Bash Reference Manual
This text is a brief description of the features that are present in
the Bash shell.
This is Edition 2.5a, last updated 13 November 2001,
of The GNU Bash Reference Manual,
for Bash, Version 2.05a.
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.
| 7. Job Control |
|
A chapter describing what job control is
and how Bash allows you to use it. |
| Concept Index |
|
General index for concepts described in
this manual. |
1. Introduction
1.1 What is Bash?
Bash is the shell, or command language interpreter,
for the GNU operating system.
The name is an acronym for the `Bourne-Again SHell',
a pun on Stephen 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 largely compatible with sh and incorporates useful
features from the Korn shell ksh and the C shell csh.
It is 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 provides other shells, including
a version of csh, Bash is 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 MS-DOS, OS/2,
Windows 95/98, and Windows NT.
1.2 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 GNU utilities,
and a programming language, allowing these utilitites to be
combined. Files containing commands can be created, and become
commands themselves. These new commands have the same status as
system commands in directories such as `/bin', allowing users
or groups to establish custom environments.
A shell allows execution of GNU commands, both synchronously and
asynchronously.
The shell waits for synchronous commands to complete before accepting
more input; asynchronous commands continue to execute in parallel
with the shell while it reads and executes additional commands.
The redirection constructs permit
fine-grained control of the input and output of those commands.
Moreover, the shell allows control over the contents of commands'
environments.
Shells may be used interactively or non-interactively: they accept
input typed from the keyboard or from a file.
Shells also provide a small set of built-in
commands (builtins) implementing functionality impossible
or inconvenient to obtain via separate utilities.
For example, cd, break, continue, and
exec) cannot be implemented outside of the shell because
they directly manipulate the shell itself.
The history, getopts, kill, or pwd
builtins, among others, could be implemented in separate utilities,
but they are more convenient to use as builtin commands.
All of the shell builtins are described in
subsequent sections.
While executing commands is essential, most of the power (and
complexity) of shells is due to their embedded programming
languages. Like any high-level language, the shell provides
variables, flow control constructs, quoting, and functions.
Shells offer features geared specifically for
interactive use rather than to augment the programming language.
These interactive features include job control, command line
editing, history and aliases. Each of these features is
described in this manual.
2. 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. The value is restricted
to eight bits, so the maximum value is 255.
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. Names are used as
shell variable and function names.
Also referred to as an identifier.
operator
-
A
control operator or a redirection operator.
See section 3.6 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 kernel
of an event occurring in the system.
special builtin
-
A shell builtin command that has been classified as special by the
POSIX 1003.2 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.
3. 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.
3.1 Shell Syntax
When the shell reads input, it proceeds through a
sequence of operations. If the input indicates the beginning of a
comment, the shell ignores the comment symbol (`#'), and the rest
of that line.
Otherwise, roughly speaking, the shell reads its input and
divides the input into words and operators, employing the quoting rules
to select which meanings to assign various words and characters.
The shell then parses these tokens into commands and other constructs,
removes the special meaning of certain words or characters, expands
others, redirects input and output as needed, executes the specified
command, waits for the command's exit status, and makes that exit status
available for further inspection or processing.
3.1.1 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:
-
Reads its input from a file (see section 3.8 Shell Scripts), from a string
supplied as an argument to the `-c' invocation option
(see section 6.1 Invoking Bash), or from the user's terminal.
-
Breaks the input into words and operators, obeying the quoting rules
described in 3.1.2 Quoting. These tokens are separated by
metacharacters. Alias expansion is performed by this step
(see section 6.6 Aliases).
-
Parses the tokens into simple and compound commands
(see section 3.2 Shell Commands).
-
Performs the various shell expansions (see section 3.5 Shell Expansions), breaking
the expanded tokens into lists of filenames (see section 3.5.8 Filename Expansion)
and commands and arguments.
-
Performs any necessary redirections (see section 3.6 Redirections) and removes
the redirection operators and their operands from the argument list.
-
Executes the command (see section 3.7 Executing Commands).
-
Optionally waits for the command to complete and collects its exit
status (see section 3.7.5 Exit Status).
3.1.2 Quoting
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 (see section 2. Definitions)
has special meaning to the shell and must be quoted if it is to
represent itself.
When the command history expansion facilities are being used, the
history expansion character, usually `!', must be quoted
to prevent history expansion. See section 9.1 Bash History Facilities, for
more details concerning history expansion.
There are three quoting mechanisms: the
escape character, single quotes, and double quotes.
3.1.2.1 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 itself is not quoted, the
\newline
is treated as a line continuation (that is, it is removed from
the input stream and effectively ignored).
3.1.2.2 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.
3.1.2.3 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 (see section 3.5 Shell Expansions).
The backslash retains its special meaning only when followed by one of
the following characters:
`$', ``', `"', `\', or newline.
Within double quotes, backslashes that are followed by one of these
characters are removed. Backslashes preceding characters without a
special meaning are left unmodified.
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 (see section 3.5.3 Shell Parameter Expansion).
3.1.2.4 ANSI-C Quoting
Words of the form $'string' are treated specially. The
word expands to string, with backslash-escaped characters replaced
as specified by the ANSI C standard. Backslash escape sequences, if
present, are decoded as follows:
\a
- alert (bell)
\b
- backspace
\e
- an escape character (not ANSI C)
\f
- form feed
\n
- newline
\r
- carriage return
\t
- horizontal tab
\v
- vertical tab
\\
- backslash
\'
- single quote
\nnn
- the eight-bit character whose value is the octal value nnn
(one to three digits)
\xHH
- the eight-bit character whose value is the hexadecimal value HH
(one or two hex digits)
The expanded result is single-quoted, as if the dollar sign had not
been present.
3.1.2.5 Locale-Specific Translation
A double-quoted string preceded by a dollar sign (`$') 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.
Some systems use the message catalog selected by the LC_MESSAGES
shell variable. Others create the name of the message catalog from the
value of the TEXTDOMAIN shell variable, possibly adding a
suffix of `.mo'. If you use the TEXTDOMAIN variable, you
may need to set the TEXTDOMAINDIR variable to the location of
the message catalog files. Still others use both variables in this
fashion:
TEXTDOMAINDIR/LC_MESSAGES/LC_MESSAGES/TEXTDOMAIN.mo.
3.1.3 Comments
In a non-interactive shell, or an interactive shell in which the
interactive_comments option to the shopt
builtin is enabled (see section 4.2 Bash Builtin Commands),
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.
See section 6.3 Interactive Shells, for a description of what makes
a shell interactive.
3.2 Shell Commands
A simple shell command such as echo a b c consists of the command
itself followed by arguments, separated by spaces.
More complex shell commands are composed of simple commands arranged together
in a variety of ways: in a pipeline in which the output of one command
becomes the input of a second, in a loop or conditional construct, or in
some other grouping.
3.2.1 Simple Commands
A simple command is the kind of command encountered most often.
It's just a sequence of words separated by blanks, terminated
by one of the shell's control operators (see section 2. Definitions). The
first word generally specifies a command to be executed, with the
rest of the words being that command's arguments.
The return status (see section 3.7.5 Exit Status) of a simple command is
its exit status as provided
by the POSIX 1003.1 waitpid function, or 128+n if
the command was terminated by signal n.
3.2.2 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 via a pipe
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 statistics currently consist of elapsed (wall-clock) time and
user and system time consumed by the command's execution.
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.
See section 5.2 Bash Variables, for a description of the available formats.
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.
If the pipeline is not executed asynchronously (see section 3.2.3 Lists of Commands), the
shell waits for all commands in the pipeline to complete.
Each command in a pipeline is executed in its own subshell
(see section 3.7.3 Command Execution Environment). 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 negation of the exit status of the last command.
3.2.3 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 asynchronously in a subshell.
This is known as executing the command in the background.
The shell does not wait for the command to finish, and the return
status is 0 (true).
When job control is not active (see section 7. Job Control),
the standard input for asynchronous commands, in the absence of any
explicit redirections, is redirected from /dev/null.
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
command2 is executed if, and only if, command1
returns an exit status of zero.
An OR list has the form
command2 is executed if, and only if, command1
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.
3.2.4 Looping Constructs
Bash supports the following looping constructs.
Note that wherever a `;' appears in the description of a
command's syntax, it may be replaced with one or more newlines.
until
-
The syntax of the
until command is:
| |
until test-commands; do consequent-commands; done
|
Execute consequent-commands as long as
test-commands has an exit status which is not zero.
The return status is the exit status of the last command executed
in consequent-commands, or zero if none was executed.
while
-
The syntax of the
while command is:
| |
while test-commands; do consequent-commands; done
|
Execute consequent-commands as long as
test-commands has an exit status of zero.
The return status is the exit status of the last command executed
in consequent-commands, or zero if none was executed.
for
-
The syntax of the
for command is:
| |
for name [in words ...]; do commands; done
|
Expand words, and execute commands once for each member
in the resultant list, with name bound to the current member.
If `in words' is not present, the for command
executes the commands once for each positional parameter that is
set, as if `in "$@"' had been specified
(see section 3.4.2 Special Parameters).
The return status is the exit status of the last command that executes.
If there are no items in the expansion of words, no commands are
executed, and the return status is zero.
An alternate form of the for command is also supported:
| |
for (( expr1 ; expr2 ; expr3 )) ; do commands ; done
|
First, the arithmetic expression expr1 is evaluated according
to the rules described below (see section 6.5 Shell Arithmetic).
The arithmetic expression expr2 is then evaluated repeatedly
until it evaluates to zero.
Each time expr2 evaluates to a non-zero value, commands are
executed and the arithmetic expression expr3 is evaluated.
If any expression is omitted, it behaves as if it evaluates to 1.
The return value is the exit status of the last command in list
that is executed, or false if any of the expressions is invalid.
The break and continue builtins (see section 4.1 Bourne Shell Builtins)
may be used to control loop execution.
3.2.5 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
|
The test-commands list is executed, and if its return status is zero,
the consequent-commands list is executed.
If test-commands returns a non-zero status, 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 alternate-consequents is executed.
The return status is the exit status of the last command executed, or
zero if no condition tested true.
case
-
The syntax of the
case command is:
| |
case word in [ [(] pattern [| pattern]...) command-list ;;]... esac
|
case will selectively execute the command-list corresponding to
the first pattern that matches word.
The `|' is used to separate multiple patterns, and the `)'
operator terminates a pattern list.
A list of patterns and an associated command-list is known
as a clause. Each clause must be terminated with `;;'.
The word undergoes tilde expansion, parameter expansion, command
substitution, arithmetic expansion, and quote removal before matching is
attempted. Each pattern undergoes tilde expansion, parameter
expansion, command substitution, and arithmetic expansion.
There may be an arbitrary number of case clauses, each terminated
by a `;;'. The first pattern that matches determines the
command-list that is executed.
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 $ANIMAL in
horse | dog | cat) echo -n "four";;
man | kangaroo ) echo -n "two";;
*) echo -n "an unknown number of";;
esac
echo " legs."
|
The return status is zero if no pattern is matched. Otherwise, the
return status is the exit status of the command-list executed.
select
-
The select construct allows the easy generation of menus.
It has almost the same syntax as the for command:
| |
select name [in words ...]; do commands; done
|
The list of words following in is expanded, generating a list
of items. The set of expanded words is printed on the standard
error output stream, each preceded by a number. If the
`in words' is omitted, the positional parameters are printed,
as if `in "$@"' had been specifed.
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 command is executed, at which
point the select command completes.
Here is an example that allows the user to pick a filename from the
current directory, and displays the name and index of the file
selected.
| |
select fname in *;
do
echo you picked $fname \($REPLY\)
break;
done
|
((...))
-
The arithmetic expression is evaluated according to the rules
described below (see section 6.5 Shell Arithmetic).
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
See section 4.2 Bash Builtin Commands, for a full description of the let builtin.
[[...]]
-
Return a status of 0 or 1 depending on the evaluation of
the conditional expression expression.
Expressions are composed of the primaries described below in
6.4 Bash Conditional Expressions.
Word splitting and filename expansion are not performed on the words
between the `[[' and `]]'; tilde expansion, parameter and
variable expansion, arithmetic expansion, command substitution, process
substitution, and quote removal are performed.
When the `==' and `!=' operators are used, the string to the
right of the operator is considered a pattern and matched according
to the rules described below in 3.5.8.1 Pattern Matching.
The return value is 0 if the string matches or does not match
the pattern, respectively, and 1 otherwise.
Any part of the pattern may be quoted to force it to be matched as a
string.
Expressions may be combined using the following operators, listed
in decreasing order of precedence:
( expression )
- Returns the value of expression.
This may be used to override the normal precedence of operators.
! expression
- True if expression is false.
expression1 && expression2
- True if both expression1 and expression2 are true.
expression1 || expression2
- True if either expression1 or expression2 is true.
The && and || commands do not execute expression2 if the
value of expression1 is sufficient to determine the return
value of the entire conditional expression.
3.2.6 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.
()
-
Placing a list of commands between parentheses causes a subshell
to be created, and each of the commands in list 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.
{}
-
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 (or newline) 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 blanks. 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.
3.3 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.
When the name of a shell function is used as a simple command name,
the list of commands associated with that function name is executed.
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.
If the function reserved
word is supplied, the parentheses are 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.
Note that for historical reasons, the curly braces that surround
the body of the function must be separated from the body by
blanks or newlines.
This is because the braces are reserved words and are only recognized
as such when they are separated by whitespace.
Also, the command-list must be terminated with a semicolon
or a newline.
When a function is executed, the arguments to the
function become the positional parameters
during its execution (see section 3.4.1 Positional Parameters).
The special parameter `#' that expands to the number of
positional parameters is updated to reflect the change.
Positional parameter 0 is unchanged.
The FUNCNAME variable is set to the name of the function
while the function is executing.
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 the function's
execution. If a numeric argument is given to return,
that is the function's return status; otherwise the function's
return status is the exit status of the last command executed
before the return.
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.
3.4 Shell Parameters
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 variable has a value and zero or more attributes.
Attributes are assigned using the declare builtin command
(see the description of the declare builtin in 4.2 Bash Builtin Commands).
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
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
integer
attribute set, then
value
is subject to arithmetic expansion even if the
$((...))
expansion is not used (see section
3.5.5 Arithmetic Expansion).
Word splitting is not performed, with the exception
of
"$@" as explained below.
Filename expansion is not performed.
Assignment statements may also appear as arguments to the
declare,
typeset,
export,
readonly,
and
local builtin commands.
3.4.1 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 parameter N may be referenced as ${N}, or
as $N when N consists of a single digit.
Positional parameters may not be assigned to with assignment statements.
The set and shift builtins are used to set and
unset them (see section 4. Shell Builtin Commands).
The positional parameters are
temporarily replaced when a shell function is executed
(see section 3.3 Shell Functions).
When a positional parameter consisting of more than a single
digit is expanded, it must be enclosed in braces.
3.4.2 Special Parameters
The shell treats several parameters specially. These parameters may
only be referenced; assignment to them is not allowed.
*
-
Expands to the positional parameters, starting from one. When the
expansion occurs within double quotes, it expands to a single word
with the value of each parameter separated by the first character
of the
IFS
special variable. That is, "$*" is equivalent
to "$1c$2c...", where c
is the first character of the value of the IFS
variable.
If IFS is unset, the parameters are separated by spaces.
If IFS is null, the parameters are joined without intervening
separators.
@
-
Expands to the positional parameters, starting from one. When the
expansion occurs within double quotes, each parameter expands to a
separate word. That is,
"$@" 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.
-
-
(A hyphen.) 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 invoking 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
(see section 3.8 Shell Scripts),
$0 is set to the name of that file.
If Bash is started with the `-c' option (see section 6.1 Invoking Bash),
then $0 is set to the first argument after the string to be
executed, if one is present. Otherwise, it is set
to the filename used to invoke Bash, as given by argument zero.
_
-
(An underscore.)
At shell startup, set to the absolute filename of the shell or shell
script being executed as passed in the argument list.
Subsequently, expands to the last argument to the previous command,
after expansion.
Also set to the full pathname of each command executed and placed in
the environment exported to that command.
When checking mail, this parameter holds the name of the mail file.
3.5 Shell Expansions
Expansion is performed on the command line after it has been split into
tokens. There are seven kinds of expansion performed:
- brace expansion
- tilde expansion
- parameter and variable expansion
- command substitution
- arithmetic expansion
- word splitting
- filename expansion
The order of expansions is: brace expansion, tilde expansion,
parameter, variable, and arithmetic expansion and
command substitution
(done in a left-to-right fashion), word splitting, and filename
expansion.
On systems that can support it, there is an additional expansion
available: process substitution. This is performed at the
same time as parameter, variable, and arithmetic expansion and
command substitution.
Only brace expansion, word splitting, and filename expansion
can change the number of words of the expansion; other expansions
expand a single word to a single word.
The only exceptions to this are the expansions of
"$@" (see section 3.4.2 Special Parameters) and "${name[@]}"
(see section 6.7 Arrays).
After all expansions, quote removal (see section 3.5.9 Quote Removal)
is performed.
3.5.1 Brace Expansion
Brace expansion is a mechanism by which arbitrary strings may be generated.
This mechanism is similar to
filename expansion (see section 3.5.8 Filename Expansion),
but the file names generated need not exist.
Patterns to be brace expanded take the form of an optional preamble,
followed by a series of comma-separated strings between a pair of braces,
followed by an optional postscript.
The preamble is prefixed to each string contained within the braces, and
the postscript is then appended to each resulting string, expanding left
to right.
Brace expansions may be nested.
The results of each expanded string are not sorted; left to right order
is preserved.
For example,
| |
bash$ 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.
To avoid conflicts with parameter expansion, the string `${'
is not considered eligible for brace expansion.
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}}
|
3.5.2 Tilde Expansion
If a word begins with an unquoted tilde character (`~'), all of the
characters up to the first unquoted slash (or all characters,
if there is no unquoted slash) are considered a tilde-prefix.
If none of the characters in the tilde-prefix are quoted, the
characters in the tilde-prefix following the tilde are treated as a
possible login name.
If this login name is the null string, the tilde is replaced with the
value of the HOME shell variable.
If HOME is unset, the home directory of the user executing the
shell is substituted instead.
Otherwise, the tilde-prefix is replaced with the home directory
associated with the specified login name.
If the tilde-prefix is `~+', the value of
the shell variable PWD replaces the tilde-prefix.
If the tilde-prefix is `~-', the value of the shell variable
OLDPWD, if it is set, is substituted.
If the characters following the tilde in the tilde-prefix consist of a
number N, optionally prefixed by a `+' or a `-',
the tilde-prefix is replaced with the
corresponding element from the directory stack, as it would be displayed
by the dirs builtin invoked with the characters following tilde
in the tilde-prefix as an argument (see section 6.8 The Directory Stack).
If the tilde-prefix, sans the tilde, consists of a number without a
leading `+' or `-', `+' is assumed.
If the login name is invalid, or the tilde expansion fails, the word is
left unchanged.
Each variable assignment is checked for unquoted tilde-prefixes immediately
following a `:' or `='.
In these cases, tilde expansion is also performed.
Consequently, one may use file names with tildes in assignments to
PATH, MAILPATH, and CDPATH,
and the shell assigns the expanded value.
The following table shows how Bash treats unquoted tilde-prefixes:
~
- The 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'
~N
- The string that would be displayed by `dirs +N'
~+N
- The string that would be displayed by `dirs +N'
~-N
- The string that would be displayed by `dirs -N'
3.5.3 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.
When braces are used, the matching ending brace is the first `}'
not escaped by a backslash or within a quoted string, and not within an
embedded arithmetic expansion, command substitution, or parameter
expansion.
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.
The exception to this is the expansion of ${!prefix*}
described below.
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. Put another way, if the colon is included,
the operator tests for both existence and that the value is not null;
if the colon is omitted, the operator tests only for existence.
${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 the character specified by offset.
If length is omitted, expands to the substring of
parameter starting at the character specified by offset.
length and offset are arithmetic expressions
(see section 6.5 Shell Arithmetic).
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.
${!prefix*}
- Expands to the names of variables whose names begin with prefix,
separated by the first character of the
IFS special variable.
${#parameter}
- The length in characters of the expanded value of parameter is
substituted.
If parameter is `*' or `@', the value substituted
is the number of positional parameters.
If parameter is an array name subscripted by `*' or `@',
the value 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 (see section 3.5.8 Filename Expansion). If the pattern matches
the beginning of the expanded value of parameter,
then the result of the expansion is the expanded 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 expanded value of
parameter, then the result of 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 the expanded value of parameter.
If pattern begins with `%', it must match at the end
of the expanded value of parameter.
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.
3.5.4 Command Substitution
Command substitution allows the output of a command to replace
the command itself.
Command substitution occurs when a command is enclosed as follows:
or
Bash performs the expansion by executing command and
replacing the command substitution with the standard output of the
command, with any trailing newlines deleted.
Embedded newlines are not deleted, but they may be removed during
word splitting.
The command substitution $(cat file) can be
replaced by the equivalent but faster $(< file).
When the old-style backquote form of substitution is used,
backslash retains its literal meaning except when followed by
`$', ``', or `\'.
The first backquote not preceded by a backslash terminates the
command substitution.
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 backquoted
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.
3.5.5 Arithmetic Expansion
Arithmetic expansion allows the evaluation of an arithmetic expression
and the substitution of the result. The format for arithmetic expansion is:
The expression is treated as if it were within double quotes, but
a double quote inside the 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 below
(see section 6.5 Shell Arithmetic).
If the expression is invalid, Bash prints a message indicating
failure to the standard error and no substitution occurs.
3.5.6 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
or
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.
Note that no space may appear between the
< or
>
and the left parenthesis, otherwise the construct would be interpreted
as a redirection.
When available, process substitution is performed simultaneously with
parameter and variable expansion, command substitution, and arithmetic
expansion.
3.5.7 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.
3.5.8 Filename Expansion
After word splitting, unless the `-f' option has been set
(see section 4.3 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 nullglob option is set, and no matches are found, the word
is removed.
If the shell option nocaseglob is enabled, the match is performed
without regard to the case of alphabetic characters.
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.
When matching a file name, the slash character must always be
matched explicitly.
In other cases, the `.' character is not treated specially.
See the description of shopt in 4.2 Bash Builtin Commands,
for a description of the nocaseglob, 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.
3.5.8.1 Pattern Matching
Any character that appears in a pattern, other than the special pattern
characters described below, matches itself. The NUL character may not
occur in a pattern. The special pattern characters must be quoted if
they are to be matched literally.
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 hyphen denotes a range expression;
any character that sorts between those two characters, inclusive,
using the current locale's collating sequence and character set,
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.
The sorting order of characters in range expressions is determined by
the current locale and the value of the
LC_COLLATE shell variable,
if set.
For example, in the default C locale, `[a-dx-z]' is equivalent to
`[abcdxyz]'. Many locales sort characters in dictionary order, and in
these locales `[a-dx-z]' is typically not equivalent to `[abcdxyz]';
it might be equivalent to `[aBbCcDdxXyYz]', for example. To obtain
the traditional interpretation of ranges in bracket expressions, you can
force the use of the C locale by setting the LC_COLLATE or
LC_ALL environment variable to the value `C'.
Within `[' and `]', character classes can be specified
using the syntax
[:class:], where class is one of the
following classes defined in the POSIX 1003.2 standard:
| |
alnum alpha ascii blank cntrl digit graph lower
print punct space upper xdigit
|
A character class matches any character belonging to that class.
Within `[' and `]', an equivalence class can be
specified using the syntax [=c=], which
matches all characters with the same collation weight (as defined
by the current locale) as the character c.
Within `[' and `]', the syntax [.symbol.]
matches the collating symbol symbol.
If the extglob shell option is enabled using the shopt
builtin, several extended pattern matching operators are recognized.
In the following description, a pattern-list is a list of one
or more patterns separated by a `|'.
Composite patterns may be formed using one or more of the following
sub-patterns:
?(pattern-list)
- Matches zero or one occurrence of the given patterns.
*(pattern-list)
- Matches zero or more occurrences of the given patterns.
+(pattern-list)
- Matches one or more occurrences of the given patterns.
@(pattern-list)
- Matches exactly one of the given patterns.
!(pattern-list)
- Matches anything except one of the given patterns.
3.5.9 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.
3.6 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 following the redirection operator in the following
descriptions, unless otherwise noted, is subjected to brace expansion,
tilde expansion, parameter expansion, command substitution, arithmetic
expansion, quote removal, filename expansion, and word splitting.
If it expands to more than one word, Bash reports an error.
Note that the order of redirections is significant. For example,
the command
directs both standard output (file descriptor 1) and standard error
(file descriptor 2) to the file
dirlist, while the command
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.
Bash handles several filenames specially when they are used in
redirections, as described in the following table:
/dev/fd/fd
- If fd is a valid integer, file descriptor fd is duplicated.
/dev/stdin
- File descriptor 0 is duplicated.
/dev/stdout
- File descriptor 1 is duplicated.
/dev/stderr
- File descriptor 2 is duplicated.
/dev/tcp/host/port
- If host is a valid hostname or Internet address, and port
is an integer port number or service name, Bash attempts to open a TCP
connection to the corresponding socket.
/dev/udp/host/port
- If host is a valid hostname or Internet address, and port
is an integer port number or service name, Bash attempts to open a UDP
connection to the corresponding socket.
A failure to open or create a file causes the redirection to fail.
3.6.1 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:
3.6.2 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:
If the redirection operator is `>', and the noclobber
option to the set builtin has been enabled, the redirection
will fail if the file whose name results from the expansion of
word exists and is a regular file.
If the redirection operator is `>|', or the redirection operator is
`>' and the noclobber option is not enabled, the redirection
is attempted even if the file named by word exists.
3.6.3 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:
3.6.4 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:
and
Of the two forms, the first is preferred.
This is semantically equivalent to
3.6.5 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, arithmetic expansion,
or filename 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.
If word is unquoted,
all lines of the here-document are subjected to parameter expansion,
command substitution, and arithmetic expansion. In the latter
case, the character sequence \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.
3.6.6 Duplicating File Descriptors
The redirection operator
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 the digits in
word do not specify a file descriptor open for
input, a redirection error occurs.
If
word
evaluates to
`-', file descriptor
n is closed. If
n is not specified, the standard input (file descriptor 0) is used.
The operator
is used similarly to duplicate output file descriptors. If
n
is not specified, the standard output (file descriptor 1) is used.
If the digits in
word do not specify a file descriptor open for
output, a redirection error occurs.
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.
3.6.7 Opening File Descriptors for Reading and Writing
The redirection operator
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.
3.7 Executing Commands
| 3.7.6 Signals |
|
What happens when Bash or a command it runs
receives a signal. |
3.7.1 Simple Command Expansion
When a simple command is executed, the shell performs the following
expansions, assignments, and redirections, from left to right.
-
The words that the parser has marked as variable assignments (those
preceding the command name) and redirections are saved for later
processing.
-
The words that are not variable assignments or redirections are
expanded (see section 3.5 Shell Expansions).
If any words remain after expansion, the first word
is taken to be the name of the command and the remaining words are
the arguments.
-
Redirections are performed as described above (see section 3.6 Redirections).
-
The text after the `=' in each variable assignment undergoes tilde
expansion, parameter expansion, command substitution, arithmetic expansion,
and quote removal before being assigned to the variable.
If no command name results, the variable assignments affect the current
shell environment. Otherwise, the variables are added to the environment
of the executed command and do not affect the current shell environment.
If any of the assignments attempts to assign a value to a readonly variable,
an error occurs, and the command exits with a non-zero status.
If no command name results, redirections are performed, but do not
affect the current shell environment. A redirection error causes the
command to exit with a non-zero status.
If there is a command name left after expansion, execution proceeds as
described below. Otherwise, the command exits. If one of the expansions
contained a command substitution, the exit status of the command is
the exit status of the last command substitution performed. If there
were no command substitutions, the command exits with a status of zero.
3.7.2 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.
-
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 in 3.3 Shell Functions.
-
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.
-
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
pathnames of executable files to avoid multiple PATH searches
(see the description of hash in 4.1 Bourne Shell Builtins).
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 an exit status of 127.
-
If the search is successful, or if the command name contains
one or more slashes, the shell executes the named program in
a separate execution environment.
Argument 0 is set to the name given, and the remaining arguments
to the command are set to the arguments supplied, if any.
-
If this execution fails because the file is not in executable
format, and the file is not a directory, it is assumed to be a
shell script and the shell executes it as described in
3.8 Shell Scripts.
-
If the command was not begun asynchronously, the shell waits for
the command to complete and collects its exit status.
3.7.3 Command Execution Environment
The shell has an execution environment, which consists of the
following:
-
open files inherited by the shell at invocation, as modified by
redirections supplied to the
exec builtin
-
the current working directory as set by
cd, pushd, or
popd, or inherited by the shell at invocation
-
the file creation mode mask as set by
umask or inherited from
the shell's parent
-
current traps set by
trap
-
shell parameters that are set by variable assignment or with
set
or inherited from the shell's parent in the environment
-
shell functions defined during execution or inherited from the shell's
parent in the environment
-
options enabled at invocation (either by default or with command-line
arguments) or by
set
-
options enabled by
shopt
-
shell aliases defined with
alias (see section 6.6 Aliases)
-
various process IDs, including those of background jobs
(see section 3.2.3 Lists of Commands), the value of
$$, and the value of
$PPID
When a simple command other than a builtin or shell function
is to be executed, it
is invoked in a separate execution environment that consists of
the following. Unless otherwise noted, the values are inherited
from the shell.
-
the shell's open files, plus any modifications and additions specified
by redirections to the command
-
the current working directory
-
the file creation mode mask
-
shell variables marked for export, along with variables exported for
the command, passed in the environment (see section 3.7.4 Environment)
-
traps caught by the shell are reset to the values inherited from the
shell's parent, and traps ignored by the shell are ignored
A command invoked in this separate environment cannot affect the
shell's execution environment.
Command substitution and asynchronous commands are invoked in a
subshell environment that is a duplicate of the shell environment,
except that traps caught by the shell are reset to the values
that the shell inherited from its parent at invocation. Builtin
commands that are invoked as part of a pipeline are also executed
in a subshell environment. Changes made to the subshell environment
cannot affect the shell's execution environment.
If a command is followed by a `&' and job control is not active, the
default standard input for the command is the empty file `/dev/null'.
Otherwise, the invoked command inherits the file descriptors of the calling
shell as modified by redirections.
3.7.4 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 provides several ways to manipulate the environment.
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 and `export -n'
commands, 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 3.4 Shell Parameters.
These assignment statements affect only the environment seen
by that command.
If the `-k' option is set (see section 4.3 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.
3.7.5 Exit Status
For the shell's purposes, 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.
If a command fails because of an error during expansion or redirection,
the exit status is greater than zero.
The exit status is used by the Bash conditional commands
(see section 3.2.5 Conditional Constructs) and some of the list
constructs (see section 3.2.3 Lists of Commands).
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.
All builtins return an exit status of 2 to indicate incorrect usage.
3.7.6 Signals
When Bash is interactive, in the absence of any traps, 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 (see section 7. Job Control), Bash
ignores SIGTTIN, SIGTTOU, and SIGTSTP.
Commands started by Bash have signal handlers set to the
values inherited by the shell from its parent.
When job control is not in effect, asynchronous commands
ignore SIGINT and SIGQUIT as well.
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, an interactive shell resends the SIGHUP to
all jobs, running or stopped.
Stopped jobs are sent SIGCONT to ensure that they receive
the SIGHUP.
To prevent the shell from sending the SIGHUP signal to a
particular job, it should be removed
from the jobs table with the disown
builtin (see section 7.2 Job Control Builtins) or marked
to not receive SIGHUP using disown -h.
If the huponexit shell option has been set with shopt
(see section 4.2 Bash Builtin Commands), Bash sends a SIGHUP to all jobs when
an interactive login shell exits.
When Bash receives a signal for which a trap has been set while waiting
for a command to complete, the trap will not be executed until the
command completes.
When Bash is waiting for an asynchronous
command via the wait builtin, the reception of a signal for
which a trap has been set will cause the wait builtin to return
immediately with an exit status greater than 128, immediately after
which the trap is executed.
3.8 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
(see section 6.1 Invoking Bash),
Bash reads and executes commands from the file, then exits. This
mode of operation creates a non-interactive shell. The shell first
searches for the file in the current directory, and looks in the
directories in $PATH if not found there.
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
is equivalent to executing
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, with the
exception that the locations of commands remembered by the parent
(see the description of hash in 4.1 Bourne Shell Builtins)
are retained by the child.
Most versions of Unix make this a part of the operating system'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.
Thus, you can specify Bash, awk, Perl, or some other
interpreter and write the rest of the script file in that language.
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.
Bash scripts often begin with #! /bin/bash (assuming that
Bash has been installed in `/bin'), since this ensures that
Bash will be used to interpret the script, even if it is executed
under another shell.
4. Shell Builtin Commands
Builtin commands are contained within the shell itself.
When the name of a builtin command is used as the first word of
a simple command (see section 3.2.1 Simple Commands), the shell executes
the command directly, without invoking another program.
Builtin commands are necessary to implement functionality impossible
or inconvenient to obtain with separate utilities.
This section briefly the builtins which Bash inherits from
the Bourne Shell, as well as the builtin commands which are unique
to or have been extended in Bash.
Several builtin commands are described in other chapters: builtin
commands which provide the Bash interface to the job control
facilities (see section 7.2 Job Control Builtins), the directory stack
(see section 6.8.1 Directory Stack Builtins), the command history
(see section 9.2 Bash History Builtins), and the programmable completion
facilities (see section 8.7 Programmable Completion Builtins).
Many of the builtins have been extended by POSIX or Bash.
4.1 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.
: (a colon)
-
Do nothing beyond expanding arguments and performing redirections.
The return status is zero.
. (a period)
-
Read and execute commands from the filename argument in the
current shell context. If filename does not contain a slash,
the
PATH variable is used to find filename.
When Bash is not in POSIX mode, the current directory is searched
if filename is not found in $PATH.
If any arguments are supplied, they become the positional
parameters when filename is executed. Otherwise the positional
parameters are unchanged.
The return status is the exit status of the last command executed, or
zero if no commands are executed. If filename is not found, or
cannot be read, the return status is non-zero.
This builtin is equivalent to source.
break
-
Exit from a
for, while, until, or select loop.
If n is supplied, the nth enclosing loop is exited.
n must be greater than or equal to 1.
The return status is zero unless n is not greater than or equal to 1.
cd
-
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; symbolic links are followed by default
or with the `-L' option.
If directory is `-', it is equivalent to $OLDPWD.
The return status is zero if the directory is successfully changed,
non-zero otherwise.
continue
-
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.
n must be greater than or equal to 1.
The return status is zero unless n is not greater than or equal to 1.
eval
-
The arguments are concatenated together into a single command, which is
then read and executed, and its exit status returned as the exit status
of
eval.
If there are no arguments or only empty arguments, the return status is
zero.
exec
-
| |
exec [-cl] [-a name] [command [arguments]]
|
If command
is supplied, it replaces the shell without creating a new process.
If the `-l' option is supplied, the shell places a dash at the
beginning of 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. If there are no redirection errors, the
return status is zero; otherwise the return status is non-zero.
exit
-
Exit the shell, returning a status of n to the shell's parent.
If n is omitted, the exit status is that of the last command executed.
Any trap on
EXIT is executed before the shell terminates.
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; otherwise the names refer to shell variables.
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.
The `-p' option displays output in a form that may be reused as input.
The return status is zero unless an invalid option is supplied, one of
the names is not a valid shell variable name, or `-f' is supplied
with a name that is not a shell function.
getopts
-
| |
getopts optstring name [args]
|
getopts is used by shell scripts to parse positional parameters.
optstring contains the option characters to be recognized; if a
character is followed by a colon, the option is expected to have an
argument, which should be separated from it by white space.
The colon (`:') and question mark (`?') may not be
used as option characters.
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.
When the end of options is encountered, getopts exits with a
return value greater than zero.
OPTIND is set to the index of the first non-option argument,
and name is set to `?'.
getopts
normally parses the positional parameters, but if more arguments are
given in args, getopts parses those instead.
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 invalid options or missing option arguments are
encountered.
If the variable OPTERR
is set to 0, no error messages will be displayed, even if the first
character of optstring is not a colon.
If an invalid 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.
hash
-
| |
hash [-r] [-p filename] [-t] [name]
|
Remember the full pathnames of commands specified as name 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 the `-t' option is supplied, the full pathname to which each
name corresponds is printed. If multiple name arguments are
supplied with `-t' the name is printed before the hashed
full pathname.
If no arguments are given, information about remembered commands is printed.
The return status is zero unless a name is not found or an invalid
option is supplied.
pwd
-
Print the absolute pathname of the current working directory.
If the `-P' option is supplied, the pathname printed will not
contain symbolic links.
If the `-L' option is supplied, the pathname printed may contain
symbolic links.
The return status is zero unless an error is encountered while
determining the name of the current directory or an invalid option
is supplied.
readonly
-
| |
readonly [-apf] [name] ...
|
Mark each name as readonly.
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.
The `-p' option causes output to be displayed in a format that
may be reused as input.
The return status is zero unless an invalid option is supplied, one of
the name arguments is not a valid shell variable or function name,
or the `-f' option is supplied with a name that is not a shell function.
return
-
Cause a shell function to exit with the return value n.
If n is not supplied, the return value is the exit status of the
last command executed in the function.
This may also be used to terminate execution of a script being executed
with the
. (or source) builtin, returning either n or
the exit status of the last command executed within the script as the exit
status of the script.
The return status is non-zero if return is used outside a function
and not during the execution of a script by . or source.
shift
-
Shift the positional parameters to the left by n.
The positional parameters from n+1 ...
$# are
renamed to $1 ... $#-n+1.
Parameters represented by the numbers $# to n+1 are unset.
n must be a non-negative number less than or equal to $#.
If n is zero or greater than $#, the positional parameters
are not changed.
If n is not supplied, it is assumed to be 1.
The return status is zero unless n is greater than $# or
less than zero, non-zero otherwise.
test
[
-
Evaluate a conditional expression expr.
Each operator and operand must be a separate argument.
Expressions are composed of the primaries described below in
6.4 Bash Conditional Expressions.
When the [ form is used, the last argument to the command must
be a ].
Expressions may be combined using the following operators, listed in
decreasing order of precedence.
! expr
- True if expr is false.
( expr )
- Returns the value of expr.
This may be used to override the normal precedence of operators.
expr1 -a expr2
- True if both expr1 and expr2 are true.
expr1 -o expr2
- True if either expr1 or expr2 is true.
The test and [ builtins evaluate conditional
expressions using a set of rules based on the number of arguments.
- 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 unary conditional operators
(see section 6.4 Bash Conditional Expressions), the expression
is true if the unary test is true.
If the first argument is not a valid unary operator, the expression is
false.
- 3 arguments
- If the second argument is one of the binary conditional
operators (see section 6.4 Bash Conditional Expressions), 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 `!', the value is the negation of
the two-argument test using the second and third arguments.
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 using the rules listed above.
- 5 or more arguments
- The expression is parsed and evaluated according to precedence
using the rules listed above.
times
-
Print out the user and system times used by the shell and its children.
The return status is zero.
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 not present and `-p' has been supplied,
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 in a form that may be reused as
shell input.
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.
If a sigspec is ERR, the command arg
is executed whenever a simple command has a non-zero exit status.
The ERR trap is not executed if the failed command is part of an
until or while loop, part of an if statement,
part of a && or || list, or if the command's return
status is being inverted using !.
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.
The return status is zero unless a sigspec does not specify a
valid signal.
umask
-
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.
If the `-p' option is supplied, and mode
is omitted, the output is in a form that may be reused as input.
The return status is zero if the mode is successfully changed or if
no mode argument is supplied, and non-zero otherwise.
Note that when the mode is interpreted as an octal number, each number
of the umask is subtracted from 7. Thus, a umask of 022
results in permissions of 755.
unset
-
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.
Readonly variables and functions may not be unset.
The return status is zero unless a name does not exist or is
readonly.
4.2 Bash Builtin Commands
This section describes builtin commands which are unique to
or have been extended in Bash.
Some of these commands are specified in the POSIX 1003.2 standard.
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.
Aliases are described in 6.6 Aliases.
bind
-
| |
bind [-m keymap] [-lpsvPSV]
bind [-m keymap] [-q function] [-u function] [-r keyseq]
bind [-m keymap] -f filename
bind [-m keymap] -x keyseq:shell-command
bind [-m keymap] keyseq:function-name
|
Display current Readline (see section 8. 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
a Readline initialization file (see section 8.3 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-move,
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 used as input or in a Readline initialization file.
-P
- List current Readline function names and bindings.
-v
- Display Readline variable names and values in such a way that they
can be used as input or in a Readline initialization file.
-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 used as input or in a Readline
initialization file.
-S
- Display Readline key sequences bound to macros and the strings they output.
-f filename
- Read key bindings from filename.
-q function
- Query about which keys invoke the named function.
-u function
- Unbind all keys bound to the named function.
-r keyseq
- Remove any current binding for keyseq.
-x keyseq:shell-command
- Cause shell-command to be executed whenever keyseq is
entered.
The return status is zero unless an invalid option is supplied or an
error occurs.
builtin
-
| |
builtin [shell-builtin [args]]
|
Run a shell builtin, passing it args, and return its exit status.
This is useful when defining a shell function with the same
name as a shell builtin, retaining the functionality of the builtin within
the function.
The return status is non-zero if shell-builtin is not a shell
builtin command.
command
-
| |
command [-pVv] command [arguments ...]
|
Runs command with arguments ignoring any shell function
named command.
Only shell builtin commands or commands found by searching the
PATH are executed.
If there is a shell function named ls, running `command ls'
within the function will execute the external command ls
instead of calling the function recursively.
The `-p' option means to use a default value for PATH
that is guaranteed to find all of the standard utilities.
The return status in this case is 127 if command cannot be
found or an error occurred, and the exit status of command
otherwise.
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 displayed; the `-V' option produces
a more verbose description. In this case, the return status is
zero if command is found, and non-zero if not.
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 (see section 6.7 Arrays).
-f
- Use function names only.
-i
- The variable is to be treated as
an integer; arithmetic evaluation (see section 6.5 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 or unset.
-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.
The return status is zero unless an invalid option is encountered,
an attempt is made to define a function using `-f foo=bar',
an attempt is made to assign a value to a readonly variable,
an attempt is made to assign a value to an array variable without
using the compound assignment syntax (see section 6.7 Arrays),
one of the names is not a valid shell variable name,
an attempt is made to turn off readonly status for a readonly variable,
an attempt is made to turn off array status for an array variable,
or an attempt is made to display a non-existent function with `-f'.
echo
-
Output the args, 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.
The
xpg_echo shell option may be used to
dynamically determine whether or not echo expands these
escape characters 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 eight-bit character whose value is the octal value nnn
(one to three digits)
\xHH
- the eight-bit character whose value is the hexadecimal value HH
(one or two hex digits)
enable
-
| |
enable [-n] [-p] [-f filename] [-ads] [name ...]
|
Enable and disable builtin shell commands.
Disabling a builtin allows a disk command which has the same name
as a shell builtin to be executed without specifying a full pathname,
even though the shell normally searches for builtins before disk commands.
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 special
builtins. If `-s' is used with `-f', the new builtin becomes
a special builtin (see section 4.4 Special Builtins).
The return status is zero unless a name is not a shell builtin
or there is an error loading a new builtin from a shared object.
help
-
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.
The `-s' option restricts the information displayed to a short
usage synopsis.
The return status is zero unless no command matches pattern.
let
-
| |
let expression [expression]
|
The let builtin allows arithmetic to be performed on shell
variables. Each expression is evaluated according to the
rules given below in 6.5 Shell Arithmetic. If the
last expression evaluates to 0, let returns 1;
otherwise 0 is returned.
local
-
| |
local [option] name[=value]
|
For each argument, a local variable named name is created,
and assigned value.
The option can be any of the options accepted by declare.
local can only be used within a function; it makes the variable
name have a visible scope restricted to that function and its
children. The return status is zero unless local is used outside
a function, an invalid name is supplied, or name is a
readonly variable.
logout
-
Exit a login shell, returning a status of n to the shell's
parent.
printf
-
| |
printf format [arguments]
|
Write the formatted arguments to the standard output under the
control of the format.
The format is a character string which contains three types of objects:
plain characters, which are simply copied to standard output, character
escape sequences, which are converted and copied to the standard output, and
format specifications, each of which causes printing of the next successive
argument.
In addition to the standard printf(1) formats, `%b' causes
printf to expand backslash escape sequences in the corresponding
argument, and `%q' causes printf to output the
corresponding argument in a format that can be reused as shell input.
The format is reused as necessary to consume all of the arguments.
If the format requires more arguments than are supplied, the
extra format specifications behave as if a zero value or null string, as
appropriate, had been supplied. The return value is zero on success,
non-zero on failure.
read
-
| |
read [-ers] [-a aname] [-p prompt] [-t timeout] [-n nchars] [-d delim] [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 and their intervening separators assigned
to the last name.
If there are fewer words read from the standard input than names,
the remaining names are assigned empty values.
The characters in the value of the IFS variable
are used to split the line into words.
The backslash character `\' may be used to remove any special
meaning for the next character read and for line continuation.
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 or read
times out.
Options, if supplied, have the following meanings:
-a aname
- The words are assigned to sequential indices of the array variable
aname, starting at 0.
All elements are removed from aname before the assignment.
Other name arguments are ignored.
-d delim
- The first character of delim is used to terminate the input line,
rather than newline.
-e
- Readline (see section 8. Command Line Editing) is used to obtain the line.
-n nchars
read returns after reading nchars characters rather than
waiting for a complete line of input.
-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.
-r
- If this option is given, backslash does not act as an escape character.
The backslash is considered to be part of the line.
In particular, a backslash-newline pair may not be used as a line
continuation.
-s
- Silent mode. If input is coming from a terminal, characters are
not echoed.
-t timeout
- Cause
read to time out and return failure if a complete line of
input is not read within timeout seconds.
This option has no effect if read is not reading input from the
terminal or a pipe.
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.
The `-p' option causes output to be displayed in a form that
may be reused as input.
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 (see section 4.3 The Set Builtin).
If either `-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 valid 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.
expand_aliases
- If set, aliases are expanded as described below under Aliases,
6.6 Aliases.
This option is enabled by default for interactive shells.
extglob
- If set, the extended pattern matching features described above
(see section 3.5.8.1 Pattern Matching) are enabled.
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 containing a `@' is being
completed (see section 8.4.6 Letting Readline Type For You). This option is enabled
by default.
huponexit
- If set, Bash will send
SIGHUP to all jobs when an interactive
login shell exits (see section 3.7.6 Signals).
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.
login_shell
- The shell sets this option if it is started as a login shell
(see section 6.1 Invoking Bash).
The value may not be changed.
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.
no_empty_cmd_completion
- If set, and Readline is being used, Bash will not attempt to search
the
PATH for possible completions when completion is attempted
on an empty line.
nocaseglob
- If set, Bash matches filenames in a case-insensitive fashion when
performing filename expansion.
nullglob
- If set, Bash allows filename patterns which match no
files to expand to a null string, rather than themselves.
progcomp
- If set, the programmable completion facilities
(see section 8.6 Programmable Completion) are enabled.
This option is enabled by default.
promptvars
- If set, prompt strings undergo variable and parameter expansion after
being expanded (see section 6.9 Controlling the Prompt).
This option is enabled by default.
restricted_shell
- The shell sets this option if it is started in restricted mode
(see section 6.10 The Restricted Shell).
The value may not be changed.
This is not reset when the startup files are executed, allowing
the startup files to discover whether or not a shell is restricted.
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 option is enabled by default.
xpg_echo
- If set, the
echo builtin expands backslash-escape sequences
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 valid shell option.
source
-
A synonym for
. (see section 4.1 Bourne Shell Builtins).
type
-
For each name, indicate how it would be interpreted if used as a
command name.
If the `-t' option is used, type prints 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 `-p' option is used, type either returns the name
of the disk file that would be executed, or nothing if `-t'
would not return `file'.
If the `-a' option is used, type returns all of the places
that contain an executable named file.
This includes aliases and functions, if and only if the `-p' option
is not also used.
The return status is zero if any of the names are found, non-zero
if none are found.
typeset
-
| |
typeset [-afFrxi] [-p] [name[=value]]
|
The typeset command is supplied for compatibility with the Korn
shell; however, it has been deprecated in favor of the declare
builtin command.
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;
the special limit values hard, soft, and
unlimited stand for the current hard limit, the current soft limit,
and no limit, respectively.
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.
The return status is zero unless an invalid option or argument is supplied,
or an error occurs while setting a new limit.
unalias
-
Remove each name from the list of aliases. If `-a' is
supplied, all aliases are removed.
Aliases are described in 6.6 Aliases.
4.3 The Set Builtin
This builtin is so complicated that it deserves its own section.
set
-
| |
set [--abefhkmnptuvxBCHP] [-o option] [argument ...]
|
If no options or arguments are supplied, set displays the names
and values of all shell variables and functions, sorted according to the
current locale, in a format that may be reused as input.
When options are supplied, they set or unset shell attributes.
Options, if specified, have the following meanings:
-a
- Mark variables and function which are modified or created for export
to the environment of subsequent commands.
-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 (see section 3.2.1 Simple Commands) exits
with a non-zero status, unless the command that fails is part of an
until or while loop, part of an if statement,
part of a && or || list, or if the command's return
status is being inverted using !.
A trap on ERR, if set, is executed before the shell exits.
-f
- Disable file name generation (globbing).
-h
- Locate and remember (hash) commands as they are looked up for execution.
This option is enabled by default.
-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 (see section 7. Job Control).
-n
- Read commands but do not execute them; this may be used to check a
script for syntax errors.
This option is ignored by interactive shells.
-o option-name
-
Set the option corresponding to option-name:
allexport
- Same as
-a.
braceexpand
- Same as
-B.
emacs
- Use an
emacs-style line editing interface (see section 8. Command Line Editing).
errexit
- Same as
-e.
hashall
- Same as
-h.
histexpand
- Same as
-H.
history
- Enable command history, as described in 9.1 Bash History Facilities.
This option is on by default in interactive shells.
ignoreeof
- An interactive 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.
nolog
- Currently ignored.
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
(see section 6.11 Bash POSIX Mode).
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 and $ENV files are not
processed, shell functions are not inherited from the environment,
and the SHELLOPTS variable, if it appears in the environment,
is ignored.
If the shell is started with the effective user (group) id not equal to the
real user (group) id, and the -p option is not supplied, these actions
are taken and the effective user id is set to the real user id.
If the -p option is supplied at startup, the effective user id is
not reset.
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 performing parameter expansion.
An error message will be written to the standard error, and a non-interactive
shell will exit.
-v
- Print shell input lines as they are read.
-x
- Print a trace of simple commands and their arguments after they are
expanded and before they are executed.
-B
- The shell will perform brace expansion (see section 3.5.1 Brace Expansion).
This option is on by default.
-C
- Prevent output redirection using `>', `>&', and `<>'
from overwriting existing files.
-H
- Enable `!' style history substitution (see section 9.3 History Expansion).
This option 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 symbolic 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 option, 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 options to be
turned off. The options can also be used upon invocation of the
shell. The current set of options may be found in $-.
The remaining N arguments are positional parameters and are
assigned, in order, to $1, $2, ... $N.
The special parameter # is set to N.
The return status is always zero unless an invalid option is supplied.
4.4 Special Builtins
For historical reasons, the POSIX 1003.2 standard has classified
several builtin commands as special.
When Bash is executing in POSIX mode, the special builtins
differ from other builtin commands in three respects:
-
Special builtins are found before shell functions during command lookup.
-
If a special builtin returns an error status, a non-interactive shell exits.
-
Assignment statements preceding the command stay in effect in the shell
environment after the command completes.
When Bash is not executing in POSIX mode, these builtins behave no
differently than the rest of the Bash builtin commands.
The Bash POSIX mode is described in 6.11 Bash POSIX Mode.
These are the POSIX special builtins:
| |
break : . continue eval exec exit export readonly return set
shift trap unset
|
5. Shell Variables
This chapter describes the shell variables that Bash uses.
Bash automatically assigns default values to a number of variables.
5.1 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.
CDPATH
-
A colon-separated list of directories used as a search path for
the
cd builtin command.
HOME
-
The current user's home directory; the default for the
cd builtin
command.
The value of this variable is also used by tilde expansion
(see section 3.5.2 Tilde Expansion).
IFS
-
A list of characters that separate fields; used when the shell splits
words as part of expansion.
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.
MAILPATH
-
A colon-separated list of filenames which the shell periodically checks
for new mail.
Each list entry can specify the message that is printed when new mail
arrives in the mail file by separating the file name from the message with
a `?'.
When used in the text of the message,
$_ expands to the name of
the current mail file.
OPTARG
-
The value of the last option argument processed by the
getopts builtin.
OPTIND
-
The index of the last option argument processed by the
getopts builtin.
PATH
-
A colon-separated list of directories in which the shell looks for
commands.
PS1
-
The primary prompt string. The default value is `\s-\v\$ '.
See section 6.9 Controlling the Prompt, for the complete list of escape
sequences that are expanded before
PS1 is displayed.
PS2
-
The secondary prompt string. The default value is `> '.
5.2 Bash Variables
These variables are set or used by Bash, but other shells
do not normally treat them specially.
A few variables used by Bash are described in different chapters:
variables for controlling the job control facilities
(see section 7.3 Job Control Variables).
BASH
-
The full pathname used to execute the current instance of Bash.
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. See section 6.2 Bash Startup Files.
BASH_VERSION
-
The version number of the current instance of Bash.
BASH_VERSINFO
-
A readonly array variable (see section 6.7 Arrays)
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.
COLUMNS
-
Used by the
select builtin command to determine the terminal width
when printing selection lists. Automatically set upon receipt of a
SIGWINCH.
COMP_CWORD
-
An index into
${COMP_WORDS} of the word containing the current
cursor position.
This variable is available only in shell functions invoked by the
programmable completion facilities (see section 8.6 Programmable Completion).
COMP_LINE
-
The current command line.
This variable is available only in shell functions and external
commands invoked by the
programmable completion facilities (see section 8.6 Programmable Completion).
COMP_POINT
-
The index of the current cursor position relative to the beginning of
the current command.
If the current cursor position is at the end of the current command,
the value of this variable is equal to
${#COMP_LINE}.
This variable is available only in shell functions and external
commands invoked by the
programmable completion facilities (see section 8.6 Programmable Completion).
COMP_WORDS
-
An array variable consisting of the individual
words in the current command line.
This variable is available only in shell functions invoked by the
programmable completion facilities (see section 8.6 Programmable Completion).
COMPREPLY
-
An array variable from which Bash reads the possible completions
generated by a shell function invoked by the programmable completion
facility (see section 8.6 Programmable Completion).
DIRSTACK
-
An array variable 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.
EUID
-
The numeric effective user id of the current user. This variable
is readonly.
FCEDIT
-
The editor used as a default by the `-e' option to the
fc
builtin command.
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:~'
FUNCNAME
-
The name of any currently-executing shell function.
This variable exists only when a shell function is executing.
Assignments to
FUNCNAME have no effect and return an error status.
If FUNCNAME is unset, it loses its special properties, even if
it is subsequently reset.
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.
GROUPS
-
An array variable containing the list of groups of which the current
user is a member.
Assignments to
GROUPS have no effect and return an error status.
If GROUPS is unset, it loses its special properties, even if it is
subsequently reset.
histchars
-
Up to three characters which control history expansion, quick
substitution, and tokenization (see section 9.3 History Expansion).
The first character is the
history expansion character, 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 indicates that 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.
HISTCONTROL
-
A value of `ignorespace' means to not enter lines which
begin with a space or tab into the history list.
A value of `ignoredups' means to not 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.
The second and subsequent lines of a multi-line compound command are
not tested, and are added to the history regardless of the value of
HISTCONTROL.
HISTFILE
-
The name of the file to which the command history is saved. The
default value is `~/.bash_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 history file is also truncated to this size after
writing it when an interactive shell exits.
The default value is 500.
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 match the complete
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.
The second and subsequent lines of a multi-line compound command are
not tested, and are added to the history regardless of the value of
HISTIGNORE.
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.
HISTSIZE
-
The maximum number of commands to remember on the history list.
The default value is 500.
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.
The list of possible hostname completions may be changed while the shell
is running;
the next time hostname completion is attempted after the
value is changed, Bash adds the contents of the new file to the
existing list.
If
HOSTFILE is set, but has no value, Bash attempts to read
`/etc/hosts' to obtain the list of possible hostname completions.
When HOSTFILE is unset, the hostname list is cleared.
HOSTNAME
-
The name of the current host.
HOSTTYPE
-
A string describing the machine Bash is running on.
IGNOREEOF
-
Controls the action of the shell on receipt of an
EOF character
as the sole input. If set, the value denotes 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.
INPUTRC
-
The name of the Readline initialization file, overriding the default
of `~/.inputrc'.
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, and
determines the behavior of range expressions, equivalence classes,
and collating sequences within filename expansion and pattern matching
(see section 3.5.8 Filename Expansion).
LC_CTYPE
-
This variable determines the interpretation of characters and the
behavior of character classes within filename expansion and pattern
matching (see section 3.5.8 Filename Expansion).
LC_MESSAGES
-
This variable determines the locale used to translate double-quoted
strings preceded by a `$' (see section 3.1.2.5 Locale-Specific Translation).
LC_NUMERIC
-
This variable determines the locale category used for number formatting.
LINENO
-
The line number in the script or shell function currently executing.
LINES
-
Used by the
select builtin command to determine the column length
for printing selection lists. Automatically set upon receipt of a
SIGWINCH.
MACHTYPE
-
A string that fully describes the system type on which Bash
is executing, in the standard GNU cpu-company-system format.
MAILCHECK
-
How often (in seconds) that the shell should check for mail in the
files specified in the
MAILPATH or MAIL variables.
The default is 60 seconds. When it is time to check
for mail, the shell does so before displaying the primary prompt.
If this variable is unset, or set to a value that is not a number
greater than or equal to zero, the shell disables mail checking.
OLDPWD
-
The previous working directory as set by the
cd builtin.
OPTERR
-
If set to the value 1, Bash displays error messages
generated by the
getopts builtin command.
OSTYPE
-
A string describing the operating system Bash is running on.
PIPESTATUS
-
An array variable (see section 6.7 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).
POSIXLY_CORRECT
-
If this variable is in the environment when
bash starts, the shell
enters POSIX mode (see section 6.11 Bash POSIX Mode) before reading the
startup files, as if the `--posix' invocation option had been supplied.
If it is set while the shell is running, bash enables POSIX mode,
as if the command
had been executed.
PPID
-
The process ID of the shell's parent process. This variable
is readonly.
PROMPT_COMMAND
-
If set, the value is interpreted as a command to execute
before the printing of each primary prompt (
$PS1).
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
-
The value is the prompt printed before the command line is echoed
when the `-x' option is set (see section 4.3 The Set Builtin).
The first character of
PS4 is replicated multiple times, as
necessary, to indicate multiple levels of indirection.
The default is `+ '.
PWD
-
The current working directory as set by the
cd 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.
REPLY
-
The default variable for the
read builtin.
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.
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 (see section 4.3 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.
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.
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
| |
$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'
|
If the value is null, no timing information is displayed.
A trailing newline is added when the format string is displayed.
TMOUT
-
If set to a value greater than zero, the value is interpreted as
the number of seconds to wait for input after issuing the primary
prompt when the shell is interactive.
Bash terminates after that number of seconds if input does
not arrive.
UID
-
The numeric real user id of the current user. This variable is readonly.
6. Bash Features
This section describes features unique to Bash.
6.1 Invoking Bash
| |
bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o option] [-O shopt_option] [argument ...]
bash [long-opt] [-abefhkmnptuvxdBCDHP] [-o option] [-O shopt_option] -c string [argument ...]
bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o option] [-O shopt_option] [argument ...]
|
In addition to the single-character shell command-line options
(see section 4.3 The Set Builtin), there are several multi-character
options that you can use. These options must appear on the command
line before the single-character options in order for them
to be recognized.
--dump-po-strings
- A list of all double-quoted strings preceded by `$'
is printed on the standard ouput
in the GNU
gettext PO (portable object) file format.
Equivalent to `-D' except for the output format.
--dump-strings
- Equivalent to `-D'.
--help
- Display a usage message on standard output and exit sucessfully.
--init-file filename
--rcfile filename
- Execute commands from filename (instead of `~/.bashrc')
in an interactive shell.
--login
- Make this shell act as if it had been directly invoked by login.
When the shell is interactive, this is equivalent to starting a
login shell with `exec -l bash'.
When the shell is not interactive, the login shell startup files will
be executed.
`exec bash --login'
will replace the current shell with a Bash login shell.
See section 6.2 Bash Startup Files, for a description of the special behavior
of a login shell.
--noediting
- Do not use the GNU Readline library (see section 8. Command Line Editing)
to read command lines when the shell is interactive.
--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. See section 6.11 Bash POSIX Mode, for a description of the Bash
POSIX mode.
--restricted
- Make the shell a restricted shell (see section 6.10 The Restricted Shell).
--verbose
- Equivalent to `-v'. Print shell input lines as they're read.
--version
- Show version information for this instance of
Bash on the standard output and exit successfully.
There are several single-character options that may be supplied at
invocation 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
$0.
-i
- Force the shell to run interactively. Interactive shells are
described in 6.3 Interactive Shells.
-r
- Make the shell a restricted shell (see section 6.10 The Restricted Shell).
-s
- If this option is present, or if no arguments remain after option
processing, then commands are read from the standard input.
This option allows the positional parameters to be set
when invoking an interactive shell.
-D
- A list of all double-quoted strings preceded by `$'
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 (see section 3.1.2.5 Locale-Specific Translation).
This implies the `-n' option; no commands will be executed.
[-+]O [shopt_option]
- shopt_option is one of the shell options accepted by the
shopt builtin (see section 4. Shell Builtin Commands).
If shopt_option is present, `-O' sets the value of that option;
`+O' unsets it.
If shopt_option is not supplied, the names and values of the shell
options accepted by shopt are printed on the standard output.
If the invocation option is `+O', the output is displayed in a format
that may be reused as input.
--
- A
-- signals the end of options and disables further option
processing.
Any arguments after the -- are treated as filenames and arguments.
A login shell is one whose first character of argument zero is
`-', or one invoked with the `--login' option.
An interactive shell is one started without non-option arguments,
unless `-s' is specified,
without specifying the `-c' option, and whose input and output are both
connected to terminals (as determined by isatty(3)), or one
started with the `-i' option. See section 6.3 Interactive Shells, for more
information.
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 (see section 3.8 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.
6.2 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 (see section 3.5.2 Tilde Expansion).
Interactive shells are described in 6.3 Interactive Shells.
Invoked as an interactive login shell, or with `--login'
When Bash is invoked as an interactive login shell, or as a
non-interactive shell with the `--login' option, 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.
Invoked as an interactive non-login shell
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.
Invoked non-interactively
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.
As noted above, if a non-interactive shell is invoked with the
`--login' option, Bash attempts to read and execute commands from the
login shell startup files.
Invoked with name sh
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 an interactive login shell, or as a non-interactive
shell with the `--login' option, 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 other startup files.
When invoked as sh, Bash enters POSIX mode after
the startup files are read.
Invoked in POSIX mode
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, interactive shells expand the ENV variable
and commands are read and executed from the file whose name is the
expanded value.
No other startup files are read.
Invoked by remote shell daemon
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.
Invoked with unequal effective and real UID/GIDs
If Bash is started with the effective user (group) id not equal to the
real user (group) id, and the -p option is not supplied, no startup
files are read, shell functions are not inherited from the environment,
the SHELLOPTS variable, if it appears in the environment, is ignored,
and the effective user id is set to the real user id.
If the -p option is supplied at invocation, the startup behavior is
the same, but the effective user id is not reset.
6.3 Interactive Shells
6.3.1 What is an Interactive Shell?
An interactive shell
is one started without non-option arguments, unless `-s' is
specified, without specifiying the `-c' option, and
whose input and output are both
connected to terminals (as determined by isatty(3)),
or one started with the `-i' option.
An interactive shell generally reads from and writes to a user's
terminal.
The `-s' invocation option may be used to set the positional parameters
when an interactive shell is started.
6.3.2 Is this Shell Interactive?
To determine within a startup script whether or not Bash is
running interactively,
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
|
Alternatively, startup scripts may 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
|
6.3.3 Interactive Shell Behavior
When the shell is running interactively, it changes its behavior in
several ways.
-
Startup files are read and executed as described in 6.2 Bash Startup Files.
-
Job Control (see section 7. Job Control) is enabled by default. When job
control is in effect, Bash ignores the keyboard-generated job control
signals
SIGTTIN, SIGTTOU, and SIGTSTP.
-
Bash expands and displays
PS1 before reading the first line
of a command, and expands and displays PS2 before reading the
second and subsequent lines of a multi-line command.
-
Bash executes the value of the
PROMPT_COMMAND variable as a command
before printing the primary prompt, $PS1
(see section 5.2 Bash Variables).
-
Readline (see section 8. Command Line Editing) is used to read commands from
the user's terminal.
-
Bash inspects the value of the
ignoreeof option to set -o
instead of exiting immediately when it receives an EOF on its
standard input when reading a command (see section 4.3 The Set Builtin).
-
Command history (see section 9.1 Bash History Facilities)
and history expansion (see section 9.3 History Expansion)
are enabled by default.
Bash will save the command history to the file named by
$HISTFILE
when an interactive shell exits.
-
Alias expansion (see section 6.6 Aliases) is performed by default.
-
In the absence of any traps, Bash ignores
SIGTERM
(see section 3.7.6 Signals).
-
In the absence of any traps,
SIGINT is caught and handled
((see section 3.7.6 Signals).
SIGINT will interrupt some shell builtins.
-
An interactive login shell sends a
SIGHUP to all jobs on exit
if the hupoxexit shell option has been enabled (see section 3.7.6 Signals).
-
The `-n' invocation option is ignored, and `set -n' has
no effect (see section 4.3 The Set Builtin).
-
Bash will check for mail periodically, depending on the values of the
MAIL, MAILPATH, and MAILCHECK shell variables
(see section 5.2 Bash Variables).
-
Expansion errors due to references to unbound shell variables after
`set -u' has been enabled will not cause the shell to exit
(see section 4.3 The Set Builtin).
-
The shell will not exit on expansion errors caused by var being unset
or null in
${var:?word} expansions
(see section 3.5.3 Shell Parameter Expansion).
-
Redirection errors encountered by shell builtins will not cause the
shell to exit.
-
When running in POSIX mode, a special builtin returning an error
status will not cause the shell to exit (see section 6.11 Bash POSIX Mode).
-
A failed
exec will not cause the shell to exit
(see section 4.1 Bourne Shell Builtins).
-
Parser syntax errors will not cause the shell to exit.
-
Simple spelling correction for directory arguments to the
cd
builtin is enabled by default (see the description of the cdspell
option to the shopt builtin in 4.2 Bash Builtin Commands).
-
The shell will check the value of the
TMOUT variable and exit
if a command is not read within the specified number of seconds after
printing $PS1 (see section 5.2 Bash Variables).
6.4 Bash Conditional Expressions
Conditional expressions are used by the [[ compound command
and the test and [ builtin commands.
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.
If the file argument to one of the primaries is of the form
`/dev/fd/N', then file descriptor N is checked.
If the file argument to one of the primaries is one of
`/dev/stdin', `/dev/stdout', or `/dev/stderr', file
descriptor 0, 1, or 2, respectively, is checked.
-a file
- True if file exists.
-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 its set-group-id bit is set.
-h file
- True if file exists and is a symbolic link.
-k file
- True if file exists and its "sticky" bit is set.
-p file
- True if file exists and is a named pipe (FIFO).
-r file
- True if file exists and is readable.
-s file
- True if file exists and has a size greater than zero.
-t fd
- True if file descriptor fd is open and refers to 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.
-L file
- True if file exists and is a symbolic link.
-S file
- True if file exists and is a socket.
-N file
- True if file exists and has been modified since it was last read.
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 (see section 4.3 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
in the current locale.
string1 > string2
- True if string1 sorts after string2 lexicographically
in the current locale.
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.
6.5 Shell Arithmetic
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 operators and their precedence and associativity are the same
as in the C language.
The following list of operators is grouped into levels of
equal-precedence operators.
The levels are listed in order of decreasing precedence.
id++ id--
- variable post-increment and post-decrement
++id --id
- variable pre-increment and pre-decrement
- +
- unary minus and plus
! ~
- logical and bitwise negation
**
- exponentiation
* / %
- 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
expr1 , expr2
- comma
Shell variables are allowed as operands; parameter expansion is
performed before the expression is evaluated.
Within an expression, shell variables may also be referenced by name
without using the parameter expansion syntax.
The value of a variable is evaluated as an arithmetic expression
when it is referenced.
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.
6.6 Aliases
Aliases allow a string to be substituted for a word when it is used
as the first word of a simple command.
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 simple 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
(see section 3.3 Shell Functions).
Aliases are not expanded when the shell is not interactive,
unless the expand_aliases shell option is set using
shopt (see section 4.2 Bash Builtin Commands).
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 a 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.
For almost every purpose, shell functions are preferred over aliases.
6.7 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
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
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
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.
6.8 The Directory Stack
The directory stack is a list of recently-visited directories. The
pushd builtin adds directories to the stack as it changes
the current directory, and the popd builtin removes specified
directories from the stack and changes the current directory to
the directory removed. The dirs builtin displays the contents
of the directory stack.
The contents of the directory stack are also visible
as the value of the DIRSTACK shell variable.
6.8.1 Directory Stack Builtins
dirs
-
Display the list of currently remembered directories. Directories
are added to the list with the
pushd command; the
popd command removes directories from the list.
+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, prefixing each entry with its index in the stack.
popd
-
Remove the top entry from 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.
pushd
-
| |
pushd [dir | +N | -N] [-n]
|
Save the current directory on the top of the directory stack
and then cd to dir.
With no arguments, pushd 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
executes the equivalent of `
cd dir'.
cds to dir.
6.9 Controlling the Prompt
The value of the variable PROMPT_COMMAND is examined just before
Bash prints each primary prompt. If PROMPT_COMMAND is set and
has a non-null value, then the
value is executed just as if it had been typed 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.
\j
- The number of jobs currently managed by the shell.
\l
- The basename of the shell's terminal device name.
\n
- A newline.
\r
- A carriage return.
\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.
\A
- The time, in 24-hour HH:MM format.
\u
- The username of the current user.
\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.
\!
- The history number of this command.
\#
- The command number of this command.
\$
- If the effective uid is 0,
#, otherwise $.
\nnn
- The character whose ASCII code is the octal value 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.
The command number and the history number are usually different:
the history number of a command is its position in the history
list, which may include commands restored from the history file
(see section 9.1 Bash History Facilities), while the command number is
the position in the sequence of commands executed during the current
shell session.
After the string is decoded, it is expanded via
parameter expansion, command substitution, arithmetic
expansion, and quote removal, subject to the value of the
promptvars shell option (see section 4.2 Bash Builtin Commands).
6.10 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, PATH,
ENV, or BASH_ENV variables.
-
Specifying command names containing slashes.
-
Specifying a filename containing a slash as an argument to the
.
builtin command.
-
Specifying a filename containing a slash as an argument to the `-p'
option to the
hash builtin command.
-
Importing function definitions from the shell environment at startup.
-
Parsing the value of
SHELLOPTS 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' or `set +o restricted'.
6.11 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 1003.2 standard by changing the behavior to
match that specified by POSIX in areas where the Bash default differs.
The following list is what's changed when `POSIX mode' is in effect:
-
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'.
-
The message printed by the job control code and builtins when a job
exits with a non-zero status is `Done(status)'.
-
The message printed by the job control code and builtins when a job
is stopped is `Stopped(signame)', where signame is, for
example,
SIGTSTP.
-
Reserved words may not be aliased.
-
The POSIX 1003.2
PS1 and PS2 expansions of `!' to
the history number and `!!' to `!' are enabled,
and parameter expansion is performed on the values of PS1 and
PS2 regardless of the setting of the promptvars option.
-
Interactive comments are enabled by default. (Bash has them on by
default anyway.)
-
The POSIX 1003.2 startup files are executed (
$ENV) rather than
the normal Bash files.
-
Tilde expansion is only performed on assignments preceding a command
name, rather than on all assignment statements on the line.
-
The default history file is `~/.sh_history' (this is the
default value of
$HISTFILE).
-
The output of `kill -l' prints all the signal names on a single line,
separated by spaces.
-
Non-interactive shells exit if filename in
. filename
is not found.
-
Non-interactive shells exit if a syntax error in an arithmetic expansion
results in an invalid expression.
-
Redirection operators do not perform filename expansion on the word
in the redirection unless the shell is interactive.
-
Redirection operators do not perform word splitting on the word in the
redirection.
-
Function names must be valid shell
names. 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 invalid name
causes a fatal syntax error in non-interactive shells.
-
POSIX 1003.2 `special' builtins are found before shell functions
during command lookup.
-
If a POSIX 1003.2 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.
-
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.
-
If
CDPATH is set, the cd builtin will not implicitly
append the current directory to it. This means that cd will
fail if no valid directory name can be constructed from
any of the entries in $CDPATH, even if the a directory with
the same name as the name given as an argument to cd exists
in the current directory.
-
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 readonly variable.
-
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 readonly variable.
-
Process substitution is not available.
-
Assignment statements preceding POSIX 1003.2 special builtins
persist in the shell environment after the builtin completes.
-
Assignment statements preceding shell function calls persist in the
shell environment after the function returns, as if a POSIX
special builtin command had been executed.
-
The
export and readonly builtin commands display their
output in the format required by POSIX 1003.2.
-
The
trap builtin displays signal names without the leading
SIG.
-
The
. and source builtins do not search the current directory
for the filename argument if it is not found by searching PATH.
-
Subshells spawned to execute command substitutions inherit the value of
the `-e' option from the parent shell. When not in POSIX mode,
Bash clears the `-e' option in such subshells.
-
Alias expansion is always enabled, even in non-interactive shells.
-
When the
set builtin is invoked without options, it does not display
shell function names and definitions.
-
When the
set builtin is invoked without options, it displays
variable values without quotes, unless they contain shell metacharacters,
even if the result contains nonprinting characters.
There is other POSIX 1003.2 behavior that Bash does not implement.
Specifically:
-
Assignment statements affect the execution environment of all
builtins, not just special ones.
-
When a subshell is created to execute a shell script with execute permission,
but without a leading `#!', Bash sets
$0 to the full pathname of
the script as found by searching $PATH, rather than the command as
typed by the user.
-
When using `.' to source a shell script found in
$PATH, bash
checks execute permission bits rather than read permission bits, just as
if it were searching for a command.
7. Job Control
This chapter discusses what job control is, how it works, and how
Bash allows you to access its facilities.
7.1 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, it prints a line that looks
like:
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 operating 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 contains facilities to use it. Typing the
suspend character (typically `^Z', Control-Z) while a
process is running causes that process to be stopped and returns
control 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. The user then manipulates 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'.
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 or started
in the background. 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 `-'.
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.
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 `-b' option to the set builtin is enabled,
Bash reports such changes immediately (see section 4.3 The Set Builtin).
Any trap on SIGCHLD is executed for each child process
that exits.
If an attempt to exit Bash is while jobs are stopped, the
shell prints a message warning that there are stopped jobs.
The jobs command may then be used to inspect their status.
If a second attempt to exit is made without an intervening command,
Bash does not print another warning, and the stopped jobs are terminated.
7.2 Job Control Builtins
bg
-
Resume the suspended job jobspec in the background, as if it
had been started with `&'.
If jobspec is not supplied, the current job is used.
The return status is zero unless it is run when job control is not
enabled, or, when run with job control enabled, if jobspec was
not found or jobspec specifies a job that was started without
job control.
fg
-
Resume the job jobspec in the foreground and make it the current job.
If jobspec is not supplied, the current job is used.
The return status is that of the command placed into the foreground,
or non-zero if run when job control is disabled or, when run with
job control enabled, jobspec does not specify a valid job or
jobspec specifies a job that was started without job control.
jobs
-
| |
jobs [-lnprs] [jobspec]
jobs -x command [arguments]
|
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
the user was 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 or pid
kill -l [exit_status]
|
Send a signal specified by sigspec or signum to the process
named by job specification jobspec or process ID pid.
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.
If any arguments are supplied when `-l' is given, the names of the
signals corresponding to the arguments are listed, and the return status
is zero.
exit_status is a number specifying a signal number or the exit
status of a process terminated by a signal.
The return status is zero if at least one signal was successfully sent,
or non-zero if an error occurs or an invalid option is encountered.
wait
-
Wait until the child process specified by process ID pid or job
specification jobspec exits and return the exit status of the last
command waited for.
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, and the return status is zero.
If neither jobspec nor pid specifies an active child process
of the shell, the return status is 127.
disown
-
| |
disown [-ar] [-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, and neither the `-a' nor `-r'
option is supplied, the current job is used.
If no jobspec is supplied, the `-a' option means to remove or
mark all jobs; the `-r' option without a jobspec
argument restricts operation to running jobs.
suspend
-
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.
7.3 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 redirections 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 (see section 7.1 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.
8. Command Line Editing
This chapter describes the basic features of the GNU
command line editing interface.
Command line editing is provided by the Readline library, which is
used by several different programs, including Bash.
8.1 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.
The Meta key is labeled ALT on many keyboards.
On keyboards with two keys labeled ALT (usually to either side of
the space bar), the ALT on the left side is generally set to
work as a Meta key.
The ALT key on the right may also be configured to work as a
Meta key or may be configured as some other modifier, such as a
Compose key for typing accented characters.
If you do not have a Meta or ALT key, or another key working as
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
(see section 8.3 Readline Init File).
If your keyboard lacks a LFD key, typing C-j will
produce the desired character.
The RET key may be labeled Return or Enter on
some keyboards.
8.2 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 RET. You do not have to be at the
end of the line to press RET; the entire line is accepted
regardless of the location of the cursor within the line.
8.2.1 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 mistype a character, and
not notice the 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 bare
essentials for editing the text of an input line follows.
- C-b
- Move back one character.
- C-f
- Move forward one character.
- DEL or Backspace
- 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-_ or C-x C-u
- Undo the last editing command. You can undo all the way back to an
empty line.
(Depending on your configuration, the Backspace key be set to
delete the character to the left of the cursor and the DEL key set
to delete the character underneath the cursor, like C-d, rather
than the character to the left of the cursor.)
8.2.2 Readline Movement Commands
The above table describes the most basic 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, where a word is composed of letters and digits.
- 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.
8.2.3 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.
(`Cut' and `paste' are more recent jargon for `kill' and `yank'.)
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.
Word boundaries are the same as those used by M-f.
- M-DEL
- Kill from the cursor the start of the current word, or, if between
words, to the start of the previous word.
Word boundaries are the same as those used by M-b.
- C-w
- Kill from the cursor to the previous whitespace. This is different than
M-DEL because the word boundaries differ.
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.
8.2.4 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' typed 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',
which will delete the next ten characters on the input line.
8.2.5 Searching for Commands in the History
Readline provides commands for searching through the command history
(see section 9.1 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.
To search backward in the history for a particular string, type
C-r. Typing C-s searches forward through the history.
The characters present in the value of the isearch-terminators variable
are used to terminate an incremental search.
If that variable has not been assigned a value, the ESC and
C-J characters will terminate an incremental search.
C-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 C-r or
C-s 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 RET will terminate the search and accept
the line, thereby executing the command from the history list.
A movement command will terminate the search, make the last line found
the current line, and begin editing.
Readline remembers the last incremental search string. If two
C-rs are typed without any intervening characters defining a new
search string, any remembered search string is used.
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 be part of the contents of the current line.
8.3 Readline Init File
Although the Readline library comes with a set of Emacs-like
keybindings installed by default, it is possible to use a different set
of keybindings.
Any user can customize programs that use Readline by putting
commands in an inputrc file, conventionally in his 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.
8.3.1 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 (see section 8.3.2 Conditional Init Constructs). Other lines
denote variable settings and key bindings.
- Variable Settings
- You can modify the run-time behavior of Readline by
altering the values of variables in Readline
using the
set command within the init file.
The syntax is simple:
Here, for example, is how to
change from the default Emacs-like key binding to use
vi line editing commands:
Variable names and values, where appropriate, are recognized without regard
to case.
The bind -V command lists the current Readline variable names
and values. See section 4.2 Bash Builtin Commands.
A great deal of run-time behavior is changeable with the following
variables.
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-ignore-case
- If set to `on', Readline performs filename matching and completion
in a case-insensitive fashion.
The default value is `off'.
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.
This variable must be set to an integer value greater than or equal to 0.
The default limit is
100.
convert-meta
-
If set to `on', Readline will convert characters with the
eighth bit set to an ASCII key sequence by stripping the eighth
bit and prefixing 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 default set of
key bindings is used. 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'.
If set to `on', the history code attempts to place point at the
same location on each history line retrived with previous-history
or next-history.
horizontal-scroll-mode
-
This variable can be set to either `on' or `off'. Setting it
to `on' means that the text of the lines being edited 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'.
input-meta
-
If set to `on', Readline will enable eight-bit input (it
will not clear the eighth bit in 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.
isearch-terminators
-
The string of characters that should terminate an incremental search without
subsequently executing the character as a command (see section 8.2.5 Searching for Commands in the History).
If this variable has not been given a value, the characters ESC and
C-J will terminate an incremental search.
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-move,
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', causes Readline to display an
asterisk (`*') at the start of history lines which have been modified.
This variable is `off' by default.
match-hidden-files
-
This variable, when set to `on', causes Readline to match files whose
names begin with a `.' (hidden files) when performing filename
completion, unless the leading `.' is
supplied by the user in the filename to be completed.
This variable is `on' by default.
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'.
print-completions-horizontally
- If set to `on', Readline will display completions with matches
sorted horizontally in alphabetical order, rather than down the screen.
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 need to find the name of the command that you
want to change. The following sections contain tables of the command
name, the default keybinding, if any, and a short description of what
the command does.
Once you know the name of the command, simply place on a line
in the init file the name of the key
you wish to bind the command to, a colon, and then the name of the
command. The name of the key
can be expressed in different ways, depending on what you find most
comfortable.
In addition to command names, readline allows keys to be bound
to a string that is inserted when the key is pressed (a macro).
The bind -p command displays Readline function names and
bindings in a format that can put directly into an initialization file.
See section 4.2 Bash Builtin Commands.
- 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,
M-DEL is bound to the function backward-kill-word, 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).
A number of symbolic character names are recognized while
processing this key binding syntax:
DEL,
ESC,
ESCAPE,
LFD,
NEWLINE,
RET,
RETURN,
RUBOUT,
SPACE,
SPC,
and
TAB.
- "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 again 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 GNU Emacs style escape sequences are available when
specifying key sequences:
\C-
- control prefix
\M-
- meta prefix
\e
- an escape character
\\
- backslash
\"
- ", a double quotation mark
\'
- ', a single quote or apostrophe
In addition to the GNU Emacs style escape sequences, a second
set of backslash escapes is available:
\a
- alert (bell)
\b
- backspace
\d
- delete
\f
- form feed
\n
- newline
\r
- carriage return
\t
- horizontal tab
\v
- vertical tab
\nnn
- the eight-bit character whose value is the octal value nnn
(one to three digits)
\xHH
- the eight-bit character whose value is the hexadecimal value HH
(one or two hex digits)
When entering the text of a macro, single or double quotes must
be used to indicate a macro definition.
Unquoted text is assumed to be a function name.
In the macro body, the backslash escapes described above are expanded.
Backslash will quote any other character in the macro text,
including `"' and `''.
For example, the following binding will make `C-x \'
insert a single `\' into the line:
8.3.2 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 four 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 both 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
a particular value.
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 seen in the previous example, terminates an
$if command.
$else
- Commands in this branch of the
$if directive are executed if
the test fails.
$include
- This directive takes a single filename as an argument and reads commands
and bindings from that file.
For example, the following directive reads from `/etc/inputrc':
8.3.3 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.
#
# First, include any systemwide bindings and variable assignments from
# /etc/Inputrc
$include /etc/Inputrc
#
# 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
|
8.4 Bindable Readline Commands
This section describes Readline commands that may be bound to key
sequences.
You can list your key bindings by executing
bind -P or, for a more terse format, suitable for an
inputrc file, bind -p. (See section 4.2 Bash Builtin Commands.)
Command names without an accompanying key sequence are unbound by default.
In the following descriptions, point refers to the current cursor
position, and mark refers to a cursor position saved by the
set-mark command.
The text between the point and mark is referred to as the region.
8.4.1 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 the current or 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.
8.4.2 Commands For Manipulating The History
accept-line (Newline or 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 and HISTIGNORE variables.
If this line is a modified history line, then restore the history line
to its original state.
previous-history (C-p)
-
Move `back' through the history list, fetching the previous command.
next-history (C-n)
-
Move `forward' through the history list, fetching the next command.
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 currently
being entered.
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 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) at point.
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-. or 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.
Successive calls to yank-last-arg move back through the history
list, inserting the last argument of each line in turn.
8.4.3 Commands For Changing Text
delete-char (C-d)
-
Delete the character at point. If point is at the
beginning of the line, there are no characters in the line, and
the last character typed was not bound to
delete-char, then
return EOF.
backward-delete-char (Rubout)
-
Delete the character behind the cursor. A numeric argument means
to kill the characters instead of deleting them.
forward-backward-delete-char ()
-
Delete the character under the cursor, unless the cursor is at the
end of the line, in which case the character behind the cursor is
deleted. By default, this is not bound to a key.
quoted-insert (C-q or C-v)
-
Add the next character typed to the line verbatim. This is
how to insert key sequences like C-q, for example.
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 arguments have no effect.
transpose-words (M-t)
-
Drag the word before point past the word after point,
moving point past that word as well.
If the insertion point is at the end of the line, this transposes
the last two words on the line.
upcase-word (M-u)
-
Uppercase the current (or following) word. With a negative argument,
uppercase the previous word, but do not move the cursor.
downcase-word (M-l)
-
Lowercase the current (or following) word. With a negative argument,
lowercase the previous word, but do not move the cursor.
capitalize-word (M-c)
-
Capitalize the current (or following) word. With a negative argument,
capitalize the previous word, but do not move the cursor.
8.4.4 Killing And Yanking
kill-line (C-k)
-
Kill the text from point 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.
kill-whole-line ()
-
Kill all characters on the current line, no matter where point is.
By default, this is unbound.
kill-word (M-d)
-
Kill from point 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 point.
Word boundaries are the same as
backward-word.
unix-word-rubout (C-w)
-
Kill the word behind point, 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 in the current region.
By default, this command is unbound.
copy-region-as-kill ()
-
Copy the text in the region to the kill buffer, so it can be yanked
right away. By default, this command is unbound.
copy-backward-word ()
-
Copy the word before point to the kill buffer.
The word boundaries are the same as
backward-word.
By default, this command is unbound.
copy-forward-word ()
-
Copy the word following point to the kill buffer.
The word boundaries are the same as
forward-word.
By default, this command is unbound.
yank (C-y)
-
Yank the top of the kill ring into the buffer at point.
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.
8.4.5 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.
8.4.6 Letting Readline Type For You
complete (TAB)
-
Attempt to perform completion on the text before point.
The actual completion performed is application-specific.
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 point.
insert-completions (M-*)
-
Insert all completions of the text before point that would have
been generated by
possible-completions.
menu-complete ()
-
Similar to
complete, but replaces the word to be completed
with a single match from the list of possible completions.
Repeated execution of menu-complete steps through the list
of possible completions, inserting each match in turn.
At the end of the list of completions, the bell is rung
(subject to the setting of bell-style)
and the original text is restored.
An argument of n moves n positions forward in the list
of matches; a negative argument may be used to move backward
through the list.
This command is intended to be bound to TAB, but is unbound
by default.
delete-char-or-list ()
-
Deletes the character under the cursor if not at the beginning or
end of the line (like
delete-char).
If at the end of the line, behaves identically to
possible-completions.
This command is unbound by default.
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, shell 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 insert the list of possible completions
enclosed within braces so the list is available to the shell
(see section 3.5.1 Brace Expansion).
8.4.7 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.
8.4.8 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)
-
Metafy the next character typed. This is for keyboards
without a meta key. Typing `ESC f' is equivalent to typing
M-f.
undo (C-_ or 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 executing 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 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.
The default value of comment-begin causes this command
to make 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 output. 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 displayed, and the line is redrawn.
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 as the shell does.
This performs alias and history expansion as well as all of the shell
word expansions (see section 3.5 Shell Expansions).
history-expand-line (M-^)
-
Perform history expansion on the current line.
magic-space ()
-
Perform history expansion on the current line and insert a space
(see section 9.3 History Expansion).
alias-expand-line ()
-
Perform alias expansion on the current line (see section 6.6 Aliases).
history-and-alias-expand-line ()
-
Perform history and alias expansion on the current line.
insert-last-argument (M-. or 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.
8.5 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 (see section 4.3 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.
8.6 Programmable Completion
When word completion is attempted for an argument to a command for
which a completion specification (a compspec) has been defined
using the complete builtin (see section 8.7 Programmable Completion Builtins),
the programmable completion facilities are invoked.
First, the command name is identified.
If a compspec has been defined for that command, the
compspec is used to generate the list of possible completions for the word.
If the command word is a full pathname, a compspec for the full
pathname is searched for first.
If no compspec is found for the full pathname, an attempt is made to
find a compspec for the portion following the final slash.
Once a compspec has been found, it is used to generate the list of
matching words.
If a compspec is not found, the default Bash completion
described above (see section 8.4.6 Letting Readline Type For You) is performed.
First, the actions specified by the compspec are used.
Only matches which are prefixed by the word being completed are
returned.
When the `-f' or `-d' option is used for filename or
directory name completion, the shell variable FIGNORE is
used to filter the matches.
See section 5.2 Bash Variables, for a description of FIGNORE.
Any completions specified by a filename expansion pattern to the
`-G' option are generated next.
The words generated by the pattern need not match the word being completed.
The GLOBIGNORE shell variable is not used to filter the matches,
but the FIGNORE shell variable is used.
Next, the string specified as the argument to the `-W' option
is considered.
The string is first split using the characters in the IFS
special variable as delimiters.
Shell quoting is honored.
Each word is then expanded using
brace expansion, tilde expansion, parameter and variable expansion,
command substitution, arithmetic expansion, and pathname expansion,
as described above (see section 3.5 Shell Expansions).
The results are split using the rules described above
(see section 3.5.7 Word Splitting).
The results of the expansion are prefix-matched against the word being
completed, and the matching words become the possible completions.
After these matches have been generated, any shell function or command
specified with the `-F' and `-C' options is invoked.
When the command or function is invoked, the COMP_LINE and
COMP_POINT variables are assigned values as described above
(see section 5.2 Bash Variables).
If a shell function is being invoked, the COMP_WORDS and
COMP_CWORD variables are also set.
When the function or command is invoked, the first argument is the
name of the command whose arguments are being completed, the
second argument is the word being completed, and the third argument
is the word preceding the word being completed on the current command line.
No filtering of the generated completions against the word being completed
is performed; the function or command has complete freedom in generating
the matches.
Any function specified with `-F' is invoked first.
The function may use any of the shell facilities, including the
compgen builtin described below
(see section 8.7 Programmable Completion Builtins), to generate the matches.
It must put the possible completions in the COMPREPLY array
variable.
Next, any command specified with the `-C' option is invoked
in an environment equivalent to command substitution.
It should print a list of completions, one per line, to
the standard output.
Backslash may be used to escape a newline, if necessary.
After all of the possible completions are generated, any filter
specified with the `-X' option is applied to the list.
The filter is a pattern as used for pathname expansion; a `&'
in the pattern is replaced with the text of the word being completed.
A literal `&' may be escaped with a backslash; the backslash
is removed before attempting a match.
Any completion that matches the pattern will be removed from the list.
A leading `!' negates the pattern; in this case any completion
not matching the pattern will be removed.
Finally, any prefix and suffix specified with the `-P' and `-S'
options are added to each member of the completion list, and the result is
returned to the Readline completion code as the list of possible
completions.
If the previously-applied actions do not generate any matches, and the
`-o dirnames' option was supplied to complete when the
compspec was defined, directory name completion is attempted.
By default, if a compspec is found, whatever it generates is returned to
the completion code as the full set of possible completions.
The default Bash completions are not attempted, and the Readline default
of filename completion is disabled.
If the `-o default' option was supplied to complete when the
compspec was defined, Readline's default completion will be performed
if the compspec generates no matches.
8.7 Programmable Completion Builtins
Two builtin commands are available to manipulate the programmable completion
facilities.
compgen
-
Generate possible completion matches for word according to
the options, which may be any option accepted by the
complete
builtin with the exception of `-p' and `-r', and write
the matches to the standard output.
When using the `-F' or `-C' options, the various shell variables
set by the programmable completion facilities, while available, will not
have useful values.
The matches will be generated in the same way as if the programmable
completion code had generated them directly from a completion specification
with the same flags.
If word is specified, only those completions matching word
will be displayed.
The return value is true unless an invalid option is supplied, or no
matches were generated.
complete
-
| |
complete [-abcdefgjkvu] [-o comp-option] [-A action] [-G globpat] [-W wordlist]
[-P prefix] [-S suffix] [-X filterpat] [-F function]
[-C command] name [name ...]
complete -pr [name ...]
|
Specify how arguments to each name should be completed.
If the `-p' option is supplied, or if no options are supplied, existing
completion specifications are printed in a way that allows them to be
reused as input.
The `-r' option removes a completion specification for
each name, or, if no names are supplied, all
completion specifications.
The process of applying these completion specifications when word completion
is attempted is described above (see section 8.6 Programmable Completion).
Other options, if specified, have the following meanings.
The arguments to the `-G', `-W', and `-X' options
(and, if necessary, the `-P' and `-S' options)
should be quoted to protect them from expansion before the
complete builtin is invoked.
-o comp-option
- The comp-option controls several aspects of the compspec's behavior
beyond the simple generation of completions.
comp-option may be one of:
default
- Use readline's default completion if the compspec generates no matches.
dirnames
- Perform directory name completion if the compspec generates no matches.
filenames
- Tell Readline that the compspec generates filenames, so it can perform any
filename\-specific processing (like adding a slash to directory names or
suppressing trailing spaces). This option is intended to be used with
shell functions specified with `-F'.
-A action
- The action may be one of the following to generate a list of possible
completions:
alias
- Alias names. May also be specified as `-a'.
arrayvar
- Array variable names.
binding
- Readline key binding names (see section 8.4 Bindable Readline Commands).
builtin
- Names of shell builtin commands. May also be specified as `-b'.
command
- Command names. May also be specified as `-c'.
directory
- Directory names. May also be specified as `-d'.
disabled
- Names of disabled shell builtins.
enabled
- Names of enabled shell builtins.
export
- Names of exported shell variables. May also be specified as `-e'.
file
- File names. May also be specified as `-f'.
function
- Names of shell functions.
group
- Group names. May also be specified as `-g'.
helptopic
- Help topics as accepted by the
help builtin (see section 4.2 Bash Builtin Commands).
hostname
- Hostnames, as taken from the file specified by the
HOSTFILE shell variable (see section 5.2 Bash Variables).
job
- Job names, if job control is active. May also be specified as `-j'.
keyword
- Shell reserved words. May also be specified as `-k'.
running
- Names of running jobs, if job control is active.
setopt
- Valid arguments for the `-o' option to the
set builtin
(see section 4.3 The Set Builtin).
shopt
- Shell option names as accepted by the
shopt builtin
(see section 4.2 Bash Builtin Commands).
signal
- Signal names.
stopped
- Names of stopped jobs, if job control is active.
user
- User names. May also be specified as `-u'.
variable
- Names of all shell variables. May also be specified as `-v'.
-G globpat
- The filename expansion pattern globpat is expanded to generate
the possible completions.
-W wordlist
- The wordlist is split using the characters in the
IFS special variable as delimiters, and each resultant word
is expanded.
The possible completions are the members of the resultant list which
match the word being completed.
-C command
- command is executed in a subshell environment, and its output is
used as the possible completions.
-F function
- The shell function function is executed in the current shell
environment.
When it finishes, the possible completions are retrieved from the value
of the
COMPREPLY array variable.
-X filterpat
- filterpat is a pattern as used for filename expansion.
It is applied to the list of possible completions generated by the
preceding options and arguments, and each completion matching
filterpat is removed from the list.
A leading `!' in filterpat negates the pattern; in this
case, any completion not matching filterpat is removed.
-P prefix
- prefix is added at the beginning of each possible completion
after all other options have been applied.
-S suffix
- suffix is appended to each possible completion
after all other options have been applied.
The return value is true unless an invalid option is supplied, an option
other than `-p' or `-r' is supplied without a name
argument, an attempt is made to remove a completion specification for
a name for which no specification exists, or
an error occurs adding a completion specification.
9. 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 other programs,
see the GNU Readline Library Manual.
9.1 Bash History Facilities
When the `-o history' option to the set builtin
is enabled (see section 4.3 The Set Builtin),
the shell provides access to the command history,
the list of commands previously typed.
The value of the HISTSIZE shell variable is used as the
number of commands to save in a history list.
The text of the last $HISTSIZE
commands (default 500) is saved.
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').
The file named by the value of 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 the file
named by $HISTFILE.
If the histappend shell option is set (see section 4.2 Bash Builtin Commands),
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 may be used to list or edit and re-execute
a portion of the history list.
The history builtin may be used to display or modify the history
list and manipulate the history file.
When using command-line editing, search commands
are available in each editing mode that provide access to the
history list (see section 8.4.2 Commands For Manipulating The History).
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.
The shopt builtin is used to set these options.
See section 4.2 Bash Builtin Commands, for a description of shopt.
9.2 Bash History Builtins
Bash provides two builtin commands which manipulate the
history list and history file.
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 (see section 6.6 Aliases).
history
-
| |
history [n]
history -c
history -d offset
history [-anrw] [filename]
history -ps arg
|
With no options, display the history list with line numbers.
Lines prefixed with a `*' have been modified.
An argument of n lists only the last n lines.
Options, if supplied, have the following meanings:
-c
- Clear the history list. This may be combined
with the other options to replace the history list completely.
-d offset
- Delete the history entry at position offset.
offset should be specified as it appears when the history is
displayed.
-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.
-r
- Read the current history file and append its contents to
the history list.
-w
- Write out the current history to the history file.
-p
- Perform history substitution on the args and display the result
on the standard output, without storing the results in the history list.
-s
- The args are added to the end of
the history list as a single entry.
When any of the `-w', `-r', `-a', or `-n' options 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.
9.3 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 history list 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 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 words
surrounded by quotes are considered 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 (see section 4.2 Bash Builtin Commands) 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.
This is most useful in conjunction with Readline.
The shell allows control of the various characters used by the
history expansion mechanism with the histchars variable.
9.3.1 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.
9.3.2 Word Designators
Word designators are used to select desired words from the event.
A `:' separates the event specification from the word designator. It
may be omitted if the word designator begins with a `^', `$',
`*', `-', or `%'. Words are numbered from the beginning
of the line, with the first word being denoted by 0 (zero). Words are
inserted into the current line separated by single spaces.
For example,
!!
- designates the preceding command. When you type this, the preceding
command is repeated in toto.
!!:$
- designates the last argument of the preceding command. This may be
shortened to
!$.
!fi:2
- designates the second argument of the most recent command starting with
the letters
fi.
Here are the word designators:
0 (zero)
- The
0th 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
0th. 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.
9.3.3 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 `&'.
10. Installing Bash
This chapter provides basic instructions for installing Bash on
the various supported platforms. The distribution supports the
GNU operating systems, nearly every version of Unix, and several
non-Unix systems such as BeOS and Interix.
Other independent ports exist for
MS-DOS, OS/2, Windows 95/98, and Windows NT.
10.1 Basic Installation
These are installation instructions for Bash.
The simplest way to compile Bash is:
-
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 some time.
While running, it prints messages telling which features it is
checking for.
-
Type `make' to compile Bash and build the
bashbug bug
reporting script.
-
Optionally, type `make tests' to run the Bash test suite.
-
Type `make install' to install
bash and bashbug.
This will also install the manual pages and Info file.
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', `doc', and `support' directories,
each directory under `lib', and several others). 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.
To find out more about the options and arguments that the
configure script understands, type
| |
bash-2.04$ ./configure --help
|
at the Bash prompt in your Bash source directory.
If you need to do unusual things to compile Bash, please
try to figure out how configure could check whether or not
to do them, and mail diffs or instructions to
bash-maintainers@gnu.org 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 2.50 or
newer.
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'.
10.2 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.
10.3 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.
10.4 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',
or by specifying a value for the DESTDIR `make'
variable when running `make install'.
You can specify separate installation prefixes for
architecture-specific files and architecture-independent files.
If you give configure the option
`--exec-prefix=PATH', `make install' will use
PATH as the prefix for installing programs and libraries.
Documentation and other data files will still use the regular prefix.
10.5 Specifying the System Type
There may be some features configure can not figure out
automatically, but need to determine by the type of host Bash
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., `i386-unknown-freebsd4.2').
See the file `support/config.sub' for the possible
values of each field.
10.6 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.
10.7 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. `configure --help' prints the complete list.
10.8 Optional Features
The Bash configure has a number of `--enable-feature'
options, where feature indicates an optional part of Bash.
There are also several `--with-package' options,
where package is something like `bash-malloc' or `purify'.
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-bash-malloc
- Use the Bash 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 some space on each allocation.
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-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-gnu-malloc
- A synonym for
--with-bash-malloc.
--with-installed-readline[=PREFIX]
- Define this to make Bash link with a locally-installed version of Readline
rather than the version in `lib/readline'. This works only with
Readline 4.2 and later versions. If PREFIX is
yes or not
supplied, configure uses the values of the make variables
includedir and libdir, which are subdirectories of prefix
by default, to find the installed version of Readline if it is not in
the standard system include and library directories.
If PREFIX is no, Bash links with the version in
`lib/readline'.
If PREFIX is set to any other value, configure treats it as
a directory pathname and looks for
the installed version of Readline in subdirectories of that directory
(include files in PREFIX/include and the library in
PREFIX/lib).
--with-purify
- Define this to use the Purify memory allocation checker from Rational
Software.
--enable-minimal-config
- This produces a shell with minimal features, close to the historical
Bourne shell.
There are several `--enable-' options that alter how Bash is
compiled and linked, rather than changing run-time features.
--enable-largefile
- Enable support for large files if the operating system requires special compiler options
to build programs which can access large files.
--enable-profiling
- This builds a Bash binary that produces profiling information to be
processed by
gprof each time it is executed.
--enable-static-link
- This causes Bash to be linked statically, if
gcc is being used.
This could be used to build a version to use as root's 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
`xpg-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 (see section 6.6 Aliases).
--enable-arith-for-command
- Include support for the alternate form of the
for command
that behaves like the C language for statement
(see section 3.2.4 Looping Constructs).
--enable-array-variables
- Include support for one-dimensional array shell variables
(see section 6.7 Arrays).
--enable-bang-history
- Include support for
csh-like history substitution
(see section 9.3 History Expansion).
--enable-brace-expansion
- Include
csh-like brace expansion
( b{a,b}c ==> bac bbc ).
See 3.5.1 Brace Expansion, for a complete description.
--enable-command-timing
- Include support for recognizing
time as a reserved word and for
displaying timing statistics for the pipeline following time
(see section 3.2.2 Pipelines).
This allows pipelines as well as shell builtins and functions to be timed.
--enable-cond-command
- Include support for the
[[ conditional command
(see section 3.2.5 Conditional Constructs).
--enable-directory-stack
- Include support for a
csh-like directory stack and the
pushd, popd, and dirs builtins
(see section 6.8 The Directory Stack).
--enable-disabled-builtins
- Allow builtin commands to be invoked via `builtin xxx'
even after
xxx has been disabled using `enable -n xxx'.
See 4.2 Bash Builtin Commands, for details of the builtin and
enable builtin commands.
--enable-dparen-arithmetic
- Include support for the
((...)) command
(see section 3.2.5 Conditional Constructs).
--enable-extended-glob
- Include support for the extended pattern matching features described
above under 3.5.8.1 Pattern Matching.
--enable-help-builtin
- Include the
help builtin, which displays help on shell builtins and
variables (see section 4.2 Bash Builtin Commands).
--enable-history
- Include command history and the
fc and history
builtin commands (see section 9.1 Bash History Facilities).
--enable-job-control
- This enables the job control features (see section 7. Job Control),
if the operating system supports them.
--enable-net-redirections
- This enables the special handling of filenames of the form
/dev/tcp/host/port and
/dev/udp/host/port
when used in redirections (see section 3.6 Redirections).
--enable-process-substitution
- This enables process substitution (see section 3.5.6 Process Substitution) if
the operating system 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. See 6.9 Controlling the Prompt, for a complete list of prompt
string escape sequences.
--enable-progcomp
- Enable the programmable completion facilities
(see section 8.6 Programmable Completion).
If Readline is not enabled, this option has no effect.
--enable-readline
- Include support for command-line editing and history with the Bash
version of the Readline library (see section 8. Command Line Editing).
--enable-restricted
- Include support for a restricted shell. If this is enabled, Bash,
when called as
rbash, enters a restricted mode. See
6.10 The Restricted Shell, for a description of restricted mode.
--enable-select
- Include the
select builtin, which allows the generation of simple
menus (see section 3.2.5 Conditional Constructs).
--enable-usg-echo-default
- A synonym for
--enable-xpg-echo-default.
--enable-xpg-echo-default
- Make the
echo builtin expand backslash-escaped characters by default,
without requiring the `-e' option.
This sets the default value of the xpg_echo shell option to on,
which makes the Bash echo behave more like the version specified in
the Single Unix Specification, version 2.
See section 4.2 Bash Builtin Commands, for a description of the escape sequences that
echo recognizes.
The file `config-top.h' 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.
A. 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@gnu.org 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@po.CWRU.Edu.
B. Major Differences From 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 Bash; this
section quickly details the differences of significance. A
number of these differences are explained in greater depth in
previous sections.
This section uses the version of sh included in SVR4.2 as
the baseline reference.
-
Bash is POSIX-conformant, even where the POSIX specification
differs from traditional
sh behavior (see section 6.11 Bash POSIX Mode).
-
Bash has multi-character invocation options (see section 6.1 Invoking Bash).
-
Bash has command-line editing (see section 8. Command Line Editing) and
the
bind builtin.
-
Bash provides a programmable word completion mechanism
(see section 8.6 Programmable Completion), and two builtin commands,
complete and compgen, to manipulate it.
-
Bash has command history (see section 9.1 Bash History Facilities) and the
history and fc builtins to manipulate it.
-
Bash implements
csh-like history expansion
(see section 9.3 History Expansion).
-
Bash has one-dimensional array variables (see section 6.7 Arrays), and the
appropriate variable expansions and assignment syntax to use them.
Several of the Bash builtins take options to act on arrays.
Bash provides a number of built-in array variables.
-
The
$'...' quoting syntax, which expands ANSI-C
backslash-escaped characters in the text between the single quotes,
is supported (see section 3.1.2.4 ANSI-C Quoting).
-
Bash supports the
$"..." quoting syntax to do
locale-specific translation of the characters between the double
quotes. The `-D', `--dump-strings', and `--dump-po-strings'
invocation options list the translatable strings found in a script
(see section 3.1.2.5 Locale-Specific Translation).
-
Bash implements the
! keyword to negate the return value of
a pipeline (see section 3.2.2 Pipelines).
Very useful when an if statement needs to act only if a test fails.
-
Bash has the
time reserved word and command timing (see section 3.2.2 Pipelines).
The display of the timing statistics may be controlled with the
TIMEFORMAT variable.
-
Bash implements the
for (( expr1 ; expr2 ; expr3 ))
arithmetic for command, similar to the C language (see section 3.2.4 Looping Constructs).
-
Bash includes the
select compound command, which allows the
generation of simple menus (see section 3.2.5 Conditional Constructs).
-
Bash includes the
[[ compound command, which makes conditional
testing part of the shell grammar (see section 3.2.5 Conditional Constructs).
-
Bash includes brace expansion (see section 3.5.1 Brace Expansion) and tilde
expansion (see section 3.5.2 Tilde Expansion).
-
Bash implements command aliases and the
alias and unalias
builtins (see section 6.6 Aliases).
-
Bash provides shell arithmetic, the
(( compound command
(see section 3.2.5 Conditional Constructs),
and arithmetic expansion (see section 6.5 Shell Arithmetic).
-
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 pattern removal `%', `#', `%%'
and `##' expansions to remove leading or trailing substrings from
variable values (see section 3.5.3 Shell Parameter Expansion).
-
The expansion
${#xx}, which returns the length of ${xx},
is supported (see section 3.5.3 Shell Parameter Expansion).
-
The expansion
${var:offset[:length]},
which expands to the substring of var's value of length
length, beginning at offset, is present
(see section 3.5.3 Shell Parameter Expansion).
-
The expansion
${var/[/]pattern[/replacement]},
which matches pattern and replaces it with replacement in
the value of var, is available (see section 3.5.3 Shell Parameter Expansion).
-
The expansion
${!prefix}* expansion, which expands to
the names of all shell variables whose names begin with prefix,
is available (see section 3.5.3 Shell Parameter Expansion).
-
Bash has indirect variable expansion using
${!word}
(see section 3.5.3 Shell Parameter Expansion).
-
Bash can expand positional parameters beyond
$9 using
${num}.
-
The POSIX
$() form of command substitution
is implemented (see section 3.5.4 Command Substitution),
and preferred to the Bourne shell's " (which
is also implemented for backwards compatibility).
-
Bash has process substitution (see section 3.5.6 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). See section 5.2 Bash Variables,
for details.
-
The
IFS variable is used to split only the results of expansion,
not all words (see section 3.5.7 Word Splitting).
This closes a longstanding shell security hole.
-
Bash implements the full set of POSIX 1003.2 filename expansion operators,
including character classes, equivalence classes, and
collating symbols (see section 3.5.8 Filename Expansion).
-
Bash implements extended pattern matching features when the
extglob
shell option is enabled (see section 3.5.8.1 Pattern Matching).
-
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
(see section 4.2 Bash Builtin Commands).
-
Variable assignments preceding commands affect only that command, even
builtins and functions (see section 3.7.4 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 input and output redirection operators (see section 3.6 Redirections).
-
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 (see section 3.6 Redirections).
-
Bash treats a number of filenames specially when they are
used in redirection operators (see section 3.6 Redirections).
-
Bash can open network connections to arbitrary machines and services
with the redirection operators (see section 3.6 Redirections).
-
The
noclobber option is available to avoid overwriting existing
files with output redirection (see section 4.3 The Set Builtin).
The `>|' redirection operator may be used to override noclobber.
-
The Bash
cd and pwd builtins (see section 4.1 Bourne Shell Builtins)
each take `-L' and `-P' options to switch between logical and
physical modes.
-
Bash allows a function to override a builtin with the same name, and provides
access to that builtin's functionality within the function via the
builtin and command builtins (see section 4.2 Bash Builtin Commands).
-
The
command builtin allows selective disabling of functions
when command lookup is performed (see section 4.2 Bash Builtin Commands).
-
Individual builtins may be enabled or disabled using the
enable
builtin (see section 4.2 Bash Builtin Commands).
-
The Bash
exec builtin takes additional options that allow users
to control the contents of the environment passed to the executed
command, and what the zeroth argument to the command is to be
(see section 4.1 Bourne Shell Builtins).
-
Shell functions may be exported to children via the environment
using
export -f (see section 3.3 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
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'
(see section 4.1 Bourne Shell Builtins).
-
Bash includes a
help builtin for quick reference to shell
facilities (see section 4.2 Bash Builtin Commands).
-
The
printf builtin is available to display formatted output
(see section 4.2 Bash Builtin Commands).
-
The Bash
read builtin (see section 4.2 Bash Builtin Commands)
will read a line ending in `\' with
the `-r' option, and will use the REPLY variable as a
default if no non-option 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.
The read builtin also has additional options to control input:
the `-s' option will turn off echoing of input characters as
they are read, the `-t' option will allow read to time out
if input does not arrive within a specified number of seconds, the
`-n' option will allow reading only a specified number of
characters rather than a full line, and the `-d' option will read
until a particular character rather than newline.
-
The
return builtin may be used to abort execution of scripts
executed with the . or source builtins
(see section 4.1 Bourne Shell Builtins).
-
Bash includes the
shopt builtin, for finer control of shell
optional capabilities (see section 4.2 Bash Builtin Commands), and allows these options
to be set and unset at shell invocation (see section 6.1 Invoking Bash).
-
Bash has much more optional behavior controllable with the
set
builtin (see section 4.3 The Set Builtin).
-
The
test builtin (see section 4.1 Bourne Shell Builtins)
is slightly different, as it implements the POSIX algorithm,
which specifies the behavior based on the number of arguments.
-
The
trap builtin (see section 4.1 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 trap builtin (see section 4.1 Bourne Shell Builtins) allows an
ERR pseudo-signal specification, similar to EXIT and DEBUG.
Commands specified with an ERR trap are executed after a simple
command fails, with a few exceptions.
The ERR trap is not inherited by shell functions.
-
The Bash
type builtin is more extensive and gives more information
about the names it finds (see section 4.2 Bash Builtin Commands).
-
The Bash
umask builtin permits a `-p' option to cause
the output to be displayed in the form of a umask command
that may be reused as input (see section 4.1 Bourne Shell Builtins).
-
Bash implements a
csh-like directory stack, and provides the
pushd, popd, and dirs builtins to manipulate it
(see section 6.8 The Directory Stack).
Bash also makes the directory stack visible as the value of the
DIRSTACK shell variable.
-
Bash interprets special backslash-escaped characters in the prompt
strings when interactive (see section 6.9 Controlling the Prompt).
-
The Bash restricted mode is more useful (see section 6.10 The Restricted Shell);
the SVR4.2 shell restricted mode is too limited.
-
The
disown builtin can remove a job from the internal shell
job table (see section 7.2 Job Control Builtins) or suppress the sending
of SIGHUP to a job when the shell exits as the result of a
SIGHUP.
-
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 6. Bash Features.
B.1 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), it 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
SIGSEGV,
SIGALRM, or SIGCHLD.
-
The SVR4.2 shell does not allow the
IFS, MAILCHECK,
PATH, PS1, or PS2 variables 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 1003.2 special builtins fails, and
only for certain failures, as enumerated in the POSIX 1003.2 standard.
-
The SVR4.2 shell behaves differently when invoked as
jsh
(it turns on job control).
Index of Shell Builtin Commands
Index of Shell Reserved Words
Parameter and Variable Index
Function Index
|
Index Entry | Section |
|
| A |
|
|
|
abort (C-g) |
8.4.8 Some Miscellaneous Commands |
|
abort (C-g) |
8.4.8 Some Miscellaneous Commands |
|
accept-line (Newline or Return) |
8.4.2 Commands For Manipulating The History |
|
accept-line (Newline or Return) |
8.4.2 Commands For Manipulating The History |
|
alias-expand-line () |
8.4.8 Some Miscellaneous Commands |
|
alias-expand-line () |
8.4.8 Some Miscellaneous Commands |
|
| B |
|
|
|
backward-char (C-b) |
8.4.1 Commands For Moving |
|
backward-char (C-b) |
8.4.1 Commands For Moving |
|
backward-delete-char (Rubout) |
8.4.3 Commands For Changing Text |
|
backward-delete-char (Rubout) |
8.4.3 Commands For Changing Text |
|
backward-kill-line (C-x Rubout) |
8.4.4 Killing And Yanking |
|
backward-kill-line (C-x Rubout) |
8.4.4 Killing And Yanking |
|
backward-kill-word (M-DEL) |
8.4.4 Killing And Yanking |
|
backward-kill-word (M-DEL) |
8.4.4 Killing And Yanking |
|
backward-word (M-b) |
8.4.1 Commands For Moving |
|
backward-word (M-b) |
8.4.1 Commands For Moving |
|
beginning-of-history (M-<) |
8.4.2 Commands For Manipulating The History |
|
beginning-of-history (M-<) |
8.4.2 Commands For Manipulating The History |
|
beginning-of-line (C-a) |
8.4.1 Commands For Moving |
|
beginning-of-line (C-a) |
8.4.1 Commands For Moving |
|
| C |
|
|
|
call-last-kbd-macro (C-x e) |
8.4.7 Keyboard Macros |
|
call-last-kbd-macro (C-x e) |
8.4.7 Keyboard Macros |
|
capitalize-word (M-c) |
8.4.3 Commands For Changing Text |
|
capitalize-word (M-c) |
8.4.3 Commands For Changing Text |
|
character-search (C-]) |
8.4.8 Some Miscellaneous Commands |
|
character-search (C-]) |
8.4.8 Some Miscellaneous Commands |
|
character-search-backward (M-C-]) |
8.4.8 Some Miscellaneous Commands |
|
character-search-backward (M-C-]) |
8.4.8 Some Miscellaneous Commands |
|
clear-screen (C-l) |
8.4.1 Commands For Moving |
|
clear-screen (C-l) |
8.4.1 Commands For Moving |
|
complete (TAB) |
8.4.6 Letting Readline Type For You |
|
complete (TAB) |
8.4.6 Letting Readline Type For You |
|
complete-command (M-!) |
8.4.6 Letting Readline Type For You |
|
complete-command (M-!) |
8.4.6 Letting Readline Type For You |
|
complete-filename (M-/) |
8.4.6 Letting Readline Type For You |
|
complete-filename (M-/) |
8.4.6 Letting Readline Type For You |
|
complete-hostname (M-@) |
8.4.6 Letting Readline Type For You |
|
complete-hostname (M-@) |
8.4.6 Letting Readline Type For You |
|
complete-into-braces (M-{) |
8.4.6 Letting Readline Type For You |
|
complete-into-braces (M-{) |
8.4.6 Letting Readline Type For You |
|
complete-username (M-~) |
8.4.6 Letting Readline Type For You |
|
complete-username (M-~) |
8.4.6 Letting Readline Type For You |
|
complete-variable (M-$) |
8.4.6 Letting Readline Type For You |
|
complete-variable (M-$) |
8.4.6 Letting Readline Type For You |
|
copy-backward-word () |
8.4.4 Killing And Yanking |
|
copy-backward-word () |
8.4.4 Killing And Yanking |
|
copy-forward-word () |
8.4.4 Killing And Yanking |
|
copy-forward-word () |
8.4.4 Killing And Yanking |
|
copy-region-as-kill () |
8.4.4 Killing And Yanking |
|
copy-region-as-kill () |
8.4.4 Killing And Yanking |
|
| D |
|
|
|
delete-char (C-d) |
8.4.3 Commands For Changing Text |
|
delete-char (C-d) |
8.4.3 Commands For Changing Text |
|
delete-char-or-list () |
8.4.6 Letting Readline Type For You |
|
delete-char-or-list () |
8.4.6 Letting Readline Type For You |
|
delete-horizontal-space () |
8.4.4 Killing And Yanking |
|
delete-horizontal-space () |
8.4.4 Killing And Yanking |
|
digit-argument (M-0, M-1, <small>...</small> M--) |
8.4.5 Specifying Numeric Arguments |
|
digit-argument (M-0, M-1, <small>...</small> M--) |
8.4.5 Specifying Numeric Arguments |
|
display-shell-version (C-x C-v) |
8.4.8 Some Miscellaneous Commands |
|
display-shell-version (C-x C-v) |
8.4.8 Some Miscellaneous Commands |
|
do-uppercase-version (M-a, M-b, M-x, <small>...</small>) |
8.4.8 Some Miscellaneous Commands |
|
do-uppercase-version (M-a, M-b, M-x, <small>...</small>) |
8.4.8 Some Miscellaneous Commands |
|
downcase-word (M-l) |
8.4.3 Commands For Changing Text |
|
downcase-word (M-l) |
8.4.3 Commands For Changing Text |
|
dump-functions () |
8.4.8 Some Miscellaneous Commands |
|
dump-functions () |
8.4.8 Some Miscellaneous Commands |
|
dump-macros () |
8.4.8 Some Miscellaneous Commands |
|
dump-macros () |
8.4.8 Some Miscellaneous Commands |
|
dump-variables () |
8.4.8 Some Miscellaneous Commands |
|
dump-variables () |
8.4.8 Some Miscellaneous Commands |
|
dynamic-complete-history (M-TAB) |
8.4.6 Letting Readline Type For You |
|
dynamic-complete-history (M-TAB) |
8.4.6 Letting Readline Type For You |
|
| E |
|
|
|
emacs-editing-mode (C-e) |
8.4.8 Some Miscellaneous Commands |
|
emacs-editing-mode (C-e) |
8.4.8 Some Miscellaneous Commands |
|
end-kbd-macro (C-x )) |
8.4.7 Keyboard Macros |
|
end-kbd-macro (C-x )) |
8.4.7 Keyboard Macros |
|
end-of-history (M->) |
8.4.2 Commands For Manipulating The History |
|
end-of-history (M->) |
8.4.2 Commands For Manipulating The History |
|
end-of-line (C-e) |
8.4.1 Commands For Moving |
|
end-of-line (C-e) |
8.4.1 Commands For Moving |
|
exchange-point-and-mark (C-x C-x) |
8.4.8 Some Miscellaneous Commands |
|
exchange-point-and-mark (C-x C-x) |
8.4.8 Some Miscellaneous Commands |
|
| F |
|
|
|
forward-backward-delete-char () |
8.4.3 Commands For Changing Text |
|
forward-backward-delete-char () |
8.4.3 Commands For Changing Text |
|
forward-char (C-f) |
8.4.1 Commands For Moving |
|
forward-char (C-f) |
8.4.1 Commands For Moving |
|
forward-search-history (C-s) |
8.4.2 Commands For Manipulating The History |
|
forward-search-history (C-s) |
8.4.2 Commands For Manipulating The History |
|
forward-word (M-f) |
8.4.1 Commands For Moving |
|
forward-word (M-f) |
8.4.1 Commands For Moving |
|
| G |
|
|
|
glob-expand-word (C-x *) |
8.4.8 Some Miscellaneous Commands |
|
glob-expand-word (C-x *) |
8.4.8 Some Miscellaneous Commands |
|
glob-list-expansions (C-x g) |
8.4.8 Some Miscellaneous Commands |
|
glob-list-expansions (C-x g) |
8.4.8 Some Miscellaneous Commands |
|
| H |
|
|
|
history-and-alias-expand-line () |
8.4.8 Some Miscellaneous Commands |
|
history-and-alias-expand-line () |
8.4.8 Some Miscellaneous Commands |
|
history-expand-line (M-^) |
8.4.8 Some Miscellaneous Commands |
|
history-expand-line (M-^) |
8.4.8 Some Miscellaneous Commands |
|
history-search-backward () |
8.4.2 Commands For Manipulating The History |
|
history-search-backward () |
8.4.2 Commands For Manipulating The History |
|
history-search-forward () |
8.4.2 Commands For Manipulating The History |
|
history-search-forward () |
8.4.2 Commands For Manipulating The History |
|
| I |
|
|
|
insert-comment (M-#) |
8.4.8 Some Miscellaneous Commands |
|
insert-comment (M-#) |
8.4.8 Some Miscellaneous Commands |
|
insert-completions (M-*) |
8.4.6 Letting Readline Type For You |
|
insert-completions (M-*) |
8.4.6 Letting Readline Type For You |
|
insert-last-argument (M-. or M-_) |
8.4.8 Some Miscellaneous Commands |
|
insert-last-argument (M-. or M-_) |
8.4.8 Some Miscellaneous Commands |
|
| K |
|
|
|
kill-line (C-k) |
8.4.4 Killing And Yanking |
|
kill-line (C-k) |
8.4.4 Killing And Yanking |
|
kill-region () |
8.4.4 Killing And Yanking |
|
kill-region () |
8.4.4 Killing And Yanking |
|
kill-whole-line () |
8.4.4 Killing And Yanking |
|
kill-whole-line () |
8.4.4 Killing And Yanking |
|
kill-word (M-d) |
8.4.4 Killing And Yanking |
|
kill-word (M-d) |
8.4.4 Killing And Yanking |
|
| M |
|
|
|
magic-space () |
8.4.8 Some Miscellaneous Commands |
|
magic-space () |
8.4.8 Some Miscellaneous Commands |
|
menu-complete () |
8.4.6 Letting Readline Type For You |
|
menu-complete () |
8.4.6 Letting Readline Type For You |
|
| N |
|
|
|
next-history (C-n) |
8.4.2 Commands For Manipulating The History |
|
next-history (C-n) |
8.4.2 Commands For Manipulating The History |
|
non-incremental-forward-search-history (M-n) |
8.4.2 Commands For Manipulating The History |
|
non-incremental-forward-search-history (M-n) |
8.4.2 Commands For Manipulating The History |
|
non-incremental-reverse-search-history (M-p) |
8.4.2 Commands For Manipulating The History |
|
non-incremental-reverse-search-history (M-p) |
8.4.2 Commands For Manipulating The History |
|
| O |
|
|
|
operate-and-get-next (C-o) |
8.4.8 Some Miscellaneous Commands |
|
operate-and-get-next (C-o) |
8.4.8 Some Miscellaneous Commands |
|
| P |
|
|
|
possible-command-completions (C-x !) |
8.4.6 Letting Readline Type For You |
|
possible-command-completions (C-x !) |
8.4.6 Letting Readline Type For You |
|
possible-completions (M-?) |
8.4.6 Letting Readline Type For You |
|
possible-completions (M-?) |
8.4.6 Letting Readline Type For You |
|
possible-filename-completions (C-x /) |
8.4.6 Letting Readline Type For You |
|
possible-filename-completions (C-x /) |
8.4.6 Letting Readline Type For You |
|
possible-hostname-completions (C-x @) |
8.4.6 Letting Readline Type For You |
|
possible-hostname-completions (C-x @) |
8.4.6 Letting Readline Type For You |
|
possible-username-completions (C-x ~) |
8.4.6 Letting Readline Type For You |
|
possible-username-completions (C-x ~) |
8.4.6 Letting Readline Type For You |
|
possible-variable-completions (C-x $) |
8.4.6 Letting Readline Type For You |
|
possible-variable-completions (C-x $) |
8.4.6 Letting Readline Type For You |
|
prefix-meta (ESC) |
8.4.8 Some Miscellaneous Commands |
|
prefix-meta (ESC) |
8.4.8 Some Miscellaneous Commands |
|
previous-history (C-p) |
8.4.2 Commands For Manipulating The History |
|
previous-history (C-p) |
8.4.2 Commands For Manipulating The History |
|
| Q |
|
|
|
quoted-insert (C-q or C-v) |
8.4.3 Commands For Changing Text |
|
quoted-insert (C-q or C-v) |
8.4.3 Commands For Changing Text |
|
| R |
|
|
|
re-read-init-file (C-x C-r) |
8.4.8 Some Miscellaneous Commands |
|
re-read-init-file (C-x C-r) |
8.4.8 Some Miscellaneous Commands |
|
redraw-current-line () |
8.4.1 Commands For Moving |
|
redraw-current-line () |
8.4.1 Commands For Moving |
|
reverse-search-history (C-r) |
8.4.2 Commands For Manipulating The History |
|
reverse-search-history (C-r) |
8.4.2 Commands For Manipulating The History |
|
revert-line (M-r) |
8.4.8 Some Miscellaneous Commands |
|
revert-line (M-r) |
8.4.8 Some Miscellaneous Commands |
|
| S |
|
|
|
self-insert (a, b, A, 1, !, <small>...</small>) |
8.4.3 Commands For Changing Text |
|
self-insert (a, b, A, 1, !, <small>...</small>) |
8.4.3 Commands For Changing Text |
|
set-mark (C-@) |
8.4.8 Some Miscellaneous Commands |
|
set-mark (C-@) |
8.4.8 Some Miscellaneous Commands |
|
shell-expand-line (M-C-e) |
8.4.8 Some Miscellaneous Commands |
|
shell-expand-line (M-C-e) |
8.4.8 Some Miscellaneous Commands |
|
start-kbd-macro (C-x () |
8.4.7 Keyboard Macros |
|
start-kbd-macro (C-x () |
8.4.7 Keyboard Macros |
|
| T |
|
|
|
tilde-expand (M-&) |
8.4.8 Some Miscellaneous Commands |
|
tilde-expand (M-&) |
8.4.8 Some Miscellaneous Commands |
|
transpose-chars (C-t) |
8.4.3 Commands For Changing Text |
|
transpose-chars (C-t) |
8.4.3 Commands For Changing Text |
|
transpose-words (M-t) |
8.4.3 Commands For Changing Text |
|
transpose-words (M-t) |
8.4.3 Commands For Changing Text |
|
| U |
|
|
|
undo (C-_ or C-x C-u) |
8.4.8 Some Miscellaneous Commands |
|
undo (C-_ or C-x C-u) |
8.4.8 Some Miscellaneous Commands |
|
universal-argument () |
8.4.5 Specifying Numeric Arguments |
|
universal-argument () |
8.4.5 Specifying Numeric Arguments |
|
unix-line-discard (C-u) |
8.4.4 Killing And Yanking |
|
unix-line-discard (C-u) |
8.4.4 Killing And Yanking |
|
unix-word-rubout (C-w) |
8.4.4 Killing And Yanking |
|
unix-word-rubout (C-w) |
8.4.4 Killing And Yanking |
|
upcase-word (M-u) |
8.4.3 Commands For Changing Text |
|
upcase-word (M-u) |
8.4.3 Commands For Changing Text |
|
| Y |
|
|
|
yank (C-y) |
8.4.4 Killing And Yanking |
|
yank (C-y) |
8.4.4 Killing And Yanking |
|
yank-last-arg (M-. or M-_) |
8.4.2 Commands For Manipulating The History |
|
yank-last-arg (M-. or M-_) |
8.4.2 Commands For Manipulating The History |
|
yank-nth-arg (M-C-y) |
8.4.2 Commands For Manipulating The History |
|
yank-nth-arg (M-C-y) |
8.4.2 Commands For Manipulating The History |
|
yank-pop (M-y) |
8.4.4 Killing And Yanking |
|
yank-pop (M-y) |
8.4.4 Killing And Yanking |
|
Concept Index
|
Index Entry | Section |
|
| A |
|
|
|
alias expansion |
6.6 Aliases |
|
arithmetic evaluation |
6.5 Shell Arithmetic |
|
arithmetic expansion |
3.5.5 Arithmetic Expansion |
|
arithmetic, shell |
6.5 Shell Arithmetic |
|
arrays |
6.7 Arrays |
|
| B |
|
|
|
background |
7.1 Job Control Basics |
|
Bash configuration |
10.1 Basic Installation |
|
Bash installation |
10.1 Basic Installation |
|
Bourne shell |
3. Basic Shell Features |
|
brace expansion |
3.5.1 Brace Expansion |
|
builtin |
2. Definitions |
|
| C |
|
|
|
command editing |
8.2.1 Readline Bare Essentials |
|
command execution |
3.7.2 Command Search and Execution |
|
command expansion |
3.7.1 Simple Command Expansion |
|
command history |
9.1 Bash History Facilities |
|
command search |
3.7.2 Command Search and Execution |
|
command substitution |
3.5.4 Command Substitution |
|
command timing |
3.2.2 Pipelines |
|
commands, conditional |
3.2.5 Conditional Constructs |
|
commands, grouping |
3.2.6 Grouping Commands |
|
commands, lists |
3.2.3 Lists of Commands |
|
commands, looping |
3.2.4 Looping Constructs |
|
commands, pipelines |
3.2.2 Pipelines |
|
commands, shell |
3.2 Shell Commands |
|
commands, simple |
3.2.1 Simple Commands |
|
comments, shell |
3.1.3 Comments |
|
completion builtins |
8.7 Programmable Completion Builtins |
|
configuration |
10.1 Basic Installation |
|
control operator |
2. Definitions |
|
| D |
|
|
|
directory stack |
6.8 The Directory Stack |
|
| E |
|
|
|
editing command lines |
8.2.1 Readline Bare Essentials |
|
environment |
3.7.4 Environment |
|
evaluation, arithmetic |
6.5 Shell Arithmetic |
|
event designators |
9.3.1 Event Designators |
|
execution environment |
3.7.3 Command Execution Environment |
|
exit status |
2. Definitions |
|
exit status |
3.7.5 Exit Status |
|
expansion |
3.5 Shell Expansions |
|
expansion, arithmetic |
3.5.5 Arithmetic Expansion |
|
expansion, brace |
3.5.1 Brace Expansion |
|
expansion, filename |
3.5.8 Filename Expansion |
|
expansion, parameter |
3.5.3 Shell Parameter Expansion |
|
expansion, pathname |
3.5.8 Filename Expansion |
|
expansion, tilde |
3.5.2 Tilde Expansion |
|
expressions, arithmetic |
6.5 Shell Arithmetic |
|
expressions, conditional |
6.4 Bash Conditional Expressions |
|
| F |
|
|
|
field |
2. Definitions |
|
filename |
2. Definitions |
|
filename expansion |
3.5.8 Filename Expansion |
|
foreground |
7.1 Job Control Basics |
|
functions, shell |
3.3 Shell Functions |
|
| H |
|
|
|
history builtins |
9.2 Bash History Builtins |
|
history events |
9.3.1 Event Designators |
|
history expansion |
9.3 History Expansion |
|
history list |
9.1 Bash History Facilities |
|
History, how to use |
8.7 Programmable Completion Builtins |
|
| I |
|
|
|
identifier |
2. Definitions |
|
initialization file, readline |
8.3 Readline Init File |
|
installation |
10.1 Basic Installation |
|
interaction, readline |
8.2 Readline Interaction |
|
interactive shell |
6.1 Invoking Bash |
|
interactive shell |
6.3 Interactive Shells |
|
internationalization |
3.1.2.5 Locale-Specific Translation |
|
| J |
|
|
|
job |
2. Definitions |
|
job control |
2. Definitions |
|
job control |
7.1 Job Control Basics |
|
| K |
|
|
|
kill ring |
8.2.3 Readline Killing Commands |
|
killing text |
8.2.3 Readline Killing Commands |
|
| L |
|
|
|
localization |
3.1.2.5 Locale-Specific Translation |
|
login shell |
6.1 Invoking Bash |
|
| M |
|
|
|
matching, pattern |
3.5.8.1 Pattern Matching |
|
metacharacter |
2. Definitions |
|
| N |
|
|
|
name |
2. Definitions |
|
native languages |
3.1.2.5 Locale-Specific Translation |
|
notation, readline |
8.2.1 Readline Bare Essentials |
|
| O |
|
|
|
operator, shell |
2. Definitions |
|
| P |
|
|
|
parameter expansion |
3.5.3 Shell Parameter Expansion |
|
parameters |
3.4 Shell Parameters |
|
parameters, positional |
3.4.1 Positional Parameters |
|
parameters, special |
3.4.2 Special Parameters |
|
pathname expansion |
3.5.8 Filename Expansion |
|
pattern matching |
3.5.8.1 Pattern Matching |
|
pipeline |
3.2.2 Pipelines |
|
POSIX |
2. Definitions |
|
POSIX Mode |
6.11 Bash POSIX Mode |
|
process group |
2. Definitions |
|
process group ID |
2. Definitions |
|
process substitution |
3.5.6 Process Substitution |
|
programmable completion |
8.6 Programmable Completion |
|
prompting |
6.9 Controlling the Prompt |
|
| Q |
|
|
|
quoting |
3.1.2 Quoting |
|
quoting, ANSI |
3.1.2.4 ANSI-C Quoting |
|
| R |
|
|
|
Readline, how to use |
7.3 Job Control Variables |
|
redirection |
3.6 Redirections |
|
reserved word |
2. Definitions |
|
restricted shell |
6.10 The Restricted Shell |
|
return status |
2. Definitions |
|
| S |
|
|
|
shell arithmetic |
6.5 Shell Arithmetic |
|
shell function |
3.3 Shell Functions |
|
shell script |
3.8 Shell Scripts |
|
shell variable |
3.4 Shell Parameters |
|
shell, interactive |
6.3 Interactive Shells |
|
signal |
2. Definitions |
|
signal handling |
3.7.6 Signals |
|
special builtin |
2. Definitions |
|
special builtin |
4.4 Special Builtins |
|
startup files |
6.2 Bash Startup Files |
|
suspending jobs |
7.1 Job Control Basics |
|
| T |
|
|
|
tilde expansion |
3.5.2 Tilde Expansion |
|
token |
2. Definitions |
|
translation, native languages |
3.1.2.5 Locale-Specific Translation |
|
| V |
|
|
|
variable, shell |
3.4 Shell Parameters |
|
variables, readline |
8.3.1 Readline Init File Syntax |
|
| W |
|
|
|
word |
2. Definitions |
|
word splitting |
3.5.7 Word Splitting |
|
| Y |
|
|
|
yanking text |
8.2.3 Readline Killing Commands |
|
Table of Contents
Short Table of Contents
1. Introduction
2. Definitions
3. Basic Shell Features
4. Shell Builtin Commands
5. Shell Variables
6. Bash Features
7. Job Control
8. Command Line Editing
9. Using History Interactively
10. Installing Bash
A. Reporting Bugs
B. Major Differences From The Bourne Shell
Index of Shell Builtin Commands
Index of Shell Reserved Words
Parameter and Variable Index
Function Index
Concept Index
About this document
This document was generated by
Chet Ramey on
November, 13 2001
using
texi2html
The buttons in the navigation panels have the following meaning:
| Button |
Name |
Go to |
From 1.2.3 go to |
|
[ < ] |
Back
|
previous section in reading order
|
1.2.2
|
|
[ > ] |
Forward
|
next section in reading order
|
1.2.4
|
|
[ << ] |
FastBack
|
previous or up-and-previous section
|
1.1
|
|
[ Up ] |
Up
|
up section
|
1.2
|
|
[ >> ] |
FastForward
|
next or up-and-next section
|
1.3
|
|
[Top] |
Top
|
cover (top) of document
|
|
|
[Contents] |
Contents
|
table of contents
|
|
|
[Index] |
Index
|
concept index
|
|
|
[ ? ] |
About
|
this page
|
|
where the
Example assumes that the current position
is at
Subsubsection One-Two-Three of a document of
the following structure:
- 1. Section One
- 1.1 Subsection One-One
- 1.2 Subsection One-Two
- 1.2.1 Subsubsection One-Two-One
- 1.2.2 Subsubsection One-Two-Two
- 1.2.3 Subsubsection One-Two-Three
<== Current Position
- 1.2.4 Subsubsection One-Two-Four
- 1.3 Subsection One-Three
- 1.4 Subsection One-Four
This document was generated
by Chet Ramey on November, 13 2001
using texi2html