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BASH(1) General Commands Manual BASH(1)
bash - GNU Bourne-Again SHell
bash [options] [command_string | file]
Bash is Copyright (C) 1989-2022 by the Free Software Foundation,
Inc.
Bash is an sh-compatible command language interpreter that
executes 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.
All of the single-character shell options documented in the
description of the set builtin command, including -o, can be used
as options when the shell is invoked. In addition, bash
interprets the following options when it is invoked:
-c If the -c option is present, then commands are read from
the first non-option argument command_string. If there
are arguments after the command_string, the first argument
is assigned to $0 and any remaining arguments are assigned
to the positional parameters. The assignment to $0 sets
the name of the shell, which is used in warning and error
messages.
-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 or
when reading input through a pipe.
-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 current
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 supplied, the names
and values of the shell options accepted by shopt are
printed on the standard output. If the invocation option
is +O, the output is displayed in a format that may be
reused as input.
-- A -- signals the end of options and disables further
option processing. Any arguments after the -- are treated
as filenames and arguments. 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-
character 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
successfully.
--init-file file
--rcfile file
Execute commands from file instead of the standard
personal 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/profile 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). See SEE ALSO below for a reference to a
document that details how posix mode affects bash's
behavior.
--restricted
The shell becomes restricted (see RESTRICTED SHELL below).
--verbose
Equivalent to -v.
--version
Show version information for this instance of bash on the
standard output and exit successfully.
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.
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
(unless -s is specified) 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 $- includes i if bash is interactive, allowing a shell
script or a startup file to test this state.
The following paragraphs describe how bash executes its startup
files. If any of the files exist but cannot be read, bash
reports an error. Tildes are expanded in filenames as described
below under Tilde Expansion in the EXPANSION section.
When bash is invoked as an interactive login shell, or as a non-
interactive shell with the --login option, it first reads and
executes commands from the file /etc/profile, if that file
exists. After reading that file, it looks for ~/.bash_profile,
~/.bash_login, and ~/.profile, in that order, and reads and
executes commands from the first one that exists and is readable.
The --noprofile option may be used when the shell is started to
inhibit this behavior.
When an interactive login shell exits, or a non-interactive login
shell executes the exit builtin command, bash reads and executes
commands from the file ~/.bash_logout, if it exists.
When an interactive shell that is not a login shell is started,
bash reads and executes commands from ~/.bashrc, if that file
exists. This may be inhibited by using the --norc option. The
--rcfile file option will force bash to read and execute commands
from file instead of ~/.bashrc.
When bash is started non-interactively, to run a shell script,
for example, it looks for the variable BASH_ENV in the
environment, expands its value if it appears there, and uses the
expanded value as the name of a file to read and execute. Bash
behaves as if the following command were executed:
if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
but the value of the PATH variable is not used to search for the
filename.
If bash is invoked with the name sh, it tries to mimic the
startup behavior of historical versions of sh as closely as
possible, while conforming to the POSIX standard as well. When
invoked as an interactive login shell, or 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 standard
input connected to a network connection, as when executed by the
historical remote shell daemon, usually rshd, or the secure shell
daemon sshd. If bash determines it is being run non-
interactively in this fashion, 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 neither rshd nor sshd
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
supplied, no startup files are read, shell functions are not
inherited 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.
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 newline
control operator
A token that performs a control function. It is one of
the following symbols:
|| & && ; ;; ;& ;;& ( ) | |& <newline>
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 command (see SHELL
GRAMMAR below), the third word of a case or select command (only
in is valid), or the third word of a for command (only in and do
are valid):
! case coproc do done elif else esac fi for function if in
select then until while { } time [[ ]]
This section describes the syntax of the various forms of shell
commands.
Simple Commands
A simple command is a sequence of optional variable assignments
followed by blank-separated words and redirections, and
terminated by a control operator. The first word specifies the
command 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]] [ ! ] command1 [ [|⎪|&] command2 ... ]
The standard output of command1 is connected via a pipe to the
standard input of command2. This connection is performed before
any redirections specified by the command1(see REDIRECTION
below). If |& is used, command1's standard error, in addition to
its standard output, is connected to command2's standard input
through the pipe; it is shorthand for 2>&1 |. This implicit
redirection of the standard error to the standard output is
performed after any redirections specified by command1.
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 ! precedes
a pipeline, the exit status of that pipeline is the logical
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 information
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
newline. In this case, the shell displays the total user and
system time consumed by the shell and its children. The
TIMEFORMAT variable may be used to specify the format of the time
information.
Each command in a multi-command pipeline, where pipes are
created, is executed in a subshell, which is a separate process.
See COMMAND EXECUTION ENVIRONMENT for a description of subshells
and a subshell environment. If the lastpipe option is enabled
using the shopt builtin (see the description of shopt below), the
last element of a pipeline may be run by the shell process when
job control is not active.
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,
followed 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. These are referred to as asynchronous commands. 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 or more pipelines separated
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 (success).
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. In most cases a list
in a command's description may be separated from the rest of the
command by one or more newlines, and may be followed by a newline
in place of a semicolon.
(list) list is executed in a subshell (see COMMAND EXECUTION
ENVIRONMENT below for a description of a subshell
environment). 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 metacharacters
( 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 separated from
list by whitespace or another shell metacharacter.
((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. The expression
undergoes the same expansions as if it were within double
quotes, but double quote characters in expression are not
treated specially and are removed.
[[ 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
CONDITIONAL EXPRESSIONS. The words between the [[ and ]]
do not undergo word splitting and pathname expansion. The
shell performs tilde expansion, parameter and variable
expansion, arithmetic expansion, command substitution,
process substitution, and quote removal on those words
(the expansions that would occur if the words were
enclosed in double quotes). Conditional operators such as
-f must be unquoted to be recognized as primaries.
When used with [[, the < and > operators sort
lexicographically 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, as if the extglob shell option were enabled.
The = operator is equivalent to ==. If the nocasematch
shell option 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 the quoted portion 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 a POSIX
extended regular expression and matched accordingly (using
the POSIX regcomp and regexec interfaces usually described
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 nocasematch shell option is
enabled, the match is performed without regard to the case
of alphabetic characters. If any part of the pattern is
quoted, the quoted portion is matched literally. This
means every character in the quoted portion matches
itself, instead of having any special pattern matching
meaning. If the pattern is stored in a shell variable,
quoting the variable expansion forces the entire pattern
to be matched literally. Treat bracket expressions in
regular expressions carefully, since normal quoting and
pattern characters lose their meanings between brackets.
The pattern will match if it matches any part of the
string. Anchor the pattern using the ^ and $ regular
expression operators to force it to match the entire
string. The array variable BASH_REMATCH records which
parts of the string matched the pattern. The element of
BASH_REMATCH with index 0 contains the portion of the
string matching the entire regular expression. Substrings
matched by parenthesized subexpressions within the regular
expression are saved in the remaining BASH_REMATCH
indices. The element of BASH_REMATCH with index n is the
portion of the string matching the nth parenthesized
subexpression. Bash sets BASH_REMATCH in the global
scope; declaring it as a local variable will lead to
unexpected results.
Expressions may be combined using the following operators,
listed in decreasing order of precedence:
( expression )
Returns the value of expression. This may be used
to override the normal precedence of operators.
! expression
True if expression is false.
expression1 && expression2
True if both expression1 and expression2 are true.
expression1 || expression2
True if either expression1 or expression2 is true.
The && and || 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 commands 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 executed
and the arithmetic expression expr3 is evaluated. If any
expression is omitted, it behaves as if it evaluates to 1.
The return value is the exit status of the last command in
list that is executed, or false if any of the expressions
is invalid.
select name [ in word ] ; do list ; done
The list of words following in is expanded, generating a
list of items, and 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). select then displays the PS3
prompt and reads a line from the standard input. If the
line consists of a number corresponding to one of the
displayed words, then the value of name is set to that
word. If the line is empty, the words and prompt are
displayed again. If EOF is read, the select command
completes and returns 1. 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 matching rules
described under Pattern Matching below. The word is
expanded using tilde expansion, parameter and variable
expansion, arithmetic expansion, command substitution,
process substitution and quote removal. Each pattern
examined is expanded using tilde expansion, parameter and
variable expansion, arithmetic expansion, command
substitution, process substitution, and quote removal. If
the nocasematch shell option 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 execution 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, continuing the case
statement execution as if the pattern list had not
matched. The exit status is zero if no pattern matches.
Otherwise, it is the exit status of the last command
executed 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
executed in turn, and if its exit status is zero, the
corresponding 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 executed, 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 syntax for a coprocess is:
coproc [NAME] command [redirections]
This creates a coprocess named NAME. command may be either a
simple command or a compound command (see above). NAME is a
shell variable name. If NAME is not supplied, the default name
is COPROC.
The recommended form to use for a coprocess is
coproc NAME { command [redirections]; }
This form is recommended because simple commands result in the
coprocess always being named COPROC, and it is simpler to use and
more complete than the other compound commands.
If command is a compound command, NAME is optional. The word
following coproc determines whether that word is interpreted as a
variable name: it is interpreted as NAME if it is not a reserved
word that introduces a compound command. If command is a simple
command, NAME is not allowed; this is to avoid confusion between
NAME and the first word of the simple command.
When the coprocess 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 established before any redirections specified by the
command (see REDIRECTION below). The file descriptors can be
utilized as arguments to shell commands and redirections using
standard word expansions. Other than those created to execute
command and process substitutions, the file descriptors are not
available in subshells.
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.
Since the coprocess is created as an asynchronous command, the
coproc command always returns success. 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
command and executes a compound command with a new set of
positional parameters. Shell functions are declared as follows:
fname () compound-command [redirection]
function fname [()] compound-command [redirection]
This defines a function named fname. 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. If the function reserved
word is used, but the parentheses are not supplied, the
braces are recommended. compound-command is executed
whenever fname is specified as the name of a simple
command. When in posix mode, fname must be a valid shell
name and may not be the name of one of the POSIX special
builtins. In default mode, a function name can be any
unquoted shell word that does not contain $. 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.)
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_comments
option is on by default in interactive shells.
Quoting is used to remove the special meaning of certain
characters or words to the shell. Quoting can be used to disable
special treatment for special characters, to prevent reserved
words from being recognized as such, and to prevent parameter
expansion.
Each of the metacharacters listed above under DEFINITIONS has
special meaning to the shell and must be quoted if it is to
represent itself.
When the command history expansion facilities are being used (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 preserves
the literal value of the next character that follows, with the
exception of <newline>. If a \<newline> pair appears, and the
backslash is not 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 backslash.
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, !. When the shell is
in posix mode, the ! has no special meaning within double quotes,
even when history expansion is enabled. The characters $ and `
retain their special meaning within double quotes. The backslash
retains its special meaning only when followed by one of the
following characters: $, `, ", \, or <newline>. A double quote
may be quoted within double quotes by preceding it with a
backslash. If enabled, history expansion will be performed
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
double quotes (see PARAMETERS below).
Character sequences of the form $'string' are treated as a
special variant of single quotes. The sequence expands to
string, with backslash-escaped characters in string replaced as
specified by the ANSI C standard. Backslash escape sequences, if
present, are decoded as follows:
\a alert (bell)
\b backspace
\e
\E an escape character
\f form feed
\n new line
\r carriage return
\t horizontal tab
\v vertical tab
\\ backslash
\' single quote
\" double quote
\? question mark
\nnn the eight-bit character whose value is the octal
value nnn (one to three octal digits)
\xHH the eight-bit character whose value is the
hexadecimal value HH (one or two hex digits)
\uHHHH the Unicode (ISO/IEC 10646) character whose value
is the hexadecimal value HHHH (one to four hex
digits)
\UHHHHHHHH
the Unicode (ISO/IEC 10646) character whose value
is the hexadecimal value HHHHHHHH (one to eight hex
digits)
\cx a control-x character
The expanded result is single-quoted, as if the dollar sign had
not been present.
A double-quoted string preceded by a dollar sign ($"string") will
cause the string to be translated according to the current
locale. The gettext infrastructure performs the lookup and
translation, using the LC_MESSAGES, TEXTDOMAINDIR, and TEXTDOMAIN
shell variables. If the current locale is C or POSIX, if there
are no translations available, or if the string is not
translated, the dollar sign is ignored. This is a form of double
quoting, so the string remains double-quoted by default, whether
or not it is translated and replaced. If the
noexpand_translation option is enabled using the shopt builtin,
translated strings are single-quoted instead of double-quoted.
See the description of shopt below under SHELLBUILTINCOMMANDS.
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
expression even if the $((...)) expansion is not used (see
Arithmetic Expansion below). Word splitting and pathname
expansion are not performed. Assignment statements may also
appear as arguments to the alias, declare, typeset, export,
readonly, and local builtin commands (declaration commands).
When in posix mode, these builtins may appear in a command after
one or more instances of the command builtin and retain these
assignment statement properties.
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. This
includes arguments to builtin commands such as declare that
accept assignment statements (declaration commands). 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 assignment (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.
A variable can be assigned the nameref attribute using the -n
option to the declare or local builtin commands (see the
descriptions of declare and local below) to create a nameref, or
a reference to another variable. This allows variables to be
manipulated indirectly. Whenever the nameref variable is
referenced, assigned to, unset, or has its attributes modified
(other than using or changing the nameref attribute itself), the
operation is actually performed on the variable specified by the
nameref variable's value. A nameref is commonly used within
shell functions to refer to a variable whose name is passed as an
argument to the function. For instance, if a variable name is
passed to a shell function as its first argument, running
declare -n ref=$1
inside the function creates a nameref variable ref whose value is
the variable name passed as the first argument. References and
assignments to ref, and changes to its attributes, are treated as
references, assignments, and attribute modifications to the
variable whose name was passed as $1. If the control variable in
a for loop has the nameref attribute, the list of words can be a
list of shell variables, and a name reference will be established
for each word in the list, in turn, when the loop is executed.
Array variables cannot be given the nameref attribute. However,
nameref variables can reference array variables and subscripted
array variables. Namerefs can be unset using the -n option to
the unset builtin. Otherwise, if unset is executed with the name
of a nameref variable as an argument, the variable referenced by
the nameref variable will be unset.
Positional Parameters
A positional parameter is a parameter denoted by one or more
digits, other than the single digit 0. Positional parameters are
assigned from the shell's arguments when it is invoked, and may
be reassigned using the set builtin command. Positional
parameters may not be assigned to with assignment statements.
The positional parameters are temporarily replaced when a shell
function is executed (see FUNCTIONS below).
When a positional parameter consisting of more than a single
digit is expanded, it must be enclosed in braces (see EXPANSION
below).
Special Parameters
The shell treats several parameters specially. These parameters
may only be referenced; assignment to them is not allowed.
* Expands to the positional parameters, starting from one.
When the expansion is not within double quotes, each
positional parameter expands to a separate word. In
contexts where it is performed, those words are subject to
further word splitting and pathname expansion. When the
expansion occurs within double quotes, it expands to a
single word with the value of each parameter separated by
the first character of the IFS special variable. That is,
"$*" is equivalent to "$1c$2c...", where c is the first
character of the value of the IFS variable. If IFS is
unset, the parameters are separated by spaces. If IFS is
null, the parameters are joined without intervening
separators.
@ Expands to the positional parameters, starting from one.
In contexts where word splitting is performed, this
expands each positional parameter to a separate word; if
not within double quotes, these words are subject to word
splitting. In contexts where word splitting is not
performed, this expands to a single word with each
positional parameter separated by a space. When the
expansion occurs within double quotes, each parameter
expands to a separate word. That is, "$@" is equivalent
to "$1" "$2" ... If the double-quoted expansion occurs
within a word, the expansion of the first parameter is
joined with the beginning part of the original word, and
the expansion of the last parameter is joined with the
last part of the original word. When there are no
positional parameters, "$@" and $@ expand to nothing
(i.e., they are removed).
# Expands to the number of positional parameters in decimal.
? Expands to the exit status of the most recently executed
foreground pipeline.
- Expands to the current option flags as specified upon
invocation, by the set builtin command, or those set by
the shell itself (such as the -i option).
$ Expands to the process ID of the shell. In a subshell, it
expands to the process ID of the current shell, not the
subshell.
! Expands to the process ID of the job most recently placed
into the background, whether executed as an asynchronous
command or using the bg builtin (see JOB CONTROL below).
0 Expands to the name of the shell or shell script. This is
set at shell initialization. If bash is invoked with a
file of commands, $0 is set to the name of that file. If
bash is started with the -c option, then $0 is set to the
first argument after the string to be executed, if one is
present. Otherwise, it is set to the filename used to
invoke bash, as given by argument zero.
Shell Variables
The following variables are set by the shell:
_ At shell startup, set to the 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 simple command executed
in the foreground, after expansion. Also set to the full
pathname used to invoke each command executed and placed
in the environment exported to that command. When
checking mail, this parameter holds the name of the mail
file currently being checked.
BASH Expands to the full filename 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.
Assignments to BASHPID have no effect. If BASHPID is
unset, it loses its special properties, even if it is
subsequently reset.
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; however, unsetting array elements currently does not
cause aliases to be removed from the alias list. If
BASH_ALIASES is unset, it loses its special properties,
even if it is subsequently reset.
BASH_ARGC
An array variable whose values are the number of
parameters in each frame of the current bash execution
call stack. The number of parameters to the current
subroutine (shell function or script executed with . or
source) is at the top of the stack. When a subroutine is
executed, 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). Setting extdebug after the
shell has started to execute a script, or referencing this
variable when extdebug is not set, may result in
inconsistent values.
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). Setting
extdebug after the shell has started to execute a script,
or referencing this variable when extdebug is not set, may
result in inconsistent values.
BASH_ARGV0
When referenced, this variable expands to the name of the
shell or shell script (identical to $0; see the
description of special parameter 0 above). Assignment to
BASH_ARGV0 causes the value assigned to also be assigned
to $0. If BASH_ARGV0 is unset, it loses its special
properties, even if it is subsequently reset.
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; however, unsetting array elements currently
does not cause command names to be removed from the hash
table. If BASH_CMDS is unset, it loses its special
properties, even if it is subsequently reset.
BASH_COMMAND
The command currently being executed or about to be
executed, unless the shell is executing a command as the
result of a trap, in which case it is the command
executing at the time of the trap. If BASH_COMMAND is
unset, it loses its special properties, even if it is
subsequently reset.
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 ${FUNCNAME[$i]}
was called (or ${BASH_LINENO[$i-1]} if referenced within
another shell function). Use LINENO to obtain the current
line number.
BASH_LOADABLES_PATH
A colon-separated list of directories in which the shell
looks for dynamically loadable builtins specified by the
enable command.
BASH_REMATCH
An array variable whose members are assigned by the =~
binary operator to the [[ conditional command. The
element 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
parenthesized subexpression.
BASH_SOURCE
An array variable whose members are the source filenames
where the corresponding shell function names in the
FUNCNAME 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 within each subshell or subshell
environment when the shell begins executing in that
environment. The initial value is 0. If BASH_SUBSHELL is
unset, it loses its special properties, even if it is
subsequently reset.
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 variable
is available only in shell functions and external commands
invoked by the programmable completion facilities (see
Programmable Completion below).
COMP_TYPE
Set to an integer value corresponding to the type of
completion attempted that caused a completion function to
be called: TAB, for normal completion, ?, for listing
completions after successive tabs, !, for listing
alternatives 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 properties,
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
programmable 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
current contents of the directory stack. Directories
appear in the stack in the order they are displayed by the
dirs builtin. Assigning to members of this array variable
may be used to modify directories already in the stack,
but the pushd and popd builtins must be used to add and
remove directories. Assignment to this variable will not
change the current directory. If DIRSTACK is unset, it
loses its special properties, even if it is subsequently
reset.
EPOCHREALTIME
Each time this parameter is referenced, it expands to the
number of seconds since the Unix Epoch (see time(3)) as a
floating point value with micro-second granularity.
Assignments to EPOCHREALTIME are ignored. If
EPOCHREALTIME is unset, it loses its special properties,
even if it is subsequently reset.
EPOCHSECONDS
Each time this parameter is referenced, it expands to the
number of seconds since the Unix Epoch (see time(3)).
Assignments to EPOCHSECONDS are ignored. If EPOCHSECONDS
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
functions 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. 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
current 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. 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. Assignments to HISTCMD are ignored. If
HISTCMD is unset, it loses its special 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
substitutes a decimal number representing the current
sequential 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 operating
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, it expands to a
random integer between 0 and 32767. Assigning a value to
RANDOM initializes (seeds) the sequence of random numbers.
If RANDOM is unset, it loses its special properties, even
if it is subsequently reset.
READLINE_ARGUMENT
Any numeric argument given to a readline command that was
defined using "bind -x" (see SHELL BUILTIN COMMANDS below)
when it was invoked.
READLINE_LINE
The contents of the readline line buffer, for use with
"bind -x" (see SHELL BUILTIN COMMANDS below).
READLINE_MARK
The position of the mark (saved insertion point) in the
readline line buffer, for use with "bind -x" (see SHELL
BUILTIN COMMANDS below). The characters between the
insertion point and the mark are often called the region.
READLINE_POINT
The position of the insertion point in the readline line
buffer, for use with "bind -x" (see SHELL BUILTIN COMMANDS
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, it expands to the
number of seconds since shell invocation. If a value is
assigned to SECONDS, the value returned upon subsequent
references is the number of seconds since the assignment
plus the value assigned. The number of seconds at shell
invocation and the current time are always determined by
querying the system clock. If SECONDS is unset, it loses
its special properties, even if it is subsequently 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.
SRANDOM
This variable expands to a 32-bit pseudo-random number
each time it is referenced. The random number generator is
not linear on systems that support /dev/urandom or
arc4random, so each returned number has no relationship to
the numbers preceding it. The random number generator
cannot be seeded, so assignments to this variable have no
effect. If SRANDOM is unset, it loses its special
properties, even if it is subsequently reset.
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_COMPAT
The value is used to set the shell's compatibility level.
See SHELL COMPATIBILITY MODE below for a description of
the various compatibility levels and their effects. The
value may be a decimal number (e.g., 4.2) or an integer
(e.g., 42) corresponding to the desired compatibility
level. If BASH_COMPAT is unset or set to the empty
string, the compatibility level is set to the default for
the current version. If BASH_COMPAT is set to a value
that is not one of the valid compatibility levels, the
shell prints an error message and sets the compatibility
level to the default for the current version. The valid
values correspond to the compatibility levels described
below under SHELL COMPATIBILITY MODE. For example, 4.2
and 42 are valid values that correspond to the compat42
shopt option and set the compatibility level to 42. The
current version is also a valid value.
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 filename. PATH is not used to
search for the resultant filename.
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
assigning 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-
separated list of directories in which the shell looks for
destination directories specified by the cd command. A
sample value is ".:~:/usr".
CHILD_MAX
Set the number of exited child status values for the shell
to remember. Bash will not allow this value to be
decreased below a POSIX-mandated minimum, and there is a
maximum value (currently 8192) that this may not exceed.
The minimum value is system-dependent.
COLUMNS
Used by the select compound command to determine the
terminal width when printing selection lists.
Automatically set if the checkwinsize option is enabled or
in an interactive shell upon receipt of a SIGWINCH.
COMPREPLY
An array variable from which bash reads the possible
completions generated by a shell function invoked by the
programmable completion facility (see Programmable
Completion below). Each array element contains one
possible completion.
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
editing.
ENV Expanded and executed similarly to BASH_ENV (see
INVOCATION above) when an interactive shell is invoked in
posix mode.
EXECIGNORE
A colon-separated list of shell patterns (see Pattern
Matching) defining the list of filenames to be ignored by
command search using PATH. Files whose full pathnames
match one of these patterns are not considered executable
files for the purposes of completion and command execution
via PATH lookup. This does not affect the behavior of the
[, test, and [[ commands. Full pathnames in the command
hash table are not subject to EXECIGNORE. Use this
variable to ignore shared library files that have the
executable bit set, but are not executable files. The
pattern matching honors the setting of the extglob shell
option.
FCEDIT The default editor for the fc builtin command.
FIGNORE
A colon-separated list of suffixes to ignore when
performing filename completion (see READLINE below). A
filename whose suffix matches one of the entries in
FIGNORE 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
maximum 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
file names to be ignored by pathname expansion. If a file
name 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 shorthand
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_history. If unset, the command history is not
saved when a shell exits.
HISTFILESIZE
The maximum number of lines contained in the history file.
When this variable is assigned a value, the history file
is truncated, if necessary, to contain no more than that
number of lines by removing the oldest entries. The
history file is also truncated to this size after writing
it when a shell exits. If the value is 0, the history
file is truncated to zero size. Non-numeric values and
numeric values less than zero inhibit truncation. The
shell sets the default value to the value of HISTSIZE
after reading any startup files.
HISTIGNORE
A colon-separated list of patterns used to decide which
command lines should be saved on the history list. Each
pattern is anchored at the beginning of the line and must
match the complete line (no implicit `*' is appended).
Each pattern is tested against the line after the checks
specified by HISTCONTROL are applied. In addition to the
normal shell pattern matching characters, `&' matches the
previous history line. `&' may be escaped using a
backslash; the backslash is removed before attempting a
match. The second and subsequent lines of a multi-line
compound command are not tested, and are added to the
history regardless of the value of HISTIGNORE. The
pattern matching honors the setting of the extglob shell
option.
HISTSIZE
The number of commands to remember in the command history
(see HISTORY below). If the value is 0, commands are not
saved in the history list. Numeric values less than zero
result in every command being saved on the history list
(there is no limit). The shell sets the default value to
500 after reading any startup files.
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
argument for the cd builtin command. The value of this
variable 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
completions may be changed while the shell is running; the
next time hostname completion is attempted after the value
is changed, bash adds the contents of the new file to the
existing list. If HOSTFILE is set, but has no value, 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
splitting 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).
INSIDE_EMACS
If this variable appears in the environment when the shell
starts, bash assumes that it is running inside an Emacs
shell buffer and may disable line editing, depending on
the value of TERM.
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.
LC_TIME
This variable determines the locale category used for data
and time formatting.
LINES Used by the select compound command to determine the
column length for printing selection lists. Automatically
set if the checkwinsize option is enabled or in an
interactive shell 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 filenames to be checked for
mail. The message to be printed when mail arrives in a
particular file may be specified by separating the
filename 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 can be configured to supply a default value for this
variable (there is no value by default), 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
generated 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
adjacent 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/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin''.
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
supplied. If it is set while the shell is running, bash
enables posix mode, as if the command set -o posix had
been executed. When the shell enters posix mode, it sets
this variable if it was not already set.
PROMPT_COMMAND
If this variable is set, and is an array, the value of
each set element is executed as a command prior to issuing
each primary prompt. If this is set but not an array
variable, its value is used as a command to execute
instead.
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.
PS0 The value of this parameter is expanded (see PROMPTING
below) and displayed by interactive shells after reading a
command and before the command is executed.
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 the
expanded value of PS4 is replicated multiple times, as
necessary, to indicate multiple levels of indirection.
The default is ``+ ''.
SHELL This variable expands to the full pathname to the shell.
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
prefixed with the time reserved word should be displayed.
The % character introduces an escape sequence that is
expanded to a time value or other information. The escape
sequences and their meanings are as follows; the braces
denote optional portions.
%% A literal %.
%[p][l]R
The elapsed time in seconds.
%[p][l]U
The number of CPU seconds spent in user mode.
%[p][l]S
The number of CPU seconds spent in system mode.
%P The CPU percentage, computed as (%U + %S) / %R.
The optional p is a digit specifying the precision, the
number of fractional digits after a decimal point. A
value of 0 causes no decimal point or fraction to be
output. At most three places after the decimal point may
be specified; values of p greater than 3 are changed to 3.
If p is not specified, the value 3 is used.
The optional l specifies a longer format, including
minutes, of the form MMmSS.FFs. The value of p determines
whether or not the fraction is included.
If this variable is not set, bash acts as if it had the
value $'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'. If the
value is null, no timing information is displayed. A
trailing newline is added when the format string is
displayed.
TMOUT If set to a value greater than zero, 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 a line of input after issuing the
primary prompt. Bash terminates after waiting for that
number of seconds if a complete line of 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 substring, the string
supplied needs to match a substring of the name of a
stopped job. The substring value provides functionality
analogous to the %? job identifier (see JOB CONTROL
below). If set to any other value, the supplied string
must be a prefix of a stopped job's name; this provides
functionality analogous to the %string job identifier.
histchars
The two or three characters which control history
expansion 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 substitution character, which is used as shorthand
for re-running the previous command entered, substituting
one string for another in the command. The default is
`^'. The optional third character is the character which
indicates that the remainder of the line is a comment when
found as the first character of a word, 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. Unless otherwise noted, indexed array indices must be
non-negative integers.
An indexed array is created automatically if any variable is
assigned to using the syntax name[subscript]=value. The
subscript is treated as an arithmetic expression that must
evaluate to a number. To explicitly declare an indexed array,
use declare -a name (see SHELL BUILTIN COMMANDS below). declare
-a name[subscript] 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 may be of the form
[subscript]=string. Indexed array assignments do not require
anything but string. Each value in the list is expanded using
all the shell expansions described below under EXPANSION. 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 words in a compound
assignment may be either assignment statements, for which the
subscript is required, or a list of words that is interpreted as
a sequence of alternating keys and values: name=( key1 value1
key2 value2 ...). These are treated identically to name=(
[key1]=value1 [key2]=value2 ...). The first word in the list
determines how the remaining words are interpreted; all
assignments in a list must be of the same type. When using
key/value pairs, the keys may not be missing or empty; a final
missing value is treated like the empty string.
This syntax is also accepted by the declare builtin. Individual
array elements may be assigned to using the name[subscript]=value
syntax introduced above. When assigning to an indexed array, if
name is subscripted by a negative number, that number is
interpreted as relative to one greater than the maximum index of
name, so negative indices count back from the end of the array,
and an index of -1 references the last element.
The += operator will append to an array variable when assigning
using the compound assignment syntax; see PARAMETERS above.
Any element of an array may be referenced using
${name[subscript]}. The braces are required to avoid conflicts
with pathname 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 variable, 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
beginning 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. If
the subscript used to reference an element of an indexed array
evaluates to a number less than zero, it is interpreted as
relative to one greater than the maximum index of the array, so
negative indices count back from the end of the array, and an
index of -1 references the last element.
Referencing an array variable without a subscript is equivalent
to referencing the array with a subscript of 0. Any reference to
a variable using a valid subscript is legal, and bash will create
an array if necessary.
An array variable is considered set if a subscript has been
assigned a value. The null string is a valid value.
It is possible to obtain the keys (indices) of an array as well
as the values. ${!name[@]} and ${!name[*]} expand to the indices
assigned in array variable name. The treatment when in double
quotes is similar to the expansion of the special parameters @
and * within double quotes.
The unset builtin is used to destroy arrays. unset
name[subscript] destroys the array element at index subscript,
for both indexed and associative arrays. Negative subscripts to
indexed arrays are interpreted as described above. Unsetting the
last element of an array variable does not unset the variable.
unset name, where name is an array, removes the entire array.
unset name[subscript], where subscript is * or @, behaves
differently depending on whether name is an indexed or
associative array. If name is an associative array, this unsets
the element with subscript * or @. If name is an indexed array,
unset removes all of the elements but does not remove the array
itself.
When using a variable name with a subscript as an argument to a
command, such as with unset, without using the word expansion
syntax described above, the argument is subject to pathname
expansion. If pathname expansion is not desired, the argument
should be quoted.
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 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
expansion, command substitution, arithmetic expansion, word
splitting, and pathname expansion.
The order of expansions is: brace expansion; tilde expansion,
parameter and variable expansion, arithmetic expansion, and
command substitution (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. This is performed at the same
time as tilde, parameter, variable, and arithmetic expansion and
command substitution.
After these expansions are performed, quote characters present in
the original word are removed unless they have been quoted
themselves (quote removal).
Only brace expansion, word splitting, and pathname expansion can
increase 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[@]}", and, in most
cases, $* 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
expression between a pair of braces, followed by an optional
postscript. The preamble is prefixed to each string contained
within the braces, and the postscript is then appended to each
resulting string, expanding left to right.
Brace expansions may be nested. The results of each expanded
string are not sorted; left to right order is preserved. For
example, 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 letters, and incr, an optional
increment, is an integer. When integers are supplied, the
expression expands to each number between x and y, inclusive.
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 letters are
supplied, the expression expands to each character
lexicographically between x and y, inclusive, using the default C
locale. Note that both x and y must be of the same type (integer
or letter). 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
syntactic interpretation to the context of the expansion or the
text between the braces.
A correctly-formed brace expansion must contain unquoted opening
and closing braces, and at least one unquoted comma or a valid
sequence expression. Any incorrectly formed brace expansion is
left unchanged. A { or , may be quoted with a backslash to
prevent its being considered part of a brace expression. To
avoid conflicts with parameter expansion, the string ${ is not
considered eligible for brace expansion, and inhibits brace
expansion until the closing }.
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
historical versions of sh. sh does not treat opening or closing
braces specially when they appear as part of a word, and
preserves 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
characters, if there is no unquoted slash) are considered a
tilde-prefix. If none of the characters in the tilde-prefix are
quoted, the characters in the tilde-prefix following the tilde
are treated as a possible login name. If this login name is the
null string, the tilde is replaced with the value of the 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
substituted. If the characters following the tilde in the tilde-
prefix consist of a number N, optionally prefixed by a `+' or a
`-', the tilde-prefix is replaced with the corresponding element
from the directory stack, as it would be displayed by the dirs
builtin invoked with the 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 filenames
with tildes in assignments to PATH, MAILPATH, and CDPATH, and the
shell assigns the expanded value.
Bash also performs tilde expansion on words satisfying the
conditions of variable assignments (as described above under
PARAMETERS) when they appear as arguments to simple commands.
Bash does not do this, except for the declaration commands listed
above, when in posix mode.
Parameter Expansion
The `$' character introduces parameter expansion, command
substitution, or arithmetic expansion. The parameter name or
symbol to be expanded may be enclosed in braces, which are
optional but serve to protect the variable to be expanded from
characters immediately following it which could be interpreted as
part of the name.
When braces are used, the matching ending brace is the first `}'
not escaped by a backslash or within a quoted string, and not
within an embedded arithmetic expansion, command substitution, or
parameter expansion.
${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. The parameter is a shell parameter as described
above PARAMETERS) or an array reference (Arrays).
If the first character of parameter is an exclamation point (!),
and parameter is not a nameref, it introduces a level of
indirection. Bash uses the value formed by expanding the rest of
parameter as the new parameter; this is then expanded and that
value is used in the rest of the expansion, rather than the
expansion of the original parameter. This is known as indirect
expansion. The value is subject to tilde expansion, parameter
expansion, command substitution, and arithmetic expansion. If
parameter is a nameref, this expands to the name of the parameter
referenced by parameter instead of performing the complete
indirect expansion. The exceptions to this are the expansions of
${!prefix*} and ${!name[@]} described below. The exclamation
point must immediately 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
expansion.
When not performing substring expansion, using the forms
documented below (e.g., :-), 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.
Otherwise, 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 the value of parameter starting at the character
specified by offset. If parameter is @ or *, an indexed
array subscripted by @ or *, or an associative array name,
the results differ as described below. If length is
omitted, expands to the substring of the value of
parameter starting at the character specified by offset
and extending to the end of the value. length and offset
are arithmetic expressions (see ARITHMETIC EVALUATION
below).
If offset evaluates to a number less than zero, the value
is used as an offset in characters from the end of the
value of parameter. If length evaluates to a number less
than zero, it is interpreted as an offset in characters
from the end of the value of parameter rather than a
number of characters, and the expansion is the characters
between offset and that result. Note that a negative
offset must be separated from the colon by at least one
space to avoid being confused with the :- expansion.
If parameter is @ or *, the result is length positional
parameters beginning at offset. A negative offset is
taken relative to one greater than the greatest positional
parameter, so an offset of -1 evaluates to the last
positional parameter. It is an expansion error if length
evaluates to a number less than zero.
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. It is an expansion error if length
evaluates to a number less than zero.
Substring expansion applied to an associative array
produces undefined results.
Substring indexing is zero-based unless the positional
parameters are used, in which case the indexing 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 separate 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.
If parameter is an indexed array name subscripted by a
negative number, that number is interpreted as relative to
one greater than the maximum index of parameter, so
negative indices count back from the end of the array, and
an index of -1 references the last element.
${parameter#word}
${parameter##word}
Remove matching prefix pattern. The word is expanded to
produce a pattern just as in pathname expansion, and
matched against the expanded value of parameter using the
rules described under Pattern Matching below. 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 parameter is
an array variable subscripted with @ or *, the pattern
removal operation is applied to each member of the array
in turn, and the expansion is the resultant list.
${parameter%word}
${parameter%%word}
Remove matching suffix pattern. The word is expanded to
produce a pattern just as in pathname expansion, and
matched against the expanded value of parameter using the
rules described under Pattern Matching below. 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}
${parameter//pattern/string}
${parameter/#pattern/string}
${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. string undergoes tilde
expansion, parameter and variable expansion, arithmetic
expansion, command and process substitution, and quote
removal. The match is performed using the rules described
under Pattern Matching below. In the first form above,
only the first match is replaced. If there are two
slashes separating parameter and pattern (the second form
above), all matches of pattern are replaced with string.
If pattern is preceded by # (the third form above), it
must match at the beginning of the expanded value of
parameter. If pattern is preceded by % (the fourth form
above), it must match at the end of the expanded value of
parameter. If the expansion of string is null, matches of
pattern are deleted. If string is null, matches of
pattern are deleted and the / following pattern may be
omitted.
If the patsub_replacement shell option is enabled using
shopt, any unquoted instances of & in string are replaced
with the matching portion of pattern.
Quoting any part of string inhibits replacement in the
expansion of the quoted portion, including replacement
strings stored in shell variables. Backslash will escape
& in string; the backslash is removed in order to permit a
literal & in the replacement string. Backslash can also
be used to escape a backslash; \\ results in a literal
backslash in the replacement. Users should take care if
string is double-quoted to avoid unwanted interactions
between the backslash and double-quoting, since backslash
has special meaning within double quotes. Pattern
substitution performs the check for unquoted & after
expanding string; shell programmers should quote any
occurrences of & they want to be taken literally in the
replacement and ensure any instances of & they want to be
replaced are unquoted.
If the nocasematch shell option is enabled, the match is
performed without regard to the case of alphabetic
characters. If parameter is @ or *, the substitution
operation is applied to each positional parameter in turn,
and the expansion is the resultant list. If parameter is
an array variable subscripted with @ or *, the
substitution operation is applied to each member of the
array in turn, and the expansion is the resultant list.
${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
expansion. Each character in the expanded value of
parameter is tested against pattern, and, if it matches
the pattern, its case is converted. The pattern should
not attempt to match more than one character. 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 character 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 modification operation
is applied to each member of the array in turn, and the
expansion is the resultant list.
${parameter@operator}
Parameter transformation. The expansion is either a
transformation of the value of parameter or information
about parameter itself, depending on the value of
operator. Each operator is a single letter:
U The expansion is a string that is the value of
parameter with lowercase alphabetic characters
converted to uppercase.
u The expansion is a string that is the value of
parameter with the first character converted to
uppercase, if it is alphabetic.
L The expansion is a string that is the value of
parameter with uppercase alphabetic characters
converted to lowercase.
Q The expansion is a string that is the value of
parameter quoted in a format that can be reused as
input.
E The expansion is a string that is the value of
parameter with backslash escape sequences expanded
as with the $'...' quoting mechanism.
P The expansion is a string that is the result of
expanding the value of parameter as if it were a
prompt string (see PROMPTING below).
A The expansion is a string in the form of an
assignment statement or declare command that, if
evaluated, will recreate parameter with its
attributes and value.
K Produces a possibly-quoted version of the value of
parameter, except that it prints the values of
indexed and associative arrays as a sequence of
quoted key-value pairs (see Arrays above).
a The expansion is a string consisting of flag values
representing parameter's attributes.
k Like the K transformation, but expands the keys and
values of indexed and associative arrays to
separate words after word splitting.
If parameter is @ or *, the 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 operation is applied to each
member of the array in turn, and the expansion is the
resultant list.
The result of the expansion is subject to word splitting
and pathname expansion as described below.
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 in a subshell
environment and replacing the command substitution with the
standard output of the command, with any trailing newlines
deleted. Embedded newlines are not deleted, but they may be
removed during word splitting. The command substitution $(cat
file) can be replaced by the equivalent but faster $(< file).
When the old-style backquote form of substitution is used,
backslash retains its literal meaning except when followed by $,
`, or \. The first backquote not preceded by a backslash
terminates the command substitution. When using the $(command)
form, all characters between the parentheses make up the command;
none are treated specially.
Command substitutions may be nested. To nest when using the
backquoted form, escape the inner backquotes with backslashes.
If the substitution appears within double quotes, word splitting
and 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 undergoes the same expansions as if it were within
double quotes, but double quote characters in expression are not
treated specially and are removed. All tokens in the expression
undergo parameter and variable expansion, command substitution,
and quote removal. The result is treated as the arithmetic
expression to be evaluated. 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 allows a process's input or output to be
referred to using a filename. It takes the form of <(list) or
>(list). The process list is run asynchronously, and its input
or output appears as a filename. This filename 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. Process
substitution is supported on systems that support named pipes
(FIFOs) or the /dev/fd method of naming open files.
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
substitution, and arithmetic expansion that did not occur within
double quotes for word splitting.
The shell treats each character of IFS as a delimiter, and splits
the results of the other expansions into words using these
characters as field terminators. 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, tab, and newline 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 and passed to
commands as empty strings. Unquoted implicit null arguments,
resulting from the expansion of parameters that have no values,
are removed. If a parameter with no value is expanded within
double quotes, a null argument results and is retained and passed
to a command as an empty string. When a quoted null argument
appears as part of a word whose expansion is non-null, the null
argument is removed. That is, the word -d'' becomes -d after
word splitting and null argument removal.
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, and is not quoted, then the word is regarded
as a pattern, and replaced with an alphabetically sorted list of
filenames matching the pattern (see Pattern Matching below). If
no matching filenames 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 immediately following a slash must be matched
explicitly, unless the shell option dotglob is set. In order to
match the filenames ``.'' and ``..'', the pattern must begin
with ``.'' (for example, ``.?''), even if dotglob is set. If the
globskipdots shell option is enabled, the filenames ``.'' and
``..'' are never matched, even if the pattern begins with a
``.''. When not matching pathnames, the ``.'' character is not
treated specially. When matching a pathname, the slash character
must always be matched explicitly by a slash in the pattern, but
in other matching contexts it can be matched by a special pattern
character as described below under Pattern Matching. See the
description of shopt below under SHELL BUILTIN COMMANDS for a
description of the nocaseglob, nullglob, globskipdots, 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
GLOBIGNORE is removed from the list of matches. If the
nocaseglob option is set, the matching against the patterns in
GLOBIGNORE is performed without regard to case. The filenames
``.'' 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
filenames beginning with a ``.'' will match. To get the old
behavior of ignoring filenames beginning with a ``.'', make
``.*'' one of the patterns in GLOBIGNORE. The dotglob option is
disabled when GLOBIGNORE is unset. The pattern matching honors
the setting of the extglob shell option.
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 adjacent
*s used as a single pattern will match all files
and zero or more directories and subdirectories.
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 falls 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, and the characters included in the
range, are determined by the current locale and the
values of the LC_COLLATE or LC_ALL shell variables,
if set. To obtain the traditional interpretation
of range expressions, where [a-d] is equivalent to
[abcd], set value of the LC_ALL shell variable to
C, or enable the globasciiranges shell option. 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
standard:
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
specified using the syntax [=c=], which matches all
characters with the same collation weight (as
defined by the current locale) as the character c.
Within [ and ], the syntax [.symbol.] matches the
collating symbol symbol.
If the extglob shell option is enabled using the shopt builtin,
the shell recognizes several extended pattern matching operators.
In the following description, a pattern-list is a list of one or
more patterns separated by a |. Composite patterns may be formed
using one or more of the following sub-patterns:
?(pattern-list)
Matches zero or one occurrence of the given
patterns
*(pattern-list)
Matches zero or more occurrences of the given
patterns
+(pattern-list)
Matches one or more occurrences of the given
patterns
@(pattern-list)
Matches one of the given patterns
!(pattern-list)
Matches anything except one of the given patterns
Theextglob option changes the behavior of the parser, since the
parentheses are normally treated as operators with syntactic
meaning. To ensure that extended matching patterns are parsed
correctly, make sure that extglob is enabled before parsing
constructs containing the patterns, including shell functions and
command substitutions.
When matching filenames, the dotglob shell option determines the
set of filenames that are tested: when dotglob is enabled, the
set of filenames includes all files beginning with ``.'', but
``.'' and ``..'' must be matched by a pattern or sub-pattern that
begins with a dot; when it is disabled, the set does not include
any filenames beginning with ``.'' unless the pattern or sub-
pattern begins with a ``.''. As above, ``.'' only has a special
meaning when matching filenames.
Complicated extended pattern matching against long strings is
slow, especially when the patterns contain alternations and the
strings contain multiple matches. Using separate matches against
shorter strings, or using arrays of strings instead of a single
long string, may be faster.
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.
Before a command is executed, its input and output may be
redirected using a special notation interpreted by the shell.
Redirection allows commands' file handles to be duplicated,
opened, closed, made to refer to different files, and can change
the files the command reads from and writes to. Redirection may
also be used to modify file handles in the current shell
execution environment. The following redirection operators may
precede or appear anywhere within a simple command or may follow
a command. Redirections are processed in the order they appear,
from left to right.
Each redirection that may be preceded by a file descriptor number
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 or equal to 10 and
assign it to varname. If >&- or <&- is preceded by {varname},
the value of varname defines the file descriptor to close. If
{varname} is supplied, the redirection persists beyond the scope
of the command, allowing the shell programmer to manage the file
descriptor's lifetime manually. The varredir_close shell option
manages this behavior.
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 and variable expansion,
command substitution, 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 example,
the command
ls > dirlist 2>&1
directs both standard output and standard error to the file
dirlist, while the command
ls 2>&1 > dirlist
directs only the standard output to file dirlist, because the
standard error was duplicated 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. If the
operating system on which bash is running provides these special
files, bash will use them; otherwise it will emulate them
internally with the behavior described below.
/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 the corresponding TCP 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 the corresponding UDP 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 descriptor n,
or the standard output (file descriptor 1) if n is not specified.
If the file does not exist it is created; if it does exist it is
truncated to zero size.
The general format for redirecting output is:
[n]>word
If the redirection operator is >, and the 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
redirected to the file whose name is the expansion of word.
There are two formats for redirecting standard output and
standard error:
&>word
and
>&word
Of the two forms, the first is preferred. This is semantically
equivalent to
>word 2>&1
When using the second form, word may not expand to a number or -.
If it does, other redirection operators apply (see Duplicating
File Descriptors below) for compatibility reasons.
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
(see Duplicating File Descriptors below).
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 (or file descriptor n
if n is specified) for a command.
The format of here-documents is:
[n]<<[-]word
here-document
delimiter
No parameter and variable expansion, command substitution,
arithmetic expansion, or pathname expansion is performed on word.
If any part of word is 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, the character sequence \<newline> is
ignored, and \ must be used to quote the characters \, $, and `.
If the redirection operator is <<-, then all leading tab
characters are stripped from input lines and the line containing
delimiter. This allows here-documents within shell scripts to be
indented in a natural fashion.
Here Strings
A variant of here documents, the format is:
[n]<<<word
The word undergoes tilde expansion, parameter and variable
expansion, command substitution, arithmetic expansion, and quote
removal. Pathname expansion and word splitting are not
performed. The result is supplied as a single string, with a
newline appended, to the command on its standard input (or file
descriptor n if n is specified).
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. If word evaluates to -, file
descriptor n is closed. As a special case, if n is omitted, and
word does not expand to one or more digits or -, 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 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, use a shell function (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
somewhat confusing. Bash always reads at least one complete line
of input, and all lines that make up a compound command, before
executing any of the commands on that line or the compound
command. Aliases are expanded when a command is read, not when
it is executed. Therefore, an alias definition appearing on the
same line as another command does not take effect until the next
line of input is read. The commands following the alias
definition on that line are not affected by the new alias. This
behavior is also an issue when functions are executed. Aliases
are expanded when a function definition is read, not when the
function is executed, because a function definition is itself a
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
functions.
A shell function, defined as described above under SHELL GRAMMAR,
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 during
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
identical 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 (local variables). Ordinarily, variables and
their values are shared between the function and its caller. If
a variable is declared local, the variable's visible scope is
restricted to that function and its children (including the
functions it calls).
In the following description, the current scope is a currently-
executing function. Previous scopes consist of that function's
caller and so on, back to the "global" scope, where the shell is
not executing any shell function. Consequently, a local variable
at the current scope is a variable declared using the local or
declare builtins in the function that is currently executing.
Local variables "shadow" variables with the same name declared at
previous scopes. For instance, a local variable declared in a
function hides a global variable of the same name: references and
assignments refer to the local variable, leaving the global
variable unmodified. When the function returns, the global
variable is once again visible.
The shell uses dynamic scoping to control a variable's visibility
within functions. With dynamic scoping, visible variables and
their values are a result of the sequence of function calls that
caused execution to reach the current function. The value of a
variable that a function sees depends on its value within its
caller, if any, whether that caller is the "global" scope or
another shell function. This is also the value that a local
variable declaration "shadows", and the value that is restored
when the function returns.
For example, if a variable var is declared as local in function
func1, and func1 calls another function func2, references to var
made from within func2 will resolve to the local variable var
from func1, shadowing any global variable named var.
The unset builtin also acts using the same dynamic scope: if a
variable is local to the current scope, unset will unset it;
otherwise the unset will refer to the variable found in any
calling scope as described above. If a variable at the current
local scope is unset, it will remain so (appearing as unset)
until it is reset in that scope or until the function returns.
Once the function returns, any instance of the variable at a
previous scope will become visible. If the unset acts on a
variable at a previous scope, any instance of a variable with
that name that had been shadowed will become visible (see below
how the localvar_unset shell option changes this behavior).
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
completes, 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 child
shell processes (those created when executing a separate shell
invocation) 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.
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.
The shell allows arithmetic expressions to be evaluated, under
certain circumstances (see the let and declare builtin commands,
the (( compound command, 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 precedence, associativity, and values are the
same as in the C language. The following list of operators is
grouped into levels of equal-precedence operators. The levels
are listed in order of decreasing precedence.
id++ id--
variable post-increment and post-decrement
- + unary minus and plus
++id --id
variable pre-increment and pre-decrement
! ~ 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
expression, 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.
Integer constants follow the C language definition, without
suffixes or character constants. 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. When specifying n, if
a non-digit is required, the digits greater than 9 are
represented by the lowercase letters, the uppercase letters, @,
and _, in that order. If base is less than or equal to 36,
lowercase and uppercase letters may be used 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
precedence rules above.
Conditional expressions are used by the [[ compound command and
the test and [ builtin commands to test file attributes and
perform string and arithmetic comparisons. The test and [
commands determine their behavior based on the number of
arguments; see the descriptions of those commands for any other
command-specific actions.
Expressions are formed from the following unary or binary
primaries. Bash handles several filenames specially when they
are used in expressions. If the operating system on which bash
is running provides these special files, bash will use them;
otherwise it will emulate them internally with this behavior: If
any file argument to one of the primaries is of the form
/dev/fd/n, then file descriptor n is checked. If the file
argument to one of the primaries is one of /dev/stdin,
/dev/stdout, or /dev/stderr, file descriptor 0, 1, or 2,
respectively, is checked.
Unless otherwise specified, primaries that operate on files
follow 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
terminal.
-u file
True if file exists and its set-user-id bit is set.
-w file
True if file exists and is writable.
-x file
True if file exists and is executable.
-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).
-R varname
True if the shell variable varname is set and is a name
reference.
-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. When used with the [[
command, this performs pattern matching as described above
(Compound Commands).
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,
respectively. Arg1 and arg2 may be positive or negative
integers. When used with the [[ command, Arg1 and Arg2
are evaluated as arithmetic expressions (see ARITHMETIC
EVALUATION above).
When a simple command is executed, the shell performs the
following expansions, assignments, and redirections, from left to
right, in the following order.
1. The words that the parser has marked as variable
assignments (those preceding the command name) and
redirections are saved for later processing.
2. The words that are not variable assignments or
redirections 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
REDIRECTION.
4. The text after the = in each variable assignment undergoes
tilde expansion, parameter expansion, command
substitution, arithmetic expansion, and quote removal
before being assigned to the variable.
If no command name results, the variable assignments affect the
current shell environment. In the case of such a command (one
that consists only of assignment statements and redirections),
assignment statements are performed before redirections.
Otherwise, the variables are added to the environment of the
executed command and do not affect the current shell environment.
If any of the assignments attempts to assign a value to a
readonly variable, an error occurs, and the command exits with a
non-zero status.
If no command name results, redirections are performed, but do
not affect the current shell environment. A redirection error
causes the command to exit with a non-zero status.
If there is a command name left after expansion, execution
proceeds as described below. Otherwise, the command exits. If
one of the expansions contained a command substitution, the exit
status of the command is the exit status of the last command
substitution performed. If there were no command substitutions,
the command exits with a status of zero.
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
contains 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
command_not_found_handle. If that function exists, it is invoked
in a separate execution environment with the original command and
the original command's arguments as its arguments, and the
function's exit status becomes the exit status of that subshell.
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
separate 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, and the shell
creates a new instance of itself 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.
The shell has an execution environment, which consists of the
following:
• open files inherited by the shell at invocation, as
modified by redirections supplied to the exec builtin
• the current working directory as set by cd, pushd, or
popd, or inherited by the shell at invocation
• the file creation mode mask as set by umask or inherited
from the shell's parent
• current traps set by trap
• shell parameters that are set by variable assignment or
with set or inherited from the shell's parent in the
environment
• shell functions defined during execution or inherited from
the shell's parent in the environment
• options enabled at invocation (either by default or with
command-line arguments) or by set
• options enabled by shopt
• shell aliases defined with alias
• 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 environment
that consists of the following. Unless otherwise noted, the
values are inherited from the shell.
• the shell's open files, plus any modifications and
additions specified by redirections to the command
• the current working directory
• the file creation mode mask
• shell variables 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
inherited from the shell's parent, and traps ignored by
the shell are ignored
A command invoked in this separate environment cannot affect the
shell's execution environment.
A subshell is a copy of the shell process.
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 subshell
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.
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
environment. The export and declare -x commands allow parameters
and functions to be added to and deleted from the environment.
If the value of a parameter in the environment is modified, the
new value becomes part of the environment, replacing the old.
The environment inherited by any executed command consists of the
shell's initial environment, whose values may be modified in the
shell, less any pairs removed by the unset command, plus any
additions via the export and declare -x commands.
The environment for any simple command or function may be
augmented temporarily by prefixing it with parameter assignments,
as described 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 filename of the command and passed to that command in
its environment.
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
terminates 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
redirection, the exit status is greater than zero.
Shell builtin commands return a status of 0 (true) if successful,
and non-zero (false) if an error occurs while they execute. All
builtins return an exit status of 2 to indicate incorrect usage,
generally invalid options or missing arguments.
The exit status of the last command is available in the special
parameter $?.
Bash itself returns the exit status of the last command executed,
unless a syntax error occurs, in which case it exits with a non-
zero value. See also the exit builtin command below.
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-generated job
control signals SIGTTIN, SIGTTOU, and SIGTSTP.
The shell exits by default upon receipt of a SIGHUP. Before
exiting, an interactive shell resends the SIGHUP to all jobs,
running or stopped. Stopped jobs are sent SIGCONT to ensure that
they receive the SIGHUP. To prevent the shell from sending the
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
signal for which a trap has been set, the trap will not be
executed until the command completes. When bash is waiting for
an asynchronous command via the wait builtin, the reception of a
signal for which a trap has been set will cause the wait builtin
to return immediately with an exit status greater than 128,
immediately after which the trap is executed.
When job control is not enabled, and bash is waiting for a
foreground command to complete, the shell receives keyboard-
generated signals such as SIGINT (usually generated by ^C) that
users commonly intend to send to that command. This happens
because the shell and the command are in the same process group
as the terminal, and ^C sends SIGINT to all processes in that
process group.
When bash is running without job control enabled and receives
SIGINT while waiting for a foreground command, it waits until
that foreground command terminates and then decides what to do
about the SIGINT:
1. If the command terminates due to the SIGINT, bash
concludes that the user meant to end the entire script,
and acts on the SIGINT (e.g., by running a SIGINT trap or
exiting itself);
2. If the command does not terminate due to SIGINT, the
program handled the SIGINT itself and did not treat it as
a fatal signal. In that case, bash does not treat SIGINT
as a fatal signal, either, instead assuming that the
SIGINT was used as part of the program's normal operation
(e.g., emacs uses it to abort editing commands) or
deliberately discarded. However, bash will run any trap
set on SIGINT, as it does with any other trapped signal it
receives while it is waiting for the foreground command to
complete, for compatibility.
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
background), it prints a line that looks like:
[1] 25647
indicating that this job is job number 1 and that the process ID
of the last process in the pipeline associated with this job is
25647. All of the processes in a single pipeline are members of
the same job. Bash uses the job abstraction as the basis for job
control.
To facilitate the implementation of the user interface to job
control, the operating system maintains the notion of a current
terminal process group ID. Members of this process group
(processes whose process group ID is equal to the current
terminal process group ID) receive keyboard-generated signals
such as SIGINT. These processes are said to be in the
foreground. Background processes are those whose process group
ID differs from the terminal's; such processes are immune to
keyboard-generated signals. Only foreground processes are
allowed to read from or, 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 causing
pending output and typeahead to be discarded.
There are a number of ways to refer to a job in the shell. The
character % introduces a job specification (jobspec). Job number
n may be referred to as %n. A job may also be referred to using
a prefix of the name used to start it, or using a substring that
appears in its command line. For example, %ce refers to a
stopped job whose command name begins with ce. 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 background
into the foreground. Similarly, ``%1 &'' resumes job 1 in the
background, equivalent to ``bg %1''.
The shell learns immediately whenever a job changes state.
Normally, bash waits until it is about to print a prompt before
reporting changes in a job's status so as to not interrupt any
other output. If the -b option to the set builtin 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
statuses. The jobs command may then be used to inspect their
status. 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.
When the shell is waiting for a job or process using the wait
builtin, and job control is enabled, wait will return when the
job changes state. The -f option causes wait to wait until the
job or process terminates before returning.
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
displays PS0 after it reads a command but before executing it.
Bash displays PS4 as described above before tracing each command
when the -x option is enabled. Bash allows these prompt strings
to be customized by inserting a number of backslash-escaped
special characters that are decoded as follows:
\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 format
results in a locale-specific time representation.
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 $0 (the
portion following the final slash)
\t the current time in 24-hour HH:MM:SS format
\T the current time in 12-hour HH:MM:SS format
\@ the current time in 12-hour am/pm format
\A the current time in 24-hour HH:MM format
\u the username of the current user
\v the version of bash (e.g., 2.00)
\V the release of bash, version + patch level (e.g.,
2.00.0)
\w the value of the PWD shell variable ($PWD), with
$HOME abbreviated with a tilde (uses the value of
the PROMPT_DIRTRIM variable)
\W the basename of $PWD, 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
session. After the string is decoded, it is expanded via
parameter expansion, command substitution, arithmetic expansion,
and quote removal, subject to the value of the promptvars shell
option (see the description of the shopt command under SHELL
BUILTIN COMMANDS below). This can have unwanted side effects if
escaped portions of the string appear within command substitution
or contain characters special to word expansion.
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
commands 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
keystrokes. 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. If that file does not exist or cannot be
read, the ultimate default is /etc/inputrc. When a program which
uses the readline 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
universal-argument, M-DEL is bound to the function
backward-kill-word, and C-o is bound to run the macro expressed
on the right hand side (that is, to insert the text ``> output''
into the line).
In the second form, "keyseq":function-name or macro, keyseq
differs 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
recognized.
"\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
universal-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
hexadecimal value HH (one or two hex digits)
When entering the text of a macro, single or double quotes must
be used to indicate a macro definition. Unquoted text is assumed
to be a function name. In the macro body, the backslash escapes
described above are expanded. Backslash will quote any other
character in the macro text, including " and '.
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
or using the bind builtin command (see SHELL BUILTIN COMMANDS
below).
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:
active-region-start-color
A string variable that controls the text color and
background when displaying the text in the active region
(see the description of enable-active-region below). This
string must not take up any physical character positions
on the display, so it should consist only of terminal
escape sequences. It is output to the terminal before
displaying the text in the active region. This variable
is reset to the default value whenever the terminal type
changes. The default value is the string that puts the
terminal in standout mode, as obtained from the terminal's
terminfo description. A sample value might be
"\e[01;33m".
active-region-end-color
A string variable that "undoes" the effects of
active-region-start-color and restores "normal" terminal
display appearance after displaying text in the active
region. This string must not take up any physical
character positions on the display, so it should consist
only of terminal escape sequences. It is output to the
terminal after displaying the text in the active region.
This variable is reset to the default value whenever the
terminal type changes. The default value is the string
that restores the terminal from standout mode, as obtained
from the terminal's terminfo description. A sample value
might be "\e[0m".
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
characters treated specially by the kernel's terminal
driver to their readline equivalents.
blink-matching-paren (Off)
If set to On, readline attempts to briefly move the cursor
to an opening parenthesis when a closing parenthesis is
inserted.
colored-completion-prefix (Off)
If set to On, when listing completions, readline displays
the common prefix of the set of possible completions using
a different color. The color definitions are taken from
the value of the LS_COLORS environment variable. If there
is a color definition in $LS_COLORS for the custom suffix
"readline-colored-completion-prefix", readline uses this
color for the common prefix instead of its default.
colored-stats (Off)
If set to On, readline displays possible completions using
different colors to indicate their file type. The color
definitions are taken from the value of the LS_COLORS
environment variable.
comment-begin (``#'')
The string that is inserted when the readline
insert-comment command is executed. This command is bound
to M-# in emacs mode and to # in vi command mode.
completion-display-width (-1)
The number of screen columns used to display possible
matches when performing completion. The value is ignored
if it is less than 0 or greater than the terminal screen
width. A value of 0 will cause matches to be displayed
one per line. The default value is -1.
completion-ignore-case (Off)
If set to On, readline performs filename matching and
completion in a case-insensitive fashion.
completion-map-case (Off)
If set to On, and completion-ignore-case is enabled,
readline treats hyphens (-) and underscores (_) as
equivalent when performing case-insensitive filename
matching and completion.
completion-prefix-display-length(0)
The length in characters of the common prefix of a list of
possible completions that is displayed without
modification. 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
possible-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, readline will ask whether or
not the user wishes to view them; otherwise they are
simply listed on the terminal. A zero value means
readline should never ask; negative values are treated as
zero.
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). The default is On, but
readline will set it to Off if the locale contains eight-
bit characters. This variable is dependent on the
LC_CTYPE locale category, and may change if the locale is
changed.
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.
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.
editing-mode (emacs)
Controls whether readline begins with a set of key
bindings similar to Emacs or vi. editing-mode can be set
to either emacs or vi.
emacs-mode-string (@)
If the show-mode-in-prompt variable is enabled, this
string is displayed immediately before the last line of
the primary prompt when emacs editing mode is active. The
value is expanded like a key binding, so the standard set
of meta- and control prefixes and backslash escape
sequences is available. Use the \1 and \2 escapes to
begin and end sequences of non-printing characters, which
can be used to embed a terminal control sequence into the
mode string.
enable-active-region (On)
The point is the current cursor position, and mark refers
to a saved cursor position. The text between the point
and mark is referred to as the region. When this variable
is set to On, readline allows certain commands to
designate the region as active. When the region is
active, readline highlights the text in the region using
the value of the active-region-start-color, which defaults
to the string that enables the terminal's standout mode.
The active region shows the text inserted by bracketed-
paste and any matching text found by incremental and non-
incremental history searches.
enable-bracketed-paste (On)
When set to On, readline configures the terminal to insert
each paste into the editing buffer as a single string of
characters, instead of treating each character as if it
had been read from the keyboard. This prevents readline
from executing any editing commands bound to key sequences
appearing in the pasted text.
enable-keypad (Off)
When set to On, readline will try to enable the
application keypad when it is called. Some systems need
this to enable the arrow keys.
enable-meta-key (On)
When set to On, readline will try to enable any meta
modifier 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 (unset)
Set the maximum number of history entries saved in the
history list. If set to zero, any existing history
entries are deleted and no new entries are saved. If set
to a value less than zero, the number of history entries
is not limited. By default, the number of history entries
is set to the value of the HISTSIZE shell variable. If an
attempt is made to set history-size to a non-numeric
value, the maximum number of history entries will be set
to 500.
horizontal-scroll-mode (Off)
When set to On, makes readline use a single line for
display, scrolling the input horizontally on a single
screen line when it becomes longer than the screen width
rather than wrapping to a new line. This setting is
automatically enabled for terminals of height 1.
input-meta (Off)
If set to On, readline will enable eight-bit input (that
is, it will not strip the eighth bit from the characters
it reads), regardless of what the terminal claims it can
support. The name meta-flag is a synonym for this
variable. The default is Off, but readline will set it to
On if the locale contains eight-bit characters. This
variable is dependent on the LC_CTYPE locale category, and
may change if the locale is changed.
isearch-terminators (``C-[C-J'')
The string of characters that should terminate an
incremental search without subsequently executing the
character 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.
keyseq-timeout (500)
Specifies the duration readline will wait for a character
when reading an ambiguous key sequence (one that can form
a complete key sequence using the input read so far, or
can take additional input to complete a longer key
sequence). If no input is received within the timeout,
readline will use the shorter but complete key sequence.
The value is specified in milliseconds, so a value of 1000
means that readline will wait one second for additional
input. If this variable is set to a value less than or
equal to zero, or to a non-numeric value, readline will
wait until another key is pressed to decide which key
sequence to complete.
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
leading `.' 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. The default is Off, but readline will
set it to On if the locale contains eight-bit characters.
This variable is dependent on the LC_CTYPE locale
category, and may change if the locale is changed.
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
individual undo lists across calls to readline.
show-all-if-ambiguous (Off)
This alters the default behavior of the completion
functions. If set to On, words which have more than one
possible completion cause the matches to be listed
immediately instead of ringing the bell.
show-all-if-unmodified (Off)
This alters the default behavior of the completion
functions in a fashion similar to show-all-if-ambiguous.
If set to On, words which have more than one possible
completion without any possible partial completion (the
possible completions don't share a common prefix) cause
the matches to be listed immediately instead of ringing
the bell.
show-mode-in-prompt (Off)
If set to On, add a string to the beginning of the prompt
indicating the editing mode: emacs, vi command, or vi
insertion. The mode strings are user-settable (e.g.,
emacs-mode-string).
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 following the
cursor are not duplicated.
vi-cmd-mode-string ((cmd))
If the show-mode-in-prompt variable is enabled, this
string is displayed immediately before the last line of
the primary prompt when vi editing mode is active and in
command mode. The value is expanded like a key binding,
so the standard set of meta- and control prefixes and
backslash escape sequences is available. Use the \1 and
\2 escapes to begin and end sequences of non-printing
characters, which can be used to embed a terminal control
sequence into the mode string.
vi-ins-mode-string ((ins))
If the show-mode-in-prompt variable is enabled, this
string is displayed immediately before the last line of
the primary prompt when vi editing mode is active and in
insertion mode. The value is expanded like a key binding,
so the standard set of meta- and control prefixes and
backslash escape sequences is available. Use the \1 and
\2 escapes to begin and end sequences of non-printing
characters, which can be used to embed a terminal control
sequence into the mode string.
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
conditional compilation features of the C preprocessor which
allows key bindings and variable settings to be performed as the
result of tests. There are four parser directives used.
$if The $if construct allows bindings to be made based on the
editing mode, the terminal being used, or the application
using readline. The text of the test, after any
comparison operator,
extends to the end of the line; unless otherwise noted,
no characters are required to isolate it.
mode The mode= form of the $if directive is used to test
whether readline is in emacs or vi mode. This may
be used in conjunction with the set keymap command,
for instance, to set bindings in the emacs-standard
and emacs-ctlx keymaps only if readline is starting
out in emacs mode.
term The term= form may be used to include terminal-
specific key bindings, perhaps to bind the key
sequences output by the terminal's function keys.
The word on the right side of the = is tested
against both the full name of the terminal and the
portion of the terminal name before the first -.
This allows sun to match both sun and sun-cmd, for
instance.
version
The version test may be used to perform comparisons
against specific readline versions. The version
expands to the current readline version. The set
of comparison operators includes =, (and ==), !=,
<=, >=, <, and >. The version number supplied on
the right side of the operator consists of a major
version number, an optional decimal point, and an
optional minor version (e.g., 7.1). If the minor
version is omitted, it is assumed to be 0. The
operator may be separated from the string version
and from the version number argument by whitespace.
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 particular
value. This could be used to bind key sequences to
functions useful for a specific program. For
instance, the following command adds a key sequence
that quotes the current or previous word in bash:
$if Bash
# Quote the current or previous word
"\C-xq": "\eb\"\ef\""
$endif
variable
The variable construct provides simple equality
tests for readline variables and values. The
permitted comparison operators are =, ==, and !=.
The variable name must be separated from the
comparison operator by whitespace; the operator may
be separated from the value on the right hand side
by whitespace. Both string and boolean variables
may be tested. Boolean variables must be tested
against the values on and off.
$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-
incremental.
Incremental searches begin before the user has finished typing
the search string. As each character of the search string is
typed, readline displays the next entry from the history matching
the string typed so far. An incremental search requires only as
many characters as needed to find the desired history entry. The
characters present in the value of the isearch-terminators
variable are used to terminate an incremental search. If that
variable has not been assigned a value the Escape and Control-J
characters will terminate an incremental search. Control-G will
abort an incremental search and restore the original line. When
the search is terminated, the history entry containing the search
string becomes the current line.
To find other matching entries in the history list, type Control-
S or Control-R as appropriate. This will search backward or
forward in the history for the next entry matching the search
string typed so far. Any other key sequence bound to a readline
command will terminate the search and execute that command. For
instance, a newline will terminate the search and accept the
line, thereby executing the command from the history list.
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
composed 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.
previous-screen-line
Attempt to move point to the same physical screen column
on the previous physical screen line. This will not have
the desired effect if the current readline line does not
take up more than one physical line or if point is not
greater than the length of the prompt plus the screen
width.
next-screen-line
Attempt to move point to the same physical screen column
on the next physical screen line. This will not have the
desired effect if the current readline line does not take
up more than one physical line or if the length of the
current readline line is not greater than the length of
the prompt plus the screen width.
clear-display (M-C-l)
Clear the screen and, if possible, the terminal's
scrollback buffer, then redraw the current line, leaving
the current line at the top of the screen.
clear-screen (C-l)
Clear the screen, then redraw the current line, 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
forward 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
currently being entered.
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. A numeric argument, if supplied, specifies the
history entry to use instead of the current line.
fetch-history
With a numeric argument, fetch that entry from the history
list and make it the current line. Without an argument,
move back to the first entry in the history list.
reverse-search-history (C-r)
Search backward starting at the current line and moving
`up' through the history as necessary. This is an
incremental search.
forward-search-history (C-s)
Search forward starting at the current line and moving
`down' through the history as necessary. This is an
incremental search.
non-incremental-reverse-search-history (M-p)
Search backward through the history starting at the
current 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-incremental
search for a string supplied by the user.
history-search-forward
Search forward through the history for the string of
characters between the start of the current line and the
point. This is a non-incremental search.
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.
history-substring-search-backward
Search backward through the history for the string of
characters between the start of the current line and the
current cursor position (the point). The search string
may match anywhere in a history line. This is a non-
incremental search.
history-substring-search-forward
Search forward through the history for the string of
characters between the start of the current line and the
point. The search string may match anywhere in a history
line. This is a non-incremental search.
yank-nth-arg (M-C-y)
Insert the first argument to the previous command (usually
the second word on the previous line) at point. With an
argument n, insert the nth word from the previous command
(the words in the previous command begin with word 0). A
negative argument inserts the nth word from the end of the
previous command. Once the argument n is computed, the
argument is extracted as if the "!n" history 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
history (back or forward). The history expansion
facilities are used to extract the last word, 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 description
of history expansion.
history-expand-line (M-^)
Perform history expansion on the current line. See
HISTORY EXPANSION below for a description of history
expansion.
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.
edit-and-execute-command (C-x C-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
end-of-file (usually C-d)
The character indicating end-of-file as set, for example,
by ``stty''. If this character is read when there are no
characters on the line, and point is at the beginning of
the line, readline interprets it as the end of input and
returns EOF.
delete-char (C-d)
Delete the character at point. If this function is bound
to the same character as the tty EOF character, as C-d
commonly is, see above for the effects.
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 character
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
negative argument, uppercase the previous word, but do not
move point.
downcase-word (M-l)
Lowercase the current (or following) word. With a
negative argument, lowercase the previous word, but do not
move point.
capitalize-word (M-c)
Capitalize the current (or following) word. With a
negative 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
overwrite 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
backward-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
boundaries 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
Kill from point to the end of the current word, or if
between words, to the end of the next word. Word
boundaries are the same as those used by
shell-forward-word.
shell-backward-kill-word
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
command is followed by one or more digits, optionally with
a leading minus sign, those digits define the argument.
If the command is followed by digits, executing
universal-argument again ends the numeric argument, but is
otherwise ignored. As a special case, if this command is
immediately followed by a character that is neither a
digit nor minus sign, the argument count for the next
command is multiplied by four. The argument count is
initially one, so executing this function the first time
makes the argument count four, a second time makes the
argument count sixteen, and so on.
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 $), username (if the text begins
with ~), hostname (if the text begins with @), or command
(including aliases and functions) in turn. If none of
these produces a match, filename completion is attempted.
possible-completions (M-?)
List the possible completions of the text before point.
insert-completions (M-*)
Insert all completions of the text before point that would
have been generated by possible-completions.
menu-complete
Similar to complete, but replaces the word to be completed
with a single match from the list of possible completions.
Repeated execution of menu-complete steps through the list
of possible completions, inserting each match in turn. At
the end of the list of completions, the bell is rung
(subject to the setting of bell-style) and the original
text is restored. An argument of n moves n positions
forward in the list of matches; a negative argument may be
used to move backward through the list. This command is
intended to be bound to TAB, but is unbound by default.
menu-complete-backward
Identical to menu-complete, but moves backward through the
list of possible completions, as if menu-complete had been
given a negative argument. This command is unbound by
default.
delete-char-or-list
Deletes the character under the cursor if not at the
beginning or end of the line (like delete-char). If at
the end of the line, behaves identically to
possible-completions. This command is unbound by default.
complete-filename (M-/)
Attempt filename completion on the text before point.
possible-filename-completions (C-x /)
List the possible completions of the text before point,
treating it as a filename.
complete-username (M-~)
Attempt completion on the text before point, treating it
as a username.
possible-username-completions (C-x ~)
List the possible completions of the text before point,
treating it as a username.
complete-variable (M-$)
Attempt completion on the text before point, treating it
as a shell variable.
possible-variable-completions (C-x $)
List the possible completions of the text before point,
treating it as a shell variable.
complete-hostname (M-@)
Attempt completion on the text before point, treating it
as a hostname.
possible-hostname-completions (C-x @)
List the possible completions of the text before point,
treating it as a hostname.
complete-command (M-!)
Attempt completion on the text before point, treating it
as a command name. Command completion attempts to match
the text against aliases, reserved words, shell functions,
shell builtins, and finally executable filenames, in that
order.
possible-command-completions (C-x !)
List the possible completions of the text before point,
treating it as a command name.
dynamic-complete-history (M-TAB)
Attempt completion on the text before point, comparing the
text against lines from the history list for possible
completion matches.
dabbrev-expand
Attempt menu completion on the text before point,
comparing the text against lines from the history list for
possible completion matches.
complete-into-braces (M-{)
Perform filename completion and insert the list of
possible completions enclosed within braces so the list is
available to the shell (see Brace Expansion above).
Keyboard Macros
start-kbd-macro (C-x ()
Begin saving the characters typed into the current
keyboard macro.
end-kbd-macro (C-x ))
Stop saving the characters typed into the current keyboard
macro and 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
keyboard.
print-last-kbd-macro ()
Print the last keyboard macro defined in a format suitable
for the inputrc file.
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-lowercase-version (M-A, M-B, M-x, ...)
If the metafied character x is uppercase, run the command
that is bound to the corresponding metafied lowercase
character. The behavior is undefined if x is already
lowercase.
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
executing 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
supplied, the mark is set to that position.
exchange-point-and-mark (C-x C-x)
Swap the point with the mark. The current cursor position
is set to the saved position, and the old cursor position
is saved as the mark.
character-search (C-])
A character is read and point is moved to the next
occurrence of that character. A negative argument
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 argument
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
comment-begin, the value is inserted, otherwise the
characters 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
comment-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.
spell-correct-word (C-x s)
Perform spelling correction on the current word, treating
it as a directory or filename, in the same way as the
cdspell shell option. Word boundaries are the same as
those used by shell-forward-word.
glob-complete-word (M-g)
The word before point is treated as a pattern for pathname
expansion, with an asterisk implicitly appended. This
pattern is used to generate a list of matching filenames
for possible completions.
glob-expand-word (C-x *)
The word before point is treated as a pattern for pathname
expansion, and the list of matching filenames is inserted,
replacing the word. If a numeric argument is supplied, an
asterisk is appended before pathname expansion.
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
supplied, 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
argument 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 compspec for
the full pathname is searched for first. If no compspec is found
for the full pathname, an attempt is made to find a compspec for
the portion following the final slash. If those searches do not
result in a compspec, any compspec defined with the -D option to
complete is used as the default. If there is no default
compspec, bash attempts alias expansion on the command word as a
final resort, and attempts to find a compspec for the command
word from any successful expansion.
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 pattern
need not match the word being completed. The GLOBIGNORE shell
variable is not used to filter the matches, but the FIGNORE
variable is used.
Next, the string specified as the argument to the -W option is
considered. The string is first split using the characters in
the IFS special variable as delimiters. Shell quoting is
honored. Each word is then expanded using brace expansion, tilde
expansion, parameter and variable expansion, command
substitution, and arithmetic expansion, as described above under
EXPANSION. 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 argument
($1) is the name of the command whose arguments are being
completed, the second argument ($2) is the word being completed,
and the third argument ($3) is the word preceding the word being
completed on the current command line. No filtering of the
generated completions against the word being completed is
performed; the function or command has complete freedom in
generating the matches.
Any function specified with -F is invoked first. The function
may use any of the shell facilities, including the compgen
builtin described below, to generate the matches. It must put
the possible completions in the COMPREPLY array variable, one per
array element.
Next, any command specified with the -C option is invoked in an
environment equivalent to command substitution. It should print
a list of completions, one per line, to the standard output.
Backslash may be used to escape a newline, if necessary.
After all of the possible completions are generated, any filter
specified with the -X option is applied to the list. The filter
is a pattern as used for pathname expansion; a & in the pattern
is replaced with the text of the word being completed. A literal
& may be escaped with a backslash; the backslash is removed
before attempting a match. Any completion that matches the
pattern will be removed from the list. A leading ! negates the
pattern; in this case any completion not matching the pattern
will be removed. If the nocasematch shell option is enabled, the
match is performed without regard to the case of alphabetic
characters.
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
completions. 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
readline variable, regardless of the setting of the mark-
symlinked-directories readline variable.
There is some support for dynamically modifying completions.
This is most useful when used in combination with a default
completion specified with complete -D. It's possible for shell
functions executed as completion handlers to indicate that
completion should be retried by returning an exit status of 124.
If a shell function returns 124, and changes the compspec
associated 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 -o bashdefault -o default
When the -o history option to the set builtin is enabled, the
shell provides access to the command history, the list of
commands 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
variables 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
HISTFILESIZE. If HISTFILESIZE is unset, or set to null, a non-
numeric value, or a numeric value less than zero, the history
file is not truncated. When the history file is read, lines
beginning with the history comment character followed immediately
by a digit are interpreted as timestamps for the following
history line. These timestamps are optionally displayed
depending on the value of the HISTTIMEFORMAT variable. When a
shell with history enabled 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 history file is overwritten. If HISTFILE is
unset, or if the history file is unwritable, the history is not
saved. If the HISTTIMEFORMAT variable is set, time stamps are
written to the history 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 unset, or set to null, a non-numeric value, or a
numeric value less than zero, the history file is not truncated.
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
command-line editing, search commands are available in each
editing mode that provide access to the history list.
The shell allows control over which commands are saved on the
history list. The HISTCONTROL and HISTIGNORE variables may be
set to cause the shell to save only a subset of the commands
entered. The cmdhist shell option, if enabled, causes the shell
to attempt to save each line of a multi-line command in the same
history entry, adding semicolons where necessary to preserve
syntactic correctness. The lithist shell option causes the shell
to save the command with embedded newlines instead of semicolons.
See the description of the shopt builtin below under SHELL
BUILTIN COMMANDS for information on setting and unsetting shell
options.
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, and is performed
on each line individually without taking quoting on previous
lines into account. 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 portions of that line that are
acted upon are words. Various modifiers 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 introduced by the appearance of
the history expansion character, which is ! by default. Only
backslash (\) and single quotes can quote the history expansion
character, but the history expansion character is also treated as
quoted if it immediately precedes the closing double quote in a
double-quoted string.
Several characters inhibit history expansion if found immediately
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 substitutions are not
immediately passed to the shell parser. Instead, the expanded
line is reloaded into the readline editing buffer for further
modification. If readline is being used, and the histreedit
shell option is enabled, a failed history substitution 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 comment
character to mark history timestamps when writing the history
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
position in the history list containing string. The
trailing ? may be omitted if string is followed
immediately by a newline. If string is missing, the
string from the most recent search is used; it is an error
if there is no previous search string.
^string1^string2^
Quick substitution. Repeat the previous command,
replacing 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 designator.
It may be omitted if the word designator begins with a ^, $, *,
-, or %. Words are numbered from the beginning of the line, with
the first word being denoted by 0 (zero). Words are inserted
into the current line separated by single spaces.
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 word. This is usually the last argument, but
will expand to the zeroth word if there is only one word
in the line.
% The first word matched by the most recent `?string?'
search, if the search string begins with a character that
is part of a word.
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 x is
missing, it defaults to 0.
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
`:'. These modify, or edit, the word or words selected from the
history event.
h Remove a trailing filename component, leaving only the
head.
t Remove all leading filename 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
substitutions.
x Quote the substituted words as with q, but break into
words at blanks and newlines. The q and x modifiers are
mutually exclusive; the last one supplied is used.
s/old/new/
Substitute new for the first occurrence of old in the
event line. Any character may be used as the delimiter in
place of /. The final delimiter is optional if it is the
last character 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. If
new is null, each matching old is deleted.
& 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 delimiter
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' or `&' modifier once to each word
in the event line.
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, return, break, continue, let, and shift builtins accept
and process arguments beginning with - without requiring --.
Other builtins that accept arguments but are not specified as
accepting 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. The
return status is zero.
. 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, filenames in PATH are used to find the
directory containing filename, but filename does not need
to be executable. The file searched for in PATH need not
be executable. When bash is not in posix mode, it
searches the current directory 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. If the -T option is
enabled, . inherits any trap on DEBUG; if it is not, any
DEBUG trap string is saved and restored around the call to
., and . unsets the DEBUG trap while it executes. If -T
is not set, and the sourced file changes the DEBUG trap,
the new value is retained when . completes. 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
substitution 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 disabled or, when
run with job control enabled, any specified jobspec was
not found or was started without job control.
bind [-m keymap] [-lpsvPSVX]
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 [-m keymap] keyseq:readline-command
bind readline-command-line
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 a readline initialization file such
as .inputrc, but each binding or command must be passed as
a separate argument; e.g., '"\C-x\C-r":
re-read-init-file'. Options, if supplied, have the
following meanings:
-m keymap
Use keymap as the keymap to be affected by the
subsequent bindings. Acceptable keymap names are
emacs, emacs-standard, emacs-meta, emacs-ctlx, vi,
vi-move, vi-command, and vi-insert. vi is
equivalent to vi-command (vi-move is also a
synonym); 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
contents of the readline line buffer and the
READLINE_POINT and READLINE_MARK variables to the
current location of the insertion point and the
saved insertion point (the mark), respectively.
The shell assigns any numeric argument the user
supplied to the READLINE_ARGUMENT variable. If
there was no argument, that variable is not set.
If the executed command changes the value of any of
READLINE_LINE, READLINE_POINT, or READLINE_MARK,
those new values will be reflected in the editing
state.
-X List all key sequences bound to shell commands and
the associated commands in a format that can be
reused as input.
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 0 unless n is not
greater than or equal to 1.
builtin shell-builtin [arguments]
Execute the specified shell builtin, passing it arguments,
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 redefined 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
corresponding 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. if dir is not
supplied, the value of the HOME shell variable is the
default. The variable CDPATH defines the search path for
the directory containing dir: each directory name in
CDPATH is searched for dir. Alternative 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 causes cd to use the physical
directory structure by resolving symbolic links while
traversing dir and before processing instances of .. in
dir (see also the -P option to the set builtin command);
the -L option forces symbolic links to be followed by
resolving the link after processing instances of .. in
dir. If .. appears in dir, it is processed by removing
the immediately previous pathname component from dir, back
to a slash or the beginning of dir. If the -e option is
supplied with -P, and the current working directory cannot
be successfully determined after a successful directory
change, cd will return an unsuccessful status. On systems
that support it, the -@ option presents the extended
attributes associated with a file as a directory. An
argument of - is converted to $OLDPWD before the directory
change is attempted. 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. If the directory change is successful, cd sets
the value of the PWD environment variable to the new
directory name, and sets the OLDPWD environment variable
to the value of the current working directory before the
change. 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
function 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
utilities. If either the -V or -v option is supplied, a
description of command is printed. The -v option causes a
single word indicating the command or filename used to
invoke command to be displayed; the -V option produces a
more verbose description. If the -V or -v option is
supplied, 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
supplied, or no matches were generated.
complete [-abcdefgjksuv] [-o comp-option] [-DEI] [-A action] [-G
globpat] [-W wordlist]
[-F function] [-C command] [-X filterpat] [-P prefix] [-S
suffix] name [name ...]
complete -pr [-DEI] [name ...]
Specify how arguments to each name should be completed.
If the -p option is supplied, or if no options are
supplied, existing completion specifications are printed
in a way that allows them to be reused as input. The -r
option removes a completion specification for each name,
or, if no names are supplied, all completion
specifications. The -D option indicates that other
supplied options and actions should apply to the
``default'' command completion; that is, completion
attempted on a command for which no completion has
previously been defined. The -E option indicates that
other supplied options and actions should apply to
``empty'' command completion; that is, completion
attempted on a blank line. The -I option indicates that
other supplied options and actions should apply to
completion on the initial non-assignment word on the line,
or after a command delimiter such as ; or |, which is
usually command name completion. If multiple options are
supplied, the -D option takes precedence over -E, and both
take precedence over -I. If any of -D, -E, or -I are
supplied, any other name arguments are ignored; these
completions only apply to the case specified by the
option.
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
necessary, the -P and -S options) should be quoted to
protect them from expansion before the complete builtin is
invoked.
-o comp-option
The comp-option controls several aspects of the
compspec's behavior beyond the simple generation
of completions. comp-option may be one of:
bashdefault
Perform the rest of the default bash
completions if the compspec generates no
matches.
default Use readline's default filename completion
if the compspec generates no matches.
dirnames
Perform directory name completion if the
compspec generates no matches.
filenames
Tell readline that the compspec generates
filenames, so it can perform any
filename-specific processing (like adding
a slash to directory names, quoting
special characters, or suppressing
trailing spaces). Intended to be used
with shell functions.
noquote Tell readline not to quote the completed
words if they are filenames (quoting
filenames is the default).
nosort Tell readline not to sort the list of
possible completions alphabetically.
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 generate
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
specified 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
specified 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 completions.
Arguments are passed as with the -F option.
-F function
The shell function function is executed in the
current shell environment. When the function is
executed, the first argument ($1) is the name of
the command whose arguments are being completed,
the second argument ($2) is the word being
completed, and the third argument ($3) is the word
preceding the word being completed on the current
command line. 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. Shell quoting is
honored within wordlist, in order to provide a
mechanism for the words to contain shell
metacharacters or characters in the value of IFS.
The possible completions 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 filterpat
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
supplied, an option other than -p or -r is supplied
without a name argument, an attempt is made to remove a
completion specification for a name for which no
specification exists, or an error occurs adding a
completion specification.
compopt [-o option] [-DEI] [+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
completion. The possible values of option are those valid
for the complete builtin described above. The -D option
indicates that other supplied options should apply to the
``default'' command completion; that is, completion
attempted on a command for which no completion has
previously been defined. The -E option indicates that
other supplied options should apply to ``empty'' command
completion; that is, completion attempted on a blank line.
The -I option indicates that other supplied options should
apply to completion on the initial non-assignment word on
the line, or after a command delimiter such as ; or |,
which is usually command name completion.
The return value is true unless an invalid option is
supplied, 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. The return value is
0 unless n is not greater than or equal to 1.
declare [-aAfFgiIlnrtux] [-p] [name[=value] ...]
typeset [-aAfFgiIlnrtux] [-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, additional
options, other than -f and -F, 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 each name 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 -I
option causes local variables to inherit the attributes
(except the nameref attribute) and value of any existing
variable with the same name at a surrounding scope. If
there is no existing variable, the local variable is
initially unset. 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.
-n Give each name the nameref attribute, making it a
name reference to another variable. That other
variable is defined by the value of name. All
references, assignments, and attribute
modifications to name, except those using or
changing the -n attribute itself, are performed on
the variable referenced by name's value. The
nameref attribute cannot be applied to array
variables.
-r Make names readonly. These names cannot then be
assigned values by subsequent assignment statements
or unset.
-t Give each name the trace attribute. Traced
functions 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 and +A may not be used to
destroy array variables and +r will not remove the
readonly attribute. When used in a function, declare and
typeset make 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. When using -a or -A and the compound assignment
syntax to create array variables, additional attributes do
not take effect until subsequent assignments. 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 [-clpv] [+n] [-n]
Without options, displays the list of currently remembered
directories. The default display is on a single line with
directory names separated by spaces. Directories are
added to the list with the pushd command; the popd command
removes entries from the list. The current directory is
always the first directory in the stack.
-c Clears the directory stack by deleting all of the
entries.
-l Produces a listing using full pathnames; 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.
+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.
The return value is 0 unless an invalid option is supplied
or n indexes beyond the end of the directory stack.
disown [-ar] [-h] [jobspec ... | pid ... ]
Without options, remove each jobspec from the table of
active jobs. If jobspec is not present, and neither the
-a nor the -r option is supplied, 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 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
newline. The return status is 0 unless a write error
occurs. If -n is specified, the trailing newline is
suppressed. If the -e option is given, interpretation of
the following backslash-escaped characters is enabled.
The -E option disables the interpretation of these escape
characters, even on systems where they are interpreted by
default. The xpg_echo shell option may be used to
dynamically determine whether or not echo expands these
escape characters by default. echo 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
hexadecimal 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. Bash will use the value of the
BASH_LOADABLES_PATH variable as a colon-separated list of
directories in which to search for filename. The default
is system-dependent. 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 consists 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
indication of whether or not each is enabled. If -s is
supplied, the output is restricted to the POSIX special
builtins. If no options are supplied and a name is not a
shell builtin, enable will attempt to load name from a
shared object named name, as if the command were ``enable
-f name name . 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 environment.
If -a is supplied, the shell passes name as the zeroth
argument to the executed command. If command cannot be
executed for some reason, a non-interactive shell exits,
unless the execfail shell option is enabled. In that
case, it returns failure. An interactive shell returns
failure if the file cannot be executed. A subshell exits
unconditionally if exec fails. If command 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
executed. A trap on EXIT is executed before the shell
terminates.
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 names of all exported variables 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 encountered, one
of the names is not a valid shell variable name, or -f is
supplied with a name that is not a function.
fc [-e ename] [-lnr] [first] [last]
fc -s [pat=rep] [cmd]
The first form selects a range of commands from first to
last from the history list and displays or edits and re-
executes them. 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). When listing, a first or last of
0 is equivalent to -1 and -0 is equivalent to the current
command (usually the fc command); otherwise 0 is
equivalent to -1 and -0 is invalid. 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 specified, it is set to
the previous command for editing and -16 for listing.
The -n option suppresses the command numbers when listing.
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. Command is
interpreted the same as first above. 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 supplied,
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 control
enabled, if jobspec does not specify a valid job or
jobspec specifies a job that was started without job
control.
getopts optstring name [arg ...]
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 processed
into the variable OPTIND. OPTIND is initialized to 1 each
time the shell or a shell script is invoked. When an
option requires an argument, getopts places that argument
into the variable OPTARG. The shell does not reset OPTIND
automatically; it must be manually reset between multiple
calls to getopts within the same shell invocation if a new
set of parameters is to be used.
When the end of options is encountered, getopts exits with
a return value greater than zero. OPTIND is set to the
index of the first non-option argument, and name is set to
?.
getopts normally parses the positional parameters, but if
more arguments are supplied as arg values, getopts parses
those instead.
getopts can report errors in two ways. If the first
character of optstring is a colon, silent error reporting
is used. In normal operation, diagnostic messages are
printed when invalid options or missing option arguments
are encountered. If the variable OPTERR is set to 0, no
error messages will be displayed, even if the first
character of optstring is not a colon.
If an invalid option is seen, getopts places ? into name
and, if not silent, prints an error message and unsets
OPTARG. If getopts is silent, the option character found
is placed in OPTARG and no diagnostic message is printed.
If a required argument is not found, and getopts is not
silent, a question mark (?) is placed in name, OPTARG is
unset, and a diagnostic message is printed. If getopts is
silent, then a colon (:) is placed in name and OPTARG is
set to the option character found.
getopts returns true if an option, specified or
unspecified, 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
command 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
filename 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
arguments 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,
information 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
manpage-like format
-s Display only a short usage synopsis for each
pattern
The return status is 0 unless no command matches pattern.
history [n]
history -c
history -d offset
history -d start-end
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 supplied, it
is used as the name of the history file; if not, the value
of HISTFILE is used. Options, if supplied, have the
following meanings:
-c Clear the history list by deleting all the entries.
-d offset
Delete the history entry at position offset. If
offset is negative, it is interpreted as relative
to one greater than the last history position, so
negative indices count back from the end of the
history, and an index of -1 refers to the current
history -d command.
-d start-end
Delete the range of history entries between
positions start and end, inclusive. Positive and
negative values for start and end are interpreted
as described above.
-a Append the ``new'' history lines to the history
file. These are history lines entered since the
beginning of the current bash session, but not
already appended 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 append
them to the current history list.
-w Write the current history list 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 beginning
with the history comment character followed immediately by
a digit are interpreted as timestamps for the following
history entry. The return value is 0 unless an invalid
option is encountered, an error occurs while reading or
writing the history file, an invalid offset or range 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
information.
-n Display information only about jobs that have
changed status since the user was last notified of
their status.
-p List only the process ID of the job's process group
leader.
-r Display only running jobs.
-s Display only 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|-L [sigspec | exit_status]
Send the signal named by sigspec or signum to the
processes 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. The -L option
is equivalent to -l. 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 created,
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. If
name is -, the set of shell options is made local to the
function in which local is invoked: shell options changed
using the set builtin inside the function are restored to
their original values when the function returns. The
restore is effected as if a series of set commands were
executed to restore the values that were in place before
the function. 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 supplied, or name is a readonly variable.
logout Exit a login shell.
mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd]
[-C callback] [-c quantum] [array]
readarray [-d delim] [-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 meanings:
-d The first character of delim is used to terminate
each input line, rather than newline. If delim is
the empty string, mapfile will terminate a line
when it reads a NUL character.
-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 delim (default 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
arguments. 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. The elements
are numbered from 0 starting at the first directory listed
by dirs. With no arguments, popd removes the top
directory from the stack, and changes to the new top
directory. Arguments, if supplied, 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, from the
stack. 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 top element of the directory stack is modified, and
the -n option was not supplied, popd uses the cd builtin
to change to the directory at the top of the stack. If
the cd fails, popd returns a non-zero value.
Otherwise, popd returns false if an invalid option is
encountered, the directory stack is empty, or a non-
existent directory stack entry is specified.
If the popd command is successful, bash runs dirs to show
the final contents of the directory stack, and the return
status is 0.
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 interprets the
following extensions:
%b causes printf to expand backslash escape sequences
in the corresponding argument in the same way as
echo -e.
%q causes printf to output the corresponding argument
in a format that can be reused as shell input.
%Q like %q, but applies any supplied precision to the
argument before quoting it.
%(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
represents the time the shell was invoked. If no
argument is specified, conversion behaves as if -1
had been given. This is an exception to the usual
printf behavior.
The %b, %q, and %T directives all use the field width and
precision arguments from the format specification and
write that many bytes from (or use that wide a field for)
the expanded argument, which usually contains more
characters than the original.
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
double 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, pushd
exchanges the top two elements of the directory stack.
Arguments, if supplied, have the following meanings:
-n Suppresses the normal change of directory when
rotating or 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
After the stack has been modified, if the -n option was
not supplied, pushd uses the cd builtin to change to the
directory at the top of the stack. If the cd fails, pushd
returns a non-zero value.
Otherwise, if no arguments are supplied, pushd returns 0
unless the directory stack is empty. When rotating the
directory stack, pushd returns 0 unless the directory
stack is empty or a non-existent directory stack element
is specified.
If the pushd command is successful, bash runs dirs to show
the final contents of the directory stack.
pwd [-LP]
Print the absolute pathname of the current working
directory. 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 reading 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,
split into words as described above under Word Splitting,
and the first word is assigned to the first name, the
second word to the second name, and so on. If there are
more words than names, the remaining words and their
intervening delimiters are 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
using the same rules the shell uses for expansion
(described above under Word Splitting). 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. If delim is
the empty string, read will terminate a line when
it reads a NUL character.
-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, but uses readline's default filename
completion.
-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
honors a delimiter if fewer than nchars characters
are read before the delimiter.
-N nchars
read returns after reading exactly nchars
characters 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. The
result is not split on the characters in IFS; the
intent is that the variable is assigned exactly the
characters read (with the exception of backslash;
see the -r option below).
-p prompt
Display prompt on standard error, without a
trailing 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 then
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 (or a specified number of
characters) 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 read
times out, read saves any partial input read into
the specified variable name. If timeout is 0, read
returns immediately, without trying to read any
data. The exit status is 0 if input is available
on the specified file descriptor, or the read will
return EOF, non-zero 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, without the
ending delimiter but otherwise unmodified, is assigned to
the variable REPLY. The exit status is zero, unless end-
of-file is encountered, read times out (in which case the
status is greater than 128), a variable assignment error
(such as assigning to a readonly variable) occurs, 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
variable name, or -f is supplied with a name that is not a
function.
return [n]
Causes a function to stop executing and return the value
specified by n to its caller. If n is omitted, the return
status is that of the last command executed in the
function body. If return is executed by a trap handler,
the last command used to determine the status is the last
command executed before the trap handler. If return is
executed during a DEBUG trap, the last command used to
determine the status is the last command executed by the
trap handler before return was invoked. If return is used
outside a function, but during execution of a script by
the . (source) command, it causes the shell to stop
executing 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 n is supplied, the
return value is its least significant 8 bits. The return
status is non-zero if return is supplied a non-numeric
argument, or is used outside a function and not during
execution of a script by . or source. 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, display the name and value of each shell
variable in a format that can be reused as input for
setting or resetting the currently-set variables. 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 arguments 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 Each variable or function that is created or
modified is given the export attribute and marked
for export to the environment 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 list, or a compound
command (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
!. If a compound command other than a subshell
returns a non-zero status because a command failed
while -e was being ignored, the shell does not
exit. A trap on ERR, if set, is executed before
the shell exits. This option applies to the shell
environment and each subshell environment
separately (see COMMAND EXECUTION ENVIRONMENT
above), and may cause subshells to exit before
executing all the commands in the subshell.
If a compound command or shell function executes
in a context where -e is being ignored, none of
the commands executed within the compound command
or function body will be affected by the -e
setting, even if -e is set and a command returns a
failure status. If a compound command or shell
function sets -e while executing in a context
where -e is ignored, that setting will not have
any effect until the compound command or the
command containing the function call completes.
-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 statements
are placed in the environment for a command, 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).
All processes run in a separate process group.
When a background job completes, the shell prints
a line containing its exit status.
-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
successfully. 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). See SEE ALSO below for a reference
to a document that details how posix mode
affects bash's behavior.
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
GLOBIGNORE variables, if they appear in the
environment, 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
effective user id is set to the real user id. If
the -p option is supplied at startup, the
effective user id is not reset. Turning this
option off causes the effective user and group ids
to be set to the real user and group ids.
-r Enable restricted shell mode. This option cannot
be unset once it has been set.
-t Exit after reading and executing one command.
-u Treat unset variables and parameters other than
the special parameters "@" and "*", or array
variables subscripted with "@" or "*", as an error
when performing parameter expansion. If expansion
is attempted on an unset variable or parameter,
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,
followed 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 interactive.
-P If set, the shell does not resolve symbolic links
when executing commands such as cd that change the
current working directory. It uses the physical
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
inherited 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 settings controlling optional shell
behavior. The settings can be either those listed below,
or, if the -o option is used, those available with the -o
option to the set builtin command. 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; if optnames are supplied, the output is restricted to
those options. The -p option causes output to be
displayed in a form that may be reused as input. Other
options have the following meanings:
-s Enable (set) each optname.
-u Disable (unset) each optname.
-q Suppresses normal output (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,
shopt shows only 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:
assoc_expand_once
If set, the shell suppresses multiple evaluation
of associative array subscripts during arithmetic
expression evaluation, while executing builtins
that can perform variable assignments, and while
executing builtins that perform array
dereferencing.
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
directory 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
filename 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
external (non-builtin) command and, if necessary,
updates the values of LINES and COLUMNS. This
option is enabled by default.
cmdhist If set, bash attempts to save all lines of a
multiple-line command in the same history entry.
This allows easy re-editing of multi-line
commands. This option is enabled by default, but
only has an effect if command history is enabled,
as described above under HISTORY.
compat31
compat32
compat40
compat41
compat42
compat43
compat44
compat50
These control aspects of the shell's compatibility
mode (see SHELL COMPATIBILITY MODE below).
complete_fullquote
If set, bash quotes all shell metacharacters in
filenames and directory names when performing
completion. If not set, bash removes
metacharacters such as the dollar sign from the
set of characters that will be quoted in completed
filenames when these metacharacters appear in
shell variable references in words to be
completed. This means that dollar signs in
variable names that expand to directories will not
be quoted; however, any dollar signs appearing in
filenames will not be quoted, either. This is
active only when bash is using backslashes to
quote completed filenames. This variable is set
by default, which is the default bash behavior in
versions through 4.2.
direxpand
If set, bash replaces directory names with the
results of word expansion when performing filename
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. The
filenames ``.'' and ``..'' must always be
matched explicitly, even if dotglob is set.
execfail
If set, a non-interactive shell will not exit if
it cannot execute the file specified as an
argument to the exec builtin command. An
interactive shell does not exit if exec fails.
expand_aliases
If set, aliases are expanded as described above
under ALIASES. This option is enabled by default
for interactive shells.
extdebug
If set at shell invocation, or in a shell startup
file, arrange to execute the debugger profile
before the shell starts, identical to the
--debugger option. If set after invocation,
behavior intended for use by debuggers is enabled:
1. The -F option to the declare builtin
displays the source file name and line
number corresponding to each function name
supplied 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 function
or a shell script executed by the . or
source builtins), the shell simulates a
call to return.
4. BASH_ARGC and BASH_ARGV are updated as
described in their descriptions above).
5. Function tracing is enabled: command
substitution, shell functions, and
subshells invoked with ( command ) inherit
the DEBUG and RETURN traps.
6. Error tracing is enabled: command
substitution, 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
performed 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
FIGNORE. This option is enabled by default.
globasciiranges
If set, range expressions used in pattern matching
bracket expressions (see Pattern Matching above)
behave as if in the traditional C locale when
performing comparisons. That is, the current
locale's collating sequence is not taken into
account, so b will not collate between A and B,
and upper-case and lower-case ASCII characters
will collate together.
globskipdots
If set, pathname expansion will never match the
filenames ``.'' and ``..'', even if the pattern
begins with a ``.''. This option is enabled by
default.
globstar
If set, the pattern ** used in a pathname
expansion context will match all files and zero or
more directories and subdirectories. If the
pattern 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 resulting line is
loaded into the readline editing buffer, allowing
further modification.
hostcomplete
If set, and readline is being used, bash will
attempt to perform hostname completion when a word
containing a @ is being completed (see Completing
under READLINE above). This is enabled by
default.
huponexit
If set, bash will send SIGHUP to all jobs when an
interactive login shell exits.
inherit_errexit
If set, command substitution inherits the value of
the errexit option, instead of unsetting it in the
subshell environment. This option is enabled when
posix mode is enabled.
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
environment.
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.
localvar_inherit
If set, local variables inherit the value and
attributes of a variable of the same name that
exists at a previous scope before any new value is
assigned. The nameref attribute is not inherited.
localvar_unset
If set, calling unset on local variables in
previous function scopes marks them so subsequent
lookups find them unset until that function
returns. This is identical to the behavior of
unsetting local variables at the current function
scope.
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
completions when completion is attempted on an
empty line.
nocaseglob
If set, bash matches filenames in a
case-insensitive fashion when performing pathname
expansion (see Pathname Expansion above).
nocasematch
If set, bash matches patterns in a
case-insensitive fashion when performing matching
while executing case or [[ conditional commands,
when performing pattern substitution word
expansions, or when filtering possible completions
as part of programmable completion.
noexpand_translation
If set, bash encloses the translated results of
$"..." quoting in single quotes instead of double
quotes. If the string is not translated, this has
no effect.
nullglob
If set, bash allows patterns which match no files
(see Pathname Expansion above) to expand to a null
string, rather than themselves.
patsub_replacement
If set, bash expands occurrences of & in the
replacement string of pattern substitution to the
text matched by the pattern, as described under
Parameter Expansion above. This option is enabled
by default.
progcomp
If set, the programmable completion facilities
(see Programmable Completion above) are enabled.
This option is enabled by default.
progcomp_alias
If set, and programmable completion is enabled,
bash treats a command name that doesn't have any
completions as a possible alias and attempts alias
expansion. If it has an alias, bash attempts
programmable completion using the command word
resulting from the expanded alias.
promptvars
If set, prompt strings undergo parameter
expansion, 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
positional parameters.
sourcepath
If set, the . (source) builtin uses the value of
PATH to find the directory containing the file
supplied as an argument. This option is enabled
by default.
varredir_close
If set, the shell automatically closes file
descriptors assigned using the {varname}
redirection syntax (see REDIRECTION above) instead
of leaving them open when the command completes.
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. A login shell, or a shell without job
control enabled, cannot be suspended; the -f option can be
used to override this and force the suspension. The
return status is 0 unless the shell is a login shell or
job control is not enabled and -f is not supplied.
test expr
[ expr ]
Return a status of 0 (true) or 1 (false) depending on the
evaluation of the conditional expression expr. Each
operator and operand must be a separate argument.
Expressions are composed 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 operators,
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
EXPRESSIONS, 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
expression 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-argument test using the second and third
arguments. If the first argument is exactly ( and
the third argument is exactly ), the result is the
one-argument test of the second argument.
Otherwise, the expression is false.
4 arguments
The following conditions are applied in the order
listed. If the first argument is !, the result is
the negation of the three-argument expression
composed of the remaining arguments. the two-
argument test using the second and third arguments.
If the first argument is exactly ( and the fourth
argument is exactly ), the result is the two-
argument test of the second and third 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
lexicographically 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 associated
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
command, 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 pipeline (which may consist of a single simple command),
a list, or a compound command returns 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 immediately following a while or until
keyword, part of the test in an if statement, part of a
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 using !. These are the same conditions obeyed by
the errexit (-e) option.
Signals ignored upon entry to the shell cannot be trapped
or reset. 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
interpreted if used as a command name. If the -t option
is used, type prints a string which is one of alias,
keyword, 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,
which is 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 [-HS] -a
ulimit [-HS] [-bcdefiklmnpqrstuvxPRT [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, if appropriate, are
printed before the value. Other options are interpreted
as follows:
-a All current limits are reported; no limits are set
-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
-k The maximum number of kqueues that may be allocated
-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
-P The maximum number of pseudoterminals
-R The maximum time a real-time process can run before
blocking, in microseconds
-T The maximum number of threads
If limit is given, and the -a option is not used, limit is
the new value of the specified resource. If no option is
given, then -f is assumed. Values are in 1024-byte
increments, except for -t, which is in seconds; -R, which
is in microseconds; -p, which is in units of 512-byte
blocks; -P, -T, -b, -k, -n, and -u, which are unscaled
values; and, when in posix mode, -c and -f, which are in
512-byte increments. The return status is 0 unless an
invalid option or argument is supplied, or an error occurs
while setting a new limit.
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 number;
otherwise it is interpreted as a symbolic mode mask
similar to that accepted by chmod(1). If mode is omitted,
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] [-n] [name ...]
For each name, remove the corresponding variable or
function. If the -v option is given, each name refers to
a shell variable, and that variable is removed. Read-only
variables may not be unset. If -f is specified, each name
refers to a shell function, and the function definition is
removed. If the -n option is supplied, and name is a
variable with the nameref attribute, name will be unset
rather than the variable it references. -n has no effect
if the -f option is supplied. If no options are supplied,
each name refers to a variable; if there is no variable by
that name, a function with that name, if any, is unset.
Each unset variable or function is removed from the
environment passed to subsequent commands. If any of
BASH_ALIASES, BASH_ARGV0, BASH_CMDS, BASH_COMMAND,
BASH_SUBSHELL, BASHPID, COMP_WORDBREAKS, DIRSTACK,
EPOCHREALTIME, EPOCHSECONDS, FUNCNAME, GROUPS, HISTCMD,
LINENO, RANDOM, SECONDS, or SRANDOM are unset, they lose
their special properties, even if they are subsequently
reset. The exit status is true unless a name is readonly
or may not be unset.
wait [-fn] [-p varname] [id ...]
Wait for each specified child process and return its
termination status. Each id may be a process ID or a job
specification; if a job spec is given, all processes in
that job's pipeline are waited for. If id is not given,
wait waits for all running background jobs and the last-
executed process substitution, if its process id is the
same as $!, and the return status is zero. If the -n
option is supplied, wait waits for a single job from the
list of ids or, if no ids are supplied, any job, to
complete and returns its exit status. If none of the
supplied arguments is a child of the shell, or if no
arguments are supplied and the shell has no unwaited-for
children, the exit status is 127. If the -p option is
supplied, the process or job identifier of the job for
which the exit status is returned is assigned to the
variable varname named by the option argument. The
variable will be unset initially, before any assignment.
This is useful only when the -n option is supplied.
Supplying the -f option, when job control is enabled,
forces wait to wait for id to terminate before returning
its status, instead of returning when it changes status.
If id specifies a non-existent process or job, the return
status is 127. If wait is interrupted by a signal, the
return status will be greater than 128, as described under
SIGNALS above. Otherwise, the return status is the exit
status of the last process or job waited for.
Bash-4.0 introduced the concept of a shell compatibility level,
specified as a set of options to the shopt builtin ( compat31,
compat32, compat40, compat41, and so on). There is only one
current compatibility level -- each option is mutually exclusive.
The compatibility level is intended to allow users to select
behavior from previous versions that is incompatible with newer
versions while they migrate scripts to use current features and
behavior. It's intended to be a temporary solution.
This section does not mention behavior that is standard for a
particular version (e.g., setting compat32 means that quoting the
rhs of the regexp matching operator quotes special regexp
characters in the word, which is default behavior in bash-3.2 and
subsequent versions).
If a user enables, say, compat32, it may affect the behavior of
other compatibility levels up to and including the current
compatibility level. The idea is that each compatibility level
controls behavior that changed in that version of bash, but that
behavior may have been present in earlier versions. For
instance, the change to use locale-based comparisons with the [[
command came in bash-4.1, and earlier versions used ASCII-based
comparisons, so enabling compat32 will enable ASCII-based
comparisons as well. That granularity may not be sufficient for
all uses, and as a result users should employ compatibility
levels carefully. Read the documentation for a particular
feature to find out the current behavior.
Bash-4.3 introduced a new shell variable: BASH_COMPAT. The value
assigned to this variable (a decimal version number like 4.2, or
an integer corresponding to the compatNN option, like 42)
determines the compatibility level.
Starting with bash-4.4, Bash has begun deprecating older
compatibility levels. Eventually, the options will be removed in
favor of BASH_COMPAT.
Bash-5.0 is the final version for which there will be an
individual shopt option for the previous version. Users should
use BASH_COMPAT on bash-5.0 and later versions.
The following table describes the behavior changes controlled by
each compatibility level setting. The compatNN tag is used as
shorthand for setting the compatibility level to NN using one of
the following mechanisms. For versions prior to bash-5.0, the
compatibility level may be set using the corresponding compatNN
shopt option. For bash-4.3 and later versions, the BASH_COMPAT
variable is preferred, and it is required for bash-5.1 and later
versions.
compat31
• quoting the rhs of the [[ command's regexp matching
operator (=~) has no special effect
compat32
• interrupting a command list such as "a ; b ; c"
causes the execution of the next command in the
list (in bash-4.0 and later versions, the shell
acts as if it received the interrupt, so
interrupting one command in a list aborts the
execution of the entire list)
compat40
• the < and > operators to the [[ command do not
consider the current locale when comparing strings;
they use ASCII ordering. Bash versions prior to
bash-4.1 use ASCII collation and strcmp(3);
bash-4.1 and later use the current locale's
collation sequence and strcoll(3).
compat41
• in posix mode, time may be followed by options and
still be recognized as a reserved word (this is
POSIX interpretation 267)
• in posix mode, the parser requires that an even
number of single quotes occur in the word portion
of a double-quoted parameter expansion and treats
them specially, so that characters within the
single quotes are considered quoted (this is POSIX
interpretation 221)
compat42
• the replacement string in double-quoted pattern
substitution does not undergo quote removal, as it
does in versions after bash-4.2
• in posix mode, single quotes are considered special
when expanding the word portion of a double-quoted
parameter expansion and can be used to quote a
closing brace or other special character (this is
part of POSIX interpretation 221); in later
versions, single quotes are not special within
double-quoted word expansions
compat43
• the shell does not print a warning message if an
attempt is made to use a quoted compound assignment
as an argument to declare (e.g., declare -a foo='(1
2)'). Later versions warn that this usage is
deprecated
• word expansion errors are considered non-fatal
errors that cause the current command to fail, even
in posix mode (the default behavior is to make them
fatal errors that cause the shell to exit)
• when executing a shell function, the loop state
(while/until/etc.) is not reset, so break or
continue in that function will break or continue
loops in the calling context. Bash-4.4 and later
reset the loop state to prevent this
compat44
• the shell sets up the values used by BASH_ARGV and
BASH_ARGC so they can expand to the shell's
positional parameters even if extended debugging
mode is not enabled
• a subshell inherits loops from its parent context,
so break or continue will cause the subshell to
exit. Bash-5.0 and later reset the loop state to
prevent the exit
• variable assignments preceding builtins like export
and readonly that set attributes continue to affect
variables with the same name in the calling
environment even if the shell is not in posix mode
compat50
• Bash-5.1 changed the way $RANDOM is generated to
introduce slightly more randomness. If the shell
compatibility level is set to 50 or lower, it
reverts to the method from bash-5.0 and previous
versions, so seeding the random number generator by
assigning a value to RANDOM will produce the same
sequence as in bash-5.0
• If the command hash table is empty, bash versions
prior to bash-5.1 printed an informational message
to that effect, even when producing output that can
be reused as input. Bash-5.1 suppresses that
message when the -l option is supplied.
compat51
• The unset builtin treats attempts to unset array
subscripts @ and * differently depending on whether
the array is indexed or associative, and
differently than in previous versions.
If bash is started with the name rbash, or the -r option is
supplied at invocation, the shell becomes restricted. A
restricted shell is used to set up an environment more controlled
than the standard shell. It behaves identically to bash with the
exception that the following are disallowed or not performed:
• changing directories with cd
• setting or unsetting the values of SHELL, PATH, HISTFILE,
ENV, or BASH_ENV
• specifying command names containing /
• specifying a filename containing a / as an argument to the
. builtin command
• specifying a filename containing a slash as an argument to
the history 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 shopt -u
restricted_shell.
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.
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 --
http://pubs.opengroup.org/onlinepubs/9699919799/
http://tiswww.case.edu/~chet/bash/POSIX -- a description of posix
mode
sh(1), ksh(1), csh(1)
emacs(1), vi(1)
readline(3)
/bin/bash
The bash executable
/etc/profile
The systemwide initialization file, executed for login
shells
~/.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
~/.bash_history
The default value of HISTFILE, the file in which bash
saves the command history
~/.inputrc
Individual readline initialization file
Brian Fox, Free Software Foundation
bfox@gnu.org
Chet Ramey, Case Western Reserve University
chet.ramey@case.edu
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
available from ftp://ftp.gnu.org/pub/gnu/bash/ and
http://git.savannah.gnu.org/cgit/bash.git/snapshot/bash-
master.tar.gz.
Once you have determined that a bug actually exists, use the
bashbug command to submit a bug report. If you have a fix, you
are encouraged to mail that as well! Suggestions and
`philosophical' bug reports may be mailed to bug-bash@gnu.org or
posted to the Usenet newsgroup gnu.bash.bug.
ALL bug reports should include:
The version number of bash
The hardware and operating system
The compiler used to compile
A description of the bug behaviour
A short script or `recipe' which exercises the bug
bashbug inserts the first three items automatically into the
template it provides for filing a bug report.
Comments and bug reports concerning this manual page should be
directed to chet.ramey@case.edu.
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
stoppable/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.
This page is part of the bash (Bourne again shell) project.
Information about the project can be found at
⟨http://www.gnu.org/software/bash/⟩. If you have a bug report for
this manual page, see ⟨http://www.gnu.org/software/bash/⟩. This
page was obtained from the project's upstream Git repository
⟨git://git.savannah.gnu.org/bash.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-01-13.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
GNU Bash 5.2 2022 September 19 BASH(1)
Pages that refer to this page: getopt(1), intro(1), kill(1), pmdabash(1), pv(1), quilt(1), systemctl(1), systemd-notify(1), systemd-run(1), time(1), setpgid(2), getopt(3), history(3), readline(3), strcmp(3), termios(3), ulimit(3), core(5), credentials(7), environ(7), suffixes(7), time_namespaces(7), cupsenable(8), dpkg-fsys-usrunmess(8), wg(8), wg-quick(8)
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