beginning with a `.' will match. To get the old
behavior of ignoring filenames beginning with a `.', make `.*' one of
the patterns in `GLOBIGNORE'. The `dotglob' option is disabled when
`GLOBIGNORE' is unset.
The special pattern characters have the following meanings:
`*'
Matches any string, including the null string.
`?'
Matches any single character.
`[...]'
Matches any one of the enclosed characters. A pair of characters
separated by a minus sign denotes a RANGE; any character lexically
between those two characters, inclusive, is matched. If the first
character following the `[' is a `!' or a `^' then any character
not enclosed is matched. A `-' may be matched by including it as
the first or last character in the set. A `]' may be matched by
including it as the first character in the set.

File: bashref.info, Node: Quote Removal, Prev: Filename Expansion, Up: Shell Expansions
Quote Removal
-------------
After the preceding expansions, all unquoted occurrences of the
characters `\', `'', and `"' that did not result from one of the above
expansions are removed.

File: bashref.info, Node: Redirections, Next: Executing Commands, Prev: Shell Expansions, Up: Basic Shell Features
Redirections
============
Before a command is executed, its input and output may be REDIRECTED
using a special notation interpreted by the shell. Redirection may
also be used to open and close files for the current shell execution
environment. The following redirection operators may precede or appear
anywhere within a simple command or may follow a command. Redirections
are processed in the order they appear, from left to right.
In the following descriptions, if the file descriptor number is
omitted, and the first character of the redirection operator is `<',
the redirection refers to the standard input (file descriptor 0). If
the first character of the redirection operator is `>', the redirection
refers to the standard output (file descriptor 1).
The word that follows the redirection operator in the following
descriptions is subjected to brace expansion, tilde expansion,
parameter expansion, command substitution, arithmetic expansion, quote
removal, and filename expansion. If it expands to more than one word,
Bash reports an error.
Note that the order of redirections is significant. For example,
the command
ls > DIRLIST 2>&1
directs both standard output and standard error to the file DIRLIST,
while the command
ls 2>&1 > DIRLIST
directs only the standard output to file DIRLIST, because the standard
error was duplicated as standard output before the standard output was
redirected to DIRLIST.
Redirecting Input
-----------------
Redirection of input causes the file whose name results from the
expansion of WORD to be opened for reading on file descriptor `n', or
the standard input (file descriptor 0) if `n' is not specified.
The general format for redirecting input is:
[n]<WORD
Redirecting Output
------------------
Redirection of output causes the file whose name results from the
expansion of WORD to be opened for writing on file descriptor `n', or
the standard output (file descriptor 1) if `n' is not specified. If
the file does not exist it is created; if it does exist it is truncated
to zero size.
The general format for redirecting output is:
[n]>[|]WORD
If the redirection operator is `>', and the `-C' option to the `set'
builtin has been enabled, the redirection will fail if the filename
whose name results from the expansion of WORD exists. If the
redirection operator is `>|', then the value of the `-C' option to the
`set' builtin command is not tested, and the redirection is attempted
even if the file named by WORD exists.
Appending Redirected Output
---------------------------
Redirection of output in this fashion causes the file whose name
results from the expansion of WORD to be opened for appending on file
descriptor `n', or the standard output (file descriptor 1) if `n' is
not specified. If the file does not exist it is created.
The general format for appending output is:
[n]>>WORD
Redirecting Standard Output and Standard Error
----------------------------------------------
Bash allows both the standard output (file descriptor 1) and the
standard error output (file descriptor 2) to be redirected to the file
whose name is the expansion of WORD with this construct.
There are two formats for redirecting standard output and standard
error:
&>WORD
and
>&WORD
Of the two forms, the first is preferred. This is semantically
equivalent to
>WORD 2>&1
Here Documents
--------------
This type of redirection instructs the shell to read input from the
current source until a line containing only WORD (with no trailing
blanks) is seen. All of the lines read up to that point are then used
as the standard input for a command.
The format of here-documents is as follows:
<<[-]WORD
HERE-DOCUMENT
DELIMITER
No parameter expansion, command substitution, filename expansion, or
arithmetic expansion is performed on WORD. If any characters in WORD
are quoted, the DELIMITER is the result of quote removal on WORD, and
the lines in the here-document are not expanded. Otherwise, all lines
of the here-document are subjected to parameter expansion, command
substitution, and arithmetic expansion. In the latter case, the pair
`\newline' is ignored, and `\' must be used to quote the characters
`\', `$', and ``'.
If the redirection operator is `<<-', then all leading tab
characters are stripped from input lines and the line containing
DELIMITER. This allows here-documents within shell scripts to be
indented in a natural fashion.
Duplicating File Descriptors
----------------------------
The redirection operator
[n]<&WORD
is used to duplicate input file descriptors. If WORD expands to one or
more digits, the file descriptor denoted by `n' is made to be a copy of
that file descriptor. If WORD evaluates to `-', file descriptor `n' is
closed. If `n' is not specified, the standard input (file descriptor
0) is used.
The operator
[n]>&WORD
is used similarly to duplicate output file descriptors. If `n' is not
specified, the standard output (file descriptor 1) is used. As a
special case, if `n' is omitted, and WORD does not expand to one or
more digits, the standard output and standard error are redirected as
described previously.
Opening File Descriptors for Reading and Writing
------------------------------------------------
The redirection operator
[n]<>WORD
causes the file whose name is the expansion of WORD to be opened for
both reading and writing on file descriptor `n', or on file descriptor
0 if `n' is not specified. If the file does not exist, it is created.

File: bashref.info, Node: Executing Commands, Next: Shell Scripts, Prev: Redirections, Up: Basic Shell Features
Executing Commands
==================
* Menu:
* Command Search and Execution:: How Bash finds commands and runs them.
* Environment:: The environment given to a command.
* Exit Status:: The status returned by commands and how Bash
interprets it.
* Signals:: What happens when Bash or a command it runs
receives a signal.

File: bashref.info, Node: Command Search and Execution, Next: Environment, Up: Executing Commands
Command Search and Execution
----------------------------
After a command has been split into words, if it results in a simple
command and an optional list of arguments, the following actions are
taken.
1. If the command name contains no slashes, the shell attempts to
locate it. If there exists a shell function by that name, that
function is invoked as described above in *Note Shell Functions::.
2. If the name does not match a function, the shell searches for it
in the list of shell builtins. If a match is found, that builtin
is invoked.
3. If the name is neither a shell function nor a builtin, and
contains no slashes, Bash searches each element of `$PATH' for a
directory containing an executable file by that name. Bash uses a
hash table to remember the full filenames of executable files (see
the description of `hash' in *Note Bourne Shell Builtins::) to
avoid multiple `PATH' searches. A full search of the directories
in `$PATH' is performed only if the command is not found in the
hash table. If the search is unsuccessful, the shell prints an
error message and returns a nonzero exit status.
4. If the search is successful, or if the command name contains one
or more slashes, the shell executes the named program. Argument 0
is set to the name given, and the remaining arguments to the
command are set to the arguments supplied, if any.
5. If this execution fails because the file is not in executable
format, and the file is not a directory, it is assumed to be SHELL
SCRIPT (*note Shell Scripts::.).

File: bashref.info, Node: Environment, Next: Exit Status, Prev: Command Search and Execution, Up: Executing Commands
Environment
-----------
When a program is invoked it is given an array of strings called the
ENVIRONMENT. This is a list of name-value pairs, of the form
`name=value'.
Bash allows you to manipulate the environment in several ways. On
invocation, the shell scans its own environment and creates a parameter
for each name found, automatically marking it for EXPORT to child
processes. Executed commands inherit the environment. The `export'
and `declare -x' commands allow parameters and functions to be added to
and deleted from the environment. If the value of a parameter in the
environment is modified, the new value becomes part of the environment,
replacing the old. The environment inherited by any executed command
consists of the shell's initial environment, whose values may be
modified in the shell, less any pairs removed by the `unset' command,
plus any additions via the `export' and `declare -x' commands.
The environment for any simple command or function may be augmented
temporarily by prefixing it with parameter assignments, as described in
*Note Shell Parameters::. These assignment statements affect only the
environment seen by that command.
If the `-k' flag is set (*note The Set Builtin::., then all
parameter assignments are placed in the environment for a command, not
just those that precede the command name.
When Bash invokes an external command, the variable `$_' is set to
the full path name of the command and passed to that command in its
environment.

File: bashref.info, Node: Exit Status, Next: Signals, Prev: Environment, Up: Executing Commands
Exit Status
-----------
For the purposes of the shell, a command which exits with a zero
exit status has succeeded. A non-zero exit status indicates failure.
This seemingly counter-intuitive scheme is used so there is one
well-defined way to indicate success and a variety of ways to indicate
various failure modes. When a command terminates on a fatal signal
whose number is N, Bash uses the value 128+N as the exit status.
If a command is not found, the child process created to execute it
returns a status of 127. If a command is found but is not executable,
the return status is 126.
The exit status is used by the Bash conditional commands (*note
Conditional Constructs::.) and some of the list constructs (*note
Lists::.).
All of the Bash builtins return an exit status of zero if they
succeed and a non-zero status on failure, so they may be used by the
conditional and list constructs.

File: bashref.info, Node: Signals, Prev: Exit Status, Up: Executing Commands
Signals
-------
When Bash is interactive, it ignores `SIGTERM' (so that `kill 0'
does not kill an interactive shell), and `SIGINT' is caught and handled
(so that the `wait' builtin is interruptible). When Bash receives a
`SIGINT', it breaks out of any executing loops. In all cases, Bash
ignores `SIGQUIT'. If job control is in effect (*note Job Control::.),
Bash ignores `SIGTTIN', `SIGTTOU', and `SIGTSTP'.
Synchronous jobs started by Bash have signals set to the values
inherited by the shell from its parent. When job control is not in
effect, background jobs (commands terminated with `&') ignore `SIGINT'
and `SIGQUIT'. Commands run as a result of command substitution ignore
the keyboard-generated job control signals `SIGTTIN', `SIGTTOU', and
`SIGTSTP'.
The shell exits by default upon receipt of a `SIGHUP'. Before
exiting, it resends the `SIGHUP' to all jobs, running or stopped. To
prevent the shell from sending the `SIGHUP' signal to a particular job,
remove it from the jobs table with the `disown' builtin (*note Job
Control Builtins::.) or use `disown -h' to mark it to not receive
`SIGHUP'.

File: bashref.info, Node: Shell Scripts, Prev: Executing Commands, Up: Basic Shell Features
Shell Scripts
=============
A shell script is a text file containing shell commands. When such
a file is used as the first non-option argument when invoking Bash, and
neither the `-c' nor `-s' option is supplied (*note Invoking Bash::.),
Bash reads and executes commands from the file, then exits. This mode
of operation creates a non-interactive shell. When Bash runs a shell
script, it sets the special parameter `0' to the name of the file,
rather than the name of the shell, and the positional parameters are
set to the remaining arguments, if any are given. If no additional
arguments are supplied, the positional parameters are unset.
A shell script may be made executable by using the `chmod' command
to turn on the execute bit. When Bash finds such a file while
searching the `$PATH' for a command, it spawns a subshell to execute
it. In other words, executing
filename ARGUMENTS
is equivalent to executing
bash filename ARGUMENTS
if `filename' is an executable shell script. This subshell
reinitializes itself, so that the effect is as if a new shell had been
invoked to interpret the script.
Most versions of Unix make this a part of the kernel's command
execution mechanism. If the first line of a script begins with the two
characters `#!', the remainder of the line specifies an interpreter for
the program. The arguments to the interpreter consist of a single
optional argument following the interpreter name on the first line of
the script file, followed by the name of the script file, followed by
the rest of the arguments. Bash will perform this action on operating
systems that do not handle it themselves. Note that some older
versions of Unix limit the interpreter name and argument to a maximum
of 32 characters.

File: bashref.info, Node: Bourne Shell Features, Next: Csh Features, Prev: Basic Shell Features, Up: Top
Bourne Shell Style Features
***************************
* Menu:
* Bourne Shell Builtins:: Builtin commands inherited from the Bourne
Shell.
* Bourne Shell Variables:: Variables which Bash uses in the same way
as the Bourne Shell.
* Other Bourne Shell Features:: Addtional aspects of Bash which behave in
the same way as the Bourne Shell.
This section briefly summarizes things which Bash inherits from the
Bourne Shell: builtins, variables, and other features. It also lists
the significant differences between Bash and the Bourne Shell.

File: bashref.info, Node: Bourne Shell Builtins, Next: Bourne Shell Variables, Up: Bourne Shell Features
Bourne Shell Builtins
=====================
The following shell builtin commands are inherited from the Bourne
Shell. These commands are implemented as specified by the POSIX 1003.2
standard.
`:'
: [ARGUMENTS]
Do nothing beyond expanding ARGUMENTS and performing redirections.
`.'
. FILENAME
Read and execute commands from the FILENAME argument in the
current shell context.
`break'
break [N]
Exit from a `for', `while', `until', or `select' loop. If N is
supplied, the Nth enclosing loop is exited.
`cd'
cd [-LP] [DIRECTORY]
Change the current working directory to DIRECTORY. If DIRECTORY
is not given, the value of the `HOME' shell variable is used. If
the shell variable `CDPATH' exists, it is used as a search path.
If DIRECTORY begins with a slash, `CDPATH' is not used. The `-P'
option means to not follow symbolic links; symlinks are followed
by default or with the `-L' option.
`continue'
continue [N]
Resume the next iteration of an enclosing `for', `while', `until',
or `select' loop. If N is supplied, the execution of the Nth
enclosing loop is resumed.
`eval'
eval [ARGUMENTS]
The arguments are concatenated together into a single command,
which is then read and executed.
`exec'
exec [-cl] [-a NAME] [COMMAND] [ARGUMENTS]
If COMMAND is supplied, it replaces the shell. If the `-l' option
is supplied, the shell places a dash in the zeroth arg passed to
COMMAND. This is what the `login' program does. The `-c' option
causes COMMAND to be executed with an empty environment. If `-a'
is supplied, the shell passes NAME as the zeroth argument to
COMMAND. If no COMMAND is specified, redirections may be used to
affect the current shell environment.
`exit'
exit [N]
Exit the shell, returning a status of N to the shell's parent.
`export'
export [-fn] [-p] [NAME[=VALUE]]
Mark each NAME to be passed to child processes in the environment.
If the `-f' option is supplied, the NAMEs refer to shell
functions. The `-n' option means to no longer mark each NAME for
export. If no NAMES are supplied, or if the `-p' option is given,
a list of exported names is displayed.
`getopts'
getopts OPTSTRING NAME [ARGS]
`getopts' is used by shell scripts to parse positional parameters.
OPTSTRING contains the option letters to be recognized; if a letter
is followed by a colon, the option is expected to have an
argument, which should be separated from it by white space. Each
time it is invoked, `getopts' places the next option in the shell
variable NAME, initializing NAME if it does not exist, and the
index of the next argument to be processed into the variable
`OPTIND'. `OPTIND' is initialized to 1 each time the shell or a
shell script is invoked. When an option requires an argument,
`getopts' places that argument into the variable `OPTARG'. The
shell does not reset `OPTIND' automatically; it must be manually
reset between multiple calls to `getopts' within the same shell
invocation if a new set of parameters is to be used.
`getopts' can report errors in two ways. If the first character of
OPTSTRING is a colon, SILENT error reporting is used. In normal
operation diagnostic messages are printed when illegal options or
missing option arguments are encountered. If the variable `OPTERR'
is set to 0, no error message will be displayed, even if the first
character of `optstring' is not a colon.
If an illegal option is seen, `getopts' places `?' into NAME and,
if not silent, prints an error message and unsets `OPTARG'. If
`getopts' is silent, the option character found is placed in
`OPTARG' and no diagnostic message is printed.
If a required argument is not found, and `getopts' is not silent,
a question mark (`?') is placed in NAME, `OPTARG' is unset, and a
diagnostic message is printed. If `getopts' is silent, then a
colon (`:') is placed in NAME and `OPTARG' is set to the option
character found.
`getopts' normally parses the positional parameters, but if more
arguments are given in ARGS, `getopts' parses those instead.
`hash'
hash [-r] [-p FILENAME] [NAME]
Remember the full filenames of commands specified as arguments, so
they need not be searched for on subsequent invocations. The
commands are found by searching through the directories listed in
`$PATH'. The `-p' option inhibits the path search, and FILENAME
is used as the location of NAME. The `-r' option causes the shell
to forget all remembered locations. If no arguments are given,
information about remembered commands is printed.
`pwd'
pwd [-LP]
Print the current working directory. If the `-P' option is
supplied, the path printed will not contain symbolic links. If
the `-L' option is supplied, the path printed may contain symbolic
links.
`readonly'
readonly [-apf] [NAME] ...
Mark each NAME as unchangable. The values of these names may not
be changed by subsequent assignment. If the `-f' option is
supplied, each NAME refers to a shell function. The `-a' option
means each NAME refers to an array variable. If no NAME arguments
are given, or if the `-p' option is supplied, a list of all
readonly names is printed.
`return'
return [N]
Cause a shell function to exit with value N. This may also be used
to terminate execution of a script being executed with the `.'
builtin.
`shift'
shift [N]
Shift positional parameters to the left by N. The positional
parameters from N+1 ... are renamed to `$1' ... . Parameters
represented by the numbers `$#' to N+1 are unset. N must be a
non-negative number less than or equal to `$#'.
`test'
`['
Evaluate a conditional expression (*note Bash Conditional
Expressions::.).
`times'
times
Print out the user and system times used by the shell and its
children.
`trap'
trap [-lp] [ARG] [SIGSPEC ...]
The commands in ARG are to be read and executed when the shell
receives signal SIGSPEC. If ARG is absent or equal to `-', all
specified signals are reset to the values they had when the shell
was started. If ARG is the null string, then the signal specified
by each SIGSPEC is ignored by the shell and commands it invokes.
If ARG is `-p', the shell displays the trap commands associated
with each SIGSPEC. If no arguments are supplied, or only `-p' is
given, `trap' prints the list of commands associated with each
signal number. Each SIGSPEC is either a signal name such as
`SIGINT' (with or without the `SIG' prefix) or a signal number.
If a SIGSPEC is `0' or `EXIT', ARG is executed when the shell
exits. If a SIGSPEC is `DEBUG', the command ARG is executed after
every simple command. The `-l' option causes the shell to print a
list of signal names and their corresponding numbers.
Signals ignored upon entry to the shell cannot be trapped or reset.
Trapped signals are reset to their original values in a child
process when it is created.
`umask'
umask [-S] [MODE]
Set the shell process's file creation mask to MODE. If MODE
begins with a digit, it is interpreted as an octal number; if not,
it is interpreted as a symbolic mode mask similar to that accepted
by the `chmod' command. If MODE is omitted, the current value of
the mask is printed. If the `-S' option is supplied without a
MODE argument, the mask is printed in a symbolic format.
`unset'
unset [-fv] [NAME]
Each variable or function NAME is removed. If no options are
supplied, or the `-v' option is given, each NAME refers to a shell
variable. If the `-f' option is given, the NAMEs refer to shell
functions, and the function definition is removed. Read-only
variables and functions may not be unset.

File: bashref.info, Node: Bourne Shell Variables, Next: Other Bourne Shell Features, Prev: Bourne Shell Builtins, Up: Bourne Shell Features
Bourne Shell Variables
======================
Bash uses certain shell variables in the same way as the Bourne
shell. In some cases, Bash assigns a default value to the variable.
`IFS'
A list of characters that separate fields; used when the shell
splits words as part of expansion.
`PATH'
A colon-separated list of directories in which the shell looks for
commands.
`HOME'
The current user's home directory; the default for the `cd' builtin
command.
`CDPATH'
A colon-separated list of directories used as a search path for
the `cd' command.
`MAILPATH'
A colon-separated list of files which the shell periodically checks
for new mail. You can also specify what message is printed by
separating the file name from the message with a `?'. When used
in the text of the message, `$_' stands for the name of the
current mailfile.
`MAIL'
If this parameter is set to a filename and the `MAILPATH' variable
is not set, Bash informs the user of the arrival of mail in the
specified file.
`PS1'
The primary prompt string. The default value is `\s-\v\$ '.
`PS2'
The secondary prompt string. The default value is `> '.
`OPTIND'
The index of the last option processed by the `getopts' builtin.
`OPTARG'
The value of the last option argument processed by the `getopts'
builtin.

File: bashref.info, Node: Other Bourne Shell Features, Prev: Bourne Shell Variables, Up: Bourne Shell Features
Other Bourne Shell Features
===========================
* Menu:
* Major Differences From The Bourne Shell:: Major differences between
Bash and the Bourne shell.
Bash implements essentially the same grammar, parameter and variable
expansion, redirection, and quoting as the Bourne Shell. Bash uses the
POSIX 1003.2 standard as the specification of how these features are to
be implemented. There are some differences between the traditional
Bourne shell and the POSIX standard; this section quickly details the
differences of significance. A number of these differences are
explained in greater depth in subsequent sections.

File: bashref.info, Node: Major Differences From The Bourne Shell, Up: Other Bourne Shell Features
Major Differences From The SVR4.2 Bourne Shell
----------------------------------------------
Bash is POSIX-conformant, even where the POSIX specification differs
from traditional `sh' behavior.
Bash has multi-character invocation options (*note Invoking Bash::.).
Bash has command-line editing (*note Command Line Editing::.) and
the `bind' builtin.
Bash has command history (*note Bash History Facilities::.) and the
`history' and `fc' builtins to manipulate it.
Bash implements `csh'-like history expansion (*note History
Interaction::.).
Bash has one-dimensional array variables (*note Arrays::.), and the
appropriate variable expansions and assignment syntax to use them.
Some of the Bash builtins take options to act on arrays. Bash provides
some built-in array variables.
Bash implements the `!' keyword to negate the return value of a
pipeline (*note Pipelines::.). Very useful when an `if' statement
needs to act only if a test fails.
Bash includes the `select' compound command, which allows the
generation of simple menus (*note Korn Shell Constructs::.).
Bash includes brace expansion (*note Brace Expansion::.) and tilde
expansion (*note Tilde Expansion::.).
Bash implements command aliases and the `alias' and `unalias'
builtins (*note Aliases::.).
Bash provides shell arithmetic and arithmetic expansion (*note Shell
Arithmetic::.).
The POSIX and `ksh'-style `$()' form of command substitution is
implemented (*note Command Substitution::.), and preferred to the
Bourne shell's ```' (which is also implemented for backwards
compatibility).
Variables present in the shell's initial environment are
automatically exported to child processes. The Bourne shell does not
normally do this unless the variables are explicitly marked using the
`export' command.
Bash includes the POSIX and `ksh'-style pattern removal `%', `#',
`%%' and `##' constructs to remove leading or trailing substrings from
variable values (*note Shell Parameter Expansion::.).
The expansion `${#xx}', which returns the length of `$xx', is
supported (*note Shell Parameter Expansion::.).
The `$'...'' quoting syntax, which expands ANSI-C backslash-escaped
characters in the text between the single quotes, is supported (*note
ANSI-C Quoting::.).
Bash supports the `$"..."' quoting syntax to do locale-specific
translation of the characters between the double quotes. The `-D' and
`--dump-strings' invocation options list the translatable strings found
in a script (*note Locale Translation::.).
The expansion `${var:'OFFSET`[:'LENGTH`]}', which expands to the
substring of `var''s value of length LENGTH, optionally beginning at
OFFSET, is present (*note Shell Parameter Expansion::.).
The expansion `${var/[/]'PATTERN`[/'REPLACEMENT`]}', which matches
PATTERN and replaces it with REPLACEMENT in the value of `var', is
available (*note Shell Parameter Expansion::.).
Bash has INDIRECT variable expansion using `${!word}' (*note Shell
Parameter Expansion::.).
Bash can expand positional parameters beyond `$9' using `${NUM}'.
Bash has process substitution (*note Process Substitution::.).
Bash automatically assigns variables that provide information about
the current user (`UID', `EUID', and `GROUPS'), the current host
(`HOSTTYPE', `OSTYPE', `MACHTYPE', and `HOSTNAME'), and the instance of
Bash that is running (`BASH', `BASH_VERSION', and `BASH_VERSINFO'.
*Note Bash Variables::, for details.
The `IFS' variable is used to split only the results of expansion,
not all words (*note Word Splitting::.). This closes a longstanding
shell security hole.
It is possible to have a variable and a function with the same name;
`sh' does not separate the two name spaces.
Bash functions are permitted to have local variables using the
`local' builtin, and thus useful recursive functions may be written.
Variable assignments preceding commands affect only that command,
even builtins and functions (*note Environment::.). In `sh', all
variable assignments preceding commands are global unless the command
is executed from the file system.
Bash performs filename expansion on filenames specified as operands
to output redirection operators.
Bash contains the `<>' redirection operator, allowing a file to be
opened for both reading and writing, and the `&>' redirection operator,
for directing standard output and standard error to the same file
(*note Redirections::.).
The `noclobber' option is available to avoid overwriting existing
files with output redirection (*note The Set Builtin::.). The `>|'
redirection operator may be used to override `noclobber'.
Bash interprets special backslash-escaped characters in the prompt
strings when interactive (*note Printing a Prompt::.).
Bash allows you to write a function to override a builtin, and
provides access to that builtin's functionality within the function via
the `builtin' and `command' builtins (*note Bash Builtins::.).
The `command' builtin allows selective disabling of functions when
command lookup is performed (*note Bash Builtins::.).
Individual builtins may be enabled or disabled using the `enable'
builtin (*note Bash Builtins::.).
The Bash `hash' builtin allows a name to be associated with an
arbitrary filename, even when that filename cannot be found by
searching the `$PATH', using `hash -p'.
Shell functions may be exported to children via the environment
(*note Shell Functions::.).
Bash includes a `help' builtin for quick reference to shell
facilities (*note Bash Builtins::.).
The Bash `read' builtin (*note Bash Builtins::.) will read a line
ending in `\' with the `-r' option, and will use the `REPLY' variable
as a default if no arguments are supplied. The Bash `read' builtin
also accepts a prompt string with the `-p' option and will use Readline
to obtain the line when given the `-e' option.
Bash includes the `shopt' builtin, for finer control of shell
optional capabilities (*note Bash Builtins::.).
Bash has much more optional behavior controllable with the `set'
builtin (*note The Set Builtin::.).
The `disown' builtin can remove a job from the internal shell job
table (*note Job Control Builtins::.).
The `return' builtin may be used to abort execution of scripts
executed with the `.' or `source' builtins (*note Bourne Shell
Builtins::.).
The `test' builtin (*note Bourne Shell Builtins::.) is slightly
different, as it implements the POSIX 1003.2 algorithm, which specifies
the behavior based on the number of arguments.
The `trap' builtin (*note Bourne Shell Builtins::.) allows a `DEBUG'
pseudo-signal specification, similar to `EXIT'. Commands specified
with a `DEBUG' trap are executed after every simple command. The
`DEBUG' trap is not inherited by shell functions.
The Bash `export', `readonly', and `declare' builtins can take a
`-f' option to act on shell functions, a `-p' option to display
variables with various attributes set in a format that can be used as
shell input, a `-n' option to remove various variable attributes, and
`name=value' arguments to set variable attributes and values
simultaneously.
The Bash `cd' and `pwd' builtins (*note Bourne Shell Builtins::.)
each take `-L' and `-P' builtins to switch between logical and physical
modes.
The Bash `type' builtin is more extensive and gives more information
about the names it finds (*note Bash Builtins::.).
Bash implements a `csh'-like directory stack, and provides the
`pushd', `popd', and `dirs' builtins to manipulate it (*note C Shell
Builtins::.). Bash also makes the directory stack visible as the value
of the `DIRSTACK' shell variable.
The Bash restricted mode is more useful (*note The Restricted
Shell::.); the SVR4.2 shell restricted mode is too limited.
Bash has the `time' reserved word and command timing (*note
Pipelines::.). The display of the timing statistics may be controlled
with the `TIMEFORMAT' variable.
The SVR4.2 shell has two privilege-related builtins (`mldmode' and
`priv') not present in Bash.
Bash does not have the `stop' or `newgrp' builtins.
Bash does not use the `SHACCT' variable or perform shell accounting.
The SVR4.2 `sh' uses a `TIMEOUT' variable like Bash uses `TMOUT'.
More features unique to Bash may be found in *Note Bash Features::.
Implementation Differences From The SVR4.2 Shell
------------------------------------------------
Since Bash is a completely new implementation, it does not suffer
from many of the limitations of the SVR4.2 shell. For instance:
* Bash does not fork a subshell when redirecting into or out of a
shell control structure such as an `if' or `while' statement.
* Bash does not allow unbalanced quotes. The SVR4.2 shell will
silently insert a needed closing quote at `EOF' under certain
circumstances. This can be the cause of some hard-to-find errors.
* The SVR4.2 shell uses a baroque memory management scheme based on
trapping `SIGSEGV'. If the shell is started from a process with
`SIGSEGV' blocked (e.g., by using the `system()' C library
function call), the shell misbehaves badly.
* In a questionable attempt at security, the SVR4.2 shell, when
invoked without the `-p' option, will alter its real and effective
UID and GID if they are less than some magic threshold value,
commonly 100. This can lead to unexpected results.
* The SVR4.2 shell does not allow users to trap `SIGALRM' or
`SIGCHLD'.
* For some reason, the SVR4.2 shell does not allow the `MAILCHECK'
variable to be unset.
* The SVR4.2 shell treats `^' as the undocumented equivalent of `|'.
* Bash allows multiple option arguments when it is invoked (`-x -v');
the SVR4.2 shell allows only one option argument (`-xv'). In
fact, some versions of the shell dump core if the second argument
begins with a `-'.
* The SVR4.2 shell exits a script if any builtin fails; Bash exits a
script only if one of the POSIX.2 special builtins fails, and only
for certain failures, as enumerated in the POSIX.2 standard.
* The SVR4.2 shell behaves differently when invoked as `jsh' (it
turns on job control).

File: bashref.info, Node: Csh Features, Next: Korn Shell Features, Prev: Bourne Shell Features, Up: Top
C-Shell Style Features
**********************
The C-Shell ("`csh'") was created by Bill Joy at The University of
California at Berkeley. It is generally considered to have better
features for interactive use than the original Bourne shell. Some of
the `csh' features present in Bash include job control, history
expansion, `protected' redirection, and several variables to control
the interactive behaviour of the shell (e.g., `IGNOREEOF').
*Note Using History Interactively::, for details on history
expansion.
* Menu:
* Brace Expansion:: Expansion of expressions within braces.
* Tilde Expansion:: Expansion of the ~ character.
* C Shell Builtins:: Builtin commands adopted from the C Shell.
* C Shell Variables:: Variables which Bash uses in essentially
the same way as the C Shell.

File: bashref.info, Node: Brace Expansion, Next: Tilde Expansion, Up: Csh Features
Brace Expansion
===============
Brace expansion is a mechanism by which arbitrary strings may be
generated. This mechanism is similar to FILENAME EXPANSION (*note
Filename Expansion::.), but the file names generated need not exist.
Patterns to be brace expanded take the form of an optional PREAMBLE,
followed by a series of comma-separated strings between a pair of
braces, followed by an optional POSTAMBLE. The preamble is prepended
to each string contained within the braces, and the postamble is then
appended to each resulting string, expanding left to right.
Brace expansions may be nested. The results of each expanded string
are not sorted; left to right order is preserved. For example,
bash$ echo a{d,c,b}e
ade ace abe
Brace expansion is performed before any other expansions, and any
characters special to other expansions are preserved in the result. It
is strictly textual. Bash does not apply any syntactic interpretation
to the context of the expansion or the text between the braces.
A correctly-formed brace expansion must contain unquoted opening and
closing braces, and at least one unquoted comma. Any incorrectly
formed brace expansion is left unchanged.
This construct is typically used as shorthand when the common prefix
of the strings to be generated is longer than in the above example:
mkdir /usr/local/src/bash/{old,new,dist,bugs}
or
chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}

File: bashref.info, Node: Tilde Expansion, Next: C Shell Builtins, Prev: Brace Expansion, Up: Csh Features
Tilde Expansion
===============
Bash has tilde (~) expansion, similar, but not identical, to that of
`csh'. The following table shows what unquoted words beginning with a
tilde expand to.
`~'
The current value of `$HOME'.
`~/foo'
`$HOME/foo'
`~fred/foo'
The subdirectory `foo' of the home directory of the user `fred'.
`~+/foo'
`$PWD/foo'
`~-/foo'
`$OLDPWD/foo'
Bash will also tilde expand words following redirection operators
and words following `=' in assignment statements.

File: bashref.info, Node: C Shell Builtins, Next: C Shell Variables, Prev: Tilde Expansion, Up: Csh Features
C Shell Builtins
================
Bash has several builtin commands whose definition is very similar
to `csh'.
`pushd'
pushd [DIR | +N | -N] [-n]
Save the current directory on a list and then `cd' to DIR. With no
arguments, exchanges the top two directories.
`+N'
Brings the Nth directory (counting from the left of the list
printed by `dirs', starting with zero) to the top of the list
by rotating the stack.
`-N'
Brings the Nth directory (counting from the right of the list
printed by `dirs', starting with zero) to the top of the list
by rotating the stack.
`-n'
Suppresses the normal change of directory when adding
directories to the stack, so that only the stack is
manipulated.
`DIR'
Makes the current working directory be the top of the stack,
and then `cd's to DIR. You can see the saved directory list
with the `dirs' command.
`popd'
popd [+N | -N] [-n]
Pop the directory stack, and `cd' to the new top directory. When
no arguments are given, `popd' removes the top directory from the
stack and performs a `cd' to the new top directory. The elements
are numbered from 0 starting at the first directory listed with
`dirs'; i.e., `popd' is equivalent to `popd +0'.
`+N'
Removes the Nth directory (counting from the left of the list
printed by `dirs'), starting with zero.
`-N'
Removes the Nth directory (counting from the right of the
list printed by `dirs'), starting with zero.
`-n'
Suppresses the normal change of directory when removing
directories from the stack, so that only the stack is
manipulated.
`dirs'
dirs [+N | -N] [-clvp]
Display the list of currently remembered directories. Directories
find their way onto the list with the `pushd' command; you can get
back up through the list with the `popd' command.
`+N'
Displays the Nth directory (counting from the left of the
list printed by `dirs' when invoked without options), starting
with zero.
`-N'
Displays the Nth directory (counting from the right of the
list printed by `dirs' when invoked without options), starting
with zero.
`-c'
Clears the directory stack by deleting all of the elements.
`-l'
Produces a longer listing; the default listing format uses a
tilde to denote the home directory.
`-p'
Causes `dirs' to print the directory stack with one entry per
line.
`-v'
Causes `dirs' to print the directory stack with one entry per
line, prepending each entry with its index in the stack.
`history'
history [-c] [N]
history [-anrw] [FILENAME]
history -ps ARG
Display the history list with line numbers. Lines prefixed with
with a `*' have been modified. An argument of N says to list only
the last N lines. Options, if supplied, have the following
meanings:
`-w'
Write out the current history to the history file.
`-r'
Read the current history file and append its contents to the
history list.
`-a'
Append the new history lines (history lines entered since the
beginning of the current Bash session) to the history file.
`-n'
Append the history lines not already read from the history
file to the current history list. These are lines appended
to the history file since the beginning of the current Bash
session.
`-c'
Clear the history list. This may be combined with the other
options to replace the history list completely.
`-s'
The ARGs are added to the end of the history list as a single
entry.
`-p'
Perform history substitution on the ARGs and display the
result on the standard output, without storing the results in
the history list.
When the `-w', `-r', `-a', or `-n' option is used, if FILENAME is
given, then it is used as the history file. If not, then the
value of the `HISTFILE' variable is used.
`logout'
Exit a login shell.
`source'
A synonym for `.' (*note Bourne Shell Builtins::.).

File: bashref.info, Node: C Shell Variables, Prev: C Shell Builtins, Up: Csh Features
C Shell Variables
=================
`IGNOREEOF'
If this variable is set, its value is used the number of
consecutive `EOF's Bash will read before exiting. By default,
Bash will exit upon reading a single `EOF'. If `IGNOREEOF' is not
set to a numeric value, Bash acts as if its value were 10.

File: bashref.info, Node: Korn Shell Features, Next: Bash Features, Prev: Csh Features, Up: Top
Korn Shell Style Features
*************************
This section describes features primarily inspired by the Korn Shell
(`ksh'). In some cases, the POSIX 1003.2 standard has adopted these
commands and variables from the Korn Shell; Bash implements those
features using the POSIX standard as a guide.
* Menu:
* Korn Shell Constructs:: Shell grammar constructs adopted from the
Korn Shell
* Korn Shell Builtins:: Builtin commands adopted from the Korn Shell.
* Korn Shell Variables:: Variables which Bash uses in essentially
the same way as the Korn Shell.
* Aliases:: Substituting one command for another.

File: bashref.info, Node: Korn Shell Constructs, Next: Korn Shell Builtins, Up: Korn Shell Features
Korn Shell Constructs
=====================
Bash includes the Korn Shell `select' construct. This construct
allows the easy generation of menus. It has almost the same syntax as
the `for' command.
The syntax of the `select' command is:
select NAME [in WORDS ...]; do COMMANDS; done
The list of words following `in' is expanded, generating a list of
items. The set of expanded words is printed on the standard error,
each preceded by a number. If the `in WORDS' is omitted, the
positional parameters are printed. The `PS3' prompt is then displayed
and a line is read from the standard input. If the line consists of a
number corresponding to one of the displayed words, then the value of
NAME is set to that word. If the line is empty, the words and prompt
are displayed again. If `EOF' is read, the `select' command completes.
Any other value read causes NAME to be set to null. The line read is
saved in the variable `REPLY'.
The COMMANDS are executed after each selection until a `break' or
`return' command is executed, at which point the `select' command
completes.
Bash also has adopted command timing from the Korn shell. If the
`time' reserved word precedes a pipeline, which may consist of a single
command, timing statistics for the pipeline are displayed when it
completes. The statistics currently consist of elapsed (wall-clock)
time and user and system time consumed by the command's execution.
The use of `time' as a reserved word permits the timing of shell
builtins, shell functions, and pipelines. An external `time' command
cannot time these easily.

File: bashref.info, Node: Korn Shell Builtins, Next: Korn Shell Variables, Prev: Korn Shell Constructs, Up: Korn Shell Features
Korn Shell Builtins
===================
This section describes Bash builtin commands taken from `ksh'.
`fc'
`fc [-e ENAME] [-nlr] [FIRST] [LAST]'
`fc -s [PAT=REP] [COMMAND]'
Fix Command. In the first form, a range of commands from FIRST to
LAST is selected from the history list. Both FIRST and LAST may
be specified as a string (to locate the most recent command
beginning with that string) or as a number (an index into the
history list, where a negative number is used as an offset from the
current command number). If LAST is not specified it is set to
FIRST. If FIRST is not specified it is set to the previous
command for editing and -16 for listing. If the `-l' flag is
given, the commands are listed on standard output. The `-n' flag
suppresses the command numbers when listing. The `-r' flag
reverses the order of the listing. Otherwise, the editor given by
ENAME is invoked on a file containing those commands. If ENAME is
not given, the value of the following variable expansion is used:
`${FCEDIT:-${EDITOR:-vi}}'. This says to use the value of the
`FCEDIT' variable if set, or the value of the `EDITOR' variable if
that is set, or `vi' if neither is set. When editing is complete,
the edited commands are echoed and executed.
In the second form, COMMAND is re-executed after each instance of
PAT in the selected command is replaced by REP.
A useful alias to use with the `fc' command is `r='fc -s'', so
that typing `r cc' runs the last command beginning with `cc' and
typing `r' re-executes the last command (*note Aliases::.).
`let'
The `let' builtin allows arithmetic to be performed on shell
variables. For details, refer to *Note Arithmetic Builtins::.
`typeset'
The `typeset' command is supplied for compatibility with the Korn
shell; however, it has been deprecated in favor of the `declare'
command (*note Bash Builtins::.).

File: bashref.info, Node: Korn Shell Variables, Next: Aliases, Prev: Korn Shell Builtins, Up: Korn Shell Features
Korn Shell Variables
====================
`REPLY'
The default variable for the `read' builtin.
`RANDOM'
Each time this parameter is referenced, a random integer between 0
and 32767 is generated. Assigning a value to this variable seeds
the random number generator.
`SECONDS'
This variable expands to the number of seconds since the shell was
started. Assignment to this variable resets the count to the
value assigned, and the expanded value becomes the value assigned
plus the number of seconds since the assignment.
`PS3'
The value of this variable is used as the prompt for the `select'
command. If this variable is not set, the `select' command
prompts with `#? '
`PS4'
This is the prompt printed before the command line is echoed when
the `-x' option is set (*note The Set Builtin::.). The default is
`+ '.
`PWD'
The current working directory as set by the `cd' builtin.
`OLDPWD'
The previous working directory as set by the `cd' builtin.
`TMOUT'
If set to a value greater than zero, the value is interpreted as
the number of seconds to wait for input after issuing the primary
prompt. Bash terminates after that number of seconds if input does
not arrive.
`LINENO'
The line number in the script or shell function currently
executing.
`FCEDIT'
The editor used as a default by the `fc' builtin command.

File: bashref.info, Node: Aliases, Prev: Korn Shell Variables, Up: Korn Shell Features
Aliases
=======
* Menu:
* Alias Builtins:: Builtins commands to maniuplate aliases.
The shell maintains a list of ALIASES that may be set and unset with
the `alias' and `unalias' builtin commands.
The first word of each command, if unquoted, is checked to see if it
has an alias. If so, that word is replaced by the text of the alias.
The alias name and the replacement text may contain any valid shell
input, including shell metacharacters, with the exception that the
alias name may not contain <=>. The first word of the replacement text
is tested for aliases, but a word that is identical to an alias being
expanded is not expanded a second time. This means that one may alias
`ls' to `"ls -F"', for instance, and Bash does not try to recursively
expand the replacement text. If the last character of the alias value
is a space or tab character, then the next command word following the
alias is also checked for alias expansion.
Aliases are created and listed with the `alias' command, and removed
with the `unalias' command.
There is no mechanism for using arguments in the replacement text,
as in `csh'. If arguments are needed, a shell function should be used
(*note Shell Functions::.).
Aliases are not expanded when the shell is not interactive, unless
the `expand_aliases' shell option is set using `shopt' (*note Bash
Builtins::.).
The rules concerning the definition and use of aliases are somewhat
confusing. Bash always reads at least one complete line of input
before executing any of the commands on that line. Aliases are
expanded when a command is read, not when it is executed. Therefore, an
alias definition appearing on the same line as another command does not
take effect until the next line of input is read. The commands
following the alias definition on that line are not affected by the new
alias. This behavior is also an issue when functions are executed.
Aliases are expanded when the function definition is read, not when the
function is executed, because a function definition is itself a
compound command. As a consequence, aliases defined in a function are
not available until after that function is executed. To be safe,
always put alias definitions on a separate line, and do not use `alias'
in compound commands.
Note that for almost every purpose, aliases are superseded by shell
functions.

File: bashref.info, Node: Alias Builtins, Up: Aliases
Alias Builtins
--------------
`alias'
alias [`-p'] [NAME[=VALUE] ...]
Without arguments or with the `-p' option, `alias' prints the list
of aliases on the standard output in a form that allows them to be
reused as input. If arguments are supplied, an alias is defined
for each NAME whose VALUE is given. If no VALUE is given, the name
and value of the alias is printed.
`unalias'
unalias [-a] [NAME ... ]
Remove each NAME from the list of aliases. If `-a' is supplied,
all aliases are removed.

File: bashref.info, Node: Bash Features, Next: Job Control, Prev: Korn Shell Features, Up: Top
Bash Features
*************
This section describes features unique to Bash.
* Menu:
* Invoking Bash:: Command line options that you can give
to Bash.
* Bash Startup Files:: When and how Bash executes scripts.
* Is This Shell Interactive?:: Determining the state of a running Bash.
* Bash Builtins:: Table of builtins specific to Bash.
* The Set Builtin:: This builtin is so overloaded it
deserves its own section.
* Bash Conditional Expressions:: Primitives used in composing expressions for
the `test' builtin.
* Bash Variables:: List of variables that exist in Bash.
* Shell Arithmetic:: Arithmetic on shell variables.
* Arrays:: Array Variables
* Printing a Prompt:: Controlling the PS1 string.
* The Restricted Shell:: A more controlled mode of shell execution.
* Bash POSIX Mode:: Making Bash behave more closely to what
the POSIX standard specifies.

File: bashref.info, Node: Invoking Bash, Next: Bash Startup Files, Up: Bash Features
Invoking Bash
=============
bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o OPTION] [ARGUMENT ...]
bash [long-opt] [-abefhkmnptuvxdBCDHP] [-o OPTION] -c STRING [ARGUMENT ...]
bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o OPTION] [ARGUMENT ...]
In addition to the single-character shell command-line options
(*note The Set Builtin::.), there are several multi-character options
that you can use. These options must appear on the command line before
the single-character options in order for them to be recognized.
`--dump-strings'
Equivalent to `-D'.
`--help'
Display a usage message on standard output and exit sucessfully.
`--login'
Make this shell act as if it were directly invoked by login. This
is equivalent to `exec -l bash' but can be issued from another
shell, such as `csh'. If you wanted to replace your current login
shell with a Bash login shell, you would say `exec bash --login'.
`--noediting'
Do not use the GNU Readline library (*note Command Line Editing::.)
to read interactive command lines.
`--noprofile'
Don't load the system-wide startup file `/etc/profile' or any of
the personal initialization files `~/.bash_profile',
`~/.bash_login', or `~/.profile' when Bash is invoked as a login
shell.
`--norc'
Don't read the `~/.bashrc' initialization file in an interactive
shell. This is on by default if the shell is invoked as `sh'.
`--posix'
Change the behavior of Bash where the default operation differs
from the POSIX 1003.2 standard to match the standard. This is
intended to make Bash behave as a strict superset of that
standard. *Note Bash POSIX Mode::, for a description of the Bash
POSIX mode.
`--rcfile FILENAME'
Execute commands from FILENAME (instead of `~/.bashrc') in an
interactive shell.
`--restricted'
Make the shell a restricted shell (*note The Restricted Shell::.).
`--verbose'
Equivalent to `-v'.
`--version'
Show version information for this instance of Bash on the standard
output and exit successfully.
There are several single-character options you can give which are
not available with the `set' builtin.
`-c STRING'
Read and execute commands from STRING after processing the
options, then exit. Any remaining arguments are assigned to the
positional parameters, starting with `$0'.
`-i'
Force the shell to run interactively.
`-r'
Make the shell restricted.
`-s'
If this flag is present, or if no arguments remain after option
processing, then commands are read from the standard input. This
option allows the positional parameters to be set when invoking an
interactive shell.
`-D'
A list of all double-quoted strings preceded by `$' is printed on
the standard ouput. These are the strings that are subject to
language translation when the current locale is not `C' or `POSIX'
(*note Locale Translation::.). This implies the `-n' option; no
commands will be executed.
An *interactive* shell is one whose input and output are both
connected to terminals (as determined by `isatty()'), or one started
with the `-i' option.
If arguments remain after option processing, and neither the `-c'
nor the `-s' option has been supplied, the first argument is assumed to
be the name of a file containing shell commands (*note Shell
Scripts::.). When Bash is invoked in this fashion, `$0' is set to the
name of the file, and the positional parameters are set to the
remaining arguments. Bash reads and executes commands from this file,
then exits. Bash's exit status is the exit status of the last command
executed in the script. If no commands are executed, the exit status
is 0.

File: bashref.info, Node: Bash Startup Files, Next: Is This Shell Interactive?, Prev: Invoking Bash, Up: Bash Features
Bash Startup Files
==================
This section describs how Bash executes its startup files. If any
of the files exist but cannot be read, Bash reports an error. Tildes
are expanded in file names as described above under Tilde Expansion
(*note Tilde Expansion::.).
When Bash is invoked as an interactive login shell, it first reads
and executes commands from the file `/etc/profile', if that file exists.
After reading that file, it looks for `~/.bash_profile',
`~/.bash_login', and `~/.profile', in that order, and reads and
executes commands from the first one that exists and is readable. The
`--noprofile' option may be used when the shell is started to inhibit
this behavior.
When a login shell exits, Bash reads and executes commands from the
file `~/.bash_logout', if it exists.
When an interactive shell that is not a login shell is started, Bash
reads and executes commands from `~/.bashrc', if that file exists.
This may be inhibited by using the `--norc' option. The `--rcfile
FILE' option will force Bash to read and execute commands from FILE
instead of `~/.bashrc'.
So, typically, your `~/.bash_profile' contains the line
`if [ -f `~/.bashrc' ]; then . `~/.bashrc'; fi'
after (or before) any login-specific initializations.
When Bash is started non-interactively, to run a shell script, for
example, it looks for the variable `BASH_ENV' in the environment,
expands its value if it appears there, and uses the expanded value as
the name of a file to read and execute. Bash behaves as if the
following command were executed:
`if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi'
but the value of the `PATH' variable is not used to search for the file
name.
If Bash is invoked with the name `sh', it tries to mimic the startup
behavior of historical versions of `sh' as closely as possible, while
conforming to the POSIX standard as well.
When invoked as a login shell, it first attempts to read and execute
commands from `/etc/profile' and `~/.profile', in that order. The
`--noprofile' option may be used to inhibit this behavior. When
invoked as an interactive shell with the name `sh', `bash' looks for
the variable `ENV', expands its value if it is defined, and uses the
expanded value as the name of a file to read and execute. Since a
shell invoked as `sh' does not attempt to read and execute commands
from any other startup files, the `--rcfile' option has no effect. A
non-interactive shell invoked with the name `sh' does not attempt to
read any startup files.
When invoked as `sh', Bash enters POSIX mode after the startup files
are read.
When Bash is started in POSIX mode, as with the `--posix' command
line option, it follows the POSIX standard for startup files. In this
mode, the `ENV' variable is expanded and commands are read and executed
from the file whose name is the expanded value. No other startup files
are read. This is done by interactive shells only.
Bash attempts to determine when it is being run by the remote shell
daemon, usually `rshd'. If Bash determines it is being run by rshd, it
reads and executes commands from `~/.bashrc', if that file exists and
is readable. It will not do this if invoked as `sh'. The `--norc'
option may be used to inhibit this behavior, and the `--rcfile' option
may be used to force another file to be read, but rshd does not
generally invoke the shell with those options or allow them to be
specified.

File: bashref.info, Node: Is This Shell Interactive?, Next: Bash Builtins, Prev: Bash Startup Files, Up: Bash Features
Is This Shell Interactive?
==========================
As defined in *Note Invoking Bash::, an interactive shell is one
whose input and output are both connected to terminals (as determined
by `isatty(3)'), or one started with the `-i' option.
You may wish to determine within a startup script whether Bash is
running interactively or not. To do this, examine the variable `$PS1';
it is unset in non-interactive shells, and set in interactive shells.
Thus:
if [ -z "$PS1" ]; then
echo This shell is not interactive
else
echo This shell is interactive
fi
Alternatively, you may test the value of the `-' special parameter.
It contains `i' when the shell is interactive. For example:
case "$-" in
*i*) echo This shell is interactive ;;
*) echo This shell is not interactive ;;
esac

File: bashref.info, Node: Bash Builtins, Next: The Set Builtin, Prev: Is This Shell Interactive?, Up: Bash Features
Bash Builtin Commands
=====================
This section describes builtin commands which are unique to or have
been extended in Bash.
`bind'
bind [-m KEYMAP] [-lpsvPSV] [-q NAME] [-r KEYSEQ]
bind [-m KEYMAP] -f FILENAME
bind [-m KEYMAP] KEYSEQ:FUNCTION-NAME
Display current Readline (*note Command Line Editing::.) key and
function bindings, or bind a key sequence to a Readline function
or macro. The binding syntax accepted is identical to that of
`.inputrc' (*note Readline Init File::.), but each binding must be
passed as a separate argument: e.g.,
`"\C-x\C-r":re-read-init-file'. Options, if supplied, have the
following meanings:
`-m KEYMAP'
Use KEYMAP as the keymap to be affected by the subsequent
bindings. Acceptable KEYMAP names are `emacs',
`emacs-standard', `emacs-meta', `emacs-ctlx', `vi',
`vi-command', and `vi-insert'. `vi' is equivalent to
`vi-command'; `emacs' is equivalent to `emacs-standard'.
`-l'
List the names of all Readline functions
`-p'
Display Readline function names and bindings in such a way
that they can be re-read
`-P'
List current Readline function names and bindings
`-v'
Display Readline variable names and values in such a way that
they can be re-read
`-V'
List current Readline variable names and values
`-s'
Display Readline key sequences bound to macros and the
strings they output in such a way that they can be re-read
`-S'
Display Readline key sequences bound to macros and the
strings they output
`-f FILENAME'
Read key bindings from FILENAME
`-q'
Query about which keys invoke the named FUNCTION
`-r KEYSEQ'
Remove any current binding for KEYSEQ
`builtin'
builtin [SHELL-BUILTIN [ARGS]]
Run a shell builtin. This is useful when you wish to define a
shell function with the same name as a shell builtin, but need the
functionality of the builtin within the function itself.
`command'
command [-pVv] COMMAND [ARGS ...]
Runs COMMAND with ARG ignoring shell functions. If you have a
shell function called `ls', and you wish to call the command `ls',
you can say `command ls'. The `-p' option means to use a default
value for `$PATH' that is guaranteed to find all of the standard
utilities.
If either the `-V' or `-v' option is supplied, a description of
COMMAND is printed. The `-v' option causes a single word
indicating the command or file name used to invoke COMMAND to be
printed; the `-V' option produces a more verbose description.
`declare'
declare [-afFrxi] [-p] [NAME[=VALUE]]
Declare variables and give them attributes. If no NAMEs are
given, then display the values of variables instead.
The `-p' option will display the attributes and values of each
NAME. When `-p' is used, additional options are ignored. The
`-F' option inhibits the display of function definitions; only the
function name and attributes are printed. `-F' implies `-f'. The
following options can be used to restrict output to variables with
the specified attributes or to give variables attributes:
`-a'
Each NAME is an array variable (*note Arrays::.).
`-f'
Use function names only.
`-i'
The variable is to be treated as an integer; arithmetic
evaluation (*note Shell Arithmetic::.) is performed when the
variable is assigned a value.
`-r'
Make NAMEs readonly. These names cannot then be assigned
values by subsequent assignment statements.
`-x'
Mark each NAME for export to subsequent commands via the
environment.
Using `+' instead of `-' turns off the attribute instead. When
used in a function, `declare' makes each NAME local, as with the
`local' command.
`echo'
echo [-neE] [arg ...]
Output the `arg's, separated by spaces, terminated with a newline.
The return status is always 0. If `-n' is specified, the
trailing newline is suppressed. If the `-e' option is given,
interpretation of the following backslash-escaped characters is
enabled. The `-E' option disables the interpretation of these
escape characters, even on systems where they are interpreted by
default. `echo' interprets the following escape sequences:
`\a'
alert (bell)
`\b'
backspace
`\c'
suppress trailing newline
`\e'
escape
`\f'
form feed
`\n'
new line
`\r'
carriage return
`\t'
horizontal tab
`\v'
vertical tab
`\\'
backslash
`\nnn'
the character whose ASCII code is `nnn' (octal)
`enable'
enable [-n] [-p] [-f FILENAME] [-ads] [NAME ...]
Enable and disable builtin shell commands. This allows you to use
a disk command which has the same name as a shell builtin. If
`-n' is used, the NAMEs become disabled. Otherwise NAMEs are
enabled. For example, to use the `test' binary found via `$PATH'
instead of the shell builtin version, type `enable -n test'.
If the `-p' option is supplied, or no NAME arguments appear, a
list of shell builtins is printed. With no other arguments, the
list consists of all enabled shell builtins. The `-a' option
means to list each builtin with an indication of whether or not it
is enabled.
The `-f' option means to load the new builtin command NAME from
shared object FILENAME, on systems that support dynamic loading.
The `-d' option will delete a builtin loaded with `-f'. If there
are no options, a list of the shell builtins is displayed. The
`-s' option restricts `enable' to the POSIX.2 special builtins.
If `-s' is used with `-f', the new builtin becomes a special
builtin.
`help'
help [PATTERN]
Display helpful information about builtin commands. If PATTERN is
specified, `help' gives detailed help on all commands matching
PATTERN, otherwise a list of the builtins is printed.
`local'
local NAME[=VALUE]
For each argument, create a local variable called NAME, and give
it VALUE. `local' can only be used within a function; it makes
the variable NAME have a visible scope restricted to that function
and its children.
`logout'
logout [N]
Exit a login shell, returning a status of N to the shell's parent.
`read'
read [-a ANAME] [-p PROMPT] [-er] [NAME ...]
One line is read from the standard input, and the first word is
assigned to the first NAME, the second word to the second NAME,
and so on, with leftover words assigned to the last NAME. Only
the characters in the value of the `IFS' variable are recognized
as word delimiters. If no names are supplied, the line read is
assigned to the variable `REPLY'. The return code is zero, unless
end-of-file is encountered. Options, if supplied, have the
following meanings:
`-r'
If this option is given, a backslash-newline pair is not
ignored, and the backslash is considered to be part of the
line.
`-p PROMPT'
Display `prompt', without a trailing newline, before
attempting to read any input. The prompt is displayed only
if input is coming from a terminal.
`-a ANAME'
The words are assigned to sequential indices of the array
variable ANAME, starting at 0.
`-e'
Readline (*note Command Line Editing::.) is used to obtain
the line.
`shopt'
shopt [-pqsu] [-o] [OPTNAME ...]
Toggle the values of variables controlling optional shell behavior.
With no options, or with the `-p' option, a list of all settable
options is displayed, with an indication of whether or not each is
set. Other options have the following meanings:
`-s'
Enable (set) each OPTNAME
`-u'
Disable (unset) each OPTNAME.
`-q'
Suppresses normal output; the return status indicates whether
the OPTNAME is set or unset. If multiple OPTNAME arguments
are given with `-q', the return status is zero if all
OPTNAMES are enabled; non-zero otherwise.
`-o'
Restricts the values of OPTNAME to be those defined for the
`-o' option to the `set' builtin (*note The Set Builtin::.).
If either of `-s' or `-u' is used with no OPTNAME arguments, the
display is limited to those options which are set or unset,
respectively.
Unless otherwise noted, the `shopt' options are disabled (off) by
default.
The return status when listing options is zero if all OPTNAMES are
enabled, non-zero otherwise. When setting or unsetting options,
the return status is zero unless an OPTNAME is not a legal shell
option.
The list of `shopt' options is:
`cdable_vars'
If this is set, an argument to the `cd' builtin command that
is not a directory is assumed to be the name of a variable
whose value is the directory to change to.
`cdspell'
If set, minor errors in the spelling of a directory component
in a `cd' command will be corrected. The errors checked for
are transposed characters, a missing character, and a
character too many. If a correction is found, the corrected
path is printed, and the command proceeds. This option is
only used by interactive shells.
`checkhash'
If this is set, Bash checks that a command found in the hash
table exists before trying to execute it. If a hashed
command no longer exists, a normal path search is performed.
`checkwinsize'
If set, Bash checks the window size after each command and,
if necessary, updates the values of `LINES' and `COLUMNS'.
`cmdhist'
If set, Bash attempts to save all lines of a multiple-line
command in the same history entry. This allows easy
re-editing of multi-line commands.
`dotglob'
If set, Bash includes filenames beginning with a `.' in the
results of filename expansion.
`execfail'
If this is set, a non-interactive shell will not exit if it
cannot execute the file specified as an argument to the `exec'
builtin command. An interactive shell does not exit if `exec'
fails.
`histappend'
If set, the history list is appended to the file named by the
value of the `HISTFILE' variable when the shell exits, rather
than overwriting the file.
`histreedit'
If set, and Readline is being used, a user is given the
opportunity to re-edit a failed history substitution.
`histverify'
If set, and Readline is being used, the results of history
substitution are not immediately passed to the shell parser.
Instead, the resulting line is loaded into the Readline
editing buffer, allowing further modification.
`hostcomplete'
If set, and Readline is being used, Bash will attempt to
perform hostname completion when a word beginning with `@' is
being completed (*note Commands For Completion::.). This
option is enabled by default.
`interactive_comments'
Allow a word beginning with `#' to cause that word and all
remaining characters on that line to be ignored in an
interactive shell. This option is enabled by default.
`lithist'
If enabled, and the `cmdhist' option is enabled, multi-line
commands are saved to the history with embedded newlines
rather than using semicolon separators where possible.
`mailwarn'
If set, and a file that Bash is checking for mail has been
accessed since the last time it was checked, the message
`"The mail in MAILFILE has been read"' is displayed.
`nullglob'
If set, Bash allows filename patterns which match no files to
expand to a null string, rather than themselves.
`promptvars'
If set, prompt strings undergo variable and parameter
expansion after being expanded (*note Printing a Prompt::.).
This option is enabled by default.
`shift_verbose'
If this is set, the `shift' builtin prints an error message
when the shift count exceeds the number of positional
parameters.
`sourcepath'
If set, the `source' builtin uses the value of `PATH' to find
the directory containing the file supplied as an argument.
This is enabled by default.
`type'
type [-all] [-type | -path] [NAME ...]
For each NAME, indicate how it would be interpreted if used as a
command name.
If the `-type' flag is used, `type' returns a single word which is
one of `alias', `function', `builtin', `file' or `keyword', if
NAME is an alias, shell function, shell builtin, disk file, or
shell reserved word, respectively. If the NAME is not found, then
nothing is printed, and `type' returns a failure status.
If the `-path' flag is used, `type' either returns the name of the
disk file that would be executed, or nothing if `-type' would not
return `file'.
If the `-all' flag is used, returns all of the places that contain
an executable named FILE. This includes aliases and functions, if
and only if the `-path' flag is not also used.
`type' accepts `-a', `-t', and `-p' as equivalent to `-all',
`-type', and `-path', respectively.
`ulimit'
ulimit [-acdflmnpstuvSH] [LIMIT]
`ulimit' provides control over the resources available to processes
started by the shell, on systems that allow such control. If an
option is given, it is interpreted as follows:
`-S'
change and report the soft limit associated with a resource.
`-H'
change and report the hard limit associated with a resource.
`-a'
all current limits are reported.
`-c'
the maximum size of core files created.
`-d'
the maximum size of a process's data segment.
`-f'
the maximum size of files created by the shell.
`-l'
The maximum size that may be locked into memory.
`-m'
the maximum resident set size.
`-n'
the maximum number of open file descriptors.
`-p'
the pipe buffer size.
`-s'
the maximum stack size.
`-t'
the maximum amount of cpu time in seconds.
`-u'
the maximum number of processes available to a single user.
`-v'
the maximum amount of virtual memory available to the process.
If LIMIT is given, it is the new value of the specified resource.
Otherwise, the current value of the soft limit for the specified
resource is printed, unless the `-H' option is supplied. When
setting new limits, if neither `-H' nor `-S' is supplied, both the
hard and soft limits are set. If no option is given, then `-f' is
assumed. Values are in 1024-byte increments, except for `-t',
which is in seconds, `-p', which is in units of 512-byte blocks,
and `-n' and `-u', which are unscaled values.

File: bashref.info, Node: The Set Builtin, Next: Bash Conditional Expressions, Prev: Bash Builtins, Up: Bash Features
The Set Builtin
===============
This builtin is so overloaded that it deserves its own section.
`set'
set [-abefhkmnptuvxdBCHP] [-o OPTION] [ARGUMENT ...]
`-a'
Mark variables which are modified or created for export.
`-b'
Cause the status of terminated background jobs to be reported
immediately, rather than before printing the next primary
prompt.
`-e'
Exit immediately if a simple command exits with a non-zero
status.
`-f'
Disable file name generation (globbing).
`-h'
Locate and remember (hash) commands as they are looked up for
execution.
`-k'
All arguments in the form of assignment statements are placed
in the environment for a command, not just those that precede
the command name.
`-m'
Job control is enabled (*note Job Control::.).
`-n'
Read commands but do not execute them.
`-o OPTION-NAME'
Set the flag corresponding to OPTION-NAME:
`allexport'
same as `-a'.
`braceexpand'
same as `-B'.
`emacs'
use an `emacs'-style line editing interface (*note
Command Line Editing::.).
`errexit'
same as `-e'.
`hashall'
same as `-h'.
`histexpand'
same as `-H'.
`history'
Enable command history, as described in *Note Bash
History Facilities::. This option is on by default in
interactive shells.
`ignoreeof'
the shell will not exit upon reading EOF.
`keyword'
same as `-k'.
`monitor'
same as `-m'.
`noclobber'
same as `-C'.
`noexec'
same as `-n'.
`noglob'
same as `-f'.
`notify'
same as `-b'.
`nounset'
same as `-u'.
`onecmd'
same as `-t'.
`physical'
same as `-P'.
`posix'
change the behavior of Bash where the default operation
differs from the POSIX 1003.2 standard to match the
standard. This is intended to make Bash behave as a
strict superset of that standard.
`privileged'
same as `-p'.
`verbose'
same as `-v'.
`vi'
use a `vi'-style line editing interface.
`xtrace'
same as `-x'.
`-p'
Turn on privileged mode. In this mode, the `$BASH_ENV' file
is not processed, and shell functions are not inherited from
the environment. This is enabled automatically on startup if
the effective user (group) id is not equal to the real user
(group) id. Turning this option off causes the effective user
and group ids to be set to the real user and group ids.
`-t'
Exit after reading and executing one command.
`-u'
Treat unset variables as an error when substituting.
`-v'
Print shell input lines as they are read.
`-x'
Print commands and their arguments as they are executed.
`-B'
The shell will perform brace expansion (*note Brace
Expansion::.). This option is on by default.
`-C'
Disallow output redirection to existing files.
`-H'
Enable `!' style history substitution (*note History
Interaction::.). This flag is on by default for interactive
shells.
`-P'
If set, do not follow symbolic links when performing commands
such as `cd' which change the current directory. The
physical directory is used instead. By default, Bash follows
the logical chain of directories when performing commands
which change the current directory.
For example, if `/usr/sys' is a link to `/usr/local/sys' then:
$ cd /usr/sys; echo $PWD
/usr/sys
$ cd ..; pwd
/usr
If `set -P' is on, then:
$ cd /usr/sys; echo $PWD
/usr/local/sys
$ cd ..; pwd
/usr/local
`--'
If no arguments follow this flag, then the positional
parameters are unset. Otherwise, the positional parameters
are set to the ARGUMENTS, even if some of them begin with a
`-'.
`-'
Signal the end of options, cause all remaining ARGUMENTS to
be assigned to the positional parameters. The `-x' and `-v'
options are turned off. If there are no arguments, the
positional parameters remain unchanged.
Using `+' rather than `-' causes these flags to be turned off.
The flags can also be used upon invocation of the shell. The
current set of flags may be found in `$-'.
The remaining N ARGUMENTS are positional parameters and are
assigned, in order, to `$1', `$2', ... `$N'. If no arguments are
given, all shell variables are printed.

File: bashref.info, Node: Bash Conditional Expressions, Next: Bash Variables, Prev: The Set Builtin, Up: Bash Features
Bash Conditional Expressions
============================
Conditional expressions are used by the `test' and `[' builtins.
Expressions may be unary or binary. Unary expressions are often
used to examine the status of a file. There are string operators and
numeric comparison operators as well. Each operator and operand must
be a separate argument. If FILE is of the form `/dev/fd/N', then file
descriptor N is checked. Expressions are composed of the following
primaries:
`-b FILE'
True if FILE exists and is a block special file.
`-c FILE'
True if FILE exists and is a character special file.
`-d FILE'
True if FILE exists and is a directory.
`-e FILE'
True if FILE exists.
`-f FILE'
True if FILE exists and is a regular file.
`-g FILE'
True if FILE exists and is set-group-id.
`-k FILE'
True if FILE has its "sticky" bit set.
`-L FILE'
True if FILE exists and is a symbolic link.
`-p FILE'
True if FILE exists and is a named pipe.
`-r FILE'
True if FILE exists and is readable.
`-s FILE'
True if FILE exists and has a size greater than zero.
`-S FILE'
True if FILE exists and is a socket.
`-t FD'
True if FD is opened on a terminal.
`-u FILE'
True if FILE exists and its set-user-id bit is set.
`-w FILE'
True if FILE exists and is writable.
`-x FILE'
True if FILE exists and is executable.
`-O FILE'
True if FILE exists and is owned by the effective user id.
`-G FILE'
True if FILE exists and is owned by the effective group id.
`FILE1 -nt FILE2'
True if FILE1 is newer (according to modification date) than FILE2.
`FILE1 -ot FILE2'
True if FILE1 is older than FILE2.
`FILE1 -ef FILE2'
True if FILE1 and FILE2 have the same device and inode numbers.
`-o OPTNAME'
True if shell option OPTNAME is enabled. The list of options
appears in the description of the `-o' option to the `set' builtin
(*note The Set Builtin::.).
`-z STRING'
True if the length of STRING is zero.
`-n STRING'
`STRING'
True if the length of STRING is non-zero.
`STRING1 = STRING2'
True if the strings are equal. `==' may be used in place of `='.
`STRING1 != STRING2'
True if the strings are not equal.
`STRING1 < STRING2'
True if STRING1 sorts before STRING2 lexicographically.
`STRING1 > STRING2'
True if STRING1 sorts after STRING2 lexicographically.
`! EXPR'
True if EXPR is false.
`EXPR1 -a EXPR2'
True if both EXPR1 and EXPR2 are true.
`EXPR1 -o EXPR2'
True if either EXPR1 and EXPR2 is true.
`ARG1 OP ARG2'
`OP' is one of `-eq', `-ne', `-lt', `-le', `-gt', or `-ge'. These
arithmetic binary operators return true if ARG1 is equal to, not
equal to, less than, less than or equal to, greater than, or
greater than or equal to ARG2, respectively. ARG1 and ARG2 may be
positive or negative integers.
The Bash `test' and `[' builtins evaluate conditional expressions
using a set of rules based on the number of arguments. These are the
rules:
0 arguments
The expression is false.
1 argument
The expression is true if and only if the argument is not null.
2 arguments
If the first argument is `!', the expression is true if and only
if the second argument is null. If the first argument is one of
the listed unary operators, the expression is true if the unary
test is true. If the first argument is not a legal unary
operator, the expression is false.
3 arguments
If the first argument is `!', the value is the negation of the
two-argument test using the second and third arguments. If the
second argument is one of the binary operators, the result of the
expression is the result of the binary test using the first and
third arguments as operands. If the first argument is exactly `('
and the third argument is exactly `)', the result is the
one-argument test of the second argument. Otherwise, the
expression is false. The `-a' and `-o' operators are considered
binary operators in this case.
4 arguments
If the first argument is `!', the result is the negation of the
three-argument expression composed of the remaining arguments.
Otherwise, the expression is parsed and evaluated according to
precedence. `-a' has a higher precedence than `-o'.
5 or more arguments
The expression is parsed and evaluated according to precedence,
with `-a' having a higher precedence than `-o'.

File: bashref.info, Node: Bash Variables, Next: Shell Arithmetic, Prev: Bash Conditional Expressions, Up: Bash Features
Bash Variables
==============
These variables are set or used by Bash, but other shells do not
normally treat them specially.
`BASH_ENV'
If this variable is set when Bash is invoked to execute a shell
script, its value is expanded and used as the name of a startup
file to read before executing the script. *Note Bash Startup
Files::.
`TIMEFORMAT'
The value of this parameter is used as a format string specifying
how the timing information for pipelines prefixed with the `time'
reserved word should be displayed. The `%' character introduces an
escape sequence that is expanded to a time value or other
information. The escape sequences and their meanings are as
follows; the braces denote optional portions.
`%%'
A literal `%'.
`%[P][l]R'
The elapsed time in seconds.
`%[P][l]U'
The number of CPU seconds spent in user mode.
`%[P][l]S'
The number of CPU seconds spent in system mode.
`%P'
The CPU percentage, computed as (%U + %S) / %R.
The optional P is a digit specifying the precision, the number of
fractional digits after a decimal point. A value of 0 causes no
decimal point or fraction to be output. At most three places
after the decimal point may be specified; values of P greater than
3 are changed to 3. If P is not specified, the value 3 is used.
The optional `l' specifies a longer format, including minutes, of
the form MMmSS.FFs. The value of P determines whether or not the
fraction is included.
If this variable is not set, bash acts as if it had the value
`$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS''.
If the value is null, no timing information is displayed. A
trailing newline is added when the format string is displayed.
`HISTCONTROL'
Set to a value of `ignorespace', it means don't enter lines which
begin with a space or tab into the history list. Set to a value
of `ignoredups', it means don't enter lines which match the last
entered line. A value of `ignoreboth' combines the two options.
Unset, or set to any other value than those above, means to save
all lines on the history list.
`HISTIGNORE'
A colon-separated list of patterns used to decide which command
lines should be saved on the history list. Each pattern is
anchored at the beginning of the line and must fully specify the
line (no implicit `*' is appended). Each pattern is tested
against the line after the checks specified by `HISTCONTROL' are
applied. In addition to the normal shell pattern matching
characters, `&' matches the previous history line. `&' may be
escaped using a backslash. The backslash is removed before
attempting a match.
`HISTIGNORE' subsumes the function of `HISTCONTROL'. A pattern of
`&' is identical to `ignoredups', and a pattern of `[ ]*' is
identical to `ignorespace'. Combining these two patterns,
separating them with a colon, provides the functionality of
`ignoreboth'.
`HISTFILE'
The name of the file to which the command history is saved. The
default is `~/.bash_history'.
`HISTSIZE'
If set, this is the maximum number of commands to remember in the
history.
`HISTFILESIZE'
The maximum number of lines contained in the history file. When
this variable is assigned a value, the history file is truncated,
if necessary, to contain no more than that number of lines. The
default value is 500. The history file is also truncated to this
size after writing it when an interactive shell exits.
`histchars'
Up to three characters which control history expansion, quick
substitution, and tokenization (*note History Interaction::.).
The first character is the "history-expansion-char", that is, the
character which signifies the start of a history expansion,
normally `!'. The second character is the character which
signifies `quick substitution' when seen as the first character on
a line, normally `^'. The optional third character is the
character which signifies the remainder of the line is a comment,
when found as the first character of a word, usually `#'. The
history comment character causes history substitution to be
skipped for the remaining words on the line. It does not
necessarily cause the shell parser to treat the rest of the line
as a comment.
`HISTCMD'
The history number, or index in the history list, of the current
command. If `HISTCMD' is unset, it loses its special properties,
even if it is subsequently reset.
`HOSTFILE'
Contains the name of a file in the same format as `/etc/hosts' that
should be read when the shell needs to complete a hostname. You
can change the file interactively; the next time you attempt to
complete a hostname, Bash will add the contents of the new file to
the already existing database.
`MAILCHECK'
How often (in seconds) that the shell should check for mail in the
files specified in `MAILPATH'.
`PROMPT_COMMAND'
If present, this contains a string which is a command to execute
before the printing of each primary prompt (`$PS1').
`UID'
The numeric real user id of the current user.
`EUID'
The numeric effective user id of the current user.
`GROUPS'
An array variable containing the list of groups of which the
current user is a member.
`PPID'
The process id of the shell's parent process.
`HOSTNAME'
The name of the current host.
`HOSTTYPE'
A string describing the machine Bash is running on.
`OSTYPE'
A string describing the operating system Bash is running on.
`MACHTYPE'
A string that fully describes the system type on which Bash is
executing, in the standard GNU CPU-COMPANY-SYSTEM format.
`SHELLOPTS'
A colon-separated list of enabled shell options. Each word in the
list is a valid argument for the `-o' option to the `set' builtin
command (*note The Set Builtin::.). The options appearing in
`SHELLOPTS' are those reported as `on' by `set -o'. If this
variable is in the environment when Bash starts up, each shell
option in the list will be enabled before reading any startup
files. This variable is readonly.
`FIGNORE'
A colon-separated list of suffixes to ignore when performing
filename completion. A file name whose suffix matches one of the
entries in `FIGNORE' is excluded from the list of matched file
names. A sample value is `.o:~'
`GLOBIGNORE'
A colon-separated list of patterns defining the set of filenames to
be ignored by filename expansion. If a filename matched by a
filename expansion pattern also matches one of the patterns in
`GLOBIGNORE', it is removed from the list of matches.
`DIRSTACK'
An array variable (*note Arrays::.) containing the current
contents of the directory stack. Directories appear in the stack
in the order they are displayed by the `dirs' builtin. Assigning
to members of this array variable may be used to modify
directories already in the stack, but the `pushd' and `popd'
builtins must be used to add and remove directories. Assignment
to this variable will not change the current directory. If
`DIRSTACK' is unset, it loses its special properties, even if it
is subsequently reset.
`PIPESTATUS'
An array variable (*note Arrays::.) containing a list of exit
status values from the processes in the most-recently-executed
foreground pipeline (which may contain only a single command).
`INPUTRC'
The name of the Readline startup file, overriding the default of
`~/.inputrc'.
`BASH'
The full filename used to execute the current instance of Bash.
`BASH_VERSION'
The version number of the current instance of Bash.
`BASH_VERSINFO'
An array variable whose members hold version information for this
instance of Bash. The values assigned to the array members are as
follows:
`BASH_VERSINFO[0]'
The major version number (the RELEASE).
`BASH_VERSINFO[1]'
The minor version number (the VERSION).
`BASH_VERSINFO[2]'
The patch level.
`BASH_VERSINFO[3]'
The build version.
`BASH_VERSINFO[4]'
The release status (e.g., BETA1).
`BASH_VERSINFO[5]'
The value of `MACHTYPE'.
`SHLVL'
Incremented by one each time a new instance of Bash is started.
This is intended to be a count of how deeply your Bash shells are
nested.
`OPTERR'
If set to the value 1, Bash displays error messages generated by
the `getopts' builtin command.
`LANG'
Used to determine the locale category for any category not
specifically selected with a variable starting with `LC_'.
`LC_ALL'
This variable overrides the value of `LANG' and any other `LC_'
variable specifying a locale category.
`LC_COLLATE'
This variable determines the collation order used when sorting the
results of filename expansion (*note Filename Expansion::.).
`LC_MESSAGES'
This variable determines the locale used to translate double-quoted
strings preceded by a `$' (*note Locale Translation::.).
`IGNOREEOF'
Controls the action of the shell on receipt of an `EOF' character
as the sole input. If set, then the value of it is the number of
consecutive `EOF' characters that can be read as the first
character on an input line before the shell will exit. If the
variable exists but does not have a numeric value (or has no
value) then the default is 10. If the variable does not exist,
then `EOF' signifies the end of input to the shell. This is only
in effect for interactive shells.

File: bashref.info, Node: Shell Arithmetic, Next: Arrays, Prev: Bash Variables, Up: Bash Features
Shell Arithmetic
================
* Menu:
* Arithmetic Evaluation:: How shell arithmetic works.
* Arithmetic Expansion:: How to use arithmetic in shell expansions.
* Arithmetic Builtins:: Builtin commands that use shell arithmetic.
Bash includes several mechanisms to evaluate arithmetic expressions
and display the result or use it as part of a command.

File: bashref.info, Node: Arithmetic Evaluation, Next: Arithmetic Expansion, Up: Shell Arithmetic
Arithmetic Evaluation
---------------------
The shell allows arithmetic expressions to be evaluated, as one of
the shell expansions or by the `let' builtin.
Evaluation is done in long integers with no check for overflow,
though division by 0 is trapped and flagged as an error. The following
list of operators is grouped into levels of equal-precedence operators.
The levels are listed in order of decreasing precedence.
`- +'
unary minus and plus
`! ~'
logical and bitwise negation
`* / %'
multiplication, division, remainder
`+ -'
addition, subtraction
`<< >>'
left and right bitwise shifts
`<= >= < >'
comparison
`== !='
equality and inequality
`&'
bitwise AND
`^'
bitwise exclusive OR
`|'
bitwise OR
`&&'
logical AND
`||'
logical OR
`expr ? expr : expr'
conditional evaluation
`= *= /= %= += -= <<= >>= &= ^= |='
assignment
Shell variables are allowed as operands; parameter expansion is
performed before the expression is evaluated. The value of a parameter
is coerced to a long integer within an expression. A shell variable
need not have its integer attribute turned on to be used in an
expression.
Constants with a leading 0 are interpreted as octal numbers. A
leading `0x' or `0X' denotes hexadecimal. Otherwise, numbers take the
form [BASE`#']N, where BASE is a decimal number between 2 and 64
representing the arithmetic base, and N is a number in that base. If
BASE is omitted, then base 10 is used. The digits greater than 9 are
represented by the lowercase letters, the uppercase letters, `_', and
`@', in that order. If BASE is less than or equal to 36, lowercase and
uppercase letters may be used interchangably to represent numbers
between 10 and 35.
Operators are evaluated in order of precedence. Sub-expressions in
parentheses are evaluated first and may override the precedence rules
above.

File: bashref.info, Node: Arithmetic Expansion, Next: Arithmetic Builtins, Prev: Arithmetic Evaluation, Up: Shell Arithmetic
Arithmetic Expansion
--------------------
Arithmetic expansion allows the evaluation of an arithmetic
expression and the substitution of the result. The format for
arithmetic expansion is:
$(( EXPRESSION ))
The expression is treated as if it were within double quotes, but a
double quote inside the braces or parentheses is not treated specially.
All tokens in the expression undergo parameter expansion, command
substitution, and quote removal. Arithmetic substitutions may be
nested.
The evaluation is performed according to the rules listed above. If
the expression is invalid, Bash prints a message indicating failure and
no substitution occurs.

File: bashref.info, Node: Arithmetic Builtins, Prev: Arithmetic Expansion, Up: Shell Arithmetic
Arithmetic Builtins
-------------------
`let'
let EXPRESSION [EXPRESSION]
The `let' builtin allows arithmetic to be performed on shell
variables. Each EXPRESSION is evaluated according to the rules
given previously (*note Arithmetic Evaluation::.). If the last
EXPRESSION evaluates to 0, `let' returns 1; otherwise 0 is
returned.

File: bashref.info, Node: Arrays, Next: Printing a Prompt, Prev: Shell Arithmetic, Up: Bash Features
Arrays
======
Bash provides one-dimensional array variables. Any variable may be
used as an array; the `declare' builtin will explicitly declare an
array. There is no maximum limit on the size of an array, nor any
requirement that members be indexed or assigned contiguously. Arrays
are zero-based.
An array is created automatically if any variable is assigned to
using the syntax
name[SUBSCRIPT]=VALUE
The SUBSCRIPT is treated as an arithmetic expression that must evaluate
to a number greater than or equal to zero. To explicitly declare an
array, use
declare -a NAME
The syntax
declare -a NAME[SUBSCRIPT]
is also accepted; the SUBSCRIPT is ignored. Attributes may be
specified for an array variable using the `declare' and `readonly'
builtins. Each attribute applies to all members of an array.
Arrays are assigned to using compound assignments of the form
name=(value1 ... valueN)
where each VALUE is of the form `[[SUBSCRIPT]=]'STRING. If the
optional subscript is supplied, that index is assigned to; otherwise
the index of the element assigned is the last index assigned to by the
statement plus one. Indexing starts at zero. This syntax is also
accepted by the `declare' builtin. Individual array elements may be
assigned to using the `name['SUBSCRIPT`]='VALUE syntax introduced above.
Any element of an array may be referenced using
`${name['SUBSCRIPT`]}'. The braces are required to avoid conflicts
with the shell's filename expansion operators. If the SUBSCRIPT is `@'
or `*', the word expands to all members of the array NAME. These
subscripts differ only when the word appears within double quotes. If
the word is double-quoted, `${name[*]}' expands to a single word with
the value of each array member separated by the first character of the
`IFS' variable, and `${name[@]}' expands each element of NAME to a
separate word. When there are no array members, `${name[@]}' expands
to nothing. This is analogous to the expansion of the special
parameters `@' and `*'. `${#name['SUBSCRIPT`]}' expands to the length
of `${name['SUBSCRIPT`]}'. If SUBSCRIPT is `@' or `*', the expansion
is the number of elements in the array. Referencing an array variable
without a subscript is equivalent to referencing element zero.
The `unset' builtin is used to destroy arrays. `unset'
NAME[SUBSCRIPT] destroys the array element at index SUBSCRIPT. `unset'
NAME, where NAME is an array, removes the entire array. A subscript of
`*' or `@' also removes the entire array.
The `declare', `local', and `readonly' builtins each accept a `-a'
option to specify an array. The `read' builtin accepts a `-a' option
to assign a list of words read from the standard input to an array, and
can read values from the standard input into individual array elements.
The `set' and `declare' builtins display array values in a way that
allows them to be reused as input.

File: bashref.info, Node: Printing a Prompt, Next: The Restricted Shell, Prev: Arrays, Up: Bash Features
Controlling the Prompt
======================
The value of the variable `PROMPT_COMMAND' is examined just before
Bash prints each primary prompt. If it is set and non-null, then the
value is executed just as if you had typed it on the command line.
In addition, the following table describes the special characters
which can appear in the prompt variables:
`\a'
a bell character.
`\d'
the date, in "Weekday Month Date" format (e.g., "Tue May 26").
`\e'
an escape character.
`\h'
the hostname, up to the first `.'.
`\H'
the hostname.
`\n'
newline.
`\s'
the name of the shell, the basename of `$0' (the portion following
the final slash).
`\t'
the time, in 24-hour HH:MM:SS format.
`\T'
the time, in 12-hour HH:MM:SS format.
`\@'
the time, in 12-hour am/pm format.
`\v'
the version of Bash (e.g., 2.00)
`\V'
the release of Bash, version + patchlevel (e.g., 2.00.0)
`\w'
the current working directory.
`\W'
the basename of `$PWD'.
`\u'
your username.
`\!'
the history number of this command.
`\#'
the command number of this command.
`\$'
if the effective uid is 0, `#', otherwise `$'.
`\nnn'
the character corresponding to the octal number `nnn'.
`\\'
a backslash.
`\['
begin a sequence of non-printing characters. This could be used to
embed a terminal control sequence into the prompt.
`\]'
end a sequence of non-printing characters.

File: bashref.info, Node: The Restricted Shell, Next: Bash POSIX Mode, Prev: Printing a Prompt, Up: Bash Features
The Restricted Shell
====================
If Bash is started with the name `rbash', or the `--restricted'
option is supplied at invocation, the shell becomes restricted. A
restricted shell is used to set up an environment more controlled than
the standard shell. A restricted shell behaves identically to `bash'
with the exception that the following are disallowed:
* Changing directories with the `cd' builtin.
* Setting or unsetting the values of the `SHELL' or `PATH' variables.
* Specifying command names containing slashes.
* Specifying a filename containing a slash as an argument to the `.'
builtin command.
* Importing function definitions from the shell environment at
startup.
* Redirecting output using the `>', `>|', `<>', `>&', `&>', and `>>'
redirection operators.
* Using the `exec' builtin to replace the shell with another command.
* Adding or deleting builtin commands with the `-f' and `-d' options
to the `enable' builtin.
* Specifying the `-p' option to the `command' builtin.
* Turning off restricted mode with `set +r'.

File: bashref.info, Node: Bash POSIX Mode, Prev: The Restricted Shell, Up: Bash Features
Bash POSIX Mode
===============
Starting Bash with the `--posix' command-line option or executing
`set -o posix' while Bash is running will cause Bash to conform more
closely to the POSIX.2 standard by changing the behavior to match that
specified by POSIX.2 in areas where the Bash default differs.
The following list is what's changed when `POSIX mode' is in effect:
1. When a command in the hash table no longer exists, Bash will
re-search `$PATH' to find the new location. This is also
available with `shopt -s checkhash'.
2. The `>&' redirection does not redirect stdout and stderr.
3. The message printed by the job control code and builtins when a job
exits with a non-zero status is `Done(status)'.
4. Reserved words may not be aliased.
5. The POSIX.2 `PS1' and `PS2' expansions of `!' to the history
number and `!!' to `!' are enabled, and parameter expansion is
performed on the value regardless of the setting of the
`promptvars' option.
6. Interactive comments are enabled by default. (Note that Bash has
them on by default anyway.)
7. The POSIX.2 startup files are executed (`$ENV') rather than the
normal Bash files.
8. Tilde expansion is only performed on assignments preceding a
command name, rather than on all assignment statements on the line.
9. The default history file is `~/.sh_history' (this is the default
value of `$HISTFILE').
10. The output of `kill -l' prints all the signal names on a single
line, separated by spaces.
11. Non-interactive shells exit if FILENAME in `.' FILENAME is not
found.
12. Redirection operators do not perform filename expansion on the word
in the redirection unless the shell is interactive.
13. Function names must be valid shell `name's. That is, they may not
contain characters other than letters, digits, and underscores, and
may not start with a digit. Declaring a function with an illegal
name causes a fatal syntax error in non-interactive shells.
14. POSIX.2 `special' builtins are found before shell functions during
command lookup.
15. If a POSIX.2 special builtin returns an error status, a
non-interactive shell exits. The fatal errors are those listed in
the POSIX.2 standard, and include things like passing incorrect
options, redirection errors, variable assignment errors for
assignments preceding the command name, and so on.
16. If the `cd' builtin finds a directory to change to using
`$CDPATH', the value it assigns to the `PWD' variable does not
contain any symbolic links, as if `cd -P' had been executed.
17. A non-interactive shell exits with an error status if a variable
assignment error occurs when no command name follows the assignment
statements. A variable assignment error occurs, for example, when
trying to assign a value to a read-only variable.
18. A non-interactive shell exits with an error status if the iteration
variable in a `for' statement or the selection variable in a
`select' statement is a read-only variable.
19. Process substitution is not available.
20. Assignment statements preceding POSIX.2 `special' builtins persist
in the shell environment after the builtin completes.
21. The `export' and `readonly' builtin commands display their output
in the format required by POSIX.2.
There is other POSIX.2 behavior that Bash does not implement.
Specifically:
1. Assignment statements affect the execution environment of all
builtins, not just special ones.

File: bashref.info, Node: Job Control, Next: Using History Interactively, Prev: Bash Features, Up: Top
Job Control
***********
This chapter disusses what job control is, how it works, and how
Bash allows you to access its facilities.
* Menu:
* Job Control Basics:: How job control works.
* Job Control Builtins:: Bash builtin commands used to interact
with job control.
* Job Control Variables:: Variables Bash uses to customize job
control.

File: bashref.info, Node: Job Control Basics, Next: Job Control Builtins, Up: Job Control
Job Control Basics
==================
Job control refers to the ability to selectively stop (suspend) the
execution of processes and continue (resume) their execution at a later
point. A user typically employs this facility via an interactive
interface supplied jointly by the system's terminal driver and Bash.
The shell associates a JOB with each pipeline. It keeps a table of
currently executing jobs, which may be listed with the `jobs' command.
When Bash starts a job asynchronously (in the background), it prints a
line that looks like:
[1] 25647
indicating that this job is job number 1 and that the process ID of the
last process in the pipeline associated with this job is 25647. All of
the processes in a single pipeline are members of the same job. Bash
uses the JOB abstraction as the basis for job control.
To facilitate the implementation of the user interface to job
control, the system maintains the notion of a current terminal process
group ID. Members of this process group (processes whose process group
ID is equal to the current terminal process group ID) receive
keyboard-generated signals such as `SIGINT'. These processes are said
to be in the foreground. Background processes are those whose process
group ID differs from the terminal's; such processes are immune to
keyboard-generated signals. Only foreground processes are allowed to
read from or write to the terminal. Background processes which attempt
to read from (write to) the terminal are sent a `SIGTTIN' (`SIGTTOU')
signal by the terminal driver, which, unless caught, suspends the
process.
If the operating system on which Bash is running supports job
control, Bash allows you to use it. Typing the SUSPEND character
(typically `^Z', Control-Z) while a process is running causes that
process to be stopped and returns you to Bash. Typing the DELAYED
SUSPEND character (typically `^Y', Control-Y) causes the process to be
stopped when it attempts to read input from the terminal, and control to
be returned to Bash. You may then manipulate the state of this job,
using the `bg' command to continue it in the background, the `fg'
command to continue it in the foreground, or the `kill' command to kill
it. A `^Z' takes effect immediately, and has the additional side
effect of causing pending output and typeahead to be discarded.
There are a number of ways to refer to a job in the shell. The
character `%' introduces a job name. Job number `n' may be referred to
as `%n'. A job may also be referred to using a prefix of the name used
to start it, or using a substring that appears in its command line.
For example, `%ce' refers to a stopped `ce' job. Using `%?ce', on the
other hand, refers to any job containing the string `ce' in its command
line. If the prefix or substring matches more than one job, Bash
reports an error. The symbols `%%' and `%+' refer to the shell's
notion of the current job, which is the last job stopped while it was
in the foreground. The previous job may be referenced using `%-'. In
output pertaining to jobs (e.g., the output of the `jobs' command), the
current job is always flagged with a `+', and the previous job with a
`-'.
Simply naming a job can be used to bring it into the foreground:
`%1' is a synonym for `fg %1', bringing job 1 from the background into
the foreground. Similarly, `%1 &' resumes job 1 in the background,
equivalent to `bg %1'
The shell learns immediately whenever a job changes state.
Normally, Bash waits until it is about to print a prompt before
reporting changes in a job's status so as to not interrupt any other
output. If the the `-b' option to the `set' builtin is set, Bash
reports such changes immediately (*note The Set Builtin::.).
If you attempt to exit Bash while jobs are stopped, the shell prints
a message warning you that you have stopped jobs. You may then use the
`jobs' command to inspect their status. If you do this, or try to exit
again immediately, you are not warned again, and the stopped jobs are
terminated.

File: bashref.info, Node: Job Control Builtins, Next: Job Control Variables, Prev: Job Control Basics, Up: Job Control
Job Control Builtins
====================
`bg'
bg [JOBSPEC]
Place JOBSPEC into the background, as if it had been started with
`&'. If JOBSPEC is not supplied, the current job is used.
`fg'
fg [JOBSPEC]
Bring JOBSPEC into the foreground and make it the current job. If
JOBSPEC is not supplied, the current job is used.
`jobs'
jobs [-lpnrs] [JOBSPEC]
jobs -x COMMAND [JOBSPEC]
The first form lists the active jobs. The options have the
following meanings:
`-l'
List process IDs in addition to the normal information
`-n'
Display information only about jobs that have changed status
since you were last notified of their status.
`-p'
List only the process ID of the job's process group leader.
`-r'
Restrict output to running jobs.
`-s'
Restrict output to stopped jobs.
If JOBSPEC is given, output is restricted to information about
that job. If JOBSPEC is not supplied, the status of all jobs is
listed.
If the `-x' option is supplied, `jobs' replaces any JOBSPEC found
in COMMAND or ARGUMENTS with the corresponding process group ID,
and executes COMMAND, passing it ARGUMENTs, returning its exit
status.
`kill'
kill [-s SIGSPEC] [-n SIGNUM] [-SIGSPEC] JOBSPEC
kill -l [SIGSPEC]
Send a signal specified by SIGSPEC or SIGNUM to the process named
by JOBSPEC. SIGSPEC is either a signal name such as `SIGINT'
(with or without the `SIG' prefix) or a signal number; SIGNUM is a
signal number. If SIGSPEC and SIGNUM are not present, `SIGTERM'
is used. The `-l' option lists the signal names, or the signal
name corresponding to SIGSPEC.
`wait'
wait [JOBSPEC|PID]
Wait until the child process specified by process ID PID or job
specification JOBSPEC exits and report its exit status. If a job
spec is given, all processes in the job are waited for. If no
arguments are given, all currently active child processes are
waited for.
`disown'
disown [-h] [JOBSPEC ...]
Without options, each JOBSPEC is removed from the table of active
jobs. If the `-h' option is given, the job is not removed from
the table, but is marked so that `SIGHUP' is not sent to the job
if the shell receives a `SIGHUP'. If JOBSPEC is not present, the
current job is used.
`suspend'
suspend [-f]
Suspend the execution of this shell until it receives a `SIGCONT'
signal. The `-f' option means to suspend even if the shell is a
login shell.
When job control is not active, the `kill' and `wait' builtins do
not accept JOBSPEC arguments. They must be supplied process IDs.

File: bashref.info, Node: Job Control Variables, Prev: Job Control Builtins, Up: Job Control
Job Control Variables
=====================
`auto_resume'
This variable controls how the shell interacts with the user and
job control. If this variable exists then single word simple
commands without redirects are treated as candidates for resumption
of an existing job. There is no ambiguity allowed; if there is
more than one job beginning with the string typed, then the most
recently accessed job will be selected. The name of a stopped
job, in this context, is the command line used to start it. If
this variable is set to the value `exact', the string supplied
must match the name of a stopped job exactly; if set to
`substring', the string supplied needs to match a substring of the
name of a stopped job. The `substring' value provides
functionality analogous to the `%?' job ID (*note Job Control
Basics::.). If set to any other value, the supplied string must
be a prefix of a stopped job's name; this provides functionality
analogous to the `%' job ID.

File: bashref.info, Node: Using History Interactively, Next: Command Line Editing, Prev: Job Control, Up: Top
Using History Interactively
***************************
This chapter describes how to use the GNU History Library
interactively, from a user's standpoint. It should be considered a
user's guide. For information on using the GNU History Library in your
own programs, see the GNU Readline Library Manual.
* Menu:
* Bash History Facilities:: How Bash lets you manipulate your command
history.
* History Interaction:: What it feels like using History as a user.

File: bashref.info, Node: Bash History Facilities, Next: History Interaction, Up: Using History Interactively
Bash History Facilities
=======================
When the `-o history' option to the `set' builtin is enabled (*note
The Set Builtin::.), the shell provides access to the COMMAND HISTORY,
the list of commands previously typed. The text of the last `HISTSIZE'
commands (default 500) is saved in a history list. The shell stores
each command in the history list prior to parameter and variable
expansion but after history expansion is performed, subject to the
values of the shell variables `HISTIGNORE' and `HISTCONTROL'. When the
shell starts up, the history is initialized from the file named by the
`HISTFILE' variable (default `~/.bash_history'). `HISTFILE' is
truncated, if necessary, to contain no more than the number of lines
specified by the value of the `HISTFILESIZE' variable. When an
interactive shell exits, the last `HISTSIZE' lines are copied from the
history list to `HISTFILE'. If the `histappend' shell option is set
(*note Bash Builtins::.), the lines are appended to the history file,
otherwise the history file is overwritten. If `HISTFILE' is unset, or
if the history file is unwritable, the history is not saved. After
saving the history, the history file is truncated to contain no more
than `$HISTFILESIZE' lines. If `HISTFILESIZE' is not set, no
truncation is performed.
The builtin command `fc' (*note Korn Shell Builtins::.) may be used
to list or edit and re-execute a portion of the history list. The
`history' builtin (*note C Shell Builtins::.) can be used to display or
modify the history list and manipulate the history file. When using
the command-line editing, search commands are available in each editing
mode that provide access to the history list.
The shell allows control over which commands are saved on the history
list. The `HISTCONTROL' and `HISTIGNORE' variables may be set to cause
the shell to save only a subset of the commands entered. The `cmdhist'
shell option, if enabled, causes the shell to attempt to save each line
of a multi-line command in the same history entry, adding semicolons
where necessary to preserve syntactic correctness. The `lithist' shell
option causes the shell to save the command with embedded newlines
instead of semicolons. *Note Bash Builtins:: for a description of
`shopt'.

File: bashref.info, Node: History Interaction, Prev: Bash History Facilities, Up: Using History Interactively
Interactive History Expansion
=============================
The History library provides a history expansion feature that is
similar to the history expansion provided by `csh'. This section
describes the syntax used to manipulate the history information.
History expansions introduce words from the history list into the
input stream, making it easy to repeat commands, insert the arguments
to a previous command into the current input line, or fix errors in
previous commands quickly.
History expansion takes place in two parts. The first is to
determine which line from the previous history should be used during
substitution. The second is to select portions of that line for
inclusion into the current one. The line selected from the previous
history is called the "event", and the portions of that line that are
acted upon are called "words". Various "modifiers" are available to
manipulate the selected words. The line is broken into words in the
same fashion that Bash does, so that several English (or Unix) words
surrounded by quotes are considered as one word. History expansions
are introduced by the appearance of the history expansion character,
which is `!' by default. Only `\' and `'' may be used to escape the
history expansion character.
Several shell options settable with the `shopt' builtin (*note Bash
Builtins::.) may be used to tailor the behavior of history expansion.
If the `histverify' shell option is enabled, and Readline is being
used, history substitutions are not immediately passed to the shell
parser. Instead, the expanded line is reloaded into the Readline
editing buffer for further modification. If Readline is being used,
and the `histreedit' shell option is enabled, a failed history
expansion will be reloaded into the Readline editing buffer for
correction. The `-p' option to the `history' builtin command may be
used to see what a history expansion will do before using it. The `-s'
option to the `history' builtin may be used to add commands to the end
of the history list without actually executing them, so that they are
available for subsequent recall.
The shell allows control of the various characters used by the
history expansion mechanism with the `histchars' variable.
* Menu:
* Event Designators:: How to specify which history line to use.
* Word Designators:: Specifying which words are of interest.
* Modifiers:: Modifying the results of substitution.

File: bashref.info, Node: Event Designators, Next: Word Designators, Up: History Interaction
Event Designators
-----------------
An event designator is a reference to a command line entry in the
history list.
`!'
Start a history substitution, except when followed by a space, tab,
the end of the line, <=> or <(>.
`!N'
Refer to command line N.
`!-N'
Refer to the command N lines back.
`!!'
Refer to the previous command. This is a synonym for `!-1'.
`!STRING'
Refer to the most recent command starting with STRING.
`!?STRING[?]'
Refer to the most recent command containing STRING. The trailing
`?' may be omitted if the STRING is followed immediately by a
newline.
`^STRING1^STRING2^'
Quick Substitution. Repeat the last command, replacing STRING1
with STRING2. Equivalent to `!!:s/STRING1/STRING2/'.
`!#'
The entire command line typed so far.

File: bashref.info, Node: Word Designators, Next: Modifiers, Prev: Event Designators, Up: History Interaction
Word Designators
----------------
Word designators are used to select desired words from the event. A
`:' separates the event specification from the word designator. It can
be omitted if the word designator begins with a `^', `$', `*', `-', or
`%'. Words are numbered from the beginning of the line, with the first
word being denoted by 0 (zero). Words are inserted into the current
line separated by single spaces.
`0 (zero)'
The `0'th word. For many applications, this is the command word.
`N'
The Nth word.
`^'
The first argument; that is, word 1.
`$'
The last argument.
`%'
The word matched by the most recent `?STRING?' search.
`X-Y'
A range of words; `-Y' abbreviates `0-Y'.
`*'
All of the words, except the `0'th. This is a synonym for `1-$'.
It is not an error to use `*' if there is just one word in the
event; the empty string is returned in that case.
`X*'
Abbreviates `X-$'
`X-'
Abbreviates `X-$' like `X*', but omits the last word.
If a word designator is supplied without an event specification, the
previous command is used as the event.

File: bashref.info, Node: Modifiers, Prev: Word Designators, Up: History Interaction
Modifiers
---------
After the optional word designator, you can add a sequence of one or
more of the following modifiers, each preceded by a `:'.
`h'
Remove a trailing pathname component, leaving only the head.
`t'
Remove all leading pathname components, leaving the tail.
`r'
Remove a trailing suffix of the form `.SUFFIX', leaving the
basename.
`e'
Remove all but the trailing suffix.
`p'
Print the new command but do not execute it.
`q'
Quote the substituted words, escaping further substitutions.
`x'
Quote the substituted words as with `q', but break into words at
spaces, tabs, and newlines.
`s/OLD/NEW/'
Substitute NEW for the first occurrence of OLD in the event line.
Any delimiter may be used in place of `/'. The delimiter may be
quoted in OLD and NEW with a single backslash. If `&' appears in
NEW, it is replaced by OLD. A single backslash will quote the
`&'. The final delimiter is optional if it is the last character
on the input line.
`&'
Repeat the previous substitution.
`g'
Cause changes to be applied over the entire event line. Used in
conjunction with `s', as in `gs/OLD/NEW/', or with `&'.

File: bashref.info, Node: Command Line Editing, Next: Installing Bash, Prev: Using History Interactively, Up: Top
Command Line Editing
********************
This chapter describes the basic features of the GNU command line
editing interface.
* Menu:
* Introduction and Notation:: Notation used in this text.
* Readline Interaction:: The minimum set of commands for editing a line.
* Readline Init File:: Customizing Readline from a user's view.
* Bindable Readline Commands:: A description of most of the Readline commands
available for binding
* Readline vi Mode:: A short description of how to make Readline
behave like the vi editor.

File: bashref.info, Node: Introduction and Notation, Next: Readline Interaction, Up: Command Line Editing
Introduction to Line Editing
============================
The following paragraphs describe the notation used to represent
keystrokes.
The text <C-k> is read as `Control-K' and describes the character
produced when the <k> key is pressed while the Control key is depressed.
The text <M-k> is read as `Meta-K' and describes the character
produced when the meta key (if you have one) is depressed, and the <k>
key is pressed. If you do not have a meta key, the identical keystroke
can be generated by typing <ESC> first, and then typing <k>. Either
process is known as "metafying" the <k> key.
The text <M-C-k> is read as `Meta-Control-k' and describes the
character produced by "metafying" <C-k>.
In addition, several keys have their own names. Specifically,
<DEL>, <ESC>, <LFD>, <SPC>, <RET>, and <TAB> all stand for themselves
when seen in this text, or in an init file (*note Readline Init
File::.).

File: bashref.info, Node: Readline Interaction, Next: Readline Init File, Prev: Introduction and Notation, Up: Command Line Editing
Readline Interaction
====================
Often during an interactive session you type in a long line of text,
only to notice that the first word on the line is misspelled. The
Readline library gives you a set of commands for manipulating the text
as you type it in, allowing you to just fix your typo, and not forcing
you to retype the majority of the line. Using these editing commands,
you move the cursor to the place that needs correction, and delete or
insert the text of the corrections. Then, when you are satisfied with
the line, you simply press <RETURN>. You do not have to be at the end
of the line to press <RETURN>; the entire line is accepted regardless
of the location of the cursor within the line.
* Menu:
* Readline Bare Essentials:: The least you need to know about Readline.
* Readline Movement Commands:: Moving about the input line.
* Readline Killing Commands:: How to delete text, and how to get it back!
* Readline Arguments:: Giving numeric arguments to commands.
* Searching:: Searching through previous lines.

File: bashref.info, Node: Readline Bare Essentials, Next: Readline Movement Commands, Up: Readline Interaction
Readline Bare Essentials
------------------------
In order to enter characters into the line, simply type them. The
typed character appears where the cursor was, and then the cursor moves
one space to the right. If you mistype a character, you can use your
erase character to back up and delete the mistyped character.
Sometimes you may miss typing a character that you wanted to type,
and not notice your error until you have typed several other
characters. In that case, you can type <C-b> to move the cursor to the
left, and then correct your mistake. Afterwards, you can move the
cursor to the right with <C-f>.
When you add text in the middle of a line, you will notice that
characters to the right of the cursor are `pushed over' to make room
for the text that you have inserted. Likewise, when you delete text
behind the cursor, characters to the right of the cursor are `pulled
back' to fill in the blank space created by the removal of the text. A
list of the basic bare essentials for editing the text of an input line
follows.
<C-b>
Move back one character.
<C-f>
Move forward one character.
<DEL>
Delete the character to the left of the cursor.
<C-d>
Delete the character underneath the cursor.
Printing characters
Insert the character into the line at the cursor.
<C-_>
Undo the last thing that you did. You can undo all the way back
to an empty line.

File: bashref.info, Node: Readline Movement Commands, Next: Readline Killing Commands, Prev: Readline Bare Essentials, Up: Readline Interaction
Readline Movement Commands
--------------------------
The above table describes the most basic possible keystrokes that
you need in order to do editing of the input line. For your
convenience, many other commands have been added in addition to <C-b>,
<C-f>, <C-d>, and <DEL>. Here are some commands for moving more rapidly
about the line.
<C-a>
Move to the start of the line.
<C-e>
Move to the end of the line.
<M-f>
Move forward a word.
<M-b>
Move backward a word.
<C-l>
Clear the screen, reprinting the current line at the top.
Notice how <C-f> moves forward a character, while <M-f> moves
forward a word. It is a loose convention that control keystrokes
operate on characters while meta keystrokes operate on words.

File: bashref.info, Node: Readline Killing Commands, Next: Readline Arguments, Prev: Readline Movement Commands, Up: Readline Interaction
Readline Killing Commands
-------------------------
"Killing" text means to delete the text from the line, but to save
it away for later use, usually by "yanking" (re-inserting) it back into
the line. If the description for a command says that it `kills' text,
then you can be sure that you can get the text back in a different (or
the same) place later.
When you use a kill command, the text is saved in a "kill-ring".
Any number of consecutive kills save all of the killed text together, so
that when you yank it back, you get it all. The kill ring is not line
specific; the text that you killed on a previously typed line is
available to be yanked back later, when you are typing another line.
Here is the list of commands for killing text.
<C-k>
Kill the text from the current cursor position to the end of the
line.
<M-d>
Kill from the cursor to the end of the current word, or if between
words, to the end of the next word.
<M-DEL>
Kill from the cursor the start of the previous word, or if between
words, to the start of the previous word.
<C-w>
Kill from the cursor to the previous whitespace. This is
different than <M-DEL> because the word boundaries differ.
And, here is how to "yank" the text back into the line. Yanking
means to copy the most-recently-killed text from the kill buffer.
<C-y>
Yank the most recently killed text back into the buffer at the
cursor.
<M-y>
Rotate the kill-ring, and yank the new top. You can only do this
if the prior command is <C-y> or <M-y>.

File: bashref.info, Node: Readline Arguments, Next: Searching, Prev: Readline Killing Commands, Up: Readline Interaction
Readline Arguments
------------------
You can pass numeric arguments to Readline commands. Sometimes the
argument acts as a repeat count, other times it is the sign of the
argument that is significant. If you pass a negative argument to a
command which normally acts in a forward direction, that command will
act in a backward direction. For example, to kill text back to the
start of the line, you might type `M-- C-k'.
The general way to pass numeric arguments to a command is to type
meta digits before the command. If the first `digit' you type is a
minus sign (<->), then the sign of the argument will be negative. Once
you have typed one meta digit to get the argument started, you can type
the remainder of the digits, and then the command. For example, to give
the <C-d> command an argument of 10, you could type `M-1 0 C-d'.

File: bashref.info, Node: Searching, Prev: Readline Arguments, Up: Readline Interaction
Searching for Commands in the History
-------------------------------------
Readline provides commands for searching through the command history
(*note Bash History Facilities::.) for lines containing a specified
string. There are two search modes: INCREMENTAL and NON-INCREMENTAL.
Incremental searches begin before the user has finished typing the
search string. As each character of the search string is typed,
readline displays the next entry from the history matching the string
typed so far. An incremental search requires only as many characters
as needed to find the desired history entry. The Escape character is
used to terminate an incremental search. Control-J will also terminate
the search. Control-G will abort an incremental search and restore the
original line. When the search is terminated, the history entry
containing the search string becomes the current line. To find other
matching entries in the history list, type Control-S or Control-R as
appropriate. This will search backward or forward in the history for
the next entry matching the search string typed so far. Any other key
sequence bound to a readline command will terminate the search and
execute that command. For instance, a `newline' will terminate the
search and accept the line, thereby executing the command from the
history list.
Non-incremental searches read the entire search string before
starting to search for matching history lines. The search string may be
typed by the user or part of the contents of the current line.

File: bashref.info, Node: Readline Init File, Next: Bindable Readline Commands, Prev: Readline Interaction, Up: Command Line Editing
Readline Init File
==================
Although the Readline library comes with a set of `emacs'-like
keybindings installed by default, it is possible that you would like to
use a different set of keybindings. You can customize programs that
use Readline by putting commands in an "inputrc" file in your home
directory. The name of this file is taken from the value of the shell
variable `INPUTRC'. If that variable is unset, the default is
`~/.inputrc'.
When a program which uses the Readline library starts up, the init
file is read, and the key bindings are set.
In addition, the `C-x C-r' command re-reads this init file, thus
incorporating any changes that you might have made to it.
* Menu:
* Readline Init File Syntax:: Syntax for the commands in the inputrc file.
* Conditional Init Constructs:: Conditional key bindings in the inputrc file.
* Sample Init File:: An example inputrc file.

File: bashref.info, Node: Readline Init File Syntax, Next: Conditional Init Constructs, Up: Readline Init File
Readline Init File Syntax
-------------------------
There are only a few basic constructs allowed in the Readline init
file. Blank lines are ignored. Lines beginning with a `#' are
comments. Lines beginning with a `$' indicate conditional constructs
(*note Conditional Init Constructs::.). Other lines denote variable
settings and key bindings.
Variable Settings
You can change the state of a few variables in Readline by using
the `set' command within the init file. Here is how you would
specify that you wish to use `vi' line editing commands:
set editing-mode vi
Right now, there are only a few variables which can be set; so
few, in fact, that we just list them here:
`bell-style'
Controls what happens when Readline wants to ring the
terminal bell. If set to `none', Readline never rings the
bell. If set to `visible', Readline uses a visible bell if
one is available. If set to `audible' (the default),
Readline attempts to ring the terminal's bell.
`comment-begin'
The string to insert at the beginning of the line when the
`insert-comment' command is executed. The default value is
`"#"'.
`completion-query-items'
The number of possible completions that determines when the
user is asked whether he wants to see the list of
possibilities. If the number of possible completions is
greater than this value, Readline will ask the user whether
or not he wishes to view them; otherwise, they are simply
listed. The default limit is `100'.
`convert-meta'
If set to `on', Readline will convert characters with the
eigth bit set to an ASCII key sequence by stripping the eigth
bit and prepending an <ESC> character, converting them to a
meta-prefixed key sequence. The default value is `on'.
`disable-completion'
If set to `On', readline will inhibit word completion.
Completion characters will be inserted into the line as if
they had been mapped to `self-insert'. The default is `off'.
`editing-mode'
The `editing-mode' variable controls which editing mode you
are using. By default, Readline starts up in Emacs editing
mode, where the keystrokes are most similar to Emacs. This
variable can be set to either `emacs' or `vi'.
`enable-keypad'
When set to `on', readline will try to enable the application
keypad when it is called. Some systems need this to enable
the arrow keys. The default is `off'.
`expand-tilde'
If set to `on', tilde expansion is performed when Readline
attempts word completion. The default is `off'.
`horizontal-scroll-mode'
This variable can be set to either `on' or `off'. Setting it
to `on' means that the text of the lines that you edit will
scroll horizontally on a single screen line when they are
longer than the width of the screen, instead of wrapping onto
a new screen line. By default, this variable is set to `off'.
`keymap'
Sets Readline's idea of the current keymap for key binding
commands. Acceptable `keymap' names are `emacs',
`emacs-standard', `emacs-meta', `emacs-ctlx', `vi',
`vi-command', and `vi-insert'. `vi' is equivalent to
`vi-command'; `emacs' is equivalent to `emacs-standard'. The
default value is `emacs'. The value of the `editing-mode'
variable also affects the default keymap.
`mark-directories'
If set to `on', completed directory names have a slash
appended. The default is `on'.
`mark-modified-lines'
This variable, when set to `on', says to display an asterisk
(`*') at the start of history lines which have been modified.
This variable is `off' by default.
`input-meta'
If set to `on', Readline will enable eight-bit input (it will
not strip the eighth bit from the characters it reads),
regardless of what the terminal claims it can support. The
default value is `off'. The name `meta-flag' is a synonym
for this variable.
`output-meta'
If set to `on', Readline will display characters with the
eighth bit set directly rather than as a meta-prefixed escape
sequence. The default is `off'.
`show-all-if-ambiguous'
This alters the default behavior of the completion functions.
If set to `on', words which have more than one possible
completion cause the matches to be listed immediately instead
of ringing the bell. The default value is `off'.
`visible-stats'
If set to `on', a character denoting a file's type is
appended to the filename when listing possible completions.
The default is `off'.
Key Bindings
The syntax for controlling key bindings in the init file is
simple. First you have to know the name of the command that you
want to change. The following pages contain tables of the command
name, the default keybinding, and a short description of what the
command does.
Once you know the name of the command, simply place the name of
the key you wish to bind the command to, a colon, and then the
name of the command on a line in the init file. The name of the
key can be expressed in different ways, depending on which is most
comfortable for you.
KEYNAME: FUNCTION-NAME or MACRO
KEYNAME is the name of a key spelled out in English. For
example:
Control-u: universal-argument
Meta-Rubout: backward-kill-word
Control-o: "> output"
In the above example, `C-u' is bound to the function
`universal-argument', and `C-o' is bound to run the macro
expressed on the right hand side (that is, to insert the text
`> output' into the line).
"KEYSEQ": FUNCTION-NAME or MACRO
KEYSEQ differs from KEYNAME above in that strings denoting an
entire key sequence can be specified, by placing the key
sequence in double quotes. Some GNU Emacs style key escapes
can be used, as in the following example, but the special
character names are not recognized.
"\C-u": universal-argument
"\C-x\C-r": re-read-init-file
"\e[11~": "Function Key 1"
In the above example, `C-u' is bound to the function
`universal-argument' (just as it was in the first example),
`C-x C-r' is bound to the function `re-read-init-file', and
`ESC [ 1 1 ~' is bound to insert the text `Function Key 1'.
The following escape sequences are available when specifying
key sequences:
`\C-'
control prefix
`\M-'
meta prefix
`\e'
an escape character
`\\'
backslash
`\"'
<">
`\''
<'>
When entering the text of a macro, single or double quotes
should be used to indicate a macro definition. Unquoted text
is assumed to be a function name. Backslash will quote any
character in the macro text, including `"' and `''. For
example, the following binding will make `C-x \' insert a
single `\' into the line:
"\C-x\\": "\\"

File: bashref.info, Node: Conditional Init Constructs, Next: Sample Init File, Prev: Readline Init File Syntax, Up: Readline Init File
Conditional Init Constructs
---------------------------
Readline implements a facility similar in spirit to the conditional
compilation features of the C preprocessor which allows key bindings
and variable settings to be performed as the result of tests. There
are three parser directives used.
`$if'
The `$if' construct allows bindings to be made based on the
editing mode, the terminal being used, or the application using
Readline. The text of the test extends to the end of the line; no
characters are required to isolate it.
`mode'
The `mode=' form of the `$if' directive is used to test
whether Readline is in `emacs' or `vi' mode. This may be
used in conjunction with the `set keymap' command, for
instance, to set bindings in the `emacs-standard' and
`emacs-ctlx' keymaps only if Readline is starting out in
`emacs' mode.
`term'
The `term=' form may be used to include terminal-specific key
bindings, perhaps to bind the key sequences output by the
terminal's function keys. The word on the right side of the
`=' is tested against the full name of the terminal and the
portion of the terminal name before the first `-'. This
allows `sun' to match both `sun' and `sun-cmd', for instance.
`application'
The APPLICATION construct is used to include
application-specific settings. Each program using the
Readline library sets the APPLICATION NAME, and you can test
for it. This could be used to bind key sequences to
functions useful for a specific program. For instance, the
following command adds a key sequence that quotes the current
or previous word in Bash:
$if Bash
# Quote the current or previous word
"\C-xq": "\eb\"\ef\""
$endif
`$endif'
This command, as you saw in the previous example, terminates an
`$if' command.
`$else'
Commands in this branch of the `$if' directive are executed if the
test fails.

File: bashref.info, Node: Sample Init File, Prev: Conditional Init Constructs, Up: Readline Init File
Sample Init File
----------------
Here is an example of an inputrc file. This illustrates key
binding, variable assignment, and conditional syntax.
# This file controls the behaviour of line input editing for
# programs that use the Gnu Readline library. Existing programs
# include FTP, Bash, and Gdb.
#
# You can re-read the inputrc file with C-x C-r.
# Lines beginning with '#' are comments.
#
# Set various bindings for emacs mode.
set editing-mode emacs
$if mode=emacs
Meta-Control-h: backward-kill-word Text after the function name is ignored
#
# Arrow keys in keypad mode
#
#"\M-OD": backward-char
#"\M-OC": forward-char
#"\M-OA": previous-history
#"\M-OB": next-history
#
# Arrow keys in ANSI mode
#
"\M-[D": backward-char
"\M-[C": forward-char
"\M-[A": previous-history
"\M-[B": next-history
#
# Arrow keys in 8 bit keypad mode
#
#"\M-\C-OD": backward-char
#"\M-\C-OC": forward-char
#"\M-\C-OA": previous-history
#"\M-\C-OB": next-history
#
# Arrow keys in 8 bit ANSI mode
#
#"\M-\C-[D": backward-char
#"\M-\C-[C": forward-char
#"\M-\C-[A": previous-history
#"\M-\C-[B": next-history
C-q: quoted-insert
$endif
# An old-style binding. This happens to be the default.
TAB: complete
# Macros that are convenient for shell interaction
$if Bash
# edit the path
"\C-xp": "PATH=${PATH}\e\C-e\C-a\ef\C-f"
# prepare to type a quoted word -- insert open and close double quotes
# and move to just after the open quote
"\C-x\"": "\"\"\C-b"
# insert a backslash (testing backslash escapes in sequences and macros)
"\C-x\\": "\\"
# Quote the current or previous word
"\C-xq": "\eb\"\ef\""
# Add a binding to refresh the line, which is unbound
"\C-xr": redraw-current-line
# Edit variable on current line.
"\M-\C-v": "\C-a\C-k$\C-y\M-\C-e\C-a\C-y="
$endif
# use a visible bell if one is available
set bell-style visible
# don't strip characters to 7 bits when reading
set input-meta on
# allow iso-latin1 characters to be inserted rather than converted to
# prefix-meta sequences
set convert-meta off
# display characters with the eighth bit set directly rather than
# as meta-prefixed characters
set output-meta on
# if there are more than 150 possible completions for a word, ask the
# user if he wants to see all of them
set completion-query-items 150
# For FTP
$if Ftp
"\C-xg": "get \M-?"
"\C-xt": "put \M-?"
"\M-.": yank-last-arg
$endif

File: bashref.info, Node: Bindable Readline Commands, Next: Readline vi Mode, Prev: Readline Init File, Up: Command Line Editing
Bindable Readline Commands
==========================
* Menu:
* Commands For Moving:: Moving about the line.
* Commands For History:: Getting at previous lines.
* Commands For Text:: Commands for changing text.
* Commands For Killing:: Commands for killing and yanking.
* Numeric Arguments:: Specifying numeric arguments, repeat counts.
* Commands For Completion:: Getting Readline to do the typing for you.
* Keyboard Macros:: Saving and re-executing typed characters
* Miscellaneous Commands:: Other miscellaneous commands.
This section describes Readline commands that may be bound to key
sequences.

File: bashref.info, Node: Commands For Moving, Next: Commands For History, Up: Bindable Readline Commands
Commands For Moving
-------------------
`beginning-of-line (C-a)'
Move to the start of the current line.
`end-of-line (C-e)'
Move to the end of the line.
`forward-char (C-f)'
Move forward a character.
`backward-char (C-b)'
Move back a character.
`forward-word (M-f)'
Move forward to the end of the next word. Words are composed of
letters and digits.
`backward-word (M-b)'
Move back to the start of this, or the previous, word. Words are
composed of letters and digits.
`clear-screen (C-l)'
Clear the screen and redraw the current line, leaving the current
line at the top of the screen.
`redraw-current-line ()'
Refresh the current line. By default, this is unbound.

File: bashref.info, Node: Commands For History, Next: Commands For Text, Prev: Commands For Moving, Up: Bindable Readline Commands
Commands For Manipulating The History
-------------------------------------
`accept-line (Newline, Return)'
Accept the line regardless of where the cursor is. If this line is
non-empty, add it to the history list according to the setting of
the `HISTCONTROL' variable. If this line was a history line, then
restore the history line to its original state.
`previous-history (C-p)'
Move `up' through the history list.
`next-history (C-n)'
Move `down' through the history list.
`beginning-of-history (M-<)'
Move to the first line in the history.
`end-of-history (M->)'
Move to the end of the input history, i.e., the line you are
entering.
`reverse-search-history (C-r)'
Search backward starting at the current line and moving `up'
through the history as necessary. This is an incremental search.
`forward-search-history (C-s)'
Search forward starting at the current line and moving `down'
through the the history as necessary. This is an incremental
search.
`non-incremental-reverse-search-history (M-p)'
Search backward starting at the current line and moving `up'
through the history as necessary using a non-incremental search
for a string supplied by the user.
`non-incremental-forward-search-history (M-n)'
Search forward starting at the current line and moving `down'
through the the history as necessary using a non-incremental search
for a string supplied by the user.
`history-search-forward ()'
Search forward through the history for the string of characters
between the start of the current line and the current cursor
position (the `point'). This is a non-incremental search. By
default, this command is unbound.
`history-search-backward ()'
Search backward through the history for the string of characters
between the start of the current line and the point. This is a
non-incremental search. By default, this command is unbound.
`yank-nth-arg (M-C-y)'
Insert the first argument to the previous command (usually the
second word on the previous line). With an argument N, insert the
Nth word from the previous command (the words in the previous
command begin with word 0). A negative argument inserts the Nth
word from the end of the previous command.
`yank-last-arg (M-., M-_)'
Insert last argument to the previous command (the last word of the
previous history entry). With an argument, behave exactly like
`yank-nth-arg'.

File: bashref.info, Node: Commands For Text, Next: Commands For Killing, Prev: Commands For History, Up: Bindable Readline Commands
Commands For Changing Text
--------------------------
`delete-char (C-d)'
Delete the character under the cursor. If the cursor is at the
beginning of the line, there are no characters in the line, and
the last character typed was not `C-d', then return `EOF'.
`backward-delete-char (Rubout)'
Delete the character behind the cursor. A numeric arg says to kill
the characters instead of deleting them.
`quoted-insert (C-q, C-v)'
Add the next character that you type to the line verbatim. This is
how to insert key sequences like <C-q>, for example.
`tab-insert (M-TAB)'
Insert a tab character.
`self-insert (a, b, A, 1, !, ...)'
Insert yourself.
`transpose-chars (C-t)'
Drag the character before the cursor forward over the character at
the cursor, moving the cursor forward as well. If the insertion
point is at the end of the line, then this transposes the last two
characters of the line. Negative argumentss don't work.
`transpose-words (M-t)'
Drag the word behind the cursor past the word in front of the
cursor moving the cursor over that word as well.
`upcase-word (M-u)'
Uppercase the current (or following) word. With a negative
argument, do the previous word, but do not move the cursor.
`downcase-word (M-l)'
Lowercase the current (or following) word. With a negative
argument, do the previous word, but do not move the cursor.
`capitalize-word (M-c)'
Capitalize the current (or following) word. With a negative
argument, do the previous word, but do not move the cursor.

File: bashref.info, Node: Commands For Killing, Next: Numeric Arguments, Prev: Commands For Text, Up: Bindable Readline Commands
Killing And Yanking
-------------------
`kill-line (C-k)'
Kill the text from the current cursor position to the end of the
line.
`backward-kill-line (C-x Rubout)'
Kill backward to the beginning of the line.
`unix-line-discard (C-u)'
Kill backward from the cursor to the beginning of the current line.
Save the killed text on the kill-ring.
`kill-whole-line ()'
Kill all characters on the current line, no matter where the
cursor is. By default, this is unbound.
`kill-word (M-d)'
Kill from the cursor to the end of the current word, or if between
words, to the end of the next word. Word boundaries are the same
as `forward-word'.
`backward-kill-word (M-DEL)'
Kill the word behind the cursor. Word boundaries are the same as
`backward-word'.
`unix-word-rubout (C-w)'
Kill the word behind the cursor, using white space as a word
boundary. The killed text is saved on the kill-ring.
`delete-horizontal-space ()'
Delete all spaces and tabs around point. By default, this is
unbound.
`kill-region ()'
Kill the text between the point and the *mark* (saved cursor
position. This text is referred to as the REGION. By default,
this command is unbound.
`copy-region-as-kill ()'
Copy the text in the region to the kill buffer, so you can yank it
right away. By default, this command is unbound.
`copy-backward-word ()'
Copy the word before point to the kill buffer. By default, this
command is unbound.
`copy-forward-word ()'
Copy the word following point to the kill buffer. By default,
this command is unbound.
`yank (C-y)'
Yank the top of the kill ring into the buffer at the current
cursor position.
`yank-pop (M-y)'
Rotate the kill-ring, and yank the new top. You can only do this
if the prior command is yank or yank-pop.

File: bashref.info, Node: Numeric Arguments, Next: Commands For Completion, Prev: Commands For Killing, Up: Bindable Readline Commands
Specifying Numeric Arguments
----------------------------
`digit-argument (M-0, M-1, ... M--)'
Add this digit to the argument already accumulating, or start a new
argument. <M-> starts a negative argument.
`universal-argument ()'
This is another way to specify an argument. If this command is
followed by one or more digits, optionally with a leading minus
sign, those digits define the argument. If the command is
followed by digits, executing `universal-argument' again ends the
numeric argument, but is otherwise ignored. As a special case, if
this command is immediately followed by a character that is
neither a digit or minus sign, the argument count for the next
command is multiplied by four. The argument count is initially
one, so executing this function the first time makes the argument
count four, a second time makes the argument count sixteen, and so
on. By default, this is not bound to a key.

File: bashref.info, Node: Commands For Completion, Next: Keyboard Macros, Prev: Numeric Arguments, Up: Bindable Readline Commands
Letting Readline Type For You
-----------------------------
`complete (TAB)'
Attempt to do completion on the text before the cursor. This is
application-specific. Generally, if you are typing a filename
argument, you can do filename completion; if you are typing a
command, you can do command completion, if you are typing in a
symbol to GDB, you can do symbol name completion, if you are
typing in a variable to Bash, you can do variable name completion,
and so on. Bash attempts completion treating the text as a
variable (if the text begins with `$'), username (if the text
begins with `~'), hostname (if the text begins with `@'), or
command (including aliases and functions) in turn. If none of
these produces a match, filename completion is attempted.
`possible-completions (M-?)'
List the possible completions of the text before the cursor.
`insert-completions (M-*)'
Insert all completions of the text before point that would have
been generated by `possible-completions'.
`complete-filename (M-/)'
Attempt filename completion on the text before point.
`possible-filename-completions (C-x /)'
List the possible completions of the text before point, treating
it as a filename.
`complete-username (M-~)'
Attempt completion on the text before point, treating it as a
username.
`possible-username-completions (C-x ~)'
List the possible completions of the text before point, treating
it as a username.
`complete-variable (M-$)'
Attempt completion on the text before point, treating it as a
shell variable.
`possible-variable-completions (C-x $)'
List the possible completions of the text before point, treating
it as a shell variable.
`complete-hostname (M-@)'
Attempt completion on the text before point, treating it as a
hostname.
`possible-hostname-completions (C-x @)'
List the possible completions of the text before point, treating
it as a hostname.
`complete-command (M-!)'
Attempt completion on the text before point, treating it as a
command name. Command completion attempts to match the text
against aliases, reserved words, shell functions, builtins, and
finally executable filenames, in that order.
`possible-command-completions (C-x !)'
List the possible completions of the text before point, treating
it as a command name.
`dynamic-complete-history (M-TAB)'
Attempt completion on the text before point, comparing the text
against lines from the history list for possible completion
matches.
`complete-into-braces (M-{)'
Perform filename completion and return the list of possible
completions enclosed within braces so the list is available to the
shell (*note Brace Expansion::.).

File: bashref.info, Node: Keyboard Macros, Next: Miscellaneous Commands, Prev: Commands For Completion, Up: Bindable Readline Commands
Keyboard Macros
---------------
`start-kbd-macro (C-x ()'
Begin saving the characters typed into the current keyboard macro.
`end-kbd-macro (C-x ))'
Stop saving the characters typed into the current keyboard macro
and save the definition.
`call-last-kbd-macro (C-x e)'
Re-execute the last keyboard macro defined, by making the
characters in the macro appear as if typed at the keyboard.

File: bashref.info, Node: Miscellaneous Commands, Prev: Keyboard Macros, Up: Bindable Readline Commands
Some Miscellaneous Commands
---------------------------
`re-read-init-file (C-x C-r)'
Read in the contents of the inputrc file, and incorporate any
bindings or variable assignments found there.
`abort (C-g)'
Abort the current editing command and ring the terminal's bell
(subject to the setting of `bell-style').
`do-uppercase-version (M-a, M-b, M-X, ...)'
If the metafied character X is lowercase, run the command that is
bound to the corresponding uppercase character.
`prefix-meta (ESC)'
Make the next character that you type be metafied. This is for
people without a meta key. Typing `ESC f' is equivalent to typing
`M-f'.
`undo (C-_, C-x C-u)'
Incremental undo, separately remembered for each line.
`revert-line (M-r)'
Undo all changes made to this line. This is like typing the `undo'
command enough times to get back to the beginning.
`tilde-expand (M-~)'
Perform tilde expansion on the current word.
`set-mark (C-@)'
Set the mark to the current point. If a numeric argument is
supplied, the mark is set to that position.
`exchange-point-and-mark (C-x C-x)'
Swap the point with the mark. The current cursor position is set
to the saved position, and the old cursor position is saved as the
mark.
`character-search (C-])'
A character is read and point is moved to the next occurrence of
that character. A negative count searches for previous
occurrences.
`character-search-backward (M-C-])'
A character is read and point is moved to the previous occurrence
of that character. A negative count searches for subsequent
occurrences.
`insert-comment (M-#)'
The value of the `comment-begin' variable is inserted at the
beginning of the current line, and the line is accepted as if a
newline had been typed. This makes the current line a shell
comment.
`dump-functions ()'
Print all of the functions and their key bindings to the readline
output stream. If a numeric argument is supplied, the output is
formatted in such a way that it can be made part of an INPUTRC
file. This command is unbound by default.
`dump-variables ()'
Print all of the settable variables and their values to the
readline output stream. If a numeric argument is supplied, the
output is formatted in such a way that it can be made part of an
INPUTRC file. This command is unbound by default.
`dump-macros ()'
Print all of the readline key sequences bound to macros and the
strings they ouput. If a numeric argument is supplied, the output
is formatted in such a way that it can be made part of an INPUTRC
file. This command is unbound by default.
`glob-expand-word (C-x *)'
The word before point is treated as a pattern for pathname
expansion, and the list of matching file names is inserted,
replacing the word.
`glob-list-expansions (C-x g)'
The list of expansions that would have been generated by
`glob-expand-word' is inserted into the line, replacing the word
before point.
`display-shell-version (C-x C-v)'
Display version information about the current instance of Bash.
`shell-expand-line (M-C-e)'
Expand the line the way the shell does when it reads it. This
performs alias and history expansion as well as all of the shell
word expansions.
`history-expand-line (M-^)'
Perform history expansion on the current line.
`alias-expand-line'
Perform alias expansion on the current line (*note Aliases::.).
`history-and-alias-expand-line'
Perform history and alias expansion on the current line.
`insert-last-argument (M-., M-_)'
A synonym for `yank-last-arg'.
`operate-and-get-next (C-o)'
Accept the current line for execution and fetch the next line
relative to the current line from the history for editing. Any
argument is ignored.
`emacs-editing-mode (C-e)'
When in `vi' editing mode, this causes a switch back to `emacs'
editing mode, as if the command `set -o emacs' had been executed.

File: bashref.info, Node: Readline vi Mode, Prev: Bindable Readline Commands, Up: Command Line Editing
Readline vi Mode
================
While the Readline library does not have a full set of `vi' editing
functions, it does contain enough to allow simple editing of the line.
The Readline `vi' mode behaves as specified in the POSIX 1003.2
standard.
In order to switch interactively between `emacs' and `vi' editing
modes, use the `set -o emacs' and `set -o vi' commands (*note The Set
Builtin::.). The Readline default is `emacs' mode.
When you enter a line in `vi' mode, you are already placed in
`insertion' mode, as if you had typed an `i'. Pressing <ESC> switches
you into `command' mode, where you can edit the text of the line with
the standard `vi' movement keys, move to previous history lines with
`k' and subsequent lines with `j', and so forth.

File: bashref.info, Node: Installing Bash, Next: Reporting Bugs, Prev: Command Line Editing, Up: Top
Installing Bash
***************
This chapter provides basic instructions for installing Bash on the
various supported platforms. The distribution supports nearly every
version of Unix (and, someday, GNU). Other independent ports exist for
OS/2, Windows 95, and Windows NT.
* Menu:
* Basic Installation:: Installation instructions.
* Compilers and Options:: How to set special options for various
systems.
* Compiling For Multiple Architectures:: How to compile Bash for more
than one kind of system from
the same source tree.
* Installation Names:: How to set the various paths used by the installation.
* Specifying the System Type:: How to configure Bash for a particular system.
* Sharing Defaults:: How to share default configuration values among GNU
programs.
* Operation Controls:: Options recognized by the configuration program.
* Optional Features:: How to enable and disable optional features when
building Bash.

File: bashref.info, Node: Basic Installation, Next: Compilers and Options, Up: Installing Bash
Basic Installation
==================
These are installation instructions for Bash.
The `configure' shell script attempts to guess correct values for
various system-dependent variables used during compilation. It uses
those values to create a `Makefile' in each directory of the package
(the top directory, the `builtins' and `doc' directories, and the each
directory under `lib'). It also creates a `config.h' file containing
system-dependent definitions. Finally, it creates a shell script named
`config.status' that you can run in the future to recreate the current
configuration, a file `config.cache' that saves the results of its
tests to speed up reconfiguring, and a file `config.log' containing
compiler output (useful mainly for debugging `configure'). If at some
point `config.cache' contains results you don't want to keep, you may
remove or edit it.
If you need to do unusual things to compile the package, please try
to figure out how `configure' could check whether or not to do them,
and mail diffs or instructions to `bash-maintainers@prep.ai.mit.edu' so
they can be considered for the next release.
The file `configure.in' is used to create `configure' by a program
called Autoconf. You only need `configure.in' if you want to change it
or regenerate `configure' using a newer version of Autoconf. If you do
this, make sure you are using Autoconf version 2.10 or newer.
If you need to change `configure.in' or regenerate `configure', you
will need to create two files: `_distribution' and `_patchlevel'.
`_distribution' should contain the major and minor version numbers of
the Bash distribution, for example `2.01'. `_patchlevel' should
contain the patch level of the Bash distribution, `0' for example. The
script `support/mkconffiles' has been provided to automate the creation
of these files.
The simplest way to compile Bash is:
1. `cd' to the directory containing the source code and type
`./configure' to configure Bash for your system. If you're using
`csh' on an old version of System V, you might need to type `sh
./configure' instead to prevent `csh' from trying to execute
`configure' itself.
Running `configure' takes awhile. While running, it prints some
messages telling which features it is checking for.
2. Type `make' to compile Bash and build the `bashbug' bug reporting
script.
3. Optionally, type `make tests' to run the Bash test suite.
4. Type `make install' to install `bash' and `bashbug'. This will
also install the manual pages and Info file.
You can remove the program binaries and object files from the source
code directory by typing `make clean'. To also remove the files that
`configure' created (so you can compile Bash for a different kind of
computer), type `make distclean'.

File: bashref.info, Node: Compilers and Options, Next: Compiling For Multiple Architectures, Prev: Basic Installation, Up: Installing Bash
Compilers and Options
=====================
Some systems require unusual options for compilation or linking that
the `configure' script does not know about. You can give `configure'
initial values for variables by setting them in the environment. Using
a Bourne-compatible shell, you can do that on the command line like
this:
CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
On systems that have the `env' program, you can do it like this:
env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure
The configuration process uses GCC to build Bash if it is available.

File: bashref.info, Node: Compiling For Multiple Architectures, Next: Installation Names, Prev: Compilers and Options, Up: Installing Bash
Compiling For Multiple Architectures
====================================
You can compile Bash for more than one kind of computer at the same
time, by placing the object files for each architecture in their own
directory. To do this, you must use a version of `make' that supports
the `VPATH' variable, such as GNU `make'. `cd' to the directory where
you want the object files and executables to go and run the `configure'
script from the source directory. You may need to supply the
`--srcdir=PATH' argument to tell `configure' where the source files
are. `configure' automatically checks for the source code in the
directory that `configure' is in and in `..'.
If you have to use a `make' that does not supports the `VPATH'
variable, you can compile Bash for one architecture at a time in the
source code directory. After you have installed Bash for one
architecture, use `make distclean' before reconfiguring for another
architecture.
Alternatively, if your system supports symbolic links, you can use
the `support/mkclone' script to create a build tree which has symbolic
links back to each file in the source directory. Here's an example
that creates a build directory in the current directory from a source
directory `/usr/gnu/src/bash-2.0':
bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 .
The `mkclone' script requires Bash, so you must have already built Bash
for at least one architecture before you can create build directories
for other architectures.

File: bashref.info, Node: Installation Names, Next: Specifying the System Type, Prev: Compiling For Multiple Architectures, Up: Installing Bash
Installation Names
==================
By default, `make install' will install into `/usr/local/bin',
`/usr/local/man', etc. You can specify an installation prefix other
than `/usr/local' by giving `configure' the option `--prefix=PATH'.
You can specify separate installation prefixes for
architecture-specific files and architecture-independent files. If you
give `configure' the option `--exec-prefix=PATH', the package will use
`PATH' as the prefix for installing programs and libraries.
Documentation and other data files will still use the regular prefix.

File: bashref.info, Node: Specifying the System Type, Next: Sharing Defaults, Prev: Installation Names, Up: Installing Bash
Specifying the System Type
==========================
There may be some features `configure' can not figure out
automatically, but needs to determine by the type of host the package
will run on. Usually `configure' can figure that out, but if it prints
a message saying it can not guess the host type, give it the
`--host=TYPE' option. `TYPE' can either be a short name for the system
type, such as `sun4', or a canonical name with three fields:
`CPU-COMPANY-SYSTEM' (e.g., `sparc-sun-sunos4.1.2').
See the file `support/config.sub' for the possible values of each field.

File: bashref.info, Node: Sharing Defaults, Next: Operation Controls, Prev: Specifying the System Type, Up: Installing Bash
Sharing Defaults
================
If you want to set default values for `configure' scripts to share,
you can create a site shell script called `config.site' that gives
default values for variables like `CC', `cache_file', and `prefix'.
`configure' looks for `PREFIX/share/config.site' if it exists, then
`PREFIX/etc/config.site' if it exists. Or, you can set the
`CONFIG_SITE' environment variable to the location of the site script.
A warning: the Bash `configure' looks for a site script, but not all
`configure' scripts do.

File: bashref.info, Node: Operation Controls, Next: Optional Features, Prev: Sharing Defaults, Up: Installing Bash
Operation Controls
==================
`configure' recognizes the following options to control how it
operates.
`--cache-file=FILE'
Use and save the results of the tests in FILE instead of
`./config.cache'. Set FILE to `/dev/null' to disable caching, for
debugging `configure'.
`--help'
Print a summary of the options to `configure', and exit.
`--quiet'
`--silent'
`-q'
Do not print messages saying which checks are being made.
`--srcdir=DIR'
Look for the Bash source code in directory DIR. Usually
`configure' can determine that directory automatically.
`--version'
Print the version of Autoconf used to generate the `configure'
script, and exit.
`configure' also accepts some other, not widely used, boilerplate
options.

File: bashref.info, Node: Optional Features, Prev: Operation Controls, Up: Installing Bash
Optional Features
=================
The Bash `configure' has a number of `--enable-FEATURE' options,
where FEATURE indicates an optional part of the package. There are
also several `--with-PACKAGE' options, where PACKAGE is something like
`gnu-malloc' or `purify' (for the Purify memory allocation checker). To
turn off the default use of a package, use `--without-PACKAGE'. To
configure Bash without a feature that is enabled by default, use
`--disable-FEATURE'.
Here is a complete list of the `--enable-' and `--with-' options
that the Bash `configure' recognizes.
`--with-afs'
Define if you are using the Andrew File System from Transarc.
`--with-curses'
Use the curses library instead of the termcap library. This should
be supplied if your system has an inadequate or incomplete termcap
database.
`--with-glibc-malloc'
Use the GNU libc version of `malloc' in `lib/malloc/gmalloc.c'.
This is somewhat slower than the default `malloc', but wastes
considerably less space.
`--with-gnu-malloc'
Use the GNU version of `malloc' in `lib/malloc/malloc.c'. This is
not the same `malloc' that appears in GNU libc, but an older
version derived from the 4.2 BSD `malloc'. This `malloc' is very
fast, but wastes a lot of space. This option is enabled by
default. The `NOTES' file contains a list of systems for which
this should be turned off, and `configure' disables this option
automatically for a number of systems.
`--with-purify'
Define this to use the Purify memory allocation checker from Pure
Software.
`--enable-minimal-config'
This produces a shell with minimal features, close to the
historical Bourne shell.
The `minimal-config' option can be used to disable all of the following
options, but it is processed first, so individual options may be
enabled using `enable-FEATURE'.
All of the following options except for `disabled-builtins' and
`usg-echo-default' are enabled by default, unless the operating system
does not provide the necessary support.
`--enable-alias'
Allow alias expansion and include the `alias' and `unalias'
builtins.
`--enable-array-variables'
Include support for one-dimensional array shell variables.
`--enable-bang-history'
Include support for `csh'-like history substitution.
`--enable-brace-expansion'
Include `csh'-like brace expansion ( `b{a,b}c' ==> `bac bbc' ).
`--enable-command-timing'
Include support for recognizing `time' as a reserved word and for
displaying timing statistics for the pipeline following `time'.
This allows pipelines as well as shell builtins and functions to
be timed.
`--enable-directory-stack'
Include support for a `csh'-like directory stack and the `pushd',
`popd', and `dirs' builtins.
`--enable-disabled-builtins'
Allow builtin commands to be invoked via `builtin xxx' even after
`xxx' has been disabled using `enable -n xxx'. See *Note Bash
Builtins::, for details of the `builtin' and `enable' builtin
commands.
`--enable-dparen-arithmetic'
Include support for the `ksh' `((...))' command.
`--enable-help-builtin'
Include the `help' builtin, which displays help on shell builtins
and variables.
`--enable-history'
Include command history and the `fc' and `history' builtin
commands.
`--enable-job-control'
This enables job control features, if the OS supports them.
`--enable-process-substitution'
This enables process substitution (*note Process Substitution::.)
if the OS provides the necessary support.
`--enable-prompt-string-decoding'
Turn on the interpretation of a number of backslash-escaped
characters in the `$PS1', `$PS2', `$PS3', and `$PS4' prompt
strings.
`--enable-readline'
Include support for command-line editing and history with the Bash
version of the Readline library.
`--enable-restricted'
Include support for a "restricted shell". If this is enabled,
Bash, when called as `rbash', enters a restricted mode. See *Note
The Restricted Shell::, for a description of restricted mode.
`--enable-select'
Include the `ksh' `select' builtin, which allows the generation of
simple menus.
`--enable-usg-echo-default'
Make the `echo' builtin expand backslash-escaped characters by
default, without requiring the `-e' option. This makes the Bash
`echo' behave more like the System V version.
The file `config.h.top' contains C Preprocessor `#define' statements
for options which are not settable from `configure'. Some of these are
not meant to be changed; beware of the consequences if you do. Read
the comments associated with each definition for more information about
its effect.

File: bashref.info, Node: Reporting Bugs, Next: Builtin Index, Prev: Installing Bash, Up: Top
Reporting Bugs
**************
Please report all bugs you find in Bash. But first, you should make
sure that it really is a bug, and that it appears in the latest version
of Bash that you have.
Once you have determined that a bug actually exists, use the
`bashbug' command to submit a bug report. If you have a fix, you are
encouraged to mail that as well! Suggestions and `philosophical' bug
reports may be mailed to `bug-bash@prep.ai.MIT.Edu' or posted to the
Usenet newsgroup `gnu.bash.bug'.
All bug reports should include:
* The version number of Bash.
* The hardware and operating system.
* The compiler used to compile Bash.
* A description of the bug behaviour.
* A short script or `recipe' which exercises the bug and may be used
to reproduce it.
`bashbug' inserts the first three items automatically into the template
it provides for filing a bug report.
Please send all reports concerning this manual to
`chet@ins.CWRU.Edu'.

File: bashref.info, Node: Builtin Index, Next: Reserved Word Index, Prev: Reporting Bugs, Up: Top
Index of Shell Builtin Commands
*******************************
* Menu:
* .: Bourne Shell Builtins.
* :: Bourne Shell Builtins.
* [: Bourne Shell Builtins.
* alias: Alias Builtins.
* bg: Job Control Builtins.
* bind: Bash Builtins.
* break: Bourne Shell Builtins.
* builtin: Bash Builtins.
* cd: Bourne Shell Builtins.
* command: Bash Builtins.
* continue: Bourne Shell Builtins.
* declare: Bash Builtins.
* dirs: C Shell Builtins.
* disown: Job Control Builtins.
* echo: Bash Builtins.
* enable: Bash Builtins.
* eval: Bourne Shell Builtins.
* exec: Bourne Shell Builtins.
* exit: Bourne Shell Builtins.
* export: Bourne Shell Builtins.
* fc: Korn Shell Builtins.
* fg: Job Control Builtins.
* getopts: Bourne Shell Builtins.
* hash: Bourne Shell Builtins.
* help: Bash Builtins.
* history: C Shell Builtins.
* jobs: Job Control Builtins.
* kill: Job Control Builtins.
* let <1>: Arithmetic Builtins.
* let: Korn Shell Builtins.
* local: Bash Builtins.
* logout <1>: Bash Builtins.
* logout: C Shell Builtins.
* popd: C Shell Builtins.
* pushd: C Shell Builtins.
* pwd: Bourne Shell Builtins.
* read: Bash Builtins.
* readonly: Bourne Shell Builtins.
* return: Bourne Shell Builtins.
* set: The Set Builtin.
* shift: Bourne Shell Builtins.
* shopt: Bash Builtins.
* source: C Shell Builtins.
* suspend: Job Control Builtins.
* test: Bourne Shell Builtins.
* times: Bourne Shell Builtins.
* trap: Bourne Shell Builtins.
* type: Bash Builtins.
* typeset: Korn Shell Builtins.
* ulimit: Bash Builtins.
* umask: Bourne Shell Builtins.
* unalias: Alias Builtins.
* unset: Bourne Shell Builtins.
* wait: Job Control Builtins.

File: bashref.info, Node: Reserved Word Index, Next: Variable Index, Prev: Builtin Index, Up: Top
Shell Reserved Words
********************
* Menu:
* !: Pipelines.
* case: Conditional Constructs.
* do: Looping Constructs.
* done: Looping Constructs.
* elif: Conditional Constructs.
* else: Conditional Constructs.
* esac: Conditional Constructs.
* fi: Conditional Constructs.
* for: Looping Constructs.
* function: Shell Functions.
* if: Conditional Constructs.
* in: Conditional Constructs.
* select: Korn Shell Constructs.
* then: Conditional Constructs.
* time: Pipelines.
* until: Looping Constructs.
* while: Looping Constructs.
* {: Command Grouping.
* }: Command Grouping.

File: bashref.info, Node: Variable Index, Next: Function Index, Prev: Reserved Word Index, Up: Top
Parameter and Variable Index
****************************
* Menu:
* !: Special Parameters.
* #: Special Parameters.
* $: Special Parameters.
* *: Special Parameters.
* -: Special Parameters.
* 0: Special Parameters.
* ?: Special Parameters.
* @: Special Parameters.
* _: Special Parameters.
* auto_resume: Job Control Variables.
* BASH: Bash Variables.
* BASH_ENV: Bash Variables.
* BASH_VERSINFO: Bash Variables.
* BASH_VERSION: Bash Variables.
* bell-style: Readline Init File Syntax.
* CDPATH: Bourne Shell Variables.
* comment-begin: Readline Init File Syntax.
* completion-query-items: Readline Init File Syntax.
* convert-meta: Readline Init File Syntax.
* DIRSTACK: Bash Variables.
* disable-completion: Readline Init File Syntax.
* editing-mode: Readline Init File Syntax.
* enable-keypad: Readline Init File Syntax.
* EUID: Bash Variables.
* expand-tilde: Readline Init File Syntax.
* FCEDIT: Korn Shell Variables.
* FIGNORE: Bash Variables.
* GLOBIGNORE: Bash Variables.
* GROUPS: Bash Variables.
* histchars: Bash Variables.
* HISTCMD: Bash Variables.
* HISTCONTROL: Bash Variables.
* HISTFILE: Bash Variables.
* HISTFILESIZE: Bash Variables.
* HISTIGNORE: Bash Variables.
* HISTSIZE: Bash Variables.
* HOME: Bourne Shell Variables.
* horizontal-scroll-mode: Readline Init File Syntax.
* HOSTFILE: Bash Variables.
* HOSTNAME: Bash Variables.
* HOSTTYPE: Bash Variables.
* IFS: Bourne Shell Variables.
* IGNOREEOF <1>: Bash Variables.
* IGNOREEOF: C Shell Variables.
* input-meta: Readline Init File Syntax.
* INPUTRC: Bash Variables.
* keymap: Readline Init File Syntax.
* LANG: Bash Variables.
* LC_ALL: Bash Variables.
* LC_COLLATE: Bash Variables.
* LC_MESSAGES: Bash Variables.
* LINENO: Korn Shell Variables.
* MACHTYPE: Bash Variables.
* MAIL: Bourne Shell Variables.
* MAILCHECK: Bash Variables.
* MAILPATH: Bourne Shell Variables.
* mark-modified-lines: Readline Init File Syntax.
* meta-flag: Readline Init File Syntax.
* OLDPWD: Korn Shell Variables.
* OPTARG: Bourne Shell Variables.
* OPTERR: Bash Variables.
* OPTIND: Bourne Shell Variables.
* OSTYPE: Bash Variables.
* output-meta: Readline Init File Syntax.
* PATH: Bourne Shell Variables.
* PIPESTATUS: Bash Variables.
* PPID: Bash Variables.
* PROMPT_COMMAND: Bash Variables.
* PS1: Bourne Shell Variables.
* PS2: Bourne Shell Variables.
* PS3: Korn Shell Variables.
* PS4: Korn Shell Variables.
* PWD: Korn Shell Variables.
* RANDOM: Korn Shell Variables.
* REPLY: Korn Shell Variables.
* SECONDS: Korn Shell Variables.
* SHELLOPTS: Bash Variables.
* SHLVL: Bash Variables.
* show-all-if-ambiguous: Readline Init File Syntax.
* TIMEFORMAT: Bash Variables.
* TMOUT: Korn Shell Variables.
* UID: Bash Variables.
* visible-stats: Readline Init File Syntax.

File: bashref.info, Node: Function Index, Next: Concept Index, Prev: Variable Index, Up: Top
Function Index
**************
* Menu:
* abort (C-g): Miscellaneous Commands.
* accept-line (Newline, Return): Commands For History.
* backward-char (C-b): Commands For Moving.
* backward-delete-char (Rubout): Commands For Text.
* backward-kill-line (C-x Rubout): Commands For Killing.
* backward-kill-word (M-DEL): Commands For Killing.
* backward-word (M-b): Commands For Moving.
* beginning-of-history (M-<): Commands For History.
* beginning-of-line (C-a): Commands For Moving.
* call-last-kbd-macro (C-x e): Keyboard Macros.
* capitalize-word (M-c): Commands For Text.
* character-search (C-]): Miscellaneous Commands.
* character-search-backward (M-C-]): Miscellaneous Commands.
* clear-screen (C-l): Commands For Moving.
* complete (TAB): Commands For Completion.
* copy-backward-word (): Commands For Killing.
* copy-forward-word (): Commands For Killing.
* copy-region-as-kill (): Commands For Killing.
* delete-char (C-d): Commands For Text.
* delete-horizontal-space (): Commands For Killing.
* digit-argument (M-0, M-1, ... M--): Numeric Arguments.
* do-uppercase-version (M-a, M-b, M-X, ...): Miscellaneous Commands.
* downcase-word (M-l): Commands For Text.
* dump-functions (): Miscellaneous Commands.
* dump-macros (): Miscellaneous Commands.
* dump-variables (): Miscellaneous Commands.
* end-kbd-macro (C-x )): Keyboard Macros.
* end-of-history (M->): Commands For History.
* end-of-line (C-e): Commands For Moving.
* exchange-point-and-mark (C-x C-x): Miscellaneous Commands.
* forward-char (C-f): Commands For Moving.
* forward-search-history (C-s): Commands For History.
* forward-word (M-f): Commands For Moving.
* history-search-backward (): Commands For History.
* history-search-forward (): Commands For History.
* insert-comment (M-#): Miscellaneous Commands.
* insert-completions (M-*): Commands For Completion.
* kill-line (C-k): Commands For Killing.
* kill-region (): Commands For Killing.
* kill-whole-line (): Commands For Killing.
* kill-word (M-d): Commands For Killing.
* next-history (C-n): Commands For History.
* non-incremental-forward-search-history (M-n): Commands For History.
* non-incremental-reverse-search-history (M-p): Commands For History.
* possible-completions (M-?): Commands For Completion.
* prefix-meta (ESC): Miscellaneous Commands.
* previous-history (C-p): Commands For History.
* quoted-insert (C-q, C-v): Commands For Text.
* re-read-init-file (C-x C-r): Miscellaneous Commands.
* redraw-current-line (): Commands For Moving.
* reverse-search-history (C-r): Commands For History.
* revert-line (M-r): Miscellaneous Commands.
* self-insert (a, b, A, 1, !, ...): Commands For Text.
* set-mark (C-@): Miscellaneous Commands.
* start-kbd-macro (C-x (): Keyboard Macros.
* tab-insert (M-TAB): Commands For Text.
* tilde-expand (M-~): Miscellaneous Commands.
* transpose-chars (C-t): Commands For Text.
* transpose-words (M-t): Commands For Text.
* undo (C-_, C-x C-u): Miscellaneous Commands.
* universal-argument (): Numeric Arguments.
* unix-line-discard (C-u): Commands For Killing.
* unix-word-rubout (C-w): Commands For Killing.
* upcase-word (M-u): Commands For Text.
* yank (C-y): Commands For Killing.
* yank-last-arg (M-., M-_): Commands For History.
* yank-nth-arg (M-C-y): Commands For History.
* yank-pop (M-y): Commands For Killing.

File: bashref.info, Node: Concept Index, Prev: Function Index, Up: Top
Concept Index
*************
* Menu:
* alias expansion: Aliases.
* arithmetic evaluation: Arithmetic Evaluation.
* arithmetic expansion: Arithmetic Expansion.
* arithmetic, shell: Shell Arithmetic.
* arrays: Arrays.
* background: Job Control Basics.
* Bash configuration: Basic Installation.
* Bash installation: Basic Installation.
* Bourne shell: Basic Shell Features.
* brace expansion: Brace Expansion.
* builtin: Definitions.
* command editing: Readline Bare Essentials.
* command execution: Command Search and Execution.
* command history: Bash History Facilities.
* command search: Command Search and Execution.
* command substitution: Command Substitution.
* command timing: Pipelines.
* commands, conditional: Conditional Constructs.
* commands, grouping: Command Grouping.
* commands, lists: Lists.
* commands, looping: Looping Constructs.
* commands, pipelines: Pipelines.
* commands, simple: Simple Commands.
* comments, shell: Comments.
* configuration: Basic Installation.
* control operator: Definitions.
* editing command lines: Readline Bare Essentials.
* environment: Environment.
* evaluation, arithmetic: Arithmetic Evaluation.
* event designators: Event Designators.
* exit status <1>: Definitions.
* exit status: Exit Status.
* expansion: Shell Expansions.
* expansion, arithmetic: Arithmetic Expansion.
* expansion, brace: Brace Expansion.
* expansion, filename: Filename Expansion.
* expansion, parameter: Shell Parameter Expansion.
* expansion, pathname: Filename Expansion.
* expansion, tilde: Tilde Expansion.
* expressions, arithmetic: Arithmetic Evaluation.
* expressions, conditional: Bash Conditional Expressions.
* field: Definitions.
* filename: Definitions.
* filename expansion: Filename Expansion.
* foreground: Job Control Basics.
* functions, shell: Shell Functions.
* history events: Event Designators.
* history expansion: History Interaction.
* history list: Bash History Facilities.
* History, how to use: Job Control Variables.
* identifier: Definitions.
* initialization file, readline: Readline Init File.
* installation: Basic Installation.
* interaction, readline: Readline Interaction.
* interactive shell <1>: Is This Shell Interactive?.
* interactive shell: Invoking Bash.
* job: Definitions.
* job control <1>: Definitions.
* job control: Job Control Basics.
* kill ring: Readline Killing Commands.
* killing text: Readline Killing Commands.
* localization: Locale Translation.
* metacharacter: Definitions.
* name: Definitions.
* notation, readline: Readline Bare Essentials.
* operator, shell: Definitions.
* parameter expansion: Shell Parameter Expansion.
* parameters: Shell Parameters.
* parameters, positional: Positional Parameters.
* parameters, special: Special Parameters.
* pathname expansion: Filename Expansion.
* pipeline: Pipelines.
* POSIX: Definitions.
* POSIX Mode: Bash POSIX Mode.
* process group: Definitions.
* process group ID: Definitions.
* process substitution: Process Substitution.
* prompting: Printing a Prompt.
* quoting: Quoting.
* quoting, ANSI: ANSI-C Quoting.
* Readline, how to use: Modifiers.
* redirection: Redirections.
* reserved word: Definitions.
* restricted shell: The Restricted Shell.
* return status: Definitions.
* shell function: Shell Functions.
* shell script: Shell Scripts.
* shell variable: Shell Parameters.
* signal: Definitions.
* signal handling: Signals.
* special builtin: Definitions.
* startup files: Bash Startup Files.
* suspending jobs: Job Control Basics.
* tilde expansion: Tilde Expansion.
* token: Definitions.
* variable, shell: Shell Parameters.
* word: Definitions.
* word splitting: Word Splitting.
* yanking text: Readline Killing Commands.

Tag Table:
Node: Top1179
Node: Introduction3283
Node: What is Bash?3508
Node: What is a shell?4592
Node: Definitions6473
Node: Basic Shell Features9134
Node: Shell Syntax10655
Node: Shell Operation10945
Node: Quoting12179
Node: Escape Character13214
Node: Single Quotes13645
Node: Double Quotes13974
Node: ANSI-C Quoting14670
Node: Locale Translation15402
Node: Comments15823
Node: Simple Commands16347
Node: Pipelines16936
Node: Lists18007
Node: Looping Constructs19282
Node: Conditional Constructs20459
Node: Command Grouping22526
Node: Shell Functions23912
Node: Shell Parameters25685
Node: Positional Parameters27008
Node: Special Parameters27702
Node: Shell Expansions30268
Node: Shell Parameter Expansion32272
Node: Command Substitution38280
Node: Process Substitution39280
Node: Word Splitting40186
Node: Filename Expansion41638
Node: Quote Removal44004
Node: Redirections44290
Node: Executing Commands50031
Node: Command Search and Execution50486
Node: Environment52220
Node: Exit Status53856
Node: Signals54873
Node: Shell Scripts56084
Node: Bourne Shell Features57953
Node: Bourne Shell Builtins58623
Node: Bourne Shell Variables66977
Node: Other Bourne Shell Features68514
Node: Major Differences From The Bourne Shell69271
Node: Csh Features79631
Node: Brace Expansion80549
Node: Tilde Expansion82104
Node: C Shell Builtins82736
Node: C Shell Variables87292
Node: Korn Shell Features87700
Node: Korn Shell Constructs88428
Node: Korn Shell Builtins90143
Node: Korn Shell Variables92301
Node: Aliases93860
Node: Alias Builtins96326
Node: Bash Features96942
Node: Invoking Bash97933
Node: Bash Startup Files101798
Node: Is This Shell Interactive?105373
Node: Bash Builtins106356
Node: The Set Builtin122211
Node: Bash Conditional Expressions127586
Node: Bash Variables132237
Node: Shell Arithmetic142271
Node: Arithmetic Evaluation142739
Node: Arithmetic Expansion144769
Node: Arithmetic Builtins145573
Node: Arrays146044
Node: Printing a Prompt149071
Node: The Restricted Shell150669
Node: Bash POSIX Mode151899
Node: Job Control155583
Node: Job Control Basics156048
Node: Job Control Builtins160191
Node: Job Control Variables163114
Node: Using History Interactively164261
Node: Bash History Facilities164850
Node: History Interaction167248
Node: Event Designators169810
Node: Word Designators170737
Node: Modifiers171986
Node: Command Line Editing173303
Node: Introduction and Notation173963
Node: Readline Interaction175001
Node: Readline Bare Essentials176193
Node: Readline Movement Commands177736
Node: Readline Killing Commands178648
Node: Readline Arguments180368
Node: Searching181345
Node: Readline Init File182981
Node: Readline Init File Syntax184037
Node: Conditional Init Constructs191820
Node: Sample Init File194101
Node: Bindable Readline Commands197134
Node: Commands For Moving197884
Node: Commands For History198731
Node: Commands For Text201404
Node: Commands For Killing203148
Node: Numeric Arguments205174
Node: Commands For Completion206300
Node: Keyboard Macros209262
Node: Miscellaneous Commands209820
Node: Readline vi Mode214036
Node: Installing Bash214914
Node: Basic Installation215983
Node: Compilers and Options218908
Node: Compiling For Multiple Architectures219642
Node: Installation Names221299
Node: Specifying the System Type222021
Node: Sharing Defaults222732
Node: Operation Controls223397
Node: Optional Features224302
Node: Reporting Bugs229185
Node: Builtin Index230265
Node: Reserved Word Index233732
Node: Variable Index235059
Node: Function Index240327
Node: Concept Index244750

End Tag Table
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