BASH(1) General Commands Manual BASH(1)
NAME
bash - GNU Bourne-Again SHell
SYNOPSIS
bash [options] [file]
COPYRIGHT
Bash is Copyright (C) 1989-2011 by the Free Software Foundation,
Inc.
DESCRIPTION
Bash is an sh-compatible command language interpreter that exe‐
cutes commands read from the standard input or from a file.
Bash also incorporates useful features from the Korn and C
shells (ksh and csh).
Bash is intended to be a conformant implementation of the Shell
and Utilities portion of the IEEE POSIX specification (IEEE
Standard 1003.1). Bash can be configured to be POSIX-conformant
by default.
OPTIONS
All of the single-character shell options documented in the
description of the set builtin command can be used as options
when the shell is invoked. In addition, bash interprets the
following options when it is invoked:
-c string If the -c option is present, then commands are read
from string. If there are arguments after the string,
they are assigned to the positional parameters, start‐
ing with $0.
-i If the -i option is present, the shell is interactive.
-l Make bash act as if it had been invoked as a login
shell (see INVOCATION below).
-r If the -r option is present, the shell becomes
restricted (see RESTRICTED SHELL below).
-s If the -s 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 output. These are the strings
that are subject to language translation when the cur‐
rent locale is not C or POSIX. 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 SHELL BUILTIN COMMANDS below).
If shopt_option is present, -O sets the value of that
option; +O unsets it. If shopt_option is not sup‐
plied, 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 dis‐
played 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. An argument of -
is equivalent to --.
Bash also interprets a number of multi-character options. These
options must appear on the command line before the single-char‐
acter options to be recognized.
--debugger
Arrange for the debugger profile to be executed before
the shell starts. Turns on extended debugging mode (see
the description of the extdebug option to the shopt
builtin below).
--dump-po-strings
Equivalent to -D, but the output is in the GNU gettext po
(portable object) file format.
--dump-strings
Equivalent to -D.
--help Display a usage message on standard output and exit suc‐
cessfully.
--init-file file
--rcfile file
Execute commands from file instead of the standard per‐
sonal initialization file ~/.bashrc if the shell is
interactive (see INVOCATION below).
--login
Equivalent to -l.
--noediting
Do not use the GNU readline library to read command lines
when the shell is interactive.
--noprofile
Do not read either the system-wide startup file /etc/pro‐
file or any of the personal initialization files
~/.bash_profile, ~/.bash_login, or ~/.profile. By
default, bash reads these files when it is invoked as a
login shell (see INVOCATION below).
--norc Do not read and execute the personal initialization file
~/.bashrc if the shell is interactive. This option 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 standard to match the standard
(posix mode).
--restricted
The shell becomes restricted (see RESTRICTED SHELL
below).
--rpm-requires
Produce the list of files that are required for the shell
script to run. This implies '-n' and is subject to the
same limitations as compile time error checking checking;
Command substitutions, Conditional expressions and eval
builtin are not parsed so some dependencies may be
missed.
--verbose
Equivalent to -v.
--version
Show version information for this instance of bash on the
standard output and exit successfully.
ARGUMENTS
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. If
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. An attempt is first made to open the file
in the current directory, and, if no file is found, then the
shell searches the directories in PATH for the script.
INVOCATION
A login shell is one whose first character of argument zero is a
-, or one started with the --login option.
An interactive shell is one started without non-option arguments
and without the -c option whose standard input and error are
both connected to terminals (as determined by isatty(3)), or one
started with the -i option. PS1 is set and $- includes i if
bash is interactive, allowing a shell script or a startup file
to test this state.
The following paragraphs describe how bash executes its startup
files. If any of the files exist but cannot be read, bash
reports an error. Tildes are expanded in file names as
described below under Tilde Expansion in the EXPANSION section.
When bash is invoked as an interactive login shell, or as a non-
interactive shell with the --login option, it first reads and
executes commands from the file /etc/profile, if that file
exists. After reading that file, it looks for ~/.bash_profile,
~/.bash_login, and ~/.profile, in that order, and reads and exe‐
cutes commands from the first one that exists and is readable.
The --noprofile option may be used when the shell is started to
inhibit this behavior.
When a login shell exits, bash reads and executes commands from
the files ~/.bash_logout and /etc/bash.bash_logout, if the files
exists.
When an interactive shell that is not a login shell is started,
bash reads and executes commands from ~/.bashrc, if that file
exists. This may be inhibited by using the --norc option. The
--rcfile file option will force bash to read and execute com‐
mands from file instead of ~/.bashrc.
When bash is started non-interactively, to run a shell script,
for example, it looks for the variable BASH_ENV in the environ‐
ment, expands its value if it appears there, and uses the
expanded value as the name of a file to read and execute. Bash
behaves as if the following command were executed:
if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
but the value of the PATH variable is not used to search for the
file name.
If bash is invoked with the name sh, it tries to mimic the
startup behavior of historical versions of sh as closely as pos‐
sible, while conforming to the POSIX standard as well. When
invoked as an interactive login shell, or 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.
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.
Bash attempts to determine when it is being run with its stan‐
dard input connected to a network connection, as when executed
by the remote shell daemon, usually rshd, or the secure shell
daemon sshd. If bash determines it is being run in this fash‐
ion, 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.
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 sup‐
plied, no startup files are read, shell functions are not inher‐
ited from the environment, the SHELLOPTS, BASHOPTS, CDPATH, and
GLOBIGNORE variables, if they appear in the environment, are
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.
DEFINITIONS
The following definitions are used throughout the rest of this
document.
blank A space or tab.
word A sequence of characters considered as a single unit by
the shell. Also known as a token.
name A word consisting only of alphanumeric characters and
underscores, and beginning with an alphabetic character
or an underscore. Also referred to as an identifier.
metacharacter
A character that, when unquoted, separates words. One of
the following:
| & ; ( ) < > space tab
control operator
A token that performs a control function. It is one of
the following symbols:
|| & && ; ;; ( ) | |& <newline>
RESERVED WORDS
Reserved words are words that have a special meaning to the
shell. The following words are recognized as reserved when
unquoted and either the first word of a simple command (see
SHELL GRAMMAR below) or the third word of a case or for command:
! case do done elif else esac fi for function if in select then
until while { } time [[ ]]
SHELL GRAMMAR
Simple Commands
A simple command is a sequence of optional variable assignments
followed by blank-separated words and redirections, and termi‐
nated by a control operator. The first word specifies the com‐
mand to be executed, and is passed as argument zero. The
remaining words are passed as arguments to the invoked command.
The return value of a simple command is its exit status, or
128+n if the command is terminated by signal n.
Pipelines
A pipeline is a sequence of one or more commands separated by
one of the control operators | or |&. The format for a pipeline
is:
[time [-p]] [ ! ] command [ [|⎪|&] command2 ... ]
The standard output of command is connected via a pipe to the
standard input of command2. This connection is performed before
any redirections specified by the command (see REDIRECTION
below). If |& is used, the standard error of command is con‐
nected to command2's standard input through the pipe; it is
shorthand for 2>&1 |. This implicit redirection of the standard
error is performed after any redirections specified by the com‐
mand.
The return status of a pipeline is the exit status of the last
command, unless the pipefail option is enabled. If pipefail is
enabled, the pipeline's return status is the value of the last
(rightmost) command to exit with a non-zero status, or zero if
all commands exit successfully. If the reserved word ! pre‐
cedes a pipeline, the exit status of that pipeline is the logi‐
cal negation of the exit status as described above. The shell
waits for all commands in the pipeline to terminate before
returning a value.
If the time reserved word precedes a pipeline, the elapsed as
well as user and system time consumed by its execution are
reported when the pipeline terminates. The -p option changes
the output format to that specified by POSIX. When the shell is
in posix mode, it does not recognize time as a reserved word if
the next token begins with a `-'. The TIMEFORMAT variable may
be set to a format string that specifies how the timing informa‐
tion should be displayed; see the description of TIMEFORMAT
under Shell Variables below.
When the shell is in posix mode, time may be followed by a new‐
line. In this case, the shell displays the total user and sys‐
tem time consumed by the shell and its children. The TIMEFORMAT
variable may be used to specify the format of the time informa‐
tion.
Each command in a pipeline is executed as a separate process
(i.e., in a subshell).
Lists
A list is a sequence of one or more pipelines separated by one
of the operators ;, &, &&, or ||, and optionally terminated by
one of ;, &, or <newline>.
Of these list operators, && and || have equal precedence, fol‐
lowed by ; and &, which have equal precedence.
A sequence of one or more newlines may appear in a list instead
of a semicolon to delimit commands.
If a command is terminated by the control operator &, the shell
executes the command in the background in a subshell. The shell
does not wait for the command to finish, and the return status
is 0. 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.
AND and OR lists are sequences of one of more pipelines sepa‐
rated by the && and || control operators, respectively. AND and
OR lists are executed with left associativity. An AND list has
the form
command1 && command2
command2 is executed if, and only if, command1 returns an exit
status of zero.
An OR list has the form
command1 || command2
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.
Compound Commands
A compound command is one of the following:
(list) list is executed in a subshell environment (see COMMAND
EXECUTION ENVIRONMENT below). Variable assignments and
builtin commands that affect the shell's environment do
not remain in effect after the command completes. The
return status is the exit status of list.
{ list; }
list is simply executed in the current shell environment.
list must be terminated with a newline or semicolon.
This is known as a group command. The return status is
the exit status of list. Note that unlike the metachar‐
acters ( and ), { and } are reserved words and must occur
where a reserved word is permitted to be recognized.
Since they do not cause a word break, they must be sepa‐
rated from list by whitespace or another shell metachar‐
acter.
((expression))
The expression is evaluated according to the rules
described below under ARITHMETIC EVALUATION. If the
value of the expression is non-zero, the return status is
0; otherwise the return status is 1. This is exactly
equivalent to let "expression".
[[ expression ]]
Return a status of 0 or 1 depending on the evaluation of
the conditional expression expression. Expressions are
composed of the primaries described below under CONDI‐
TIONAL EXPRESSIONS. Word splitting and pathname expan‐
sion are not performed on the words between the [[ and
]]; tilde expansion, parameter and variable expansion,
arithmetic expansion, command substitution, process sub‐
stitution, and quote removal are performed. Conditional
operators such as -f must be unquoted to be recognized as
primaries.
When used with [[, the < and > operators sort lexico‐
graphically using the current locale.
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 under Pattern
Matching. If the shell option nocasematch is enabled,
the match is performed without regard to the case of
alphabetic characters. The return value is 0 if the
string matches (==) or does not match (!=) the pattern,
and 1 otherwise. Any part of the pattern may be quoted
to force it to be matched as a string.
An additional binary operator, =~, is available, with the
same precedence as == and !=. When it is used, the
string to the right of the operator is considered an
extended regular expression and matched accordingly (as
in regex(3)). The return value is 0 if the string
matches the pattern, and 1 otherwise. If the regular
expression is syntactically incorrect, the conditional
expression's return value is 2. If the shell option
nocasematch is enabled, the match is performed without
regard to the case of alphabetic characters. Any part of
the pattern may be quoted to force it to be matched as a
string. Substrings matched by parenthesized subexpres‐
sions within the regular expression are saved in the
array variable BASH_REMATCH. The element of BASH_REMATCH
with index 0 is the portion of the string matching the
entire regular expression. The element of BASH_REMATCH
with index n is the portion of the string matching the
nth parenthesized subexpression.
Expressions may be combined using the following opera‐
tors, 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 || operators do not evaluate expression2 if
the value of expression1 is sufficient to determine the
return value of the entire conditional expression.
for name [ [ in [ word ... ] ] ; ] do list ; done
The list of words following in is expanded, generating a
list of items. The variable name is set to each element
of this list in turn, and list is executed each time. If
the in word is omitted, the for command executes list
once for each positional parameter that is set (see
PARAMETERS below). The return status is the exit status
of the last command that executes. If the expansion of
the items following in results in an empty list, no com‐
mands are executed, and the return status is 0.
for (( expr1 ; expr2 ; expr3 )) ; do list ; done
First, the arithmetic expression expr1 is evaluated
according to the rules described below under ARITHMETIC
EVALUATION. The arithmetic expression expr2 is then
evaluated repeatedly until it evaluates to zero. Each
time expr2 evaluates to a non-zero value, list is exe‐
cuted and the arithmetic expression expr3 is evaluated.
If any expression is omitted, it behaves as if it evalu‐
ates 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.
select name [ in word ] ; do list ; done
The list of words following in is expanded, generating a
list of items. The set of expanded words is printed on
the standard error, each preceded by a number. If the in
word is omitted, the positional parameters are printed
(see PARAMETERS below). The PS3 prompt is then displayed
and a line read from the standard input. If the line
consists of a number corresponding to one of the dis‐
played 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 command completes. Any other
value read causes name to be set to null. The line read
is saved in the variable REPLY. The list is executed
after each selection until a break command is executed.
The exit status of select is the exit status of the last
command executed in list, or zero if no commands were
executed.
case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ...
esac
A case command first expands word, and tries to match it
against each pattern in turn, using the same matching
rules as for pathname expansion (see Pathname Expansion
below). The word is expanded using tilde expansion,
parameter and variable expansion, arithmetic substitu‐
tion, command substitution, process substitution and
quote removal. Each pattern examined is expanded using
tilde expansion, parameter and variable expansion, arith‐
metic substitution, command substitution, and process
substitution. If the shell option nocasematch is
enabled, the match is performed without regard to the
case of alphabetic characters. When a match is found,
the corresponding list is executed. If the ;; operator
is used, no subsequent matches are attempted after the
first pattern match. Using ;& in place of ;; causes exe‐
cution to continue with the list associated with the next
set of patterns. Using ;;& in place of ;; causes the
shell to test the next pattern list in the statement, if
any, and execute any associated list on a successful
match. The exit status is zero if no pattern matches.
Otherwise, it is the exit status of the last command exe‐
cuted in list.
if list; then list; [ elif list; then list; ] ... [ else list; ]
fi
The if list is executed. If its exit status is zero, the
then list is executed. Otherwise, each elif list is exe‐
cuted in turn, and if its exit status is zero, the corre‐
sponding then list is executed and the command completes.
Otherwise, the else list is executed, if present. The
exit status is the exit status of the last command exe‐
cuted, or zero if no condition tested true.
while list-1; do list-2; done
until list-1; do list-2; done
The while command continuously executes the list list-2
as long as the last command in the list list-1 returns an
exit status of zero. The until command is identical to
the while command, except that the test is negated;
list-2 is executed as long as the last command in list-1
returns a non-zero exit status. The exit status of the
while and until commands is the exit status of the last
command executed in list-2, or zero if none was executed.
Coprocesses
A coprocess is a shell command preceded by the coproc reserved
word. A coprocess is executed asynchronously in a subshell, as
if the command had been terminated with the & control operator,
with a two-way pipe established between the executing shell and
the coprocess.
The format for a coprocess is:
coproc [NAME] command [redirections]
This creates a coprocess named NAME. If NAME is not supplied,
the default name is COPROC. NAME must not be supplied if com‐
mand is a simple command (see above); otherwise, it is inter‐
preted as the first word of the simple command. When the coproc
is executed, the shell creates an array variable (see Arrays
below) named NAME in the context of the executing shell. The
standard output of command is connected via a pipe to a file
descriptor in the executing shell, and that file descriptor is
assigned to NAME[0]. The standard input of command is connected
via a pipe to a file descriptor in the executing shell, and that
file descriptor is assigned to NAME[1]. This pipe is estab‐
lished before any redirections specified by the command (see RE‐
DIRECTION below). The file descriptors can be utilized as argu‐
ments to shell commands and redirections using standard word
expansions. The process ID of the shell spawned to execute the
coprocess is available as the value of the variable NAME_PID.
The wait builtin command may be used to wait for the coprocess
to terminate.
The return status of a coprocess is the exit status of command.
Shell Function Definitions
A shell function is an object that is called like a simple com‐
mand and executes a compound command with a new set of posi‐
tional parameters. Shell functions are declared as follows:
name () compound-command [redirection]
function name [()] compound-command [redirection]
This defines a 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 compound command compound-command (see
Compound Commands above). That command is usually a list
of commands between { and }, but may be any command
listed under Compound Commands above. compound-command
is executed whenever name is specified as the name of a
simple command. Any redirections (see REDIRECTION below)
specified when a function is defined are performed when
the function is executed. The exit status of a function
definition is zero unless a syntax error occurs or a
readonly function with the same name already exists.
When executed, the exit status of a function is the exit
status of the last command executed in the body. (See
FUNCTIONS below.)
COMMENTS
In a non-interactive shell, or an interactive shell in which the
interactive_comments option to the shopt builtin is enabled (see
SHELL BUILTIN COMMANDS below), 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_com‐
ments option is on by default in interactive shells.
QUOTING
Quoting is used to remove the special meaning of certain charac‐
ters or words to the shell. Quoting can be used to disable spe‐
cial treatment for special characters, to prevent reserved words
from being recognized as such, and to prevent parameter expan‐
sion.
Each of the metacharacters listed above under DEFINITIONS has
special meaning to the shell and must be quoted if it is to rep‐
resent itself.
When the command history expansion facilities are being used
(see HISTORY EXPANSION below), the history expansion character,
usually !, must be quoted to prevent history expansion.
There are three quoting mechanisms: the escape character, single
quotes, and double quotes.
A non-quoted backslash (\) is the escape character. It pre‐
serves the literal value of the next character that follows,
with the exception of <newline>. If a \<newline> pair appears,
and the backslash is not itself quoted, the \<newline> is
treated as a line continuation (that is, it is removed from the
input stream and effectively ignored).
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 back‐
slash.
Enclosing characters in double quotes preserves the literal
value of all characters within the quotes, with the exception of
$, `, \, and, when history expansion is enabled, !. The charac‐
ters $ and ` retain their special meaning within double quotes.
The backslash retains its special meaning only when followed by
one of the following characters: $, `, ", \, or <newline>. A
double quote may be quoted within double quotes by preceding it
with a backslash. If enabled, history expansion will be per‐
formed unless an ! appearing in double quotes is escaped using
a backslash. The backslash preceding the ! is not removed.
The special parameters * and @ have special meaning when in dou‐
ble quotes (see PARAMETERS below).
Words of the form $'string' are treated specially. The word
expands to string, with backslash-escaped characters replaced as
specified by the ANSI C standard. Backslash escape sequences,
if present, are decoded as follows:
\a alert (bell)
\b backspace
\e
\E an escape character
\f form feed
\n new line
\r carriage return
\t horizontal tab
\v vertical tab
\\ backslash
\' single quote
\" double quote
\nnn the eight-bit character whose value is the octal
value nnn (one to three digits)
\xHH the eight-bit character whose value is the hexa‐
decimal value HH (one or two hex digits)
\uHHHH the Unicode (ISO/IEC 10646) character whose value
is the hexadecimal value HHHH (one to four hex
digits)
\UHHHHHHHH
the Unicode (ISO/IEC 10646) character whose value
is the hexadecimal value HHHHHHHH (one to eight
hex digits)
\cx a control-x character
The expanded result is single-quoted, as if the dollar sign had
not been present.
A double-quoted string preceded by a dollar sign ($"string")
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 replace‐
ment is double-quoted.
PARAMETERS
A parameter is an entity that stores values. It can be a name,
a number, or one of the special characters listed below under
Special Parameters. 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
declare below in SHELL 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 (see SHELL BUILTIN
COMMANDS below).
A variable may be assigned to by a statement of the form
name=[value]
If value is not given, the variable is assigned the null string.
All values undergo tilde expansion, parameter and variable
expansion, command substitution, arithmetic expansion, and quote
removal (see EXPANSION below). If the variable has its integer
attribute set, then value is evaluated as an arithmetic expres‐
sion even if the $((...)) expansion is not used (see Arithmetic
Expansion below). Word splitting is not performed, with the
exception of "$@" as explained below under Special Parameters.
Pathname expansion is not performed. Assignment statements may
also appear as arguments to the alias, declare, typeset, export,
readonly, and local builtin commands.
In the context where an assignment statement is assigning a
value to a shell variable or array index, the += operator can be
used to append to or add to the variable's previous value. When
+= is applied to a variable for which the integer attribute has
been set, value is evaluated as an arithmetic expression and
added to the variable's current value, which is also evaluated.
When += is applied to an array variable using compound assign‐
ment (see Arrays below), the variable's value is not unset (as
it is when using =), and new values are appended to the array
beginning at one greater than the array's maximum index (for
indexed arrays) or added as additional key-value pairs in an
associative array. When applied to a string-valued variable,
value is expanded and appended to the variable's value.
Positional Parameters
A positional parameter is a parameter denoted by one or more
digits, other than the single digit 0. Positional parameters
are assigned from the shell's arguments when it is invoked, and
may be reassigned using the set builtin command. Positional
parameters may not be assigned to with assignment statements.
The positional parameters are temporarily replaced when a shell
function is executed (see FUNCTIONS below).
When a positional parameter consisting of more than a single
digit is expanded, it must be enclosed in braces (see EXPANSION
below).
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 vari‐
able. That is, "$*" is equivalent to "$1c$2c...", where
c is the first character of the value of the IFS vari‐
able. If IFS is unset, the parameters are separated by
spaces. If IFS is null, the parameters are joined with‐
out intervening separators.
@ Expands to the positional parameters, starting from one.
When the expansion occurs within double quotes, each
parameter expands to a separate word. That is, "$@" is
equivalent to "$1" "$2" ... If the double-quoted expan‐
sion occurs within a word, the expansion of the first
parameter is joined with the beginning part of the origi‐
nal word, and the expansion of the last parameter is
joined with the last part of the original word. When
there are no positional parameters, "$@" and $@ expand to
nothing (i.e., they are removed).
# Expands to the number of positional parameters in deci‐
mal.
? Expands to the exit status of the most recently executed
foreground pipeline.
- Expands to the current option flags as specified upon
invocation, by the set builtin command, or those set by
the shell itself (such as the -i option).
$ Expands to the process ID of the shell. In a () sub‐
shell, it expands to the process ID of the current shell,
not the subshell.
! Expands to the process ID of the most recently executed
background (asynchronous) command.
0 Expands to the name of the shell or shell script. This
is set at shell initialization. If bash is invoked with
a file of commands, $0 is set to the name of that file.
If bash is started with the -c option, then $0 is set to
the first argument after the string to be executed, if
one is present. Otherwise, it is set to the file name
used to invoke bash, as given by argument zero.
_ At shell startup, set to the absolute pathname used to
invoke the shell or shell script being executed as passed
in the environment or argument list. Subsequently,
expands to the last argument to the previous command,
after expansion. Also set to the full pathname used to
invoke each command executed and placed in the environ‐
ment exported to that command. When checking mail, this
parameter holds the name of the mail file currently being
checked.
Shell Variables
The following variables are set by the shell:
BASH Expands to the full file name used to invoke this
instance of bash.
BASHOPTS
A colon-separated list of enabled shell options. Each
word in the list is a valid argument for the -s option to
the shopt builtin command (see SHELL BUILTIN COMMANDS
below). The options appearing in BASHOPTS are those
reported as on by shopt. 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 read-only.
BASHPID
Expands to the process ID of the current bash process.
This differs from $$ under certain circumstances, such as
subshells that do not require bash to be re-initialized.
BASH_ALIASES
An associative array variable whose members correspond to
the internal list of aliases as maintained by the alias
builtin. Elements added to this array appear in the
alias list; unsetting array elements cause aliases to be
removed from the alias list.
BASH_ARGC
An array variable whose values are the number of parame‐
ters in each frame of the current bash execution call
stack. The number of parameters to the current subrou‐
tine (shell function or script executed with . or source)
is at the top of the stack. When a subroutine is exe‐
cuted, the number of parameters passed is pushed onto
BASH_ARGC. The shell sets BASH_ARGC only when in
extended debugging mode (see the description of the
extdebug option to the shopt builtin below)
BASH_ARGV
An array variable containing all of the parameters in the
current bash execution call stack. The final parameter
of the last subroutine call is at the top of the stack;
the first parameter of the initial call is at the bottom.
When a subroutine is executed, the parameters supplied
are pushed onto BASH_ARGV. The shell sets BASH_ARGV only
when in extended debugging mode (see the description of
the extdebug option to the shopt builtin below)
BASH_CMDS
An associative array variable whose members correspond to
the internal hash table of commands as maintained by the
hash builtin. Elements added to this array appear in the
hash table; unsetting array elements cause commands to be
removed from the hash table.
BASH_COMMAND
The command currently being executed or about to be exe‐
cuted, unless the shell is executing a command as the
result of a trap, in which case it is the command execut‐
ing at the time of the trap.
BASH_EXECUTION_STRING
The command argument to the -c invocation option.
BASH_LINENO
An array variable whose members are the line numbers in
source files where each corresponding member of FUNCNAME
was invoked. ${BASH_LINENO[$i]} is the line number in
the source file (${BASH_SOURCE[$i+1]}) where ${FUNC‐
NAME[$i]} was called (or ${BASH_LINENO[$i-1]} if refer‐
enced within another shell function). Use LINENO to
obtain the current line number.
BASH_REMATCH
An array variable whose members are assigned by the =~
binary operator to the [[ conditional command. The ele‐
ment with index 0 is the portion of the string matching
the entire regular expression. The element with index n
is the portion of the string matching the nth parenthe‐
sized subexpression. This variable is read-only.
BASH_SOURCE
An array variable whose members are the source filenames
where the corresponding shell function names in the FUNC‐
NAME array variable are defined. The shell function
${FUNCNAME[$i]} is defined in the file ${BASH_SOURCE[$i]}
and called from ${BASH_SOURCE[$i+1]}.
BASH_SUBSHELL
Incremented by one each time a subshell or subshell envi‐
ronment is spawned. The initial value is 0.
BASH_VERSINFO
A readonly array variable whose members hold version
information for this instance of bash. The values
assigned to the array members are as follows:
BASH_VERSINFO[0] The major version number (the
release).
BASH_VERSINFO[1] The minor version number (the
version).
BASH_VERSINFO[2] The patch level.
BASH_VERSINFO[3] The build version.
BASH_VERSINFO[4] The release status (e.g., beta1).
BASH_VERSINFO[5] The value of MACHTYPE.
BASH_VERSION
Expands to a string describing the version of this
instance of bash.
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 Programmable Completion below).
COMP_KEY
The key (or final key of a key sequence) used to invoke
the current completion function.
COMP_LINE
The current command line. This variable is available
only in shell functions and external commands invoked by
the programmable completion facilities (see Programmable
Completion below).
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 vari‐
able is available only in shell functions and external
commands invoked by the programmable completion facili‐
ties (see Programmable Completion below).
COMP_TYPE
Set to an integer value corresponding to the type of com‐
pletion attempted that caused a completion function to be
called: TAB, for normal completion, ?, for listing com‐
pletions after successive tabs, !, for listing alterna‐
tives on partial word completion, @, to list completions
if the word is not unmodified, or %, for menu completion.
This variable is available only in shell functions and
external commands invoked by the programmable completion
facilities (see Programmable Completion below).
COMP_WORDBREAKS
The set of characters that the readline library treats as
word separators when performing word completion. If
COMP_WORDBREAKS is unset, it loses its special proper‐
ties, even if it is subsequently reset.
COMP_WORDS
An array variable (see Arrays below) consisting of the
individual words in the current command line. The line
is split into words as readline would split it, using
COMP_WORDBREAKS as described above. This variable is
available only in shell functions invoked by the program‐
mable completion facilities (see Programmable Completion
below).
COPROC An array variable (see Arrays below) created to hold the
file descriptors for output from and input to an unnamed
coprocess (see Coprocesses above).
DIRSTACK
An array variable (see Arrays below) containing the cur‐
rent 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 Expands to the effective user ID of the current user,
initialized at shell startup. This variable is readonly.
FUNCNAME
An array variable containing the names of all shell func‐
tions currently in the execution call stack. The element
with index 0 is the name of any currently-executing shell
function. The bottom-most element (the one with the
highest index) is "main". 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.
This variable can be used with BASH_LINENO and
BASH_SOURCE. Each element of FUNCNAME has corresponding
elements in BASH_LINENO and BASH_SOURCE to describe the
call stack. For instance, ${FUNCNAME[$i]} was called
from the file ${BASH_SOURCE[$i+1]} at line number
${BASH_LINENO[$i]}. The caller builtin displays the cur‐
rent call stack using this information.
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.
HISTCMD
The history number, or index in the history list, of the
current command. If HISTCMD is unset, it loses its spe‐
cial properties, even if it is subsequently reset.
HOSTNAME
Automatically set to the name of the current host.
HOSTTYPE
Automatically set to a string that uniquely describes the
type of machine on which bash is executing. The default
is system-dependent.
LINENO Each time this parameter is referenced, the shell substi‐
tutes a decimal number representing the current sequen‐
tial line number (starting with 1) within a script or
function. When not in a script or function, the value
substituted is not guaranteed to be meaningful. If
LINENO is unset, it loses its special properties, even if
it is subsequently reset.
MACHTYPE
Automatically set to a string that fully describes the
system type on which bash is executing, in the standard
GNU cpu-company-system format. The default is system-
dependent.
MAPFILE
An array variable (see Arrays below) created to hold the
text read by the mapfile builtin when no variable name is
supplied.
OLDPWD The previous working directory as set by the cd command.
OPTARG The value of the last option argument processed by the
getopts builtin command (see SHELL BUILTIN COMMANDS
below).
OPTIND The index of the next argument to be processed by the
getopts builtin command (see SHELL BUILTIN COMMANDS
below).
OSTYPE Automatically set to a string that describes the operat‐
ing system on which bash is executing. The default is
system-dependent.
PIPESTATUS
An array variable (see Arrays below) containing a list of
exit status values from the processes in the most-
recently-executed foreground pipeline (which may contain
only a single command).
PPID The process ID of the shell's parent. This variable is
readonly.
PWD The current working directory as set by the cd command.
RANDOM Each time this parameter is referenced, a random integer
between 0 and 32767 is generated. The sequence of random
numbers may be initialized by assigning a value to RAN‐
DOM. If RANDOM is unset, it loses its special proper‐
ties, even if it is subsequently reset.
READLINE_LINE
The contents of the readline line buffer, for use with
"bind -x" (see SHELL BUILTIN COMMANDS below).
READLINE_POINT
The position of the insertion point in the readline line
buffer, for use with "bind -x" (see SHELL BUILTIN COM‐
MANDS below).
REPLY Set to the line of input read by the read builtin command
when no arguments are supplied.
SECONDS
Each time this parameter is referenced, the number of
seconds since shell invocation is returned. If a value
is assigned to SECONDS, the value returned upon subse‐
quent references is the number of seconds since the
assignment plus the value assigned. If SECONDS is unset,
it loses its special properties, even if it is subse‐
quently reset.
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 SHELL BUILTIN COMMANDS
below). 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 read-only.
SHLVL Incremented by one each time an instance of bash is
started.
UID Expands to the user ID of the current user, initialized
at shell startup. This variable is readonly.
The following variables are used by the shell. In some cases,
bash assigns a default value to a variable; these cases are
noted below.
BASH_ENV
If this parameter is set when bash is executing a shell
script, its value is interpreted as a filename containing
commands to initialize the shell, as in ~/.bashrc. The
value of BASH_ENV is subjected to parameter expansion,
command substitution, and arithmetic expansion before
being interpreted as a file name. PATH is not used to
search for the resultant file name.
BASH_XTRACEFD
If set to an integer corresponding to a valid file
descriptor, bash will write the trace output generated
when set -x is enabled to that file descriptor. The file
descriptor is closed when BASH_XTRACEFD is unset or
assigned a new value. Unsetting BASH_XTRACEFD or assign‐
ing it the empty string causes the trace output to be
sent to the standard error. Note that setting
BASH_XTRACEFD to 2 (the standard error file descriptor)
and then unsetting it will result in the standard error
being closed.
CDPATH The search path for the cd command. This is a colon-sep‐
arated list of directories in which the shell looks for
destination directories specified by the cd command. A
sample value is ".:~:/usr".
COLUMNS
Used by the select compound command to determine the ter‐
minal width when printing selection lists. Automatically
set upon receipt of a SIGWINCH.
COMPREPLY
An array variable from which bash reads the possible com‐
pletions generated by a shell function invoked by the
programmable completion facility (see Programmable Com‐
pletion below).
EMACS If bash finds this variable in the environment when the
shell starts with value "t", it assumes that the shell is
running in an Emacs shell buffer and disables line edit‐
ing.
ENV Similar to BASH_ENV; used when the shell is invoked in
POSIX mode.
FCEDIT The default editor for the fc builtin command.
FIGNORE
A colon-separated list of suffixes to ignore when per‐
forming filename completion (see READLINE below). A
filename whose suffix matches one of the entries in FIG‐
NORE is excluded from the list of matched filenames. A
sample value is ".o:~".
FUNCNEST
If set to a numeric value greater than 0, defines a maxi‐
mum function nesting level. Function invocations that
exceed this nesting level will cause the current command
to abort.
GLOBIGNORE
A colon-separated list of patterns defining the set of
filenames to be ignored by pathname expansion. If a
filename matched by a pathname expansion pattern also
matches one of the patterns in GLOBIGNORE, it is removed
from the list of matches.
HISTCONTROL
A colon-separated list of values controlling how commands
are saved on the history list. If the list of values
includes ignorespace, lines which begin with a space
character are not saved in the history list. A value of
ignoredups causes lines matching the previous history
entry to not be saved. A value of ignoreboth is short‐
hand for ignorespace and ignoredups. A value of
erasedups causes all previous lines matching the current
line to be removed from the history list before that line
is saved. Any value not in the above list is ignored.
If HISTCONTROL is unset, or does not include a valid
value, all lines read by the shell parser are saved on
the history list, subject to the value of HISTIGNORE.
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 in which command history is saved
(see HISTORY below). The default value is ~/.bash_his‐
tory. If unset, the command history is not saved when an
interactive shell exits.
HISTFILESIZE
The maximum number of lines contained in the history
file. When this variable is assigned a value, the his‐
tory file is truncated, if necessary, by removing the
oldest entries, to contain no more than that number of
lines. The default value is 500. The history file is
also truncated to this size after writing it when an
interactive shell exits.
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 back‐
slash; 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.
HISTSIZE
The number of commands to remember in the command history
(see HISTORY below). The default value is 500.
HISTTIMEFORMAT
If this variable is set and not null, its value is used
as a format string for strftime(3) to print the time
stamp associated with each history entry displayed by the
history builtin. If this variable is set, time stamps
are written to the history file so they may be preserved
across shell sessions. This uses the history comment
character to distinguish timestamps from other history
lines.
HOME The home directory of the current user; the default argu‐
ment for the cd builtin command. The value of this vari‐
able is also used when performing tilde expansion.
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 com‐
pletions 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, or does not name a readable file, bash attempts to
read /etc/hosts to obtain the list of possible hostname
completions. When HOSTFILE is unset, the hostname list
is cleared.
IFS The Internal Field Separator that is used for word split‐
ting after expansion and to split lines into words with
the read builtin command. The default value is
``<space><tab><newline>''.
IGNOREEOF
Controls the action of an interactive shell on receipt of
an EOF character as the sole input. If set, the value is
the number of consecutive EOF characters which must be
typed as the first characters on an input line before
bash exits. If the variable exists but does not have a
numeric value, or has no value, the default value is 10.
If it does not exist, EOF signifies the end of input to
the shell.
INPUTRC
The filename for the readline startup file, overriding
the default of ~/.inputrc (see READLINE below).
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 pathname expansion, and determines
the behavior of range expressions, equivalence classes,
and collating sequences within pathname expansion and
pattern matching.
LC_CTYPE
This variable determines the interpretation of characters
and the behavior of character classes within pathname
expansion and pattern matching.
LC_MESSAGES
This variable determines the locale used to translate
double-quoted strings preceded by a $.
LC_NUMERIC
This variable determines the locale category used for
number formatting.
LINES Used by the select compound command to determine the col‐
umn length for printing selection lists. Automatically
set upon receipt of a SIGWINCH.
MAIL If this parameter is set to a file or directory name and
the MAILPATH variable is not set, bash informs the user
of the arrival of mail in the specified file or Maildir-
format directory.
MAILCHECK
Specifies how often (in seconds) bash checks for mail.
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.
MAILPATH
A colon-separated list of file names to be checked for
mail. The message to be printed when mail arrives in a
particular file may be specified 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
mailfile. Example:
MAILPATH='/var/mail/bfox?"You have mail":~/shell-mail?"$_
has mail!"'
Bash supplies a default value for this variable, but the
location of the user mail files that it uses is system
dependent (e.g., /var/mail/$USER).
OPTERR If set to the value 1, bash displays error messages gen‐
erated by the getopts builtin command (see SHELL BUILTIN
COMMANDS below). OPTERR is initialized to 1 each time
the shell is invoked or a shell script is executed.
PATH The search path for commands. It is a colon-separated
list of directories in which the shell looks for commands
(see COMMAND EXECUTION below). A zero-length (null)
directory name in the value of PATH indicates the current
directory. A null directory name may appear as two adja‐
cent colons, or as an initial or trailing colon. The
default path is system-dependent, and is set by the
administrator who installs bash. A common value is
``/usr/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin''.
POSIXLY_CORRECT
If this variable is in the environment when bash starts,
the shell enters posix mode before reading the startup
files, as if the --posix invocation option had been sup‐
plied. If it is set while the shell is running, bash
enables posix mode, as if the command set -o posix had
been executed.
PROMPT_COMMAND
If set, the value is executed as a command prior to issu‐
ing each primary prompt.
PROMPT_DIRTRIM
If set to a number greater than zero, the value is used
as the number of trailing directory components to retain
when expanding the \w and \W prompt string escapes (see
PROMPTING below). Characters removed are replaced with
an ellipsis.
PS1 The value of this parameter is expanded (see PROMPTING
below) and used as the primary prompt string. The
default value is ``\s-\v\$ ''.
PS2 The value of this parameter is expanded as with PS1 and
used as the secondary prompt string. The default is ``>
''.
PS3 The value of this parameter is used as the prompt for the
select command (see SHELL GRAMMAR above).
PS4 The value of this parameter is expanded as with PS1 and
the value is printed before each command bash displays
during an execution trace. The first character of PS4 is
replicated multiple times, as necessary, to indicate mul‐
tiple levels of indirection. The default is ``+ ''.
SHELL The full pathname to the shell is kept in this environ‐
ment variable. If it is not set when the shell starts,
bash assigns to it the full pathname of the current
user's login shell.
TIMEFORMAT
The value of this parameter is used as a format string
specifying how the timing information for pipelines pre‐
fixed 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 out‐
put. 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 min‐
utes, 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%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, TMOUT is treated as
the default timeout for the read builtin. The select
command terminates if input does not arrive after TMOUT
seconds when input is coming from a terminal. In an
interactive shell, the value is interpreted as the number
of seconds to wait for input after issuing the primary
prompt. Bash terminates after waiting for that number of
seconds if input does not arrive.
TMPDIR If set, bash uses its value as the name of a directory in
which bash creates temporary files for the shell's use.
auto_resume
This variable controls how the shell interacts with the
user and job control. If this variable is set, single
word simple commands without redirections are treated as
candidates for resumption of an existing stopped job.
There is no ambiguity allowed; if there is more than one
job beginning with the string typed, the job most
recently accessed is selected. The name of a stopped
job, in this context, is the command line used to start
it. If set to the value exact, the string supplied must
match the name of a stopped job exactly; if set to sub‐
string, the string supplied needs to match a substring of
the name of a stopped job. The substring value provides
functionality analogous to the %? job identifier (see
JOB CONTROL below). If set to any other value, the sup‐
plied string must be a prefix of a stopped job's name;
this provides functionality analogous to the %string job
identifier.
histchars
The two or three characters which control history expan‐
sion and tokenization (see HISTORY EXPANSION below). The
first character is the history expansion character, the
character which signals the start of a history expansion,
normally `!'. The second character is the quick substi‐
tution character, which is used as shorthand for re-run‐
ning the previous command entered, substituting one
string for another in the command. The default is `^'.
The optional third character is the character which indi‐
cates that the remainder of the line is a comment when
found as the first character of a word, normally `#'.
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.
Arrays
Bash provides one-dimensional indexed and associative array
variables. Any variable may be used as an indexed 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. Indexed arrays are
referenced using integers (including arithmetic expressions)
and are zero-based; associative arrays are referenced using
arbitrary strings.
An indexed array is created automatically if any variable is
assigned to using the syntax name[subscript]=value. The sub‐
script is treated as an arithmetic expression that must evaluate
to a number. If subscript evaluates to a number less than zero,
it is used as an offset from one greater than the array's maxi‐
mum index (so a subcript of -1 refers to the last element of the
array). To explicitly declare an indexed array, use declare -a
name (see SHELL BUILTIN COMMANDS below). declare -a name[sub‐
script] is also accepted; the subscript is ignored.
Associative arrays are created using declare -A name.
Attributes may be specified for an array variable using the
declare and readonly builtins. Each attribute applies to all
members of an array.
Arrays are assigned to using compound assignments of the form
name=(value1 ... valuen), where each value is of the form [sub‐
script]=string. Indexed array assignments do not require the
bracket and subscript. When assigning to indexed arrays, if the
optional brackets and subscript are 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.
When assigning to an associative array, the subscript is
required.
This syntax is also accepted by the declare builtin. Individual
array elements may be assigned to using the name[sub‐
script]=value syntax introduced above.
Any element of an array may be referenced using ${name[sub‐
script]}. The braces are required to avoid conflicts with path‐
name expansion. If subscript is @ or *, the word expands to all
members of 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 special vari‐
able, and ${name[@]} expands each element of name to a separate
word. When there are no array members, ${name[@]} expands to
nothing. If the double-quoted expansion occurs within a word,
the expansion of the first parameter is joined with the begin‐
ning part of the original word, and the expansion of the last
parameter is joined with the last part of the original word.
This is analogous to the expansion of the special parameters *
and @ (see Special Parameters above). ${#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 the array with a subscript of 0.
An array variable is considered set if a subscript has been
assigned a value. The null string is a valid value.
The unset builtin is used to destroy arrays. unset name[sub‐
script] destroys the array element at index subscript. Care
must be taken to avoid unwanted side effects caused by pathname
expansion. unset name, where name is an array, or unset
name[subscript], where subscript is * or @, removes the entire
array.
The declare, local, and readonly builtins each accept a -a
option to specify an indexed array and a -A option to specify an
associative array. If both options are supplied, -A takes
precedence. The read builtin accepts a -a option to assign a
list of words read from the standard input to an array. The set
and declare builtins display array values in a way that allows
them to be reused as assignments.
EXPANSION
Expansion is performed on the command line after it has been
split into words. There are seven kinds of expansion performed:
brace expansion, tilde expansion, parameter and variable expan‐
sion, command substitution, arithmetic expansion, word split‐
ting, and pathname expansion.
The order of expansions is: brace expansion, tilde expansion,
parameter, variable and arithmetic expansion and command substi‐
tution (done in a left-to-right fashion), word splitting, and
pathname expansion.
On systems that can support it, there is an additional expansion
available: process substitution.
Only brace expansion, word splitting, and pathname 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 "$@" and "${name[@]}" as explained
above (see PARAMETERS).
Brace Expansion
Brace expansion is a mechanism by which arbitrary strings may be
generated. This mechanism is similar to pathname expansion, but
the filenames generated need not exist. Patterns to be brace
expanded take the form of an optional preamble, followed by
either a series of comma-separated strings or a sequence expres‐
sion between a pair of braces, followed by an optional post‐
script. 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, a{d,c,b}e expands into `ade ace abe'.
A sequence expression takes the form {x..y[..incr]}, where x and
y are either integers or single characters, and incr, an
optional increment, is an integer. When integers are supplied,
the expression expands to each number between x and y, inclu‐
sive. Supplied integers may be prefixed with 0 to force each
term to have the same width. When either x or y begins with a
zero, the shell attempts to force all generated terms to contain
the same number of digits, zero-padding where necessary. When
characters are supplied, the expression expands to each charac‐
ter lexicographically between x and y, inclusive. Note that
both x and y must be of the same type. When the increment is
supplied, it is used as the difference between each term. The
default increment is 1 or -1 as appropriate.
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 syn‐
tactic interpretation to the context of the expansion or the
text between the braces.
A correctly-formed brace expansion must contain unquoted opening
and closing braces, and at least one unquoted comma or a valid
sequence expression. Any incorrectly formed brace expansion is
left unchanged. A { or , may be quoted with a backslash to pre‐
vent its being considered part of a brace expression. To avoid
conflicts with parameter expansion, the string ${ is not consid‐
ered eligible for brace expansion.
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}}
Brace expansion introduces a slight incompatibility with histor‐
ical versions of sh. sh does not treat opening or closing
braces specially when they appear as part of a word, and pre‐
serves them in the output. Bash removes braces from words as a
consequence of brace expansion. For example, a word entered to
sh as file{1,2} appears identically in the output. The same
word is output as file1 file2 after expansion by bash. If
strict compatibility with sh is desired, start bash with the +B
option or disable brace expansion with the +B option to the set
command (see SHELL BUILTIN COMMANDS below).
Tilde Expansion
If a word begins with an unquoted tilde character (`~'), all of
the characters preceding the first unquoted slash (or all char‐
acters, 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 shell
parameter HOME. 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 a `~+', the value of the shell variable
PWD replaces the tilde-prefix. If the tilde-prefix is a `~-',
the value of the shell variable OLDPWD, if it is set, is substi‐
tuted. If the characters following the tilde in the tilde-pre‐
fix 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 tilde-prefix as an argument. If the
characters following the tilde in the tilde-prefix consist of a
number without a leading `+' or `-', `+' is assumed.
If the login name is invalid, or the tilde expansion fails, the
word is unchanged.
Each variable assignment is checked for unquoted tilde-prefixes
immediately following a : or the first =. 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.
Parameter Expansion
The `$' character introduces parameter expansion, command sub‐
stitution, or arithmetic expansion. The parameter name or sym‐
bol 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.
${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 which 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 exceptions to this are the expansions of ${!prefix*} and
${!name[@]} described below. The exclamation point must immedi‐
ately follow the left brace in order to introduce indirection.
In each of the cases below, word is subject to tilde expansion,
parameter expansion, command substitution, and arithmetic expan‐
sion.
When not performing substring expansion, using the forms docu‐
mented below, bash tests for a parameter that is unset or null.
Omitting the colon results in a test only for a parameter that
is unset.
${parameter:-word}
Use Default Values. If parameter is unset or null, the
expansion of word is substituted. Otherwise, the value
of parameter is substituted.
${parameter:=word}
Assign Default Values. 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}
Display Error if Null or Unset. 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. Other‐
wise, the value of parameter is substituted.
${parameter:+word}
Use Alternate Value. If parameter is null or unset,
nothing is substituted, otherwise the expansion of word
is substituted.
${parameter:offset}
${parameter:offset:length}
Substring Expansion. Expands to up to length characters
of parameter starting at the character specified by off‐
set. If length is omitted, expands to the substring of
parameter starting at the character specified by offset.
length and offset are arithmetic expressions (see ARITH‐
METIC EVALUATION below). 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 length evaluates to a
number less than zero, and parameter is not @ and not an
indexed or associative array, it is interpreted as an
offset from the end of the value of parameter rather than
a number of characters, and the expansion is the charac‐
ters between the two offsets. If parameter is @, the
result is length positional parameters beginning at off‐
set. If parameter is an indexed array name subscripted
by @ or *, the result is the length members of the array
beginning with ${parameter[offset]}. A negative offset
is taken relative to one greater than the maximum index
of the specified array. Substring expansion applied to
an associative array produces undefined results. Note
that a negative offset must be separated from the colon
by at least one space to avoid being confused with the :-
expansion. Substring indexing is zero-based unless the
positional parameters are used, in which case the index‐
ing starts at 1 by default. If offset is 0, and the
positional parameters are used, $0 is prefixed to the
list.
${!prefix*}
${!prefix@}
Names matching prefix. Expands to the names of variables
whose names begin with prefix, separated by the first
character of the IFS special variable. When @ is used
and the expansion appears within double quotes, each
variable name expands to a separate word.
${!name[@]}
${!name[*]}
List of array keys. If name is an array variable,
expands to the list of array indices (keys) assigned in
name. If name is not an array, expands to 0 if name is
set and null otherwise. When @ is used and the expansion
appears within double quotes, each key expands to a sepa‐
rate word.
${#parameter}
Parameter length. The length in characters of the 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}
Remove matching prefix pattern. The word is expanded to
produce a pattern just as in pathname expansion. If the
pattern matches the beginning of the 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 param‐
eter 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}
Remove matching suffix pattern. The word is expanded to
produce a pattern just as in pathname expansion. If the
pattern matches a trailing portion 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/pattern/string}
Pattern substitution. The pattern is expanded to produce
a pattern just as in pathname expansion. Parameter is
expanded and the longest match of pattern against its
value is replaced with string. If pattern begins with /,
all matches of pattern are replaced with string. Nor‐
mally only the first match is replaced. 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 parame‐
ter. 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 sub‐
scripted with @ or *, the substitution operation is
applied to each member of the array in turn, and the
expansion is the resultant list.
${parameter^pattern}
${parameter^^pattern}
${parameter,pattern}
${parameter,,pattern}
Case modification. This expansion modifies the case of
alphabetic characters in parameter. The pattern is
expanded to produce a pattern just as in pathname expan‐
sion. The ^ operator converts lowercase letters matching
pattern to uppercase; the , operator converts matching
uppercase letters to lowercase. The ^^ and ,, expansions
convert each matched character in the expanded value; the
^ and , expansions match and convert only the first char‐
acter in the expanded value. If pattern is omitted, it
is treated like a ?, which matches every character. If
parameter is @ or *, the case modification 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 case modifi‐
cation operation is applied to each member of the array
in turn, and the expansion is the resultant list.
Command Substitution
Command substitution allows the output of a command to replace
the command name. There are two forms:
$(command)
or
`command`
Bash performs the expansion by executing command and replacing
the command substitution with the standard output of the com‐
mand, 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 equiva‐
lent but faster $(< file).
When the old-style backquote form of substitution is used, back‐
slash retains its literal meaning except when followed by $, `,
or \. The first backquote not preceded by a backslash termi‐
nates 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 pathname expansion are not performed on the results.
Arithmetic Expansion
Arithmetic expansion allows the evaluation of an arithmetic
expression and the substitution of the result. The format for
arithmetic expansion is:
$((expression))
The expression is treated as if it were within double quotes,
but a double quote inside the parentheses is not treated spe‐
cially. All tokens in the expression undergo parameter expan‐
sion, string expansion, command substitution, and quote removal.
Arithmetic expansions may be nested.
The evaluation is performed according to the rules listed below
under ARITHMETIC EVALUATION. If expression is invalid, bash
prints a message indicating failure and no substitution occurs.
Process Substitution
Process substitution is supported on systems that support named
pipes (FIFOs) or the /dev/fd method of naming open files. It
takes the form of <(list) or >(list). The process list is run
with its input or output connected to a FIFO or some file in
/dev/fd. The name of this file is passed as an argument to the
current command as the result of the expansion. If the >(list)
form is used, writing to the file will provide input for list.
If the <(list) form is used, the file passed as an argument
should be read to obtain the output of list.
When available, process substitution is performed simultaneously
with parameter and variable expansion, command substitution, and
arithmetic expansion.
Word Splitting
The shell scans the results of parameter expansion, command sub‐
stitution, 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 sequences of <space>,
<tab>, and <newline> at the beginning and end of the results of
the previous expansions are ignored, and any sequence of IFS
characters not at the beginning or end 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 parame‐
ters 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.
Pathname Expansion
After word splitting, unless the -f option has been set, 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 match‐
ing the pattern. If no matching file names are found, and the
shell option nullglob is not enabled, the word is left
unchanged. If the nullglob option is set, and no matches are
found, the word is removed. If the failglob shell option is
set, and no matches are found, an error message is printed and
the command is not executed. 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 pathname
expansion, the character ``.'' at the start of a name or imme‐
diately following a slash must be matched explicitly, unless the
shell option dotglob is set. When matching a pathname, the
slash character must always be matched explicitly. In other
cases, the ``.'' character is not treated specially. See the
description of shopt below under SHELL BUILTIN COMMANDS for a
description of the nocaseglob, nullglob, failglob, and dotglob
shell options.
The GLOBIGNORE shell variable may be used to restrict the set of
file names matching a pattern. If GLOBIGNORE is set, each
matching file name that also matches one of the patterns in GLO‐
BIGNORE is removed from the list of matches. The file names
``.'' and ``..'' are always ignored when GLOBIGNORE is set and
not null. However, setting GLOBIGNORE to a non-null value has
the effect of enabling the dotglob shell option, so all other
file names beginning with a ``.'' will match. To get the old
behavior of ignoring file names beginning with a ``.'', make
``.*'' one of the patterns in GLOBIGNORE. The dotglob option
is disabled when GLOBIGNORE is unset.
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. A backslash escapes the
following character; the escaping backslash is discarded when
matching. 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.
When the globstar shell option is enabled, and *
is used in a pathname expansion context, two adja‐
cent *s used as a single pattern will match all
files and zero or more directories and subdirecto‐
ries. If followed by a /, two adjacent *s will
match only directories and subdirectories.
? 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. 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. 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.
Within [ and ], character classes can be specified
using the syntax [:class:], where class is one of
the following classes defined in the POSIX stan‐
dard:
alnum alpha ascii blank cntrl digit graph lower
print punct space upper word xdigit
A character class matches any character belonging
to that class. The word character class matches
letters, digits, and the character _.
Within [ and ], an equivalence class can be speci‐
fied 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.
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 pat‐
terns
*(pattern-list)
Matches zero or more occurrences of the given pat‐
terns
+(pattern-list)
Matches one or more occurrences of the given pat‐
terns
@(pattern-list)
Matches one of the given patterns
If the extglob shell option is enabled using the shopt builtin,
following pattern matching operator is recognized as well:
!(pattern-list)
Matches anything except one of the given patterns
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.
REDIRECTION
Before a command is executed, its input and output may be redi‐
rected using a special notation interpreted by the shell. Redi‐
rection may also be used to open and close files for the current
shell execution environment. The following redirection opera‐
tors 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.
Each redirection that may be preceded by a file descriptor num‐
ber may instead be preceded by a word of the form {varname}. In
this case, for each redirection operator except >&- and <&-, the
shell will allocate a file descriptor greater than 10 and assign
it to varname. If >&- or <&- is preceded by {varname}, the
value of varname defines the file descriptor to close.
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 substi‐
tution, arithmetic expansion, quote removal, pathname 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 exam‐
ple, the command
ls > dirlist 2>&1
directs both standard output and standard error to the file
dirlist, while the command
ls 2>&1 > dirlist
directs only the standard output to file dirlist, because the
standard error was duplicated from the 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.
Redirections using file descriptors greater than 9 should be
used with care, as they may conflict with file descriptors the
shell uses internally.
Redirecting Input
Redirection of input causes the file whose name results from the
expansion of word to be opened for reading on file descriptor n,
or the standard input (file descriptor 0) if n is not specified.
The general format for redirecting input is:
[n]<word
Redirecting Output
Redirection of output causes the file whose name results from
the expansion of word to be opened for writing on file descrip‐
tor n, or the standard output (file descriptor 1) if n is not
specified. If the file does not exist it is created; if it does
exist it is truncated to zero size.
The general format for redirecting output is:
[n]>word
If the redirection operator is >, and the 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 to the
set builtin command is not enabled, the redirection is attempted
even if the file named by word exists.
Appending Redirected Output
Redirection of output in this fashion causes the file whose name
results from the expansion of word to be opened for appending on
file descriptor n, or the standard output (file descriptor 1) if
n is not specified. If the file does not exist it is created.
The general format for appending output is:
[n]>>word
Redirecting Standard Output and Standard Error
This construct allows both the standard output (file descriptor
1) and the standard error output (file descriptor 2) to be redi‐
rected to the file whose name is the expansion of word.
There are two formats for redirecting standard output and stan‐
dard error:
&>word
and
>&word
Of the two forms, the first is preferred. This is semantically
equivalent to
>word 2>&1
Appending Standard Output and Standard Error
This construct allows both the standard output (file descriptor
1) and the standard error output (file descriptor 2) to be
appended to the file whose name is the expansion of word.
The format for appending standard output and standard error is:
&>>word
This is semantically equivalent to
>>word 2>&1
Here Documents
This type of redirection instructs the shell to read input from
the current source until a line containing only delimiter (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:
<<[-]word
here-document
delimiter
No parameter expansion, command substitution, arithmetic expan‐
sion, or pathname expansion is performed on word. If any char‐
acters 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 charac‐
ters are stripped from input lines and the line containing
delimiter. This allows here-documents within shell scripts to
be indented in a natural fashion.
Here Strings
A variant of here documents, the format is:
<<<word
The word is expanded and supplied to the command on its standard
input.
Duplicating File Descriptors
The redirection operator
[n]<&word
is used to duplicate input file descriptors. If word expands to
one or more digits, the file descriptor denoted by n is made to
be a copy of that file descriptor. If 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
[n]>&word
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.
Moving File Descriptors
The redirection operator
[n]<&digit-
moves the file descriptor digit to file descriptor n, or the
standard input (file descriptor 0) if n is not specified. digit
is closed after being duplicated to n.
Similarly, the redirection operator
[n]>&digit-
moves the file descriptor digit to file descriptor n, or the
standard output (file descriptor 1) if n is not specified.
Opening File Descriptors for Reading and Writing
The redirection operator
[n]<>word
causes the file whose name is the expansion of word to be opened
for both reading and writing on file descriptor n, or on file
descriptor 0 if n is not specified. If the file does not exist,
it is created.
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 (see SHELL BUILTIN COMMANDS below).
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 characters /, $, `, and = and any of the
shell metacharacters or quoting characters listed above may not
appear in an alias name. The replacement text may contain any
valid shell input, including shell metacharacters. 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
blank, 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. If arguments are needed, a shell function should be used
(see FUNCTIONS below).
Aliases are not expanded when the shell is not interactive,
unless the expand_aliases shell option is set using shopt (see
the description of shopt under SHELL BUILTIN COMMANDS below).
The rules concerning the definition and use of aliases are some‐
what 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 exe‐
cuted. 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 func‐
tion is executed, because a function definition is itself a com‐
pound 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, aliases are superseded by shell func‐
tions.
FUNCTIONS
A shell function, defined as described above under SHELL GRAM‐
MAR, stores a series of commands for later execution. 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.
Functions are executed in the context of the current shell; no
new process is created to interpret them (contrast this with the
execution of a shell script). When a function is executed, the
arguments to the function become the positional parameters dur‐
ing its execution. The special parameter # is updated to
reflect the change. Special parameter 0 is unchanged. The
first element of the FUNCNAME variable is set to the name of the
function while the function is executing.
All other aspects of the shell execution environment are identi‐
cal between a function and its caller with these exceptions:
the DEBUG and RETURN traps (see the description of the trap
builtin under SHELL BUILTIN COMMANDS below) are not inherited
unless the function has been given the trace attribute (see the
description of the declare builtin below) or the -o functrace
shell option has been enabled with the set builtin (in which
case all functions inherit the DEBUG and RETURN traps), and the
ERR trap is not inherited unless the -o errtrace shell option
has been enabled.
Variables local to the function may be declared with the local
builtin command. Ordinarily, variables and their values are
shared between the function and its caller.
The FUNCNEST variable, if set to a numeric value greater than 0,
defines a maximum function nesting level. Function invocations
that exceed the limit cause the entire command to abort.
If the builtin command return is executed in a function, the
function completes and execution resumes with the next command
after the function call. Any command associated with the RETURN
trap is executed before execution resumes. When a function com‐
pletes, the values of the positional parameters and the special
parameter # are restored to the values they had prior to the
function's execution.
Function names and definitions may be listed with the -f option
to the declare or typeset builtin commands. The -F option to
declare or typeset will list the function names only (and
optionally the source file and line number, if the extdebug
shell option is enabled). Functions may be exported so that
subshells automatically have them defined with the -f option to
the export builtin. A function definition may be deleted using
the -f option to the unset builtin. Note that shell functions
and variables with the same name may result in multiple identi‐
cally-named entries in the environment passed to the shell's
children. Care should be taken in cases where this may cause a
problem.
Functions may be recursive. The FUNCNEST variable may be used
to limit the depth of the function call stack and restrict the
number of function invocations. By default, no limit is imposed
on the number of recursive calls.
ARITHMETIC EVALUATION
The shell allows arithmetic expressions to be evaluated, under
certain circumstances (see the let and declare builtin commands
and Arithmetic Expansion). Evaluation is done in fixed-width
integers with no check for overflow, though division by 0 is
trapped and flagged as an error. The operators and their prece‐
dence, associativity, and values are the same as in the C lan‐
guage. 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 operator
= *= /= %= += -= <<= >>= &= ^= |=
assignment
expr1 , expr2
comma
Shell variables are allowed as operands; parameter expansion is
performed before the expression is evaluated. Within an expres‐
sion, shell variables may also be referenced by name without
using the parameter expansion syntax. A shell variable that is
null or unset evaluates to 0 when referenced by name without
using the parameter expansion syntax. The value of a variable
is evaluated as an arithmetic expression when it is referenced,
or when a variable which has been given the integer attribute
using declare -i is assigned a value. A null value evaluates to
0. 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 the optional 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 let‐
ters, the uppercase letters, @, and _, in that order. If base
is less than or equal to 36, lowercase and uppercase letters may
be used interchangeably 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 prece‐
dence rules above.
CONDITIONAL EXPRESSIONS
Conditional expressions are used by the [[ compound command and
the test and [ builtin commands to test file attributes and per‐
form string and arithmetic comparisons. Expressions are formed
from the following unary or binary primaries. If any file argu‐
ment 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.
Unless otherwise specified, primaries that operate on files fol‐
low symbolic links and operate on the target of the link, rather
than the link itself.
When used with [[, the < and > operators sort lexicographically
using the current locale. The test command sorts using ASCII
ordering.
-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 is set-group-id.
-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 termi‐
nal.
-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.
-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.
-N file
True if file exists and has been modified since it was
last read.
-O file
True if file exists and is owned by the effective user
id.
-S file
True if file exists and is a socket.
file1 -ef file2
True if file1 and file2 refer to the same device and
inode numbers.
file1 -nt file2
True if file1 is newer (according to modification date)
than file2, or if file1 exists and file2 does not.
file1 -ot file2
True if file1 is older than file2, or if file2 exists and
file1 does not.
-o optname
True if the shell option optname is enabled. See the
list of options under the description of the -o option to
the set builtin below.
-v varname
True if the shell variable varname is set (has been
assigned a value).
-z string
True if the length of string is zero.
string
-n string
True if the length of string is non-zero.
string1 == string2
string1 = string2
True if the strings are equal. = should be used with the
test command for POSIX conformance.
string1 != string2
True if the strings are not equal.
string1 < string2
True if string1 sorts before string2 lexicographically.
string1 > string2
True if string1 sorts after string2 lexicographically.
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, respec‐
tively. Arg1 and arg2 may be positive or negative inte‐
gers.
SIMPLE COMMAND EXPANSION
When a simple command is executed, the shell performs the fol‐
lowing expansions, assignments, and redirections, from left to
right.
1. The words that the parser has marked as variable assign‐
ments (those preceding the command name) and redirections
are saved for later processing.
2. The words that are not variable assignments or redirec‐
tions are expanded. 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.
3. Redirections are performed as described above under REDI‐
RECTION.
4. The text after the = in each variable assignment under‐
goes tilde expansion, parameter expansion, command sub‐
stitution, 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 pro‐
ceeds 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.
COMMAND 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 above in 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 con‐
tains no slashes, bash searches each element of the PATH for a
directory containing an executable file by that name. Bash uses
a hash table to remember the full pathnames of executable files
(see hash under SHELL BUILTIN COMMANDS below). 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 searches for a defined shell function named com‐
mand_not_found_handle. If that function exists, it is invoked
with the original command and the original command's arguments
as its arguments, and the function's exit status becomes the
exit status of the shell. If that function is not defined, 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 sepa‐
rate execution environment. Argument 0 is set to the name
given, and the remaining arguments to the command are set to the
arguments given, 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, a file containing shell commands. A subshell is
spawned to execute it. This subshell reinitializes itself, so
that the effect is as if a new shell had been invoked to handle
the script, with the exception that the locations of commands
remembered by the parent (see hash below under SHELL BUILTIN
COMMANDS) are retained by the child.
If the program is a file beginning with #!, the remainder of the
first line specifies an interpreter for the program. The shell
executes the specified interpreter on operating systems that do
not handle this executable format themselves. The arguments to
the interpreter consist of a single optional argument following
the interpreter name on the first line of the program, followed
by the name of the program, followed by the command arguments,
if any.
COMMAND EXECUTION ENVIRONMENT
The shell has an execution environment, which consists of the
following:
· open files inherited by the shell at invocation, as modi‐
fied 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
· various process IDs, including those of background jobs,
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 environ‐
ment that consists of the following. Unless otherwise noted,
the values are inherited from the shell.
· the shell's open files, plus any modifications and addi‐
tions specified by redirections to the command
· the current working directory
· the file creation mode mask
· shell variables and functions marked for export, along
with variables exported for the command, passed in the
environment
· traps caught by the shell are reset to the values inher‐
ited 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, commands grouped with parentheses, 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 sub‐
shell environment. Changes made to the subshell environment
cannot affect the shell's execution environment.
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.
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.
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.
The shell 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 envi‐
ronment. The export and declare -x commands allow parameters
and functions to be added to and deleted from the environment.
If the value of a parameter in the environment is modified, the
new value becomes part of the environment, replacing the old.
The environment inherited by any executed command consists of
the shell's initial environment, whose values may be modified in
the shell, less any pairs removed by the unset command, plus any
additions via the export and declare -x commands.
The environment for any simple command or function may be aug‐
mented temporarily by prefixing it with parameter assignments,
as described above in PARAMETERS. These assignment statements
affect only the environment seen by that command.
If the -k option is set (see the set builtin command below),
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 file name of the command and passed to that command in
its environment.
EXIT STATUS
The exit status of an executed command is the value returned by
the waitpid system call or equivalent function. Exit statuses
fall between 0 and 255, though, as explained below, the shell
may use values above 125 specially. Exit statuses from shell
builtins and compound commands are also limited to this range.
Under certain circumstances, the shell will use special values
to indicate specific failure modes.
For the shell's purposes, a command which exits with a zero exit
status has succeeded. An exit status of zero indicates success.
A non-zero exit status indicates failure. When a command termi‐
nates on a fatal signal N, bash uses the value of 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 redi‐
rection, the exit status is greater than zero.
Shell builtin commands return a status of 0 (true) if success‐
ful, and non-zero (false) if an error occurs while they execute.
All builtins return an exit status of 2 to indicate incorrect
usage.
Bash itself returns the exit status of the last command exe‐
cuted, unless a syntax error occurs, in which case it exits with
a non-zero value. See also the exit builtin command below.
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). In all cases, bash ignores SIGQUIT.
If job control is in effect, bash ignores SIGTTIN, SIGTTOU, and
SIGTSTP.
Non-builtin commands run 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 in addition to these inherited handlers. Commands run
as a result of command substitution ignore the keyboard-gener‐
ated 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 signal to a particular job, it should be removed from the
jobs table with the disown builtin (see SHELL BUILTIN COMMANDS
below) or marked to not receive SIGHUP using disown -h.
If the huponexit shell option has been set with shopt, bash
sends a SIGHUP to all jobs when an interactive login shell
exits.
If bash is waiting for a command to complete and receives a sig‐
nal for which a trap has been set, the trap will not be executed
until the command completes. When bash is waiting for an asyn‐
chronous 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, immedi‐
ately after which the trap is executed.
JOB CONTROL
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 operating system
kernel's terminal driver and bash.
The shell associates a job with each pipeline. It keeps a table
of currently executing jobs, which may be listed with the jobs
command. When bash starts a job asynchronously (in the back‐
ground), it prints a line that looks like:
[1] 25647
indicating that this job is job number 1 and that the process ID
of the last process in the pipeline associated with this job is
25647. All of the processes in a single pipeline are members of
the same job. Bash uses the job abstraction as the basis for
job control.
To facilitate the implementation of the user interface to job
control, the operating system maintains the notion of a current
terminal process group ID. Members of this process group (pro‐
cesses 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-gen‐
erated signals. Only foreground processes are allowed to read
from or, if the user so specifies with stty tostop, write to the
terminal. Background processes which attempt to read from
(write to when stty tostop is in effect) the terminal are sent a
SIGTTIN (SIGTTOU) signal by the kernel's 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
may then manipulate the state of this job, using the bg command
to continue it in the background, the fg command to continue it
in the foreground, or the kill command to kill it. A ^Z takes
effect immediately, and has the additional side effect of caus‐
ing 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 specification (jobspec). Job num‐
ber n may be referred to as %n. A job may also be referred to
using a prefix of the name used to start it, or using a sub‐
string that appears in its command line. For example, %ce
refers to a stopped ce job. If a prefix matches more than one
job, bash reports an error. Using %?ce, on the other hand,
refers to any job containing the string ce in its command line.
If the substring matches more than one job, bash reports an
error. The symbols %% and %+ refer to the shell's notion of the
current job, which is the last job stopped while it was in the
foreground or started in the background. The previous job may
be referenced using %-. If there is only a single job, %+ and
%- can both be used to refer to that job. 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
single % (with no accompanying job specification) also refers to
the current job.
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 back‐
ground into the foreground. Similarly, ``%1 &'' resumes job 1
in the background, equivalent to ``bg %1''.
The shell learns immediately whenever a job changes state. Nor‐
mally, 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 command is
enabled, bash reports such changes immediately. Any trap on
SIGCHLD is executed for each child that exits.
If an attempt to exit bash is made while jobs are stopped (or,
if the checkjobs shell option has been enabled using the shopt
builtin, running), the shell prints a warning message, and, if
the checkjobs option is enabled, lists the jobs and their sta‐
tuses. The jobs command may then be used to inspect their sta‐
tus. If a second attempt to exit is made without an intervening
command, the shell does not print another warning, and any
stopped jobs are terminated.
PROMPTING
When executing interactively, bash displays the primary prompt
PS1 when it is ready to read a command, and the secondary prompt
PS2 when it needs more input to complete a command. Bash allows
these prompt strings to be customized by inserting a number of
backslash-escaped special characters that are decoded as fol‐
lows:
\a an ASCII bell character (07)
\d the date in "Weekday Month Date" format (e.g.,
"Tue May 26")
\D{format}
the format is passed to strftime(3) and the result
is inserted into the prompt string; an empty for‐
mat results in a locale-specific time representa‐
tion. The braces are required
\e an ASCII escape character (033)
\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 newline
\r carriage return
\s the name of the shell, the basename of $0 (the
portion following the final slash)
\t the current time in 24-hour HH:MM:SS format
\T the current time in 12-hour HH:MM:SS format
\@ the current time in 12-hour am/pm format
\A the current 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 + patch level (e.g.,
2.00.0)
\w the current working directory, with $HOME abbrevi‐
ated with a tilde (uses the value of the
PROMPT_DIRTRIM variable)
\W the basename of the current working directory,
with $HOME abbreviated with a tilde
\! the history number of this command
\# the command number of this command
\$ if the effective UID is 0, a #, otherwise a $
\nnn the character corresponding to the octal number
nnn
\\ a backslash
\[ begin a sequence of non-printing characters, which
could be used to embed a terminal control sequence
into the prompt
\] 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 HISTORY below), while the command number is the position in
the sequence of commands executed during the current shell ses‐
sion. 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 the description of the shopt command under SHELL BUILTIN
COMMANDS below).
READLINE
This is the library that handles reading input when using an
interactive shell, unless the --noediting option is given at
shell invocation. Line editing is also used when using the -e
option to the read builtin. By default, the line editing com‐
mands are similar to those of Emacs. A vi-style line editing
interface is also available. Line editing can be enabled at any
time using the -o emacs or -o vi options to the set builtin (see
SHELL BUILTIN COMMANDS below). To turn off line editing after
the shell is running, use the +o emacs or +o vi options to the
set builtin.
Readline Notation
In this section, the Emacs-style notation is used to denote key‐
strokes. Control keys are denoted by C-key, e.g., C-n means
Control-N. Similarly, meta keys are denoted by M-key, so M-x
means Meta-X. (On keyboards without a meta key, M-x means ESC
x, i.e., press the Escape key then the x key. This makes ESC
the meta prefix. The combination M-C-x means ESC-Control-x, or
press the Escape key then hold the Control key while pressing
the x key.)
Readline commands may be given numeric arguments, which normally
act as a repeat count. Sometimes, however, it is the sign of
the argument that is significant. Passing a negative argument
to a command that acts in the forward direction (e.g.,
kill-line) causes that command to act in a backward direction.
Commands whose behavior with arguments deviates from this are
noted below.
When a command is described as killing text, the text deleted is
saved for possible future retrieval (yanking). The killed text
is saved in a kill ring. Consecutive kills cause the text to be
accumulated into one unit, which can be yanked all at once.
Commands which do not kill text separate the chunks of text on
the kill ring.
Readline Initialization
Readline is customized by putting commands in an initialization
file (the inputrc file). The name of this file is taken from
the value of the INPUTRC variable. If that variable is unset,
the default is ~/.inputrc. When a program which uses the read‐
line library starts up, the initialization file is read, and the
key bindings and variables are set. There are only a few basic
constructs allowed in the readline initialization file. Blank
lines are ignored. Lines beginning with a # are comments.
Lines beginning with a $ indicate conditional constructs. Other
lines denote key bindings and variable settings.
The default key-bindings may be changed with an inputrc file.
Other programs that use this library may add their own commands
and bindings.
For example, placing
M-Control-u: universal-argument
or
C-Meta-u: universal-argument
into the inputrc would make M-C-u execute the readline command
universal-argument.
The following symbolic character names are recognized: RUBOUT,
DEL, ESC, LFD, NEWLINE, RET, RETURN, SPC, SPACE, and TAB.
In addition to command names, readline allows keys to be bound
to a string that is inserted when the key is pressed (a macro).
Readline Key Bindings
The syntax for controlling key bindings in the inputrc file is
simple. All that is required is the name of the command or the
text of a macro and a key sequence to which it should be bound.
The name may be specified in one of two ways: as a symbolic key
name, possibly with Meta- or Control- prefixes, or as a key
sequence.
When using the form 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 univer‐
sal-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).
In the second form, "keyseq":function-name or macro, keyseq dif‐
fers from keyname above in that strings denoting an entire key
sequence may be specified by placing the sequence within double
quotes. Some GNU Emacs style key escapes can be used, as in the
following example, but the symbolic character names are not rec‐
ognized.
"\C-u": universal-argument
"\C-x\C-r": re-read-init-file
"\e[11~": "Function Key 1"
In this example, C-u is again bound to the function univer‐
sal-argument. 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 full set of GNU Emacs style escape sequences is
\C- control prefix
\M- meta prefix
\e an escape character
\\ backslash
\" literal "
\' literal '
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 hexa‐
decimal 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 '.
Bash allows the current readline key bindings to be displayed or
modified with the bind builtin command. The editing mode may be
switched during interactive use by using the -o option to the
set builtin command (see SHELL BUILTIN COMMANDS below).
Readline Variables
Readline has variables that can be used to further customize its
behavior. A variable may be set in the inputrc file with a
statement of the form
set variable-name value
Except where noted, readline variables can take the values On or
Off (without regard to case). Unrecognized variable names are
ignored. When a variable value is read, empty or null values,
"on" (case-insensitive), and "1" are equivalent to On. All
other values are equivalent to Off. The variables and their
default values are:
bell-style (audible)
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, readline attempts
to ring the terminal's bell.
bind-tty-special-chars (On)
If set to On, readline attempts to bind the control char‐
acters treated specially by the kernel's terminal driver
to their readline equivalents.
comment-begin (``#'')
The string that is inserted when the readline insert-com‐
ment command is executed. This command is bound to M-#
in emacs mode and to # in vi command mode.
completion-ignore-case (Off)
If set to On, readline performs filename matching and
completion in a case-insensitive fashion.
completion-prefix-display-length (0)
The length in characters of the common prefix of a list
of possible completions that is displayed without modifi‐
cation. When set to a value greater than zero, common
prefixes longer than this value are replaced with an
ellipsis when displaying possible completions.
completion-query-items (100)
This determines when the user is queried about viewing
the number of possible completions generated by the pos‐
sible-completions command. It may be set to any integer
value greater than or equal to zero. If the number of
possible completions is greater than or equal to the
value of this variable, the user is asked whether or not
he wishes to view them; otherwise they are simply listed
on the terminal.
convert-meta (On)
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 escape character (in effect,
using escape as the meta prefix).
disable-completion (Off)
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.
editing-mode (emacs)
Controls whether readline begins with a set of key bind‐
ings similar to Emacs or vi. editing-mode can be set to
either emacs or vi.
echo-control-characters (On)
When set to On, on operating systems that indicate they
support it, readline echoes a character corresponding to
a signal generated from the keyboard.
enable-keypad (Off)
When set to On, readline will try to enable the applica‐
tion keypad when it is called. Some systems need this to
enable the arrow keys.
enable-meta-key (On)
When set to On, readline will try to enable any meta mod‐
ifier key the terminal claims to support when it is
called. On many terminals, the meta key is used to send
eight-bit characters.
expand-tilde (Off)
If set to On, tilde expansion is performed when readline
attempts word completion.
history-preserve-point (Off)
If set to On, the history code attempts to place point at
the same location on each history line retrieved with
previous-history or next-history.
history-size (0)
Set the maximum number of history entries saved in the
history list. If set to zero, the number of entries in
the history list is not limited.
horizontal-scroll-mode (Off)
When set to On, makes readline use a single line for dis‐
play, scrolling the input horizontally on a single screen
line when it becomes longer than the screen width rather
than wrapping to a new line.
input-meta (Off)
If set to On, readline will enable eight-bit input (that
is, it will not strip the high bit from the characters it
reads), regardless of what the terminal claims it can
support. The name meta-flag is a synonym for this vari‐
able.
isearch-terminators (``C-[C-J'')
The string of characters that should terminate an incre‐
mental search without subsequently executing the charac‐
ter as a command. If this variable has not been given a
value, the characters ESC and C-J will terminate an
incremental search.
keymap (emacs)
Set the current readline keymap. The set of valid keymap
names is emacs, emacs-standard, emacs-meta, emacs-ctlx,
vi, vi-command, and vi-insert. vi is equivalent to
vi-command; emacs is equivalent to emacs-standard. The
default value is emacs; the value of editing-mode also
affects the default keymap.
mark-directories (On)
If set to On, completed directory names have a slash
appended.
mark-modified-lines (Off)
If set to On, history lines that have been modified are
displayed with a preceding asterisk (*).
mark-symlinked-directories (Off)
If set to On, completed names which are symbolic links to
directories have a slash appended (subject to the value
of mark-directories).
match-hidden-files (On)
This variable, when set to On, causes readline to match
files whose names begin with a `.' (hidden files) when
performing filename completion. If set to Off, the lead‐
ing `.' must be supplied by the user in the filename to
be completed.
menu-complete-display-prefix (Off)
If set to On, menu completion displays the common prefix
of the list of possible completions (which may be empty)
before cycling through the list.
output-meta (Off)
If set to On, readline will display characters with the
eighth bit set directly rather than as a meta-prefixed
escape sequence.
page-completions (On)
If set to On, readline uses an internal more-like pager
to display a screenful of possible completions at a time.
print-completions-horizontally (Off)
If set to On, readline will display completions with
matches sorted horizontally in alphabetical order, rather
than down the screen.
revert-all-at-newline (Off)
If set to On, readline will undo all changes to history
lines before returning when accept-line is executed. By
default, history lines may be modified and retain indi‐
vidual undo lists across calls to readline.
show-all-if-ambiguous (Off)
This alters the default behavior of the completion func‐
tions. If set to On, words which have more than one pos‐
sible completion cause the matches to be listed immedi‐
ately instead of ringing the bell.
show-all-if-unmodified (Off)
This alters the default behavior of the completion func‐
tions in a fashion similar to show-all-if-ambiguous. If
set to On, words which have more than one possible com‐
pletion without any possible partial completion (the pos‐
sible completions don't share a common prefix) cause the
matches to be listed immediately instead of ringing the
bell.
skip-completed-text (Off)
If set to On, this alters the default completion behavior
when inserting a single match into the line. It's only
active when performing completion in the middle of a
word. If enabled, readline does not insert characters
from the completion that match characters after point in
the word being completed, so portions of the word follow‐
ing the cursor are not duplicated.
visible-stats (Off)
If set to On, a character denoting a file's type as
reported by stat(2) is appended to the filename when
listing possible completions.
Readline Conditional Constructs
Readline implements a facility similar in spirit to the condi‐
tional 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 the both 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 an initialization file can test for a particu‐
lar value. This could be used to bind key
sequences to functions useful for a specific pro‐
gram. 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 would read /etc/inputrc:
$include /etc/inputrc
Searching
Readline provides commands for searching through the command
history (see HISTORY below) for lines containing a specified
string. There are two search modes: incremental and non-incre‐
mental.
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 match‐
ing the string typed so far. An incremental search requires
only as many characters as needed to find the desired history
entry. The characters present in the value of the isearch-ter‐
minators variable are used to terminate an incremental search.
If that variable has not been assigned a value the Escape and
Control-J characters will terminate an incremental search. Con‐
trol-G will abort an incremental search and restore the original
line. When the search is terminated, the history entry contain‐
ing the search string becomes the current line.
To find other matching entries in the history list, type Con‐
trol-S or Control-R as appropriate. This will search backward
or forward in the history for the next entry matching the search
string typed so far. Any other key sequence bound to a readline
command will terminate the search and execute that command. For
instance, a newline will terminate the search and accept the
line, thereby executing the command from the history list.
Readline remembers the last incremental search string. If two
Control-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.
Readline Command Names
The following is a list of the names of the commands and the
default key sequences to which they are bound. 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.
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 com‐
posed of alphanumeric characters (letters and digits).
backward-word (M-b)
Move back to the start of the current or previous word.
Words are composed of alphanumeric characters (letters
and digits).
shell-forward-word
Move forward to the end of the next word. Words are
delimited by non-quoted shell metacharacters.
shell-backward-word
Move back to the start of the current or previous word.
Words are delimited by non-quoted shell metacharacters.
clear-screen (C-l)
Clear the screen leaving the current line at the top of
the screen. With an argument, refresh the current line
without clearing the screen.
redraw-current-line
Refresh the current line.
Commands for Manipulating the History
accept-line (Newline, Return)
Accept the line regardless of where the cursor is. If
this line is non-empty, add it to the history list
according to the state of the HISTCONTROL variable. If
the line is a modified history line, then restore the
history line to its original state.
previous-history (C-p)
Fetch the previous command from the history list, moving
back in the list.
next-history (C-n)
Fetch the next command from the history list, moving for‐
ward in the list.
beginning-of-history (M-<)
Move to the first line in the history.
end-of-history (M->)
Move to the end of the input history, i.e., the line cur‐
rently 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 incre‐
mental search.
forward-search-history (C-s)
Search forward starting at the current line and moving
`down' through the history as necessary. This is an
incremental search.
non-incremental-reverse-search-history (M-p)
Search backward through the history starting at the cur‐
rent line using a non-incremental search for a string
supplied by the user.
non-incremental-forward-search-history (M-n)
Search forward through the history using a non-incremen‐
tal 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.
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.
yank-nth-arg (M-C-y)
Insert the first argument to the previous command (usu‐
ally 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. Once the argument n is
computed, the argument is extracted as if the "!n" his‐
tory expansion had been specified.
yank-last-arg (M-., M-_)
Insert the last argument to the previous command (the
last word of the previous history entry). With a numeric
argument, behave exactly like yank-nth-arg. Successive
calls to yank-last-arg move back through the history
list, inserting the last word (or the word specified by
the argument to the first call) of each line in turn.
Any numeric argument supplied to these successive calls
determines the direction to move through the history. A
negative argument switches the direction through the his‐
tory (back or forward). The history expansion facilities
are used to extract the last argument, as if the "!$"
history expansion had been specified.
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 HISTORY EXPANSION below for a descrip‐
tion of history expansion.
history-expand-line (M-^)
Perform history expansion on the current line. See HIS‐
TORY EXPANSION below for a description of history expan‐
sion.
magic-space
Perform history expansion on the current line and insert
a space. See HISTORY EXPANSION below for a description
of history expansion.
alias-expand-line
Perform alias expansion on the current line. See ALIASES
above for a description of alias expansion.
history-and-alias-expand-line
Perform history and alias expansion on the current line.
insert-last-argument (M-., M-_)
A synonym for yank-last-arg.
operate-and-get-next (C-o)
Accept the current line for execution and fetch the next
line relative to the current line from the history for
editing. Any argument is ignored.
edit-and-execute-command (C-xC-e)
Invoke an editor on the current command line, and execute
the result as shell commands. Bash attempts to invoke
$VISUAL, $EDITOR, and emacs as the editor, in that order.
Commands for Changing Text
delete-char (C-d)
Delete the character at point. If point is at the begin‐
ning 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. When given a
numeric argument, save the deleted text on the kill ring.
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.
quoted-insert (C-q, C-v)
Add the next character typed to the line verbatim. This
is how to insert characters like C-q, for example.
tab-insert (C-v TAB)
Insert a tab character.
self-insert (a, b, A, 1, !, ...)
Insert the character typed.
transpose-chars (C-t)
Drag the character before point forward over the charac‐
ter at point, moving point forward as well. If point is
at the end of the line, then this transposes the two
characters before point. Negative arguments have no
effect.
transpose-words (M-t)
Drag the word before point past the word after point,
moving point over that word as well. If 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 nega‐
tive argument, uppercase the previous word, but do not
move point.
downcase-word (M-l)
Lowercase the current (or following) word. With a nega‐
tive argument, lowercase the previous word, but do not
move point.
capitalize-word (M-c)
Capitalize the current (or following) word. With a nega‐
tive argument, capitalize the previous word, but do not
move point.
overwrite-mode
Toggle overwrite mode. With an explicit positive numeric
argument, switches to overwrite mode. With an explicit
non-positive numeric argument, switches to insert mode.
This command affects only emacs mode; vi mode does over‐
write differently. Each call to readline() starts in
insert mode. In overwrite mode, characters bound to
self-insert replace the text at point rather than pushing
the text to the right. Characters bound to back‐
ward-delete-char replace the character before point with
a space. By default, this command is unbound.
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 point to the beginning of the line.
The killed text is saved on the kill-ring.
kill-whole-line
Kill all characters on the current line, no matter where
point is.
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 bound‐
aries are the same as those used by forward-word.
backward-kill-word (M-Rubout)
Kill the word behind point. Word boundaries are the same
as those used by backward-word.
shell-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 bound‐
aries are the same as those used by shell-forward-word.
shell-backward-kill-word (M-Rubout)
Kill the word behind point. Word boundaries are the same
as those used by shell-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.
unix-filename-rubout
Kill the word behind point, using white space and the
slash character as the word boundaries. The killed text
is saved on the kill-ring.
delete-horizontal-space (M-\)
Delete all spaces and tabs around point.
kill-region
Kill the text in the current region.
copy-region-as-kill
Copy the text in the region to the kill buffer.
copy-backward-word
Copy the word before point to the kill buffer. The word
boundaries are the same as backward-word.
copy-forward-word
Copy the word following point to the kill buffer. The
word boundaries are the same as forward-word.
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. Only works
following yank or yank-pop.
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 com‐
mand 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 univer‐
sal-argument again ends the numeric argument, but is oth‐
erwise 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 com‐
mand is multiplied by four. The argument count is ini‐
tially one, so executing this function the first time
makes the argument count four, a second time makes the
argument count sixteen, and so on.
Completing
complete (TAB)
Attempt to perform completion on the text before point.
Bash attempts completion treating the text as a variable
(if the text begins with $), username (if the text begins
with ~), hostname (if the text begins with @), or command
(including aliases and functions) in turn. If none of
these produces a match, filename completion is attempted.
possible-completions (M-?)
List the possible completions of the text before point.
insert-completions (M-*)
Insert all completions of the text before point that
would have been generated by possible-completions.
menu-complete
Similar to complete, but replaces the word to be com‐
pleted with a single match from the list of possible com‐
pletions. Repeated execution of menu-complete steps
through the list of possible completions, inserting each
match in turn. At the end of the list of completions,
the bell is rung (subject to the setting of bell-style)
and the original text is restored. An argument of n
moves n positions forward in the list of matches; a nega‐
tive argument may be used to move backward through the
list. This command is intended to be bound to TAB, but
is unbound by default.
menu-complete-backward
Identical to menu-complete, but moves backward through
the list of possible completions, as if menu-complete had
been given a negative argument. This command is unbound
by default.
delete-char-or-list
Deletes the character under the cursor if not at the
beginning or end of the line (like delete-char). If at
the end of the line, behaves identically to possible-com‐
pletions. This command is unbound by default.
complete-filename (M-/)
Attempt filename completion on the text before point.
possible-filename-completions (C-x /)
List the possible completions of the text before point,
treating it as a filename.
complete-username (M-~)
Attempt completion on the text before point, treating it
as a username.
possible-username-completions (C-x ~)
List the possible completions of the text before point,
treating it as a username.
complete-variable (M-$)
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 func‐
tions, 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.
dabbrev-expand
Attempt menu completion on the text before point, compar‐
ing the text against lines from the history list for pos‐
sible completion matches.
complete-into-braces (M-{)
Perform filename completion and insert the list of possi‐
ble completions enclosed within braces so the list is
available to the shell (see Brace Expansion above).
Keyboard Macros
start-kbd-macro (C-x ()
Begin saving the characters typed into the current key‐
board macro.
end-kbd-macro (C-x ))
Stop saving the characters typed into the current key‐
board macro and store 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 key‐
board.
Miscellaneous
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. ESC f is equivalent to
Meta-f.
undo (C-_, C-x C-u)
Incremental undo, separately remembered for each line.
revert-line (M-r)
Undo all changes made to this line. This is like execut‐
ing the undo command enough times to return the line to
its initial state.
tilde-expand (M-&)
Perform tilde expansion on the current word.
set-mark (C-@, M-<space>)
Set the mark to the point. If a numeric argument is sup‐
plied, the mark is set to that position.
exchange-point-and-mark (C-x C-x)
Swap the point with the mark. The current cursor posi‐
tion 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 occur‐
rence 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.
skip-csi-sequence
Read enough characters to consume a multi-key sequence
such as those defined for keys like Home and End. Such
sequences begin with a Control Sequence Indicator (CSI),
usually ESC-[. If this sequence is bound to "\[", keys
producing such sequences will have no effect unless
explicitly bound to a readline command, instead of
inserting stray characters into the editing buffer. This
is unbound by default, but usually bound to ESC-[.
insert-comment (M-#)
Without a numeric argument, the value of the readline
comment-begin variable is inserted at the beginning of
the current line. If a numeric argument is supplied,
this command acts as a toggle: if the characters at the
beginning of the line do not match the value of com‐
ment-begin, the value is inserted, otherwise the charac‐
ters in comment-begin are deleted from the beginning of
the line. In either case, the line is accepted as if a
newline had been typed. The default value of com‐
ment-begin causes this command to make the current line a
shell comment. If a numeric argument causes the comment
character to be removed, the line will be executed by the
shell.
glob-complete-word (M-g)
The word before point is treated as a pattern for path‐
name expansion, with an asterisk implicitly appended.
This pattern is used to generate a list of matching file
names for possible completions.
glob-expand-word (C-x *)
The word before point is treated as a pattern for path‐
name expansion, and the list of matching file names is
inserted, replacing the word. If a numeric argument is
supplied, an asterisk is appended before pathname expan‐
sion.
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.
If a numeric argument is supplied, an asterisk is
appended before pathname expansion.
dump-functions
Print all of the functions and their key bindings to the
readline output stream. If a numeric argument is sup‐
plied, the output is formatted in such a way that it can
be made part of an inputrc file.
dump-variables
Print all of the settable readline variables and their
values to the readline output stream. If a numeric argu‐
ment is supplied, the output is formatted in such a way
that it can be made part of an inputrc file.
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.
display-shell-version (C-x C-v)
Display version information about the current instance of
bash.
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 SHELL BUILTIN COMMANDS
below), the programmable completion facilities are invoked.
First, the command name is identified. If the command word is
the empty string (completion attempted at the beginning of an
empty line), any compspec defined with the -E option to complete
is used. 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 comp‐
spec for the full pathname is searched for first. If no comp‐
spec is found for the full pathname, an attempt is made to find
a compspec for the portion following the final slash. If those
searches do not result in a compspec, any compspec defined with
the -D option to complete is used as the default.
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 as described above under Completing 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.
Any completions specified by a pathname expansion pattern to the
-G option are generated next. The words generated by the pat‐
tern need not match the word being completed. The GLOBIGNORE
shell variable is not used to filter the matches, but the FIG‐
NORE 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 hon‐
ored. Each word is then expanded using brace expansion, tilde
expansion, parameter and variable expansion, command substitu‐
tion, and arithmetic expansion, as described above under EXPAN‐
SION. The results are split using the rules described above
under 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, COMP_POINT,
COMP_KEY, and COMP_TYPE variables are assigned values as
described above under Shell 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 argu‐
ment is the name of the command whose arguments are being com‐
pleted, 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 comple‐
tions against the word being completed is performed; the func‐
tion 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, 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 lit‐
eral & may be escaped with a backslash; the backslash is removed
before attempting a match. Any completion that matches the pat‐
tern 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.
If the -o plusdirs option was supplied to complete when the
compspec was defined, directory name completion is attempted and
any matches are added to the results of the other actions.
By default, if a compspec is found, whatever it generates is
returned to the completion code as the full set of possible com‐
pletions. The default bash completions are not attempted, and
the readline default of filename completion is disabled. If the
-o bashdefault option was supplied to complete when the compspec
was defined, the bash default completions are attempted if the
compspec generates no matches. If the -o default option was
supplied to complete when the compspec was defined, readline's
default completion will be performed if the compspec (and, if
attempted, the default bash completions) generate no matches.
When a compspec indicates that directory name completion is
desired, the programmable completion functions force readline to
append a slash to completed names which are symbolic links to
directories, subject to the value of the mark-directories read‐
line variable, regardless of the setting of the mark-sym‐
linked-directories readline variable.
There is some support for dynamically modifying completions.
This is most useful when used in combination with a default com‐
pletion specified with complete -D. It's possible for shell
functions executed as completion handlers to indicate that com‐
pletion should be retried by returning an exit status of 124.
If a shell function returns 124, and changes the compspec asso‐
ciated with the command on which completion is being attempted
(supplied as the first argument when the function is executed),
programmable completion restarts from the beginning, with an
attempt to find a new compspec for that command. This allows a
set of completions to be built dynamically as completion is
attempted, rather than being loaded all at once.
For instance, assuming that there is a library of compspecs,
each kept in a file corresponding to the name of the command,
the following default completion function would load completions
dynamically:
_completion_loader()
{
. "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return
124
}
complete -D -F _completion_loader
HISTORY
When the -o history option to the set builtin is enabled, the
shell provides access to the command history, the list of com‐
mands previously typed. The value of the HISTSIZE 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 (see EXPANSION above) but after history
expansion is performed, subject to the values of the shell vari‐
ables HISTIGNORE and HISTCONTROL.
On startup, the history is initialized from the file named by
the variable HISTFILE (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 HIST‐
FILESIZE. When the history file is read, lines beginning with
the history comment character followed immediately by a digit
are interpreted as timestamps for the preceding history line.
These timestamps are optionally displayed depending on the value
of the HISTTIMEFORMAT variable. When an interactive shell
exits, the last $HISTSIZE lines are copied from the history list
to $HISTFILE. If the histappend shell option is enabled (see
the description of shopt under SHELL BUILTIN COMMANDS below),
the lines are appended to the history file, otherwise the his‐
tory file is overwritten. If HISTFILE is unset, or if the his‐
tory file is unwritable, the history is not saved. If the HIST‐
TIMEFORMAT variable is set, time stamps are written to the his‐
tory file, marked with the history comment character, so they
may be preserved across shell sessions. This uses the history
comment character to distinguish timestamps from other history
lines. 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 (see SHELL BUILTIN COMMANDS below) 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 com‐
mand-line editing, search commands are available in each editing
mode that provide access to the history list.
The shell allows control over which commands are saved on the
history list. The HISTCONTROL and HISTIGNORE variables may be
set to cause the shell to save only a subset of the commands
entered. The cmdhist shell option, if enabled, causes the shell
to attempt to save each line of a multi-line command in the same
history entry, adding semicolons where necessary to preserve
syntactic correctness. The lithist shell option causes the
shell to save the command with embedded newlines instead of
semicolons. See the description of the shopt builtin below
under SHELL BUILTIN COMMANDS for information on setting and
unsetting shell options.
HISTORY EXPANSION
The shell supports a history expansion feature that is similar
to the history expansion in csh. This section describes what
syntax features are available. This feature is enabled by
default for interactive shells, and can be disabled using the +H
option to the set builtin command (see SHELL BUILTIN COMMANDS
below). Non-interactive shells do not perform history expansion
by default.
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 is performed immediately after a complete line
is read, before the shell breaks it into words. It takes place
in two parts. The first is to determine which line from the
history list to use during substitution. The second is to
select portions of that line for inclusion into the current one.
The line selected from the history is the event, and the por‐
tions of that line that are acted upon are words. Various modi‐
fiers are available to manipulate the selected words. The line
is broken into words in the same fashion as when reading input,
so that several metacharacter-separated words surrounded by
quotes are considered one word. History expansions are intro‐
duced by the appearance of the history expansion character,
which is ! by default. Only backslash (\) and single quotes can
quote the history expansion character.
Several characters inhibit history expansion if found immedi‐
ately following the history expansion character, even if it is
unquoted: space, tab, newline, carriage return, and =. If the
extglob shell option is enabled, ( will also inhibit expansion.
Several shell options settable with the shopt builtin may be
used to tailor the behavior of history expansion. If the
histverify shell option is enabled (see the description of the
shopt builtin below), and readline is being used, history sub‐
stitutions 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 substi‐
tution will be reloaded into the readline editing buffer for
correction. The -p option to the history builtin command may be
used to see what a history expansion will do before using it.
The -s option to the history builtin may be used to add commands
to the end of the history list without actually executing them,
so that they are available for subsequent recall.
The shell allows control of the various characters used by the
history expansion mechanism (see the description of histchars
above under Shell Variables). The shell uses the history com‐
ment character to mark history timestamps when writing the his‐
tory file.
Event Designators
An event designator is a reference to a command line entry in
the history list. Unless the reference is absolute, events are
relative to the current position in the history list.
! Start a history substitution, except when followed by a
blank, newline, carriage return, = or ( (when the extglob
shell option is enabled using the shopt builtin).
!n Refer to command line n.
!-n Refer to the current command minus n.
!! Refer to the previous command. This is a synonym for
`!-1'.
!string
Refer to the most recent command preceding the current
position in the history list starting with string.
!?string[?]
Refer to the most recent command preceding the current
postition in the history list containing string. The
trailing ? may be omitted if string is followed immedi‐
ately by a newline.
^string1^string2^
Quick substitution. Repeat the previous command, replac‐
ing string1 with string2. Equivalent to
``!!:s/string1/string2/'' (see Modifiers below).
!# The entire command line typed so far.
Word Designators
Word designators are used to select desired words from the
event. A : separates the event specification from the word des‐
ignator. 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.
0 (zero)
The zeroth word. For the shell, 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 but the zeroth. 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.
Modifiers
After the optional word designator, there may appear a sequence
of one or more of the following modifiers, each preceded by a
`:'.
h Remove a trailing file name component, leaving only the
head.
t Remove all leading file name components, leaving the
tail.
r Remove a trailing suffix of the form .xxx, 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 substitu‐
tions.
x Quote the substituted words as with q, but break into
words at blanks and newlines.
s/old/new/
Substitute new for the first occurrence of old in the
event line. Any delimiter can be used in place of /.
The final delimiter is optional if it is the last charac‐
ter of the event line. 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 &. If old is null, it is set to the last old
substituted, or, if no previous history substitutions
took place, the last string in a !?string[?] search.
& Repeat the previous substitution.
g Cause changes to be applied over the entire event line.
This is used in conjunction with `:s' (e.g.,
`:gs/old/new/') or `:&'. If used with `:s', any delim‐
iter can be used in place of /, and the final delimiter
is optional if it is the last character of the event
line. An a may be used as a synonym for g.
G Apply the following `s' modifier once to each word in the
event line.
SHELL BUILTIN COMMANDS
Unless otherwise noted, each builtin command documented in this
section as accepting options preceded by - accepts -- to signify
the end of the options. The :, true, false, and test builtins
do not accept options and do not treat -- specially. The exit,
logout, break, continue, let, and shift builtins accept and
process arguments beginning with - without requiring --. Other
builtins that accept arguments but are not specified as accept‐
ing options interpret arguments beginning with - as invalid
options and require -- to prevent this interpretation.
: [arguments]
No effect; the command does nothing beyond expanding
arguments and performing any specified redirections. A
zero exit code is returned.
. filename [arguments]
source filename [arguments]
Read and execute commands from filename in the current
shell environment and return the exit status of the last
command executed from filename. If filename does not
contain a slash, file names in PATH are used to find the
directory containing filename. The file searched for in
PATH need not be executable. When bash is not in posix
mode, the current directory is searched if no file is
found in PATH. If the sourcepath option to the shopt
builtin command is turned off, the PATH is not searched.
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 status of the last command exited within the
script (0 if no commands are executed), and false if
filename is not found or cannot be read.
alias [-p] [name[=value] ...]
Alias with no arguments or with the -p option prints the
list of aliases in the form alias name=value on standard
output. When arguments are supplied, an alias is defined
for each name whose value is given. A trailing space in
value causes the next word to be checked for alias sub‐
stitution when the alias is expanded. For each name in
the argument list for which no value is supplied, the
name and value of the alias is printed. Alias returns
true unless a name is given for which no alias has been
defined.
bg [jobspec ...]
Resume each suspended job jobspec in the background, as
if it had been started with &. If jobspec is not
present, the shell's notion of the current job is used.
bg jobspec returns 0 unless run when job control is dis‐
abled or, when run with job control enabled, any speci‐
fied jobspec was not found or was started without job
control.
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
bind readline-command
Display current readline key and function bindings, bind
a key sequence to a readline function or macro, or set a
readline variable. Each non-option argument is a command
as it would appear in .inputrc, but each binding or com‐
mand 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 equiva‐
lent to vi-command; emacs is equivalent to
emacs-standard.
-l List the names of all readline functions.
-p Display readline function names and bindings in
such a way that they can be re-read.
-P List current readline function names and bindings.
-s Display readline key sequences bound to macros and
the strings they output in such a way that they
can be re-read.
-S Display readline key sequences bound to macros and
the strings they output.
-v Display readline variable names and values in such
a way that they can be re-read.
-V List current readline variable names and values.
-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. When shell-command is executed, the
shell sets the READLINE_LINE variable to the con‐
tents of the readline line buffer and the READ‐
LINE_POINT variable to the current location of the
insertion point. If the executed command changes
the value of READLINE_LINE or READLINE_POINT,
those new values will be reflected in the editing
state.
The return value is 0 unless an unrecognized option is
given or an error occurred.
break [n]
Exit from within a for, while, until, or select loop. If
n is specified, break n levels. n must be ≥ 1. If n is
greater than the number of enclosing loops, all enclosing
loops are exited. The return value is non-zero when n is
≤ 0; Otherwise, break returns 0 value.
builtin shell-builtin [arguments]
Execute the specified shell builtin, passing it argu‐
ments, and return its exit status. This is useful when
defining a function whose name is the same as a shell
builtin, retaining the functionality of the builtin
within the function. The cd builtin is commonly rede‐
fined this way. The return status is false if
shell-builtin is not a shell builtin command.
caller [expr]
Returns the context of any active subroutine call (a
shell function or a script executed with the . or source
builtins). Without expr, caller displays the line number
and source filename of the current subroutine call. If a
non-negative integer is supplied as expr, caller displays
the line number, subroutine name, and source file corre‐
sponding to that position in the current execution call
stack. This extra information may be used, for example,
to print a stack trace. The current frame is frame 0.
The return value is 0 unless the shell is not executing a
subroutine call or expr does not correspond to a valid
position in the call stack.
cd [-L|[-P [-e]]] [dir]
Change the current directory to dir. The variable HOME
is the default dir. The variable CDPATH defines the
search path for the directory containing dir. Alterna‐
tive directory names in CDPATH are separated by a colon
(:). A null directory name in CDPATH is the same as the
current directory, i.e., ``.''. If dir begins with a
slash (/), then CDPATH is not used. The -P option says to
use the physical directory structure instead of following
symbolic links (see also the -P option to the set builtin
command); the -L option forces symbolic links to be fol‐
lowed. If the -e option is supplied with -P, and the
current working directory cannot be successfully deter‐
mined after a successful directory change, cd will return
an unsuccessful status. An argument of - is equivalent
to $OLDPWD. If a non-empty directory name from CDPATH is
used, or if - is the first argument, and the directory
change is successful, the absolute pathname of the new
working directory is written to the standard output. The
return value is true if the directory was successfully
changed; false otherwise.
command [-pVv] command [arg ...]
Run command with args suppressing the normal shell func‐
tion lookup. Only builtin commands or commands found in
the PATH are executed. If the -p option is given, the
search for command is performed using a default value for
PATH that is guaranteed to find all of the standard util‐
ities. 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. If the -V or -v option is sup‐
plied, the exit status is 0 if command was found, and 1
if not. If neither option is supplied and an error
occurred or command cannot be found, the exit status is
127. Otherwise, the exit status of the command builtin
is the exit status of command.
compgen [option] [word]
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 sup‐
plied, or no matches were generated.
complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action] [-G
globpat] [-W wordlist] [-F function] [-C command]
[-X filterpat] [-P prefix] [-S suffix] name [name ...]
complete -pr [-DE] [name ...]
Specify how arguments to each name should be completed.
If the -p option is supplied, or if no options are sup‐
plied, 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 specifica‐
tions. The -D option indicates that the remaining
options and actions should apply to the ``default'' com‐
mand completion; that is, completion attempted on a com‐
mand for which no completion has previously been defined.
The -E option indicates that the remaining options and
actions should apply to ``empty'' command completion;
that is, completion attempted on a blank line.
The process of applying these completion specifications
when word completion is attempted is described above
under Programmable Completion.
Other options, if specified, have the following meanings.
The arguments to the -G, -W, and -X options (and, if nec‐
essary, the -P and -S options) should be quoted to pro‐
tect 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:
bashdefault
Perform the rest of the default bash com‐
pletions if the compspec generates no
matches.
default Use readline's default filename comple‐
tion 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 file‐
name-specific processing (like adding a
slash to directory names, quoting special
characters, or suppressing trailing spa‐
ces). Intended to be used with shell
functions.
nospace Tell readline not to append a space (the
default) to words completed at the end of
the line.
plusdirs
After any matches defined by the compspec
are generated, directory name completion
is attempted and any matches are added to
the results of the other actions.
-A action
The action may be one of the following to gener‐
ate a list of possible completions:
alias Alias names. May also be specified as
-a.
arrayvar
Array variable names.
binding Readline key binding names.
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.
hostname
Hostnames, as taken from the file speci‐
fied by the HOSTFILE shell variable.
job Job names, if job control is active. May
also be specified as -j.
keyword Shell reserved words. May also be speci‐
fied as -k.
running Names of running jobs, if job control is
active.
service Service names. May also be specified as
-s.
setopt Valid arguments for the -o option to the
set builtin.
shopt Shell option names as accepted by the
shopt builtin.
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.
-C command
command is executed in a subshell environment,
and its output is used as the possible comple‐
tions.
-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.
-G globpat
The pathname expansion pattern globpat is
expanded to generate the possible completions.
-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.
-W wordlist
The wordlist is split using the characters in the
IFS special variable as delimiters, and each
resultant word is expanded. The possible comple‐
tions are the members of the resultant list which
match the word being completed.
-X filterpat
filterpat is a pattern as used for pathname
expansion. It is applied to the list of possible
completions generated by the preceding options
and arguments, and each completion matching fil‐
terpat is removed from the list. A leading ! in
filterpat negates the pattern; in this case, any
completion not matching filterpat is removed.
The return value is true unless an invalid option is sup‐
plied, an option other than -p or -r is supplied without
a name argument, an attempt is made to remove a comple‐
tion specification for a name for which no specification
exists, or an error occurs adding a completion specifica‐
tion.
compopt [-o option] [-DE] [+o option] [name]
Modify completion options for each name according to the
options, or for the currently-executing completion if no
names are supplied. If no options are given, display the
completion options for each name or the current comple‐
tion. The possible values of option are those valid for
the complete builtin described above. The -D option
indicates that the remaining options should apply to the
``default'' command completion; that is, completion
attempted on a command for which no completion has previ‐
ously been defined. The -E option indicates that the
remaining options should apply to ``empty'' command com‐
pletion; that is, completion attempted on a blank line.
The return value is true unless an invalid option is sup‐
plied, an attempt is made to modify the options for a
name for which no completion specification exists, or an
output error occurs.
continue [n]
Resume the next iteration of the enclosing for, while,
until, or select loop. If n is specified, resume at the
nth enclosing loop. n must be ≥ 1. If n is greater than
the number of enclosing loops, the last enclosing loop
(the ``top-level'' loop) is resumed. When continue is
executed inside of loop, the return value is non-zero
when n is ≤ 0; Otherwise, continue returns 0 value. When
continue is executed outside of loop, the return value is
0.
declare [-aAfFgilrtux] [-p] [name[=value] ...]
typeset [-aAfFgilrtux] [-p] [name[=value] ...]
Declare variables and/or give them attributes. If no
names are given then display the values of variables.
The -p option will display the attributes and values of
each name. When -p is used with name arguments, addi‐
tional options are ignored. When -p is supplied without
name arguments, it will display the attributes and values
of all variables having the attributes specified by the
additional options. If no other options are supplied
with -p, declare will display the attributes and values
of all shell variables. The -f option will restrict the
display to shell functions. The -F option inhibits the
display of function definitions; only the function name
and attributes are printed. If the extdebug shell option
is enabled using shopt, the source file name and line
number where the function is defined are displayed as
well. The -F option implies -f. The -g option forces
variables to be created or modified at the global scope,
even when declare is executed in a shell function. It is
ignored in all other cases. The following options can be
used to restrict output to variables with the specified
attribute or to give variables attributes:
-a Each name is an indexed array variable (see Arrays
above).
-A Each name is an associative array variable (see
Arrays above).
-f Use function names only.
-i The variable is treated as an integer; arithmetic
evaluation (see ARITHMETIC EVALUATION above) is
performed when the variable is assigned a value.
-l When the variable is assigned a value, all upper-
case characters are converted to lower-case. The
upper-case attribute is disabled.
-r Make names readonly. These names cannot then be
assigned values by subsequent assignment state‐
ments or unset.
-t Give each name the trace attribute. Traced func‐
tions inherit the DEBUG and RETURN traps from the
calling shell. The trace attribute has no special
meaning for variables.
-u When the variable is assigned a value, all lower-
case characters are converted to upper-case. The
lower-case attribute is disabled.
-x Mark names for export to subsequent commands via
the environment.
Using `+' instead of `-' turns off the attribute instead,
with the exceptions that +a may not be used to destroy an
array variable and +r will not remove the readonly
attribute. When used in a function, makes each name
local, as with the local command, unless the -g option is
supplied, If a variable name is followed by =value, the
value of the variable is set to value. The return value
is 0 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 Arrays
above), 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.
dirs [+n] [-n] [-clpv]
Without options, displays the list of currently remem‐
bered directories. The default display is on a single
line with directory names separated by spaces. Directo‐
ries are added to the list with the pushd command; the
popd command removes entries from the list.
+n Displays the nth entry counting from the left of
the list shown by dirs when invoked without
options, starting with zero.
-n Displays the nth entry counting from the right of
the list shown by dirs when invoked without
options, starting with zero.
-c Clears the directory stack by deleting all of the
entries.
-l Produces a longer listing; the default listing
format uses a tilde to denote the home directory.
-p Print the directory stack with one entry per line.
-v Print the directory stack with one entry per line,
prefixing each entry with its index in the stack.
The return value is 0 unless an invalid option is sup‐
plied or n indexes beyond the end of the directory stack.
disown [-ar] [-h] [jobspec ...]
Without options, each jobspec is removed from the table
of active jobs. If jobspec is not present, and neither
-a nor -r is supplied, the shell's notion of the current
job is used. If the -h option is given, each jobspec 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 no jobspec is present, and neither the -a nor the -r
option is supplied, the current job is used. If no job‐
spec is supplied, the -a option means to remove or mark
all jobs; the -r option without a jobspec argument
restricts operation to running jobs. The return value is
0 unless a jobspec does not specify a valid job.
echo [-neE] [arg ...]
Output the args, separated by spaces, followed by a new‐
line. The return status is always 0. If -n is speci‐
fied, the trailing newline is suppressed. If the -e
option is given, interpretation of the following back‐
slash-escaped characters is enabled. The -E option dis‐
ables 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 deter‐
mine whether or not echo expands these escape characters
by default. echo does not interpret -- to mean the end
of options. echo interprets the following escape
sequences:
\a alert (bell)
\b backspace
\c suppress further output
\e
\E an escape character
\f form feed
\n new line
\r carriage return
\t horizontal tab
\v vertical tab
\\ backslash
\0nnn the eight-bit character whose value is the octal
value nnn (zero to three octal digits)
\xHH the eight-bit character whose value is the hexa‐
decimal value HH (one or two hex digits)
\uHHHH the Unicode (ISO/IEC 10646) character whose value
is the hexadecimal value HHHH (one to four hex
digits)
\UHHHHHHHH
the Unicode (ISO/IEC 10646) character whose value
is the hexadecimal value HHHHHHHH (one to eight
hex digits)
enable [-a] [-dnps] [-f filename] [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, each name
is disabled; otherwise, names are enabled. For example,
to use the test binary found via the PATH instead of the
shell builtin version, run ``enable -n test''. 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 previously
loaded with -f. If no name arguments are given, or if
the -p option is supplied, a list of shell builtins is
printed. With no other option arguments, the list con‐
sists of all enabled shell builtins. If -n is supplied,
only disabled builtins are printed. If -a is supplied,
the list printed includes all builtins, with an indica‐
tion of whether or not each is enabled. If -s is sup‐
plied, the output is restricted to the POSIX special
builtins. The return value is 0 unless a name is not a
shell builtin or there is an error loading a new builtin
from a shared object.
eval [arg ...]
The args are read and concatenated together into a single
command. This command is then read and executed by the
shell, and its exit status is returned as the value of
eval. If there are no args, or only null arguments, eval
returns 0.
exec [-cl] [-a name] [command [arguments]]
If command is specified, it replaces the shell. No new
process is created. The arguments become the arguments
to command. If the -l option is supplied, the shell
places a dash at the beginning of the zeroth argument
passed to command. This is what login(1) does. The -c
option causes command to be executed with an empty envi‐
ronment. If -a is supplied, the shell passes name as the
zeroth argument to the executed command. If command can‐
not be executed for some reason, a non-interactive shell
exits, unless the shell option execfail is enabled, in
which case it returns failure. An interactive shell
returns failure if the file cannot be executed. If com‐
mand is not specified, any redirections take effect in
the current shell, and the return status is 0. If there
is a redirection error, the return status is 1.
exit [n]
Cause the shell to exit with a status of n. If n is
omitted, the exit status is that of the last command exe‐
cuted. A trap on EXIT is executed before the shell ter‐
minates.
export [-fn] [name[=word]] ...
export -p
The supplied names are marked for automatic export to the
environment of subsequently executed commands. If the -f
option is given, the names refer to functions. If no
names are given, or if the -p option is supplied, a list
of all names that are exported in this shell is printed.
The -n option causes the export property to be removed
from each name. If a variable name is followed by =word,
the value of the variable is set to word. export returns
an exit status of 0 unless an invalid option is encoun‐
tered, one of the names is not a valid shell variable
name, or -f is supplied with a name that is not a func‐
tion.
fc [-e ename] [-lnr] [first] [last]
fc -s [pat=rep] [cmd]
Fix Command. In the first form, a range of commands from
first to last is selected from the history list. First
and last may be specified as a string (to locate the last
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 the current command
for listing (so that ``fc -l -10'' prints the last 10
commands) and to first otherwise. If first is not speci‐
fied it is set to the previous command for editing and
-16 for listing.
The -n option suppresses the command numbers when list‐
ing. The -r option reverses the order of the commands.
If the -l option is given, the commands are listed on
standard output. Otherwise, the editor given by ename is
invoked on a file containing those commands. If ename is
not given, the value of the FCEDIT variable is used, and
the value of EDITOR if FCEDIT is not set. If neither
variable is set, vi is used. When editing is complete,
the edited commands are echoed and executed.
In the second form, command is re-executed after each
instance of pat is replaced by rep. A useful alias to
use with this is ``r="fc -s"'', so that typing ``r cc''
runs the last command beginning with ``cc'' and typing
``r'' re-executes the last command.
If the first form is used, the return value is 0 unless
an invalid option is encountered or first or last specify
history lines out of range. If the -e option is sup‐
plied, the return value is the value of the last command
executed or failure if an error occurs with the temporary
file of commands. If the second form is used, the return
status is that of the command re-executed, unless cmd
does not specify a valid history line, in which case fc
returns failure.
fg [jobspec]
Resume jobspec in the foreground, and make it the current
job. If jobspec is not present, the shell's notion of
the current job is used. The return value is that of the
command placed into the foreground, or failure if run
when job control is disabled or, when run with job con‐
trol enabled, if jobspec does not specify a valid job or
jobspec specifies a job that was started without job con‐
trol.
getopts optstring name [args]
getopts is used by shell procedures 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 characters 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 pro‐
cessed 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 char‐
acter 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.
getopts returns true if an option, specified or unspeci‐
fied, is found. It returns false if the end of options
is encountered or an error occurs.
hash [-lr] [-p filename] [-dt] [name]
Each time hash is invoked, the full pathname of the com‐
mand name is determined by searching the directories in
$PATH and remembered. Any previously-remembered pathname
is discarded. If the -p option is supplied, no path
search is performed, and filename is used as the full
file name of the command. The -r option causes the shell
to forget all remembered locations. The -d option causes
the shell to forget the remembered location of each name.
If the -t option is supplied, the full pathname to which
each name corresponds is printed. If multiple name argu‐
ments are supplied with -t, the name is printed before
the hashed full pathname. The -l option causes output to
be displayed in a format that may be reused as input. If
no arguments are given, or if only -l is supplied, infor‐
mation about remembered commands is printed. The return
status is true unless a name is not found or an invalid
option is supplied.
help [-dms] [pattern]
Display helpful information about builtin commands. If
pattern is specified, help gives detailed help on all
commands matching pattern; otherwise help for all the
builtins and shell control structures is printed.
-d Display a short description of each pattern
-m Display the description of each pattern in a man‐
page-like format
-s Display only a short usage synopsis for each pat‐
tern
The return status is 0 unless no command matches pattern.
history [n]
history -c
history -d offset
history -anrw [filename]
history -p arg [arg ...]
history -s arg [arg ...]
With no options, display the command history list with
line numbers. Lines listed with a * have been modified.
An argument of n lists only the last n lines. If the
shell variable HISTTIMEFORMAT is set and not null, it is
used as a format string for strftime(3) to display the
time stamp associated with each displayed history entry.
No intervening blank is printed between the formatted
time stamp and the history line. If filename is sup‐
plied, it is used as the name of the history file; if
not, the value of HISTFILE is used. Options, if sup‐
plied, have the following meanings:
-c Clear the history list by deleting all the
entries.
-d offset
Delete the history entry at position offset.
-a Append the ``new'' history lines (history lines
entered since the beginning of the current bash
session) to the history file.
-n Read the history lines not already read from the
history file into the current history list. These
are lines appended to the history file since the
beginning of the current bash session.
-r Read the contents of the history file and use them
as the current history.
-w Write the current history to the history file,
overwriting the history file's contents.
-p Perform history substitution on the following args
and display the result on the standard output.
Does not store the results in the history list.
Each arg must be quoted to disable normal history
expansion.
-s Store the args in the history list as a single
entry. The last command in the history list is
removed before the args are added.
If the HISTTIMEFORMAT variable is set, the time stamp
information associated with each history entry is written
to the history file, marked with the history comment
character. When the history file is read, lines begin‐
ning with the history comment character followed immedi‐
ately by a digit are interpreted as timestamps for the
previous history line. The return value is 0 unless an
invalid option is encountered, an error occurs while
reading or writing the history file, an invalid offset is
supplied as an argument to -d, or the history expansion
supplied as an argument to -p fails.
jobs [-lnprs] [ jobspec ... ]
jobs -x command [ args ... ]
The first form lists the active jobs. The options have
the following meanings:
-l List process IDs in addition to the normal infor‐
mation.
-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. The return status is 0 unless an invalid
option is encountered or an invalid jobspec is supplied.
If the -x option is supplied, jobs replaces any jobspec
found in command or args with the corresponding process
group ID, and executes command passing it args, returning
its exit status.
kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
kill -l [sigspec | exit_status]
Send the signal named by sigspec or signum to the pro‐
cesses named by pid or jobspec. sigspec is either a
case-insensitive signal name such as SIGKILL (with or
without the SIG prefix) or a signal number; signum is a
signal number. If sigspec is not present, then SIGTERM
is assumed. An argument of -l 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 0. The exit_status argument to
-l is a number specifying either a signal number or the
exit status of a process terminated by a signal. kill
returns true if at least one signal was successfully
sent, or false if an error occurs or an invalid option is
encountered.
let arg [arg ...]
Each arg is an arithmetic expression to be evaluated (see
ARITHMETIC EVALUATION above). If the last arg evaluates
to 0, let returns 1; 0 is returned otherwise.
local [option] [name[=value] ...]
For each argument, a local variable named name is cre‐
ated, and assigned value. The option can be any of the
options accepted by declare. When local is used within a
function, it causes the variable name to have a visible
scope restricted to that function and its children. With
no operands, local writes a list of local variables to
the standard output. It is an error to use local when
not within a function. The return status is 0 unless
local is used outside a function, an invalid name is sup‐
plied, or name is a readonly variable.
logout Exit a login shell.
mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C call‐
back] [-c quantum] [array]
readarray [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
callback] [-c quantum] [array]
Read lines from the standard input into the indexed array
variable array, or from file descriptor fd if the -u
option is supplied. The variable MAPFILE is the default
array. Options, if supplied, have the following mean‐
ings:
-n Copy at most count lines. If count is 0, all
lines are copied.
-O Begin assigning to array at index origin. The
default index is 0.
-s Discard the first count lines read.
-t Remove a trailing newline from each line read.
-u Read lines from file descriptor fd instead of the
standard input.
-C Evaluate callback each time quantum lines are
read. The -c option specifies quantum.
-c Specify the number of lines read between each call
to callback.
If -C is specified without -c, the default quantum is
5000. When callback is evaluated, it is supplied the
index of the next array element to be assigned and the
line to be assigned to that element as additional argu‐
ments. callback is evaluated after the line is read but
before the array element is assigned.
If not supplied with an explicit origin, mapfile will
clear array before assigning to it.
mapfile returns successfully unless an invalid option or
option argument is supplied, array is invalid or
unassignable, or if array is not an indexed array.
popd [-n] [+n] [-n]
Removes entries from the directory stack. With no argu‐
ments, removes the top directory from the stack, and per‐
forms a cd to the new top directory. Arguments, if sup‐
plied, have the following meanings:
-n Suppresses the normal change of directory when
removing directories from the stack, so that only
the stack is manipulated.
+n Removes the nth entry counting from the left of
the list shown by dirs, starting with zero. For
example: ``popd +0'' removes the first directory,
``popd +1'' the second.
-n Removes the nth entry counting from the right of
the list shown by dirs, starting with zero. For
example: ``popd -0'' removes the last directory,
``popd -1'' the next to last.
If the popd command is successful, a dirs is performed as
well, and the return status is 0. popd returns false if
an invalid option is encountered, the directory stack is
empty, a non-existent directory stack entry is specified,
or the directory change fails.
printf [-v var] format [arguments]
Write the formatted arguments to the standard output
under the control of the format. The -v option causes
the output to be assigned to the variable var rather than
being printed to the standard output.
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) format specifications, printf inter‐
prets the following extensions:
%b causes printf to expand backslash escape sequences
in the corresponding argument (except that \c ter‐
minates output, backslashes in \', \", and \? are
not removed, and octal escapes beginning with \0
may contain up to four digits).
%q causes printf to output the corresponding argument
in a format that can be reused as shell input.
%(datefmt)T
causes printf to output the date-time string
resulting from using datefmt as a format string
for strftime(3). The corresponding argument is an
integer representing the number of seconds since
the epoch. Two special argument values may be
used: -1 represents the current time, and -2 rep‐
resents the time the shell was invoked.
Arguments to non-string format specifiers are treated as
C constants, except that a leading plus or minus sign is
allowed, and if the leading character is a single or dou‐
ble quote, the value is the ASCII value of the following
character.
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.
pushd [-n] [+n] [-n]
pushd [-n] [dir]
Adds a directory to the top of the directory stack, or
rotates the stack, making the new top of the stack the
current working directory. With no arguments, exchanges
the top two directories and returns 0, unless the direc‐
tory stack is empty. Arguments, if supplied, have the
following meanings:
-n Suppresses the normal change of directory when
adding directories to the stack, so that only the
stack is manipulated.
+n Rotates the stack so that the nth directory
(counting from the left of the list shown by dirs,
starting with zero) is at the top.
-n Rotates the stack so that the nth directory
(counting from the right of the list shown by
dirs, starting with zero) is at the top.
dir Adds dir to the directory stack at the top, making
it the new current working directory.
If the pushd command is successful, a dirs is performed
as well. If the first form is used, pushd returns 0
unless the cd to dir fails. With the second form, pushd
returns 0 unless the directory stack is empty, a non-
existent directory stack element is specified, or the
directory change to the specified new current directory
fails.
pwd [-LP]
Print the absolute pathname of the current working direc‐
tory. The pathname printed contains no symbolic links if
the -P option is supplied or the -o physical option to
the set builtin command is enabled. If the -L option is
used, the pathname printed may contain symbolic links.
The return status is 0 unless an error occurs while read‐
ing the name of the current directory or an invalid
option is supplied.
read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N
nchars] [-p prompt] [-t timeout] [-u fd] [name ...]
One line is read from the standard input, or from the
file descriptor fd supplied as an argument to the -u
option, and the first word is assigned to the first name,
the second word to the second name, and so on, with left‐
over words and their intervening separators assigned to
the last name. If there are fewer words read from the
input stream than names, the remaining names are assigned
empty values. The characters in IFS 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. Options, if supplied,
have the following meanings:
-a aname
The words are assigned to sequential indices of
the array variable aname, starting at 0. aname is
unset before any new values are assigned. Other
name arguments are ignored.
-d delim
The first character of delim is used to terminate
the input line, rather than newline.
-e If the standard input is coming from a terminal,
readline (see READLINE above) is used to obtain
the line. Readline uses the current (or default,
if line editing was not previously active) editing
settings.
-i text
If readline is being used to read the line, text
is placed into the editing buffer before editing
begins.
-n nchars
read returns after reading nchars characters
rather than waiting for a complete line of input,
but honor a delimiter if fewer than nchars charac‐
ters are read before the delimiter.
-N nchars
read returns after reading exactly nchars charac‐
ters rather than waiting for a complete line of
input, unless EOF is encountered or read times
out. Delimiter characters encountered in the
input are not treated specially and do not cause
read to return until nchars characters are read.
-p prompt
Display prompt on standard error, without a trail‐
ing newline, before attempting to read any input.
The prompt is displayed only if input is coming
from a terminal.
-r 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. timeout may be a decimal number with a
fractional portion following the decimal point.
This option is only effective if read is reading
input from a terminal, pipe, or other special
file; it has no effect when reading from regular
files. If timeout is 0, read returns success if
input is available on the specified file descrip‐
tor, failure otherwise. The exit status is
greater than 128 if the timeout is exceeded.
-u fd Read input from file descriptor fd.
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, read times out (in which case the
return code is greater than 128), or an invalid file
descriptor is supplied as the argument to -u.
readonly [-aAf] [-p] [name[=word] ...]
The given names are marked readonly; the values of these
names may not be changed by subsequent assignment. If
the -f option is supplied, the functions corresponding to
the names are so marked. The -a option restricts the
variables to indexed arrays; the -A option restricts the
variables to associative arrays. If both options are
supplied, -A takes precedence. If no name arguments are
given, or if the -p option is supplied, a list of all
readonly names is printed. The other options may be used
to restrict the output to a subset of the set of readonly
names. The -p option causes output to be displayed in a
format that may be reused as input. If a variable name
is followed by =word, the value of the variable is set to
word. The return status is 0 unless an invalid option is
encountered, one of the names is not a valid shell vari‐
able name, or -f is supplied with a name that is not a
function.
return [n]
Causes a function to exit with the return value specified
by n. If n is omitted, the return status is that of the
last command executed in the function body. If used out‐
side a function, but during execution of a script by the
. (source) command, it causes the shell to stop execut‐
ing that script and return either n or the exit status of
the last command executed within the script as the exit
status of the script. If used outside a function and not
during execution of a script by ., the return status is
false. Any command associated with the RETURN trap is
executed before execution resumes after the function or
script.
set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
Without options, the name and value of each shell vari‐
able are displayed in a format that can be reused as
input for setting or resetting the currently-set vari‐
ables. Read-only variables cannot be reset. In posix
mode, only shell variables are listed. The output is
sorted according to the current locale. When options are
specified, they set or unset shell attributes. Any argu‐
ments remaining after option processing are treated as
values for the positional parameters and are assigned, in
order, to $1, $2, ... $n. Options, if specified, have
the following meanings:
-a Automatically mark variables and functions which
are modified or created for export to the envi‐
ronment of subsequent commands.
-b Report the status of terminated background jobs
immediately, rather than before the next primary
prompt. This is effective only when job control
is enabled.
-e Exit immediately if a pipeline (which may consist
of a single simple command), a subshell command
enclosed in parentheses, or one of the commands
executed as part of a command list enclosed by
braces (see SHELL GRAMMAR above) exits with a
non-zero status. The shell does not exit if the
command that fails is part of the command list
immediately following a while or until keyword,
part of the test following the if or elif
reserved words, part of any command executed in a
&& or || list except the command following the
final && or ||, any command in a pipeline but the
last, or if the command's return value is being
inverted with !. A trap on ERR, if set, is exe‐
cuted before the shell exits. This option
applies to the shell environment and each sub‐
shell environment separately (see COMMAND EXECU‐
TION ENVIRONMENT above), and may cause subshells
to exit before executing all the commands in the
subshell.
-f Disable pathname expansion.
-h Remember the location of commands as they are
looked up for execution. This is enabled by
default.
-k All arguments in the form of assignment state‐
ments are placed in the environment for a com‐
mand, not just those that precede the command
name.
-m Monitor mode. Job control is enabled. This
option is on by default for interactive shells on
systems that support it (see JOB CONTROL above).
Background processes run in a separate process
group and a line containing their exit status is
printed upon their completion.
-n Read commands but do not execute them. This may
be used to check a shell script for syntax
errors. This is ignored by interactive shells.
-o option-name
The option-name can be one of the following:
allexport
Same as -a.
braceexpand
Same as -B.
emacs Use an emacs-style command line editing
interface. This is enabled by default
when the shell is interactive, unless the
shell is started with the --noediting
option. This also affects the editing
interface used for read -e.
errexit Same as -e.
errtrace
Same as -E.
functrace
Same as -T.
hashall Same as -h.
histexpand
Same as -H.
history Enable command history, as described
above under HISTORY. This option is on
by default in interactive shells.
ignoreeof
The effect is as if the shell command
``IGNOREEOF=10'' had been executed (see
Shell Variables above).
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.
pipefail
If set, the return value of a pipeline is
the value of the last (rightmost) command
to exit with a non-zero status, or zero
if all commands in the pipeline exit suc‐
cessfully. This option is disabled by
default.
posix Change the behavior of bash where the
default operation differs from the POSIX
standard to match the standard (posix
mode).
privileged
Same as -p.
verbose Same as -v.
vi Use a vi-style command line editing
interface. This also affects the editing
interface used for read -e.
xtrace Same as -x.
If -o is supplied with no option-name, the values
of the current options are printed. If +o is
supplied with no option-name, a series of set
commands to recreate the current option settings
is displayed on the standard output.
-p Turn on privileged mode. In this mode, the $ENV
and $BASH_ENV files are not processed, shell
functions are not inherited from the environment,
and the SHELLOPTS, BASHOPTS, CDPATH, and GLOBIG‐
NORE variables, if they appear in the environ‐
ment, are 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 effec‐
tive 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 and parameters other than
the special parameters "@" and "*" as an error
when performing parameter expansion. If expan‐
sion is attempted on an unset variable or parame‐
ter, the shell prints an error message, and, if
not interactive, exits with a non-zero status.
-v Print shell input lines as they are read.
-x After expanding each simple command, for command,
case command, select command, or arithmetic for
command, display the expanded value of PS4, fol‐
lowed by the command and its expanded arguments
or associated word list.
-B The shell performs brace expansion (see Brace
Expansion above). This is on by default.
-C If set, bash does not overwrite an existing file
with the >, >&, and <> redirection operators.
This may be overridden when creating output files
by using the redirection operator >| instead of
>.
-E If set, any trap on ERR is inherited by shell
functions, command substitutions, and commands
executed in a subshell environment. The ERR trap
is normally not inherited in such cases.
-H Enable ! style history substitution. This
option is on by default when the shell is inter‐
active.
-P If set, the shell does not follow symbolic links
when executing commands such as cd that change
the current working directory. It uses the phys‐
ical directory structure instead. By default,
bash follows the logical chain of directories
when performing commands which change the current
directory.
-T If set, any traps on DEBUG and RETURN are inher‐
ited by shell functions, command substitutions,
and commands executed in a subshell environment.
The DEBUG and RETURN traps are normally not
inherited in such cases.
-- If no arguments follow this option, then the
positional parameters are unset. Otherwise, the
positional parameters are set to the args, even
if some of them begin with a -.
- Signal the end of options, cause all remaining
args to be assigned to the positional parameters.
The -x and -v options are turned off. If there
are no args, the positional parameters remain
unchanged.
The options are off by default unless otherwise noted.
Using + rather than - causes these options to be turned
off. The options can also be specified as arguments to
an invocation of the shell. The current set of options
may be found in $-. The return status is always true
unless an invalid option is encountered.
shift [n]
The positional parameters from n+1 ... are renamed to $1
.... Parameters represented by the numbers $# down to
$#-n+1 are unset. n must be a non-negative number less
than or equal to $#. If n is 0, no parameters are
changed. If n is not given, it is assumed to be 1. If n
is greater than $#, the positional parameters are not
changed. The return status is greater than zero if n is
greater than $# or less than zero; otherwise 0.
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 out‐
put 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 (quiet mode); 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.
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 (unset) 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:
autocd If set, a command name that is the name of a
directory is executed as if it were the argument
to the cd command. This option is only used by
interactive shells.
cdable_vars
If 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 direc‐
tory component in a cd command will be corrected.
The errors checked for are transposed characters,
a missing character, and one character too many.
If a correction is found, the corrected file name
is printed, and the command proceeds. This
option is only used by interactive shells.
checkhash
If 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.
checkjobs
If set, bash lists the status of any stopped and
running jobs before exiting an interactive shell.
If any jobs are running, this causes the exit to
be deferred until a second exit is attempted
without an intervening command (see JOB CONTROL
above). The shell always postpones exiting if
any jobs are stopped.
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 mul‐
tiple-line command in the same history entry.
This allows easy re-editing of multi-line com‐
mands.
compat31
If set, bash changes its behavior to that of ver‐
sion 3.1 with respect to quoted arguments to the
[[ conditional command's =~ operator.
compat32
If set, bash changes its behavior to that of ver‐
sion 3.2 with respect to locale-specific string
comparison when using the [[ conditional com‐
mand's < and > operators. Bash versions prior to
bash-4.1 use ASCII collation and strcmp(3);
bash-4.1 and later use the current locale's col‐
lation sequence and strcoll(3).
compat40
If set, bash changes its behavior to that of ver‐
sion 4.0 with respect to locale-specific string
comparison when using the [[ conditional com‐
mand's < and > operators (see previous item) and
the effect of interrupting a command list.
compat41
If set, bash, when in posix mode, treats a single
quote in a double-quoted parameter expansion as a
special character. The single quotes must match
(an even number) and the characters between the
single quotes are considered quoted. This is the
behavior of posix mode through version 4.1. The
default bash behavior remains as in previous ver‐
sions.
direxpand
If set, bash replaces directory names with the
results of word expansion when performing file‐
name completion. This changes the contents of
the readline editing buffer. If not set, bash
attempts to preserve what the user typed.
dirspell
If set, bash attempts spelling correction on
directory names during word completion if the
directory name initially supplied does not exist.
dotglob If set, bash includes filenames beginning with a
`.' in the results of pathname expansion.
execfail
If set, a non-interactive shell will not exit if
it cannot execute the file specified as an argu‐
ment to the exec builtin command. An interactive
shell does not exit if exec fails.
expand_aliases
If set, aliases are expanded as described above
under ALIASES. This option is enabled by default
for interactive shells.
extdebug
If set, behavior intended for use by debuggers is
enabled:
1. The -F option to the declare builtin dis‐
plays the source file name and line number
corresponding to each function name sup‐
plied as an argument.
2. If the command run by the DEBUG trap
returns a non-zero value, the next command
is skipped and not executed.
3. If the command run by the DEBUG trap
returns a value of 2, and the shell is
executing in a subroutine (a shell func‐
tion or a shell script executed by the .
or source builtins), a call to return is
simulated.
4. BASH_ARGC and BASH_ARGV are updated as
described in their descriptions above.
5. Function tracing is enabled: command sub‐
stitution, shell functions, and subshells
invoked with ( command ) inherit the DEBUG
and RETURN traps.
6. Error tracing is enabled: command substi‐
tution, shell functions, and subshells
invoked with ( command ) inherit the ERR
trap.
extglob If set, the extended pattern matching features
described above under Pathname Expansion are
enabled.
extquote
If set, $'string' and $"string" quoting is per‐
formed within ${parameter} expansions enclosed in
double quotes. This option is enabled by
default.
failglob
If set, patterns which fail to match filenames
during pathname expansion result in an expansion
error.
force_fignore
If set, the suffixes specified by the FIGNORE
shell variable cause words to be ignored when
performing word completion even if the ignored
words are the only possible completions. See
SHELL VARIABLES above for a description of FIG‐
NORE. This option is enabled by default.
globstar
If set, the pattern ** used in a pathname expan‐
sion context will match all files and zero or
more directories and subdirectories. If the pat‐
tern is followed by a /, only directories and
subdirectories match.
gnu_errfmt
If set, shell error messages are written in the
standard GNU error message format.
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 result‐
ing line is loaded into the readline editing buf‐
fer, 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 Com‐
pleting under READLINE above). This is enabled
by default.
huponexit
If set, bash will send SIGHUP to all jobs when an
interactive login shell exits.
interactive_comments
If set, allow a word beginning with # to cause
that word and all remaining characters on that
line to be ignored in an interactive shell (see
COMMENTS above). This option is enabled by
default.
lastpipe
If set, and job control is not active, the shell
runs the last command of a pipeline not executed
in the background in the current shell environ‐
ment.
lithist If set, 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 INVOCATION above). 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 comple‐
tions when completion is attempted on an empty
line.
nocaseglob
If set, bash matches filenames in a case-insensi‐
tive fashion when performing pathname expansion
(see Pathname Expansion above).
nocasematch
If set, bash matches patterns in a case-insensi‐
tive fashion when performing matching while exe‐
cuting case or [[ conditional commands.
nullglob
If set, bash allows patterns which match no files
(see Pathname Expansion above) to expand to a
null string, rather than themselves.
progcomp
If set, the programmable completion facilities
(see Programmable Completion above) are enabled.
This option is enabled by default.
promptvars
If set, prompt strings undergo parameter expan‐
sion, command substitution, arithmetic expansion,
and quote removal after being expanded as
described in PROMPTING above. This option is
enabled by default.
restricted_shell
The shell sets this option if it is started in
restricted mode (see RESTRICTED SHELL below).
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 set, the shift builtin prints an error message
when the shift count exceeds the number of posi‐
tional 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.
syslog_history
If set, command history is logged to syslog.
xpg_echo
If set, the echo builtin expands backslash-escape
sequences by default.
suspend [-f]
Suspend the execution of this shell until it receives a
SIGCONT signal. When the suspended shell is a background
process, it can be restarted by the fg command. For more
information, read the JOB CONTROL section. The suspend
command can not suspend the login shell. However, when -f
option is specified, suspend command can suspend even
login shell. The return status is 0 unless the shell is
a login shell and -f is not supplied, or if job control
is not enabled.
test expr
[ expr ]
Return a status of 0 or 1 depending on the evaluation of
the conditional expression expr. Each operator and oper‐
and must be a separate argument. Expressions are com‐
posed of the primaries described above under CONDITIONAL
EXPRESSIONS. test does not accept any options, nor does
it accept and ignore an argument of -- as signifying the
end of options.
Expressions may be combined using the following opera‐
tors, listed in decreasing order of precedence. The
evaluation depends on the number of arguments; see below.
Operator precedence is used when there are five or more
arguments.
! 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.
test and [ 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 listed above under CONDITIONAL EXPRES‐
SIONS, the expression is true if the unary test is
true. If the first argument is not a valid unary
conditional operator, the expression is false.
3 arguments
The following conditions are applied in the order
listed. If the second argument is one of the
binary conditional operators listed above under
CONDITIONAL EXPRESSIONS, the result of the expres‐
sion is the result of the binary test using the
first and third arguments as operands. The -a and
-o operators are considered binary operators when
there are three arguments. If the first argument
is !, the value is the negation of the two-argu‐
ment test using the second and third arguments.
If the first argument is exactly ( and the third
argument is exactly ), the result is the one-argu‐
ment test of the second argument. Otherwise, the
expression is false.
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.
When used with test or [, the < and > operators sort lex‐
icographically using ASCII ordering.
times Print the accumulated user and system times for the shell
and for processes run from the shell. The return status
is 0.
trap [-lp] [[arg] sigspec ...]
The command arg is to be read and executed when the shell
receives signal(s) sigspec. If arg is absent (and there
is a single sigspec) or -, each specified signal is reset
to its original disposition (the value it had upon
entrance to the shell). If arg is the null string the
signal specified by each sigspec is ignored by the shell
and by the commands it invokes. If arg is not present
and -p has been supplied, then the trap commands associ‐
ated with each sigspec are displayed. If no arguments
are supplied or if only -p is given, trap prints the list
of commands associated with each signal. The -l option
causes the shell to print a list of signal names and
their corresponding numbers. Each sigspec is either a
signal name defined in <signal.h>, or a signal number.
Signal names are case insensitive and the SIG prefix is
optional.
If a sigspec is EXIT (0) the command arg is executed on
exit from the shell. If a sigspec is DEBUG, the command
arg is executed before every simple command, for command,
case command, select command, every arithmetic for com‐
mand, and before the first command executes in a shell
function (see SHELL GRAMMAR above). Refer to the
description of the extdebug option to the shopt builtin
for details of its effect on the DEBUG trap. If a
sigspec is RETURN, the command arg is executed each time
a shell function or a script executed with the . or
source builtins finishes executing.
If a sigspec is ERR, the command arg is executed whenever
a simple command has a non-zero exit status, subject to
the following conditions. The ERR trap is not executed
if the failed command is part of the command list immedi‐
ately following a while or until keyword, part of the
test in an if statement, part of a command executed in a
&& or || list, or if the command's return value is being
inverted via !. These are the same conditions obeyed by
the errexit option.
Signals ignored upon entry to the shell cannot be
trapped, reset or listed. Trapped signals that are not
being ignored are reset to their original values in a
subshell or subshell environment when one is created.
The return status is false if any sigspec is invalid;
otherwise trap returns true.
type [-aftpP] name [name ...]
With no options, indicate how each name would be inter‐
preted if used as a command name. If the -t option is
used, type prints a string which is one of alias, key‐
word, function, builtin, or file if name is an alias,
shell reserved word, function, builtin, or disk file,
respectively. If the name is not found, then nothing is
printed, and an exit status of false is returned. If the
-p option is used, type either returns the name of the
disk file that would be executed if name were specified
as a command name, or nothing if ``type -t name'' would
not return file. The -P option forces a PATH search for
each name, even if ``type -t name'' would not return
file. If a command is hashed, -p and -P print the hashed
value, not necessarily the file that appears first in
PATH. If the -a option is used, type prints all of the
places that contain an executable named name. This
includes aliases and functions, if and only if the -p
option is not also used. The table of hashed commands is
not consulted when using -a. The -f option suppresses
shell function lookup, as with the command builtin. type
returns true if all of the arguments are found, false if
any are not found.
ulimit [-HSTabcdefilmnpqrstuvx [limit]]
Provides control over the resources available to the
shell and to processes started by it, on systems that
allow such control. The -H and -S options specify that
the hard or soft limit is set for the given resource. A
hard limit cannot be increased by a non-root user once it
is set; a soft limit may be increased up to the value of
the hard limit. If neither -H nor -S is specified, both
the soft and hard limits are set. The value of limit can
be a number in the unit specified for the resource or one
of the special values hard, soft, or unlimited, which
stand for the current hard limit, the current soft limit,
and no limit, respectively. If limit is omitted, the
current value of the soft limit of the resource is
printed, unless the -H option is given. When more than
one resource is specified, the limit name and unit are
printed before the value. Other options are interpreted
as follows:
-a All current limits are reported
-b The maximum socket buffer size
-c The maximum size of core files created
-d The maximum size of a process's data segment
-e The maximum scheduling priority ("nice")
-f The maximum size of files written by the shell and
its children
-i The maximum number of pending signals
-l The maximum size that may be locked into memory
-m The maximum resident set size (many systems do not
honor this limit)
-n The maximum number of open file descriptors (most
systems do not allow this value to be set)
-p The pipe size in 512-byte blocks (this may not be
set)
-q The maximum number of bytes in POSIX message
queues
-r The maximum real-time scheduling priority
-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 shell and, on some systems, to its children
-x The maximum number of file locks
-T The maximum number of threads
If limit is given, it is the new value of the specified
resource (the -a option is display only). 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 -T, -b, -n, and -u,
which are unscaled values. The return status is 0 unless
an invalid option or argument is supplied, or an error
occurs while setting a new limit. In POSIX Mode 512-byte
blocks are used for the `-c' and `-f' options.
umask [-p] [-S] [mode]
The user file-creation mask is set to mode. If mode
begins with a digit, it is interpreted as an octal num‐
ber; otherwise it is interpreted as a symbolic mode mask
similar to that accepted by chmod(1). If mode is omit‐
ted, the current value of the mask is printed. The -S
option causes the mask to be printed in symbolic form;
the default output is an octal number. 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 0 if
the mode was successfully changed or if no mode argument
was supplied, and false otherwise.
unalias [-a] [name ...]
Remove each name from the list of defined aliases. If -a
is supplied, all alias definitions are removed. The
return value is true unless a supplied name is not a
defined alias.
unset [-fv] [name ...]
For each name, remove the corresponding variable or func‐
tion. If no options are supplied, or the -v option is
given, each name refers to a shell variable. Read-only
variables may not be unset. If -f is specified, each
name refers to a shell function, and the function defini‐
tion is removed. Each unset variable or function is
removed from the environment passed to subsequent com‐
mands. If any of COMP_WORDBREAKS, RANDOM, SECONDS,
LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are unset,
they lose their special properties, even if they are sub‐
sequently reset. The exit status is true unless a name
is readonly.
wait [n ...]
Wait for each specified process and return its termina‐
tion status. Each n may be a process ID or a job speci‐
fication; if a job spec is given, all processes in that
job's pipeline are waited for. If n is not given, all
currently active child processes are waited for, and the
return status is zero. If n specifies a non-existent
process or job, the return status is 127. Otherwise, the
return status is the exit status of the last process or
job waited for.
RESTRICTED SHELL
If bash is started with the name rbash, or the -r option is sup‐
plied at invocation, the shell becomes restricted. A restricted
shell is used to set up an environment more controlled than the
standard shell. It behaves identically to bash with the excep‐
tion that the following are disallowed or not performed:
· changing directories with cd
· setting or unsetting the values of SHELL, PATH, ENV, or
BASH_ENV
· specifying command names containing /
· specifying a file name containing a / 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 command to replace the shell with
another command
· adding or deleting builtin commands with the -f and -d
options to the enable builtin command
· using the enable builtin command to enable disabled shell
builtins
· specifying the -p option to the command builtin command
· turning off restricted mode with set +r or set +o
restricted.
These restrictions are enforced after any startup files are
read.
When a command that is found to be a shell script is executed
(see COMMAND EXECUTION above), rbash turns off any restrictions
in the shell spawned to execute the script.
SEE ALSO
Bash Reference Manual, Brian Fox and Chet Ramey
The Gnu Readline Library, Brian Fox and Chet Ramey
The Gnu History Library, Brian Fox and Chet Ramey
Portable Operating System Interface (POSIX) Part 2: Shell and
Utilities, IEEE
sh(1), ksh(1), csh(1)
emacs(1), vi(1)
readline(3)
FILES
/bin/bash
The bash executable
/etc/profile
The systemwide initialization file, executed for login
shells
/etc/bash.bash_logout
The systemwide login shell cleanup file, executed when a
login shell exits
~/.bash_profile
The personal initialization file, executed for login
shells
~/.bashrc
The individual per-interactive-shell startup file
~/.bash_logout
The individual login shell cleanup file, executed when a
login shell exits
~/.inputrc
Individual readline initialization file
AUTHORS
Brian Fox, Free Software Foundation
bfox@gnu.org
Chet Ramey, Case Western Reserve University
chet.ramey@case.edu
BUG REPORTS
If you find a bug in bash, you should report it. But first, you
should make sure that it really is a bug, and that it appears in
the latest version of bash. The latest version is always avail‐
able from ftp://ftp.gnu.org/pub/gnu/bash/.
Once you have determined that a bug actually exists, use the
bashbug command (from the source package) 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
A description of the bug behaviour
A short script or `recipe' which exercises the bug
Comments and bug reports concerning this manual page should be
directed to chet.ramey@case.edu.
BUGS
It's too big and too slow.
There are some subtle differences between bash and traditional
versions of sh, mostly because of the POSIX specification.
Aliases are confusing in some uses.
Shell builtin commands and functions are not stop‐
pable/restartable.
Compound commands and command sequences of the form `a ; b ; c'
are not handled gracefully when process suspension is attempted.
When a process is stopped, the shell immediately executes the
next command in the sequence. It suffices to place the sequence
of commands between parentheses to force it into a subshell,
which may be stopped as a unit.
Array variables may not (yet) be exported.
There may be only one active coprocess at a time.
GNU Bash-4.2 2010 December 28 BASH(1)
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