bash - GNU Bourne-Again SHell
bash [options] [file]
Bash is Copyright (C) 1989-2011 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 can be used as options when the shell is invoked.
In addition,
bash interprets the following options when it is invoked:
- -c string
- If the -c option is present, then commands are read from
string. If there are arguments after the string, they are
assigned to the positional parameters, starting with $0.
- -i
- If the -i option is present, the shell is interactive.
- -l
- Make bash act as if it had been invoked as a login shell (see
INVOCATION below).
- -r
- If the -r option is present, the shell becomes restricted
(see RESTRICTED SHELL below).
- -s
- If the -s option is present, or if no arguments remain after option
processing, then commands are read from the standard input. This option
allows the positional parameters to be set when invoking an interactive
shell.
- -D
- A list of all double-quoted strings preceded by $ is printed on the
standard output. These are the strings that are subject to language
translation when the 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).
- --restricted
- The shell becomes restricted (see RESTRICTED SHELL below).
- --rpm-requires
- Produce the list of files that are required for the shell script to run.
This implies '-n' and is subject to the same limitations as compile time
error checking checking; Command substitutions, Conditional expressions
and eval builtin are not parsed so some dependencies may be
missed.
- --verbose
- Equivalent to -v.
- --version
- Show version information for this instance of bash on the standard
output and exit successfully.
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 and
without the
-c option whose standard input and error are both connected
to terminals (as determined by
isatty(3)), or one started with the
-i option.
PS1 is set and
$- includes
i if
bash is interactive, allowing a shell script or a startup file to test
this state.
The following paragraphs describe how
bash executes its startup files. If
any of the files exist but cannot be read,
bash reports an error.
Tildes are expanded in file names as described below under
Tilde
Expansion in the
EXPANSION section.
When
bash is invoked as an interactive login shell, or as a
non-interactive shell with the
--login option, it first reads and
executes commands from the file
/etc/profile, if that file exists.
After reading that file, it looks for
~/.bash_profile,
~/.bash_login, and
~/.profile, in that order, and reads and
executes commands from the first one that exists and is readable. The
--noprofile option may be used when the shell is started to inhibit
this behavior.
When a login shell exits,
bash reads and executes commands from the files
~/.bash_logout and
/etc/bash.bash_logout, if the files exists.
When an interactive shell that is not a login shell is started,
bash
reads and executes commands from
~/.bashrc, if that file exists. This
may be inhibited by using the
--norc option. The
--rcfile
file option will force
bash to read and execute commands from
file instead of
~/.bashrc.
When
bash is started non-interactively, to run a shell script, for
example, it looks for the variable
BASH_ENV in the environment, expands
its value if it appears there, and uses the expanded value as the name of a
file to read and execute.
Bash behaves as if the following command were
executed:
if [ -n "$BASH_ENV" ]; then .
"$BASH_ENV"; fi
but the value of the
PATH variable is not used to search for the file
name.
If
bash is invoked with the name
sh, it tries to mimic the startup
behavior of historical versions of
sh as closely as possible, while
conforming to the POSIX standard as well. When invoked as 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 remote shell
daemon, usually
rshd, or the secure shell daemon
sshd. If
bash determines it is being run 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
rshd does not generally invoke the shell
with those options or allow them to be specified.
If the shell is started with the effective user (group) id not equal to the real
user (group) id, and the
-p option is not 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:
- 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 simple command (see
SHELL GRAMMAR below) or the third word of
a
case or
for command:
! case do done elif else esac fi for function if in select then until while {
} time [[ ]]
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.
A
pipeline is a sequence of one or more commands separated by one of the
control operators
| or
|&. The format for a pipeline is:
[
time [
-p]] [ ! ]
command [
[
|⎪
|&]
command2 ... ]
The standard output of
command is connected via a pipe to the standard
input of
command2. This connection is performed before any redirections
specified by the command (see
REDIRECTION below). If
|& is
used, the standard error of
command is connected to
command2's
standard input through the pipe; it is shorthand for
2>&1 |.
This implicit redirection of the standard error is performed after any
redirections specified by the command.
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 pipeline is executed as a separate process (i.e., in a
subshell).
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. Commands
separated by a
; are executed sequentially; the shell waits for each
command to terminate in turn. The return status is the exit status of the last
command executed.
AND and OR lists are sequences of one of more pipelines separated by the
&& and
|| control operators, respectively. AND and OR
lists are executed with left associativity. An AND list has the form
command2 is executed if, and only if,
command1 returns an exit
status of zero.
An OR list has the form
command2 is executed if and only if
command1 returns a non-zero
exit status. The return status of AND and OR lists is the exit status of the
last command executed in the list.
A
compound command is one of the following:
- (list)
- list is executed in a subshell environment (see COMMAND
EXECUTION ENVIRONMENT below). Variable assignments and builtin
commands that affect the shell's environment do not remain in effect after
the command completes. The return status is the exit status of
list.
- { list; }
- list is simply executed in the current shell environment.
list must be terminated with a newline or semicolon. This is known
as a group command. The return status is the exit status of
list. Note that unlike the 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. This
is exactly equivalent to let
"expression".
- [[ expression ]]
- Return a status of 0 or 1 depending on the evaluation of the conditional
expression expression. Expressions are composed of the primaries
described below under CONDITIONAL EXPRESSIONS. Word splitting and
pathname expansion are not performed on the words between the [[
and ]]; tilde expansion, parameter and variable expansion,
arithmetic expansion, command substitution, process substitution, and
quote removal are performed. 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. If the shell option
nocasematch is enabled, the match is performed without regard to
the case of alphabetic characters. The return value is 0 if the string
matches ( ==) or does not match ( !=) the pattern, and 1
otherwise. Any part of the pattern may be quoted to force it to be matched
as a string.
An additional binary operator, =~, is available, with the same
precedence as == and !=. When it is used, the string to the
right of the operator is considered an extended regular expression and
matched accordingly (as in regex(3)). The return value is 0 if the
string matches the pattern, and 1 otherwise. If the regular expression is
syntactically incorrect, the conditional expression's return value is 2.
If the shell option nocasematch is enabled, the match is performed
without regard to the case of alphabetic characters. Any part of the
pattern may be quoted to force it to be matched as a string. Substrings
matched by parenthesized subexpressions within the regular expression are
saved in the array variable BASH_REMATCH. The element of
BASH_REMATCH with index 0 is the portion of the string matching the
entire regular expression. The element of BASH_REMATCH with index
n is the portion of the string matching the nth
parenthesized subexpression.
Expressions may be combined using the following 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. The set of expanded words is printed on the standard error, each
preceded by a number. If the in word is omitted, the
positional parameters are printed (see PARAMETERS below). The
PS3 prompt is then displayed and a line read from the standard
input. If the line consists of a number corresponding to one of the
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 command completes. Any other value read causes name to be set
to null. The line read is saved in the variable REPLY. The
list is executed after each selection until a break command
is executed. The exit status of select is the exit status of the
last command executed in list, or zero if no commands were
executed.
- case word in [ [(] pattern [ |
pattern ] ... ) list ;; ] ... esac
- A case command first expands word, and tries to match it
against each pattern in turn, using the same matching rules as for
pathname expansion (see Pathname Expansion below). The word
is expanded using tilde expansion, parameter and variable expansion,
arithmetic substitution, command substitution, process substitution and
quote removal. Each pattern examined is expanded using tilde
expansion, parameter and variable expansion, arithmetic substitution,
command substitution, and process substitution. If the shell option
nocasematch is enabled, the match is performed without regard to
the case of alphabetic characters. When a match is found, the
corresponding list is executed. If the ;; operator is used,
no subsequent matches are attempted after the first pattern match. Using
;& in place of ;; causes 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. 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.
A
coprocess is a shell command preceded by the
coproc reserved
word. A coprocess is executed asynchronously in a subshell, as if the command
had been terminated with the
& control operator, with a two-way
pipe established between the executing shell and the coprocess.
The format for a coprocess is:
coproc [
NAME]
command [
redirections]
This creates a coprocess named
NAME. If
NAME is not supplied, the
default name is
COPROC.
NAME must not be supplied if
command is a
simple command (see above); otherwise, it is
interpreted as the first word of the simple command. When the coproc is
executed, the shell creates an array variable (see
Arrays below) named
NAME in the context of the executing shell. The standard output of
command is connected via a pipe to a file descriptor in the executing
shell, and that file descriptor is assigned to
NAME[0]. The standard
input of
command is connected via a pipe to a file descriptor in the
executing shell, and that file descriptor is assigned to
NAME[1]. This
pipe is 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. The process
ID of the shell spawned to execute the coprocess is available as the value of
the variable
NAME_PID. The
wait builtin command may be used to
wait for the coprocess to terminate.
The return status of a coprocess is the exit status of
command.
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:
- name () compound-command [redirection]
- function name [()] compound-command
[redirection]
- This defines a function named name. The reserved word
function is optional. If the function reserved word is
supplied, the parentheses are optional. The body of the function is
the compound command compound-command (see Compound Commands
above). That command is usually a list of commands between { and },
but may be any command listed under Compound Commands above.
compound-command is executed whenever name is specified as
the name of a simple command. Any redirections (see REDIRECTION
below) specified when a function is defined are performed when the
function is executed. The exit status of a function definition is zero
unless a syntax error occurs or a readonly function with the same name
already exists. When executed, the exit status of a function is the exit
status of the last command executed in the body. (See FUNCTIONS
below.)
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,
!. 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).
Words of the form
$'
string' are treated specially. The word
expands to
string, with backslash-escaped characters replaced as
specified by the ANSI C standard. Backslash escape sequences, if present, are
decoded as follows:
- \a
- alert (bell)
- \b
- backspace
- \e
- \E
- an escape character
- \f
- form feed
- \n
- new line
- \r
- carriage return
- \t
- horizontal tab
- \v
- vertical tab
- \\
- backslash
- \'
- single quote
- \"
- double quote
- \nnn
- the eight-bit character whose value is the octal value nnn (one to
three digits)
- \xHH
- the eight-bit character whose value is the 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. If the current locale is
C or
POSIX, the dollar sign is ignored. If the string is translated and
replaced, the replacement is double-quoted.
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
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
$((...)) expansion is not used (see
Arithmetic Expansion below). Word
splitting is not performed, with the exception of
"$@" as
explained below under
Special Parameters. Pathname expansion is not
performed. Assignment statements may also appear as arguments to the
alias,
declare,
typeset,
export,
readonly,
and
local builtin commands.
In the context where an assignment statement is assigning a value to a shell
variable or array index, the += operator can be used to append to or add to
the variable's previous value. When += is applied to a variable for which the
integer attribute has been set,
value is evaluated as an
arithmetic expression and added to the variable's current value, which is also
evaluated. When += is applied to an array variable using compound 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
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).
The shell treats several parameters specially. These parameters may only be
referenced; assignment to them is not allowed.
- *
- Expands to the positional parameters, starting from one. When the
expansion occurs within double quotes, it expands to a single word with
the value of each parameter separated by the first character of the
IFS special variable. That is, " $*" is equivalent
to " $1c$2c...", where
c is the first character of the value of the IFS variable.
If IFS is unset, the parameters are separated by spaces. If
IFS is null, the parameters are joined without intervening
separators.
- @
- Expands to the positional parameters, starting from one. When the
expansion occurs within double quotes, each parameter expands to a
separate word. That is, " $@" is equivalent to "
$1" " $2" ... 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 most recently executed background
(asynchronous) command.
- 0
- Expands to the name of the shell or shell script. This is set at shell
initialization. If bash is invoked with a file of commands,
$0 is set to the name of that file. If bash is started with
the -c option, then $0 is set to the first argument after
the string to be executed, if one is present. Otherwise, it is set to the
file name used to invoke bash, as given by argument zero.
- _
- At shell startup, set to the absolute pathname used to invoke the shell or
shell script being executed as passed in the environment or argument list.
Subsequently, expands to the last argument to the previous command, after
expansion. Also set to the full pathname used to invoke each command
executed and placed in the environment exported to that command. When
checking mail, this parameter holds the name of the mail file currently
being checked.
The following variables are set by the shell:
- BASH
- Expands to the full file name used to invoke this instance of
bash.
- BASHOPTS
- A colon-separated list of enabled shell options. Each word in the list is
a valid argument for the -s option to the shopt builtin
command (see SHELL BUILTIN COMMANDS below). The options appearing
in BASHOPTS are those reported as on by shopt. If
this variable is in the environment when bash starts up, each shell
option in the list will be enabled before reading any startup files. This
variable is read-only.
- BASHPID
- Expands to the process ID of the current bash process. This differs
from $$ under certain circumstances, such as subshells that do not
require bash to be re-initialized.
- BASH_ALIASES
- An associative array variable whose members correspond to the internal
list of aliases as maintained by the alias builtin. Elements added
to this array appear in the alias list; unsetting array elements cause
aliases to be removed from the alias list.
- BASH_ARGC
- An array variable whose values are the number of 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)
- BASH_ARGV
- An array variable containing all of the parameters in the current
bash execution call stack. The final parameter of the last
subroutine call is at the top of the stack; the first parameter of the
initial call is at the bottom. When a subroutine is executed, the
parameters supplied are pushed onto BASH_ARGV. The shell sets
BASH_ARGV only when in extended debugging mode (see the description
of the extdebug option to the shopt builtin below)
- BASH_CMDS
- An associative array variable whose members correspond to the internal
hash table of commands as maintained by the hash builtin. Elements
added to this array appear in the hash table; unsetting array elements
cause commands to be removed from the hash table.
- BASH_COMMAND
- The command currently being executed or about to be 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.
- 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_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. This variable is read-only.
- 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 each time a subshell or subshell environment is
spawned. The initial value is 0.
- BASH_VERSINFO
- A readonly array variable whose members hold version information for this
instance of bash. The values assigned to the array members are as
follows:
- BASH_VERSINFO[0]
- The major version number (the release).
- BASH_VERSINFO[1]
- The minor version number (the version).
- BASH_VERSINFO[2]
- The patch level.
- BASH_VERSINFO[3]
- The build version.
- BASH_VERSINFO[4]
- The release status (e.g., beta1).
- BASH_VERSINFO[5]
- The value of MACHTYPE.
- BASH_VERSION
- Expands to a string describing the version of this instance of
bash.
- COMP_CWORD
- An index into ${COMP_WORDS} of the word containing the current
cursor position. This variable is available only in shell functions
invoked by the programmable completion facilities (see Programmable
Completion below).
- COMP_KEY
- The key (or final key of a key sequence) used to invoke the current
completion function.
- COMP_LINE
- The current command line. This variable is available only in shell
functions and external commands invoked by the programmable completion
facilities (see Programmable Completion below).
- COMP_POINT
- The index of the current cursor position relative to the beginning of the
current command. If the current cursor position is at the end of the
current command, the value of this variable is equal to
${#COMP_LINE}. This 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.
- 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
and return an error status. If FUNCNAME is unset, it loses its
special properties, even if it is subsequently reset.
This variable can be used with BASH_LINENO and BASH_SOURCE.
Each element of FUNCNAME has corresponding elements in
BASH_LINENO and BASH_SOURCE to describe the call stack. For
instance, ${FUNCNAME[$i]} was called from the file
${BASH_SOURCE[$i+1]} at line number
${BASH_LINENO[ $i]}. The caller builtin
displays the 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 and return an
error status. If GROUPS is unset, it loses its special properties,
even if it is subsequently reset.
- HISTCMD
- The history number, or index in the history list, of the current command.
If HISTCMD is unset, it loses its 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, a random integer between 0 and
32767 is generated. The sequence of random numbers may be initialized by
assigning a value to RANDOM. If RANDOM is unset, it loses
its special properties, even if it is subsequently reset.
- READLINE_LINE
- The contents of the readline line buffer, for use with "bind
-x" (see SHELL BUILTIN COMMANDS below).
- READLINE_POINT
- The position of the insertion point in the readline line buffer,
for use with "bind -x" (see SHELL BUILTIN 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, the number of seconds since shell
invocation is returned. 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. 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.
- UID
- Expands to the user ID of the current user, initialized at shell startup.
This variable is readonly.
The following variables are used by the shell. In some cases,
bash
assigns a default value to a variable; these cases are noted below.
- BASH_ENV
- If this parameter is set when bash is executing a shell script, its
value is interpreted as a filename containing commands to initialize the
shell, as in ~/.bashrc. The value of BASH_ENV is subjected
to parameter expansion, command substitution, and arithmetic expansion
before being interpreted as a file name. PATH is not used to search
for the resultant file name.
- BASH_XTRACEFD
- If set to an integer corresponding to a valid file descriptor, bash
will write the trace output generated when set -x is enabled to
that file descriptor. The file descriptor is closed when
BASH_XTRACEFD is unset or assigned a new value. Unsetting
BASH_XTRACEFD or 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".
- COLUMNS
- Used by the select compound command to determine the terminal width
when printing selection lists. Automatically set 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).
- 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
- Similar to BASH_ENV; used when the shell is invoked in POSIX
mode.
- FCEDIT
- The default editor for the fc builtin command.
- FIGNORE
- A colon-separated list of suffixes to ignore when 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 filenames to be
ignored by pathname expansion. If a filename matched by a pathname
expansion pattern also matches one of the patterns in GLOBIGNORE,
it is removed from the list of matches.
- HISTCONTROL
- A colon-separated list of values controlling how commands are saved on the
history list. If the list of values includes ignorespace, lines
which begin with a space character are not saved in the history
list. A value of ignoredups causes lines matching the previous
history entry to not be saved. A value of ignoreboth is 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 an interactive 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,
by removing the oldest entries, to contain no more than that number of
lines. The default value is 500. The history file is also truncated to
this size after writing it when an interactive shell exits.
- HISTIGNORE
- A colon-separated list of patterns used to decide which command lines
should be saved on the history list. Each pattern is anchored at the
beginning of the line and must match the complete line (no implicit `
*' is appended). Each pattern is tested against the line after the
checks specified by HISTCONTROL are applied. In addition to the
normal shell pattern matching characters, ` &' matches the
previous history line. ` &' may be escaped using a 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.
- HISTSIZE
- The number of commands to remember in the command history (see
HISTORY below). The default value is 500.
- HISTTIMEFORMAT
- If this variable is set and not null, its value is used as a format string
for strftime(3) to print the time stamp associated with each
history entry displayed by the history builtin. If this variable is
set, time stamps are written to the history file so they may be preserved
across shell sessions. This uses the history comment character to
distinguish timestamps from other history lines.
- HOME
- The home directory of the current user; the default 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).
- LANG
- Used to determine the locale category for any category not specifically
selected with a variable starting with LC_.
- LC_ALL
- This variable overrides the value of LANG and any other LC_
variable specifying a locale category.
- LC_COLLATE
- This variable determines the collation order used when sorting the results
of pathname expansion, and determines the behavior of range expressions,
equivalence classes, and collating sequences within pathname expansion and
pattern matching.
- LC_CTYPE
- This variable determines the interpretation of characters and the behavior
of character classes within pathname expansion and pattern matching.
- LC_MESSAGES
- This variable determines the locale used to translate double-quoted
strings preceded by a $.
- LC_NUMERIC
- This variable determines the locale category used for number
formatting.
- LINES
- Used by the select compound command to determine the column length
for printing selection lists. Automatically set upon receipt of a
SIGWINCH.
- MAIL
- If this parameter is set to a file or directory name and the
MAILPATH variable is not set, bash informs the user of the
arrival of mail in the specified file or Maildir-format directory.
- MAILCHECK
- Specifies how often (in seconds) bash checks for mail. The default
is 60 seconds. When it is time to check for mail, the shell does so before
displaying the primary prompt. If this variable is unset, or set to a
value that is not a number greater than or equal to zero, the shell
disables mail checking.
- MAILPATH
- A colon-separated list of file names to be checked for mail. The message
to be printed when mail arrives in a particular file may be specified by
separating the file name from the message with a `?'. When used in the
text of the message, $_ expands to the name of the current
mailfile. Example:
MAILPATH='/var/mail/bfox?"You have mail":~/shell-mail?"$_
has mail!"'
Bash supplies a default value for this variable, but the location of the
user mail files that it uses is system dependent (e.g., /var/mail/
$USER).
- OPTERR
- If set to the value 1, bash displays error messages 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/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin''.
- POSIXLY_CORRECT
- If this variable is in the environment when bash starts, the shell
enters posix mode before reading the startup files, as if the
--posix invocation option had been supplied. If it is set while the
shell is running, bash enables posix mode, as if the command
set -o posix had been executed.
- PROMPT_COMMAND
- If set, the value is executed as a command prior to issuing each primary
prompt.
- PROMPT_DIRTRIM
- If set to a number greater than zero, the value is used as the number of
trailing directory components to retain when expanding the \w and
\W prompt string escapes (see PROMPTING below). Characters
removed are replaced with an ellipsis.
- PS1
- The value of this parameter is expanded (see PROMPTING below) and
used as the primary prompt string. The default value is `` \s-\v\$
''.
- PS2
- The value of this parameter is expanded as with PS1 and used as the
secondary prompt string. The default is `` > ''.
- PS3
- The value of this parameter is used as the prompt for the select
command (see SHELL GRAMMAR above).
- PS4
- The value of this parameter is expanded as with PS1 and the value
is printed before each command bash displays during an execution
trace. The first character of PS4 is replicated multiple times, as
necessary, to indicate multiple levels of indirection. The default is ``
+ ''.
- SHELL
- The full pathname to the shell is kept in this environment variable. If it
is not set when the shell starts, bash assigns to it the full
pathname of the current user's login shell.
- TIMEFORMAT
- The value of this parameter is used as a format string specifying how the
timing information for pipelines 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%3lS'. If the value is null, no
timing information is displayed. A trailing newline is added when the
format string is displayed.
- TMOUT
- If set to a value greater than zero, TMOUT is treated as the
default timeout for the read builtin. The select command
terminates if input does not arrive after TMOUT seconds when input
is coming from a terminal. In an interactive shell, the value is
interpreted as the number of seconds to wait for input after issuing the
primary prompt. Bash terminates after waiting for that number of
seconds if input does not arrive.
- TMPDIR
- If set, bash uses its value as the name of a directory in which
bash creates temporary files for the shell's use.
- auto_resume
- This variable controls how the shell interacts with the user and job
control. If this variable is set, single word simple commands without
redirections are treated as candidates for resumption of an existing
stopped job. There is no ambiguity allowed; if there is more than one job
beginning with the string typed, the job most recently accessed is
selected. The name of a stopped job, in this context, is the
command line used to start it. If set to the value exact, the
string supplied must match the name of a stopped job exactly; if set to
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.
Bash provides one-dimensional indexed and associative array variables.
Any variable may be used as an indexed array; the
declare builtin will
explicitly declare an array. There is no maximum limit on the size of an
array, nor any requirement that members be indexed or assigned contiguously.
Indexed arrays are referenced using integers (including arithmetic
expressions) and are zero-based; associative arrays are referenced using
arbitrary strings.
An indexed array is created automatically if any variable is assigned to using
the syntax
name[
subscript]=
value. The
subscript is
treated as an arithmetic expression that must evaluate to a number. If
subscript evaluates to a number less than zero, it is used as an offset
from one greater than the array's maximum index (so a subcript of -1 refers to
the last element of the array). To explicitly declare an indexed array, use
declare -a name (see
SHELL BUILTIN COMMANDS below).
declare -a name[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=
(value
1 ... value
n), where each
value is of the form [
subscript]=
string. Indexed array
assignments do not require the bracket and subscript. When assigning to
indexed arrays, if the optional brackets and subscript are supplied, that
index is assigned to; otherwise the index of the element assigned is the last
index assigned to by the statement plus one. Indexing starts at zero.
When assigning to an associative array, the subscript is required.
This syntax is also accepted by the
declare builtin. Individual array
elements may be assigned to using the
name[
subscript]=
value syntax introduced 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. Referencing an array
variable without a subscript is equivalent to referencing the array with a
subscript of 0.
An array variable is considered set if a subscript has been assigned a value.
The null string is a valid value.
The
unset builtin is used to destroy arrays.
unset
name[
subscript] destroys the array element at index
subscript. Care must be taken to avoid unwanted side effects caused by
pathname expansion.
unset name, where
name is an array,
or
unset name[
subscript], where
subscript is
* or
@, removes the entire array.
The
declare,
local, and
readonly builtins each accept a
-a option to specify an indexed array and a
-A option to specify
an associative array. If both options are supplied,
-A takes
precedence. The
read builtin accepts a
-a option to assign a
list of words read from the standard input to an array. The
set and
declare builtins display array values in a way that allows them to be
reused as assignments.
Expansion 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,
variable and 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.
Only brace expansion, word splitting, and pathname expansion can change the
number of words of the expansion; other expansions expand a single word to a
single word. The only exceptions to this are the expansions of "
$@" and "
${name[@]}" as explained
above (see
PARAMETERS).
Brace expansion 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 characters, 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 characters are supplied, the
expression expands to each character lexicographically between
x and
y, inclusive. Note that both
x and
y must be of the same
type. When the increment is supplied, it is used as the difference between
each term. The default increment is 1 or -1 as appropriate.
Brace expansion is performed before any other expansions, and any characters
special to other expansions are preserved in the result. It is strictly
textual.
Bash does not apply any 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.
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).
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 file names with tildes in
assignments to
PATH,
MAILPATH, and
CDPATH, and the shell
assigns the expanded value.
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.
If the first character of
parameter is an exclamation point (
!), a
level of variable indirection is introduced.
Bash uses the value of the
variable formed from the rest of
parameter as the name of the variable;
this variable is then expanded and that value is used in the rest of the
substitution, rather than the value of
parameter itself. This is known
as
indirect expansion. The exceptions to this are the expansions of ${
!prefix*} and ${
!name[
@]} described
below. The exclamation point must 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,
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
parameter starting at the character specified by offset. If
length is omitted, expands to the substring of parameter
starting at the character specified by offset. length and
offset are arithmetic expressions (see ARITHMETIC EVALUATION
below). If offset evaluates to a number less than zero, the value
is used as an offset from the end of the value of parameter. If
length evaluates to a number less than zero, and parameter
is not @ and not an indexed or associative array, it is interpreted
as an offset from the end of the value of parameter rather than a
number of characters, and the expansion is the characters between the two
offsets. If parameter is @, the result is length
positional parameters beginning at offset. If parameter is
an indexed array name subscripted by @ or *, the result is the
length members of the array beginning with ${
parameter[offset]}. A negative offset is taken
relative to one greater than the maximum index of the specified array.
Substring expansion applied to an associative array produces undefined
results. Note that a negative offset must be separated from the colon by
at least one space to avoid being confused with the :- expansion.
Substring indexing is zero-based unless the positional parameters are
used, in which case the 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.
- ${parameter#word}
- ${parameter##word}
- Remove matching prefix pattern. The word is expanded to
produce a pattern just as in pathname expansion. If the pattern matches
the beginning of the value of parameter, then the result of the
expansion is the expanded value of parameter with the shortest
matching pattern (the `` #'' case) or the longest matching pattern
(the `` ##'' case) deleted. If parameter is @ or
*, the pattern removal operation is applied to each positional
parameter in turn, and the expansion is the resultant list. If
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. If the pattern matches a
trailing portion of the expanded value of parameter, then the
result of the expansion is the expanded value of parameter with the
shortest matching pattern (the `` %'' case) or the longest matching
pattern (the `` %%'' case) deleted. If parameter is @
or *, the pattern removal operation is applied to each positional
parameter in turn, and the expansion is the resultant list. If
parameter is an array variable subscripted with @ or
*, the pattern removal operation is applied to each member of the
array in turn, and the expansion is the resultant list.
- ${parameter/pattern/string}
- Pattern substitution. The pattern is expanded to produce a
pattern just as in pathname expansion. Parameter is expanded and
the longest match of pattern against its value is replaced with
string. If pattern begins with /, all matches of
pattern are replaced with string. Normally only the first
match is replaced. If pattern begins with #, it must match
at the beginning of the expanded value of parameter. If
pattern begins with %, it must match at the end of the
expanded value of parameter. If string is null, matches of
pattern are deleted and the / following pattern may
be omitted. If parameter is @ or *, the substitution
operation is applied to each positional parameter in turn, and the
expansion is the resultant list. If parameter is an array variable
subscripted with @ or *, the substitution operation is
applied to each member of the array in turn, and the expansion is the
resultant list.
- ${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. 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.
Command substitution allows the output of a command to replace the
command name. There are two forms:
or
`command`
Bash performs the expansion by executing
command and replacing the
command substitution with the standard output of the command, with any
trailing newlines deleted. 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 allows the evaluation of an arithmetic expression and the
substitution of the result. The format for arithmetic expansion is:
The
expression is treated as if it were within double quotes, but a
double quote inside the parentheses is not treated specially. All tokens in
the expression undergo parameter expansion, string expansion, command
substitution, and quote removal. Arithmetic expansions may be nested.
The evaluation is performed according to the rules listed below under
ARITHMETIC EVALUATION. If
expression is invalid,
bash
prints a message indicating failure and no substitution occurs.
Process substitution is supported on systems that support named pipes (
FIFOs) or the
/dev/fd method of naming open files. It takes the
form of
<(list) or
>(list).
The process
list is run with its input or output connected to a
FIFO or some file in
/dev/fd. The name of this file is passed as
an argument to the current command as the result of the expansion. If the
>( list) form is used, writing to the file will
provide input for
list. If the
<(list) form is
used, the file passed as an argument should be read to obtain the output of
list.
When available, process substitution is performed simultaneously with parameter
and variable expansion, command substitution, and arithmetic expansion.
The shell scans the results of parameter expansion, command substitution, and
arithmetic expansion that did not occur within double quotes for
word
splitting.
The shell treats each character of
IFS as a delimiter, and splits the
results of the other expansions into words on these characters. If
IFS
is unset, or its value is exactly
<space><tab><newline>, the default, then sequences of
<space>,
<tab>, and
<newline> at the
beginning and end of the results of the previous expansions are ignored, and
any sequence of
IFS characters not at the beginning or end serves to
delimit words. If
IFS has a value other than the default, then
sequences of the whitespace characters
space and
tab are ignored
at the beginning and end of the word, as long as the whitespace character is
in the value of
IFS (an
IFS whitespace character). Any character
in
IFS that is not
IFS whitespace, along with any adjacent
IFS whitespace characters, delimits a field. A sequence of
IFS
whitespace characters is also treated as a delimiter. If the value of
IFS is null, no word splitting occurs.
Explicit null arguments (
"" or
'') are retained.
Unquoted implicit null arguments, resulting from the expansion of parameters
that have no values, are removed. If a parameter with no value is expanded
within double quotes, a null argument results and is retained.
Note that if no expansion occurs, no splitting is performed.
After word splitting, unless the
-f option has been set,
bash
scans each word for the characters
*,
?, and
[. If one of
these characters appears, then the word is regarded as a
pattern, and
replaced with an alphabetically sorted list of file names matching the
pattern. If no matching file names are found, and the shell option
nullglob is not enabled, the word is left unchanged. If the
nullglob option is set, and no matches are found, the word is removed.
If the
failglob shell option is set, and no matches are found, an error
message is printed and the command is not executed. If the shell option
nocaseglob is enabled, the match is performed without regard to the
case of alphabetic characters. When a pattern is used for pathname expansion,
the character
``.'' at the start of a name or immediately following a
slash must be matched explicitly, unless the shell option
dotglob is
set. When matching a pathname, the slash character must always be matched
explicitly. In other cases, the
``.'' character is not treated
specially. See the description of
shopt below under
SHELL BUILTIN
COMMANDS for a description of the
nocaseglob,
nullglob,
failglob, and
dotglob shell options.
The
GLOBIGNORE shell variable may be used to restrict the set of file
names matching a
pattern. If
GLOBIGNORE is set, each matching
file name that also matches one of the patterns in
GLOBIGNORE is
removed from the list of matches. The file names
``.'' and
``..'' are always ignored when
GLOBIGNORE is set and not null.
However, setting
GLOBIGNORE to a non-null value has the effect of
enabling the
dotglob shell option, so all other file names beginning
with a
``.'' will match. To get the old behavior of ignoring file names
beginning with a
``.'', make
``.*'' one of the patterns in
GLOBIGNORE. The
dotglob option is disabled when
GLOBIGNORE is unset.
Pattern Matching
Any character that appears in a pattern, other than the special pattern
characters described below, matches itself. The NUL character may not occur in
a pattern. A backslash escapes the following character; the escaping backslash
is discarded when matching. The special pattern characters must be quoted if
they are to be matched literally.
The special pattern characters have the following meanings:
- *
- Matches any string, including the null string. When the globstar
shell option is enabled, and * is used in a pathname expansion
context, two 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 sorts
between those two characters, inclusive, using the current locale's
collating sequence and character set, is matched. If the first character
following the [ is a ! or a ^ then any character not
enclosed is matched. The sorting order of characters in range expressions
is determined by the current locale and the value of the LC_COLLATE
shell variable, if set. A - may be matched by including it as the
first or last character in the set. A ] may be matched by including
it as the first character in the set.
Within [ and ], character classes can be specified
using the syntax [:class:], where class is one
of the following classes defined in the POSIX 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.
Several extended pattern matching operators are recognized. In the following
description, a
pattern-list is a list of one or more patterns separated
by a
|. Composite patterns may be formed using one or more of the
following sub-patterns:
- ?(pattern-list)
- Matches zero or one occurrence of the given patterns
- *(pattern-list)
- Matches zero or more occurrences of the given patterns
- +(pattern-list)
- Matches one or more occurrences of the given patterns
- @(pattern-list)
- Matches one of the given patterns
If the
extglob shell option is enabled using the
shopt builtin,
following pattern matching operator is recognized as well:
- !(pattern-list)
- Matches anything except one of the given patterns
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 may also be
used to open and close files for the current shell execution environment. The
following redirection operators may precede or appear anywhere within a
simple command or may follow a
command. Redirections are
processed in the order they appear, from left to right.
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 10 and assign it to
varname. If
>&- or <&- is preceded by {
varname}, the value of
varname defines the file descriptor to close.
In the following descriptions, if the file descriptor number is omitted, and the
first character of the redirection operator is
<, the redirection
refers to the standard input (file descriptor 0). If the first character of
the redirection operator is
>, the redirection refers to the
standard output (file descriptor 1).
The word following the redirection operator in the following descriptions,
unless otherwise noted, is subjected to brace expansion, tilde expansion,
parameter expansion, command 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
directs both standard output and standard error to the file
dirlist,
while the command
directs only the standard output to file
dirlist, because the standard
error was duplicated from the standard output before the standard output was
redirected to
dirlist.
Bash handles several filenames specially when they are used in
redirections, as described in the following table:
- /dev/fd/fd
- If fd is a valid integer, file descriptor fd is
duplicated.
- /dev/stdin
- File descriptor 0 is duplicated.
- /dev/stdout
- File descriptor 1 is duplicated.
- /dev/stderr
- File descriptor 2 is duplicated.
- /dev/tcp/host/port
- If host is a valid hostname or Internet address, and port is
an integer port number or service name, bash attempts to open a TCP
connection to the corresponding socket.
- /dev/udp/host/port
- If host is a valid hostname or Internet address, and port is
an integer port number or service name, bash attempts to open a UDP
connection to the corresponding socket.
A failure to open or create a file causes the redirection to fail.
Redirections using file descriptors greater than 9 should be used with care, as
they may conflict with file descriptors the shell uses internally.
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:
Redirection of output causes the file whose name results from the expansion of
word to be opened for writing on file descriptor
n, or the
standard output (file descriptor 1) if
n is not specified. If the file
does not exist it is created; if it does exist it is truncated to zero size.
The general format for redirecting output is:
If the redirection operator is
>, and the
noclobber option to
the
set builtin has been enabled, the redirection will fail if the file
whose name results from the expansion of
word exists and is a regular
file. If the redirection operator is
>|, or the redirection operator
is
> and the
noclobber option to the
set builtin
command is not enabled, the redirection is attempted even if the file named by
word exists.
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:
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:
and
>&word
Of the two forms, the first is preferred. This is semantically equivalent to
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:
This is semantically equivalent to
This type of redirection instructs the shell to read input from the current
source until a line containing only
delimiter (with no trailing blanks)
is seen. All of the lines read up to that point are then used as the standard
input for a command.
The format of here-documents is:
<<[-]word
here-document
delimiter
No parameter expansion, command substitution, arithmetic expansion, or pathname
expansion is performed on
word. If any characters in
word are
quoted, the
delimiter is the result of quote removal on
word,
and the lines in the here-document are not expanded. If
word is
unquoted, all lines of the here-document are subjected to parameter expansion,
command substitution, and arithmetic expansion. In the latter case, the
character sequence
\<newline> is ignored, and
\ must be
used to quote the characters
\,
$, and
`.
If the redirection operator is
<<-, then all leading tab characters
are stripped from input lines and the line containing
delimiter. This
allows here-documents within shell scripts to be indented in a natural
fashion.
A variant of here documents, the format is:
The
word is expanded and supplied to the command on its standard input.
The redirection operator
is used to duplicate input file descriptors. If
word expands to one or
more digits, the file descriptor denoted by
n is made to be a copy of
that file descriptor. If the digits in
word do not specify a file
descriptor open for input, a redirection error occurs. If
word
evaluates to
-, file descriptor
n is closed. If
n is not
specified, the standard input (file descriptor 0) is used.
The operator
is used similarly to duplicate output file descriptors. If
n is not
specified, the standard output (file descriptor 1) is used. If the digits in
word do not specify a file descriptor open for output, a redirection
error occurs. As a special case, if
n is omitted, and
word does
not expand to one or more digits, the standard output and standard error are
redirected as described previously.
The redirection operator
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
moves the file descriptor
digit to file descriptor
n, or the
standard output (file descriptor 1) if
n is not specified.
The redirection operator
causes the file whose name is the expansion of
word to be opened for both
reading and writing on file descriptor
n, or on file descriptor 0 if
n is not specified. If the file does not exist, it is created.
Aliases allow a string to be substituted for a word when it is used as
the first word of a simple command. The shell maintains a list of aliases that
may be set and unset with the
alias and
unalias builtin commands
(see
SHELL BUILTIN COMMANDS below). The first word of each simple
command, if unquoted, is checked to see if it has an alias. If so, that word
is replaced by the text of the alias. The characters
/,
$,
`, and
= and any of the shell
metacharacters or quoting
characters listed above may not appear in an alias name. The replacement text
may contain any valid shell input, including shell metacharacters. The first
word of the replacement text is tested for aliases, but a word that is
identical to an alias being expanded is not expanded a second time. This means
that one may alias
ls to
ls -F, for instance, and
bash
does not try to recursively expand the replacement text. If the last character
of the alias value is a
blank, then the next command word following the
alias is also checked for alias expansion.
Aliases are created and listed with the
alias command, and removed with
the
unalias command.
There is no mechanism for using arguments in the replacement text. If arguments
are needed, a shell function should be used (see
FUNCTIONS below).
Aliases are not expanded when the shell is not interactive, unless the
expand_aliases shell option is set using
shopt (see the
description of
shopt under
SHELL BUILTIN COMMANDS
below).
The rules concerning the definition and use of aliases are somewhat confusing.
Bash always reads at least one complete line of input before executing
any of the commands on that line. Aliases are expanded when a command is read,
not when it is executed. Therefore, an alias definition appearing on the same
line as another command does not take effect until the next line of input is
read. The commands following the alias definition on that line are not
affected by the new alias. This behavior is also an issue when functions are
executed. Aliases are expanded when a function definition is read, not when
the function is executed, because a function definition is itself a compound
command. As a consequence, aliases defined in a function are not available
until after that function is executed. To be safe, always put alias
definitions on a separate line, and do not use
alias in compound
commands.
For almost every purpose, 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. Ordinarily, variables and their values are shared between the
function and its caller.
The
FUNCNEST variable, if set to a numeric value greater than 0, defines
a maximum function nesting level. Function invocations that exceed the limit
cause the entire command to abort.
If the builtin command
return is executed in a function, the function
completes and execution resumes with the next command after the function call.
Any command associated with the
RETURN trap is executed before
execution resumes. When a function 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 subshells automatically
have them defined with the
-f option to the
export builtin. A
function definition may be deleted using the
-f option to the
unset builtin. Note that shell functions and variables with the same
name may result in multiple identically-named entries in the environment
passed to the shell's children. Care should be taken in cases where this may
cause a problem.
Functions may be recursive. The
FUNCNEST variable may be used to limit
the depth of the function call stack and restrict the number of function
invocations. By default, no limit is imposed on the number of recursive calls.
The shell allows arithmetic expressions to be evaluated, under certain
circumstances (see the
let and
declare builtin commands and
Arithmetic Expansion). Evaluation is done in fixed-width integers with
no check for overflow, though division by 0 is trapped and flagged as an
error. The operators and their 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
- ++id --id
- variable pre-increment and pre-decrement
- - +
- unary minus and plus
- ! ~
- logical and bitwise negation
- **
- exponentiation
- * / %
- multiplication, division, remainder
- + -
- addition, subtraction
- << >>
- left and right bitwise shifts
- <= >= < >
- comparison
- == !=
- equality and inequality
- &
- bitwise AND
- ^
- bitwise exclusive OR
- |
- bitwise OR
- &&
- logical AND
- ||
- logical OR
- expr?expr:expr
- conditional operator
- = *= /= %= += -= <<= >>= &= ^= |=
- assignment
- expr1 , expr2
- comma
Shell variables are allowed as operands; parameter expansion is performed before
the expression is evaluated. Within an 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.
Constants with a leading 0 are interpreted as octal numbers. A leading 0x or 0X
denotes hexadecimal. Otherwise, numbers take the form [
base#]n, where
the optional
base is a decimal number between 2 and 64 representing the
arithmetic base, and
n is a number in that base. If
base# is
omitted, then base 10 is used. The digits greater than 9 are represented by
the lowercase 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. Expressions are formed from the following
unary or binary primaries. 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).
- -z string
- True if the length of string is zero.
- string
- -n string
- True if the length of string is non-zero.
- string1 == string2
- string1 = string2
- True if the strings are equal. = should be used with the
test command for POSIX conformance.
- string1 != string2
- True if the strings are not equal.
- string1 < string2
- True if string1 sorts before string2 lexicographically.
- string1 > string2
- True if string1 sorts after string2 lexicographically.
- arg1 OP arg2
- OP is one of -eq, -ne, -lt, -le,
-gt, or -ge. These arithmetic binary operators return true
if arg1 is equal to, not equal to, less than, less than or equal
to, greater than, or greater than or equal to arg2, respectively.
Arg1 and arg2 may be positive or negative integers.
When a simple command is executed, the shell performs the following expansions,
assignments, and redirections, from left to right.
- 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. 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
with the original command and the original command's arguments as its
arguments, and the function's exit status becomes the exit status of the
shell. If that function is not defined, the shell prints an error message and
returns an exit status of 127.
If the search is successful, or if the command name contains one or more
slashes, the shell executes the named program in a 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. A subshell is spawned to execute it. This subshell
reinitializes itself, so that the effect is as if a new shell had been invoked
to handle the script, with the exception that the locations of commands
remembered by the parent (see
hash below under
SHELL BUILTIN
COMMANDS) are retained by the child.
If the program is a file beginning with
#!, the remainder of the first
line specifies an interpreter for the program. The shell executes the
specified interpreter on operating systems that do not handle this executable
format themselves. The arguments to the interpreter consist of a single
optional argument following the interpreter name on the first line of the
program, followed by the name of the program, followed by the command
arguments, if any.
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.
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 file name 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.
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.
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:
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
ce job. If a prefix
matches more than one job,
bash reports an error. Using
%?ce, on
the other hand, refers to any job containing the string
ce in its
command line. If the substring matches more than one job,
bash reports
an error. The symbols
%% and
%+ refer to the shell's notion of
the
current job, which is the last job stopped while it was in the
foreground or started in the background. The
previous job may be
referenced using
%-. If there is only a single job,
%+ and
%- can both be used to refer to that job. In output pertaining to jobs
(e.g., the output of the
jobs command), the current job is always
flagged with a
+, and the previous job with a
-. A single %
(with no accompanying job specification) also refers to the current job.
Simply naming a job can be used to bring it into the foreground:
%1 is a
synonym for
``fg %1'', bringing job 1 from the 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 executing interactively,
bash displays the primary prompt
PS1
when it is ready to read a command, and the secondary prompt
PS2 when
it needs more input to complete a command.
Bash allows these prompt
strings to be customized by inserting a number of backslash-escaped special
characters that are decoded as 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 current working directory, with $HOME abbreviated with a tilde
(uses the value of the PROMPT_DIRTRIM variable)
- \W
- the basename of the current working directory, with $HOME
abbreviated with a tilde
- \!
- the history number of this command
- \#
- the command number of this command
- \$
- if the effective UID is 0, a #, otherwise a $
- \nnn
- the character corresponding to the octal number nnn
- \\
- a backslash
- \[
- begin a sequence of non-printing characters, which could be used to embed
a terminal control sequence into the prompt
- \]
- end a sequence of non-printing characters
The command number and the history number are usually different: the history
number of a command is its position in the history list, which may include
commands restored from the history file (see
HISTORY below), while the
command number is the position in the sequence of commands executed during the
current shell 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 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.
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 is customized by putting commands in an initialization file (the
inputrc file). The name of this file is taken from the value of the
INPUTRC variable. If that variable is unset, the default is
~/.inputrc. When a program which uses the 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).
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 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
Except where noted, readline variables can take the values
On or
Off (without regard to case). Unrecognized variable names are ignored.
When a variable value is read, empty or null values, "on"
(case-insensitive), and "1" are equivalent to
On. All other
values are equivalent to
Off. The variables and their default values
are:
- bell-style (audible)
- Controls what happens when readline wants to ring the terminal bell. If
set to none, readline never rings the bell. If set to
visible, readline uses a visible bell if one is available. If set
to audible, readline attempts to ring the terminal's bell.
- bind-tty-special-chars (On)
- If set to On, readline attempts to bind the control characters
treated specially by the kernel's terminal driver to their readline
equivalents.
- 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-ignore-case (Off)
- If set to On, readline performs filename matching and completion in
a case-insensitive fashion.
- completion-prefix-display-length (0)
- The length in characters of the common prefix of a list of possible
completions that is displayed without 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, the user is asked whether or not he wishes to view them;
otherwise they are simply listed on the terminal.
- convert-meta (On)
- If set to On, readline will convert characters with the eighth bit
set to an ASCII key sequence by stripping the eighth bit and prefixing an
escape character (in effect, using escape as the meta prefix).
- disable-completion (Off)
- If set to On, readline will inhibit word completion. Completion
characters will be inserted into the line as if they had been mapped to
self-insert.
- editing-mode (emacs)
- Controls whether readline begins with a set of key bindings similar to
Emacs or vi. editing-mode can be set to either
emacs or vi.
- echo-control-characters (On)
- When set to On, on operating systems that indicate they support it,
readline echoes a character corresponding to a signal generated from the
keyboard.
- enable-keypad (Off)
- When set to On, readline will try to enable the 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 (0)
- Set the maximum number of history entries saved in the history list. If
set to zero, the number of entries in the history list is not
limited.
- horizontal-scroll-mode (Off)
- When set to On, makes readline use a single line for 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.
- input-meta (Off)
- If set to On, readline will enable eight-bit input (that is, it
will not strip the high bit from the characters it reads), regardless of
what the terminal claims it can support. The name meta-flag is a
synonym for this variable.
- 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.
- 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.
- 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.
- 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.
- 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 implements a facility similar in spirit to the conditional compilation
features of the C preprocessor which allows key bindings and variable settings
to be performed as the result of tests. There are four parser directives used.
- $if
- The $if construct allows bindings to be made based on the editing
mode, the terminal being used, or the application using readline. The text
of the test extends to the end of the line; no characters are required to
isolate it.
- mode
- The mode= form of the $if directive is used to test whether
readline is in emacs or vi mode. This may be used in conjunction with the
set keymap command, for instance, to set bindings in the
emacs-standard and emacs-ctlx keymaps only if readline is
starting out in emacs mode.
- term
- The term= form may be used to include terminal-specific key
bindings, perhaps to bind the key sequences output by the terminal's
function keys. The word on the right side of the = is tested
against the both full name of the terminal and the portion of the terminal
name before the first -. This allows sun to match both
sun and sun-cmd, for instance.
- application
- The application construct is used to include application-specific
settings. Each program using the readline library sets the application
name, and an initialization file can test for a particular value. This
could be used to bind key sequences to functions useful for a specific
program. For instance, the following command adds a key sequence that
quotes the current or previous word in bash:
$if Bash
# Quote the current or previous word
"\C-xq": "\eb\"\ef\""
$endif
- $endif
- This command, as seen in the previous example, terminates an $if
command.
- $else
- Commands in this branch of the $if directive are executed if the
test fails.
- $include
- This directive takes a single filename as an argument and reads commands
and bindings from that file. For example, the following directive would
read /etc/inputrc:
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.
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.
- 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.
- clear-screen (C-l)
- Clear the screen leaving the current line at the top of the screen. With
an argument, refresh the current line without clearing the screen.
- redraw-current-line
- Refresh the current line.
- 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.
- 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.
- 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 argument, as if the "!$" history
expansion had been specified.
- shell-expand-line (M-C-e)
- Expand the line as the shell does. This performs alias and history
expansion as well as all of the shell word expansions. See HISTORY
EXPANSION below for a 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.
- operate-and-get-next (C-o)
- Accept the current line for execution and fetch the next line relative to
the current line from the history for editing. Any argument is
ignored.
- edit-and-execute-command (C-xC-e)
- Invoke an editor on the current command line, and execute the result as
shell commands. Bash attempts to invoke $VISUAL,
$EDITOR, and emacs as the editor, in that order.
- delete-char (C-d)
- Delete the character at point. If point is at the beginning of the line,
there are no characters in the line, and the last character typed was not
bound to delete-char, then return EOF.
- backward-delete-char (Rubout)
- Delete the character behind the cursor. 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.
- 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 (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
shell-forward-word.
- shell-backward-kill-word (M-Rubout)
- Kill the word behind point. Word boundaries are the same as those used by
shell-backward-word.
- unix-word-rubout (C-w)
- Kill the word behind point, using white space as a word boundary. The
killed text is saved on the kill-ring.
- unix-filename-rubout
- Kill the word behind point, using white space and the slash character as
the word boundaries. The killed text is saved on the kill-ring.
- delete-horizontal-space (M-\)
- Delete all spaces and tabs around point.
- kill-region
- Kill the text in the current region.
- copy-region-as-kill
- Copy the text in the region to the kill buffer.
- copy-backward-word
- Copy the word before point to the kill buffer. The word boundaries are the
same as backward-word.
- copy-forward-word
- Copy the word following point to the kill buffer. The word boundaries are
the same as forward-word.
- yank (C-y)
- Yank the top of the kill ring into the buffer at point.
- yank-pop (M-y)
- Rotate the kill ring, and yank the new top. Only works following
yank or yank-pop.
- digit-argument (M-0, M-1, ..., M--)
- Add this digit to the argument already accumulating, or start a new
argument. M-- starts a negative argument.
- universal-argument
- This is another way to specify an argument. If this command is followed by
one or more digits, optionally with a leading minus sign, those digits
define the argument. If the command is followed by digits, executing
universal-argument again ends the numeric argument, but is
otherwise ignored. As a special case, if this command is immediately
followed by a character that is neither a digit or minus sign, the
argument count for the next command is multiplied by four. The argument
count is initially one, so executing this function the first time makes
the argument count four, a second time makes the argument count sixteen,
and so on.
- 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).
- 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.
- re-read-init-file (C-x C-r)
- Read in the contents of the inputrc file, and incorporate any
bindings or variable assignments found there.
- abort (C-g)
- Abort the current editing command and ring the terminal's bell (subject to
the setting of bell-style).
- do-uppercase-version (M-a, M-b, M-x, ...)
- If the metafied character x is lowercase, run the command that is
bound to the corresponding uppercase character.
- prefix-meta (ESC)
- Metafy the next character typed. ESC f is equivalent to
Meta-f.
- undo (C-_, C-x C-u)
- Incremental undo, separately remembered for each line.
- revert-line (M-r)
- Undo all changes made to this line. This is like 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 count searches for previous occurrences.
- character-search-backward (M-C-])
- A character is read and point is moved to the previous occurrence of that
character. A negative count searches for subsequent occurrences.
- skip-csi-sequence
- Read enough characters to consume a multi-key sequence such as those
defined for keys like Home and End. Such sequences begin with a Control
Sequence Indicator (CSI), usually ESC-[. If this sequence is bound to
"\[", keys producing such sequences will have no effect unless
explicitly bound to a readline command, instead of inserting stray
characters into the editing buffer. This is unbound by default, but
usually bound to ESC-[.
- insert-comment (M-#)
- Without a numeric argument, the value of the readline comment-begin
variable is inserted at the beginning of the current line. If a numeric
argument is supplied, this command acts as a toggle: if the characters at
the beginning of the line do not match the value of 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.
- 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 file names 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 file names 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.
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.
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 is the name of the command
whose arguments are being completed, the second argument is the word being
completed, and the third argument is the word preceding the word being
completed on the current command line. No filtering of the generated
completions against the word being completed is performed; the function or
command has complete freedom in generating the matches.
Any function specified with
-F is invoked first. The function may use any
of the shell facilities, including the
compgen builtin described below,
to generate the matches. It must put the possible completions in the
COMPREPLY array variable.
Next, any command specified with the
-C option is invoked in an
environment equivalent to command substitution. It should print a list of
completions, one per line, to the standard output. Backslash may be used to
escape a newline, if necessary.
After all of the possible completions are generated, any filter specified with
the
-X option is applied to the list. The filter is a pattern as used
for pathname expansion; a
& in the pattern is replaced with the
text of the word being completed. A literal
& may be escaped with a
backslash; the backslash is removed before attempting a match. Any completion
that matches the pattern will be removed from the list. A leading
!
negates the pattern; in this case any completion not matching the pattern will
be removed.
Finally, any prefix and suffix specified with the
-P and
-S
options are added to each member of the completion list, and the result is
returned to the readline completion code as the list of possible completions.
If the previously-applied actions do not generate any matches, and the
-o
dirnames option was supplied to
complete when the compspec was
defined, directory name completion is attempted.
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
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. When the
history file is read, lines beginning with the history comment character
followed immediately by a digit are interpreted as timestamps for the
preceding history line. These timestamps are optionally displayed depending on
the value of the
HISTTIMEFORMAT variable. When an interactive shell
exits, the last
$HISTSIZE lines are copied from the history list to
$HISTFILE. If the
histappend shell option is enabled (see the
description of
shopt under
SHELL BUILTIN COMMANDS below), the
lines are appended to the history file, otherwise the 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 not set, no
truncation is performed.
The builtin command
fc (see
SHELL BUILTIN COMMANDS below) may be
used to list or edit and re-execute a portion of the history list. The
history builtin may be used to display or modify the history list and
manipulate the history file. When using 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. 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.
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.
An event designator is a reference to a command line entry in the history list.
Unless the reference is absolute, events are relative to the current position
in the history list.
- !
- Start a history substitution, except when followed by a blank,
newline, carriage return, = or ( (when the extglob shell option is
enabled using the shopt builtin).
- !n
- Refer to command line n.
- !-n
- Refer to the current command minus n.
- !!
- Refer to the previous command. This is a synonym for `!-1'.
- !string
- Refer to the most recent command preceding the current position in the
history list starting with string.
- !?string[?]
- Refer to the most recent command preceding the current postition in the
history list containing string. The trailing ? may be
omitted if string is followed immediately by a newline.
- ^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 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 argument.
- %
- The word matched by the most recent `?string?' search.
- x-y
- A range of words; `-y' abbreviates `0-y'.
- *
- All of the words but the zeroth. This is a synonym for ` 1-$'. It
is not an error to use * if there is just one word in the event;
the empty string is returned in that case.
- x*
- Abbreviates x-$.
- x-
- Abbreviates x-$ like x*, but omits the last word.
If a word designator is supplied without an event specification, the previous
command is used as the event.
After the optional word designator, there may appear a sequence of one or more
of the following modifiers, each preceded by a `:'.
- h
- Remove a trailing file name component, leaving only the head.
- t
- Remove all leading file name components, leaving the tail.
- r
- Remove a trailing suffix of the form .xxx, leaving the
basename.
- e
- Remove all but the trailing suffix.
- p
- Print the new command but do not execute it.
- q
- Quote the substituted words, escaping further substitutions.
- x
- Quote the substituted words as with q, but break into words at
blanks and newlines.
- s/old/new/
- Substitute new for the first occurrence of old in the event
line. Any delimiter can be used in place of /. The final delimiter is
optional if it is the last 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.
- &
- 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' 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,
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. A zero exit code is returned.
- . filename [arguments]
- source filename [arguments]
- Read and execute commands from filename in the current shell
environment and return the exit status of the last command executed from
filename. If filename does not contain a slash, file names
in PATH are used to find the directory containing filename.
The file searched for in PATH need not be executable. When
bash is not in posix mode, the current directory is searched
if no file is found in PATH. If the sourcepath option to the
shopt builtin command is turned off, the PATH is not
searched. If any arguments are supplied, they become the positional
parameters when filename is executed. Otherwise the positional
parameters are unchanged. The return status is the status of the last
command exited within the script (0 if no commands are executed), and
false if filename is not found or cannot be read.
- alias [-p] [name[=value] ...]
- Alias with no arguments or with the -p option prints the
list of aliases in the form alias name=value on
standard output. When arguments are supplied, an alias is defined for each
name whose value is given. A trailing space in value
causes the next word to be checked for alias 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] [-lpsvPSV]
- bind [-m keymap] [-q function]
[-u function] [-r keyseq]
- bind [-m keymap] -f filename
- bind [-m keymap] -x
keyseq:shell-command
- bind [-m keymap]
keyseq:function-name
- bind readline-command
- Display current readline key and function bindings, bind a key
sequence to a readline function or macro, or set a readline
variable. Each non-option argument is a command as it would appear in
.inputrc, but each binding or 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; 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 variable to the current location of
the insertion point. If the executed command changes the value of
READLINE_LINE or READLINE_POINT, those new values will be
reflected in the editing state.
The return value is 0 unless an unrecognized option is given or an error
occurred.
- break [n]
- Exit from within a for, while, until, or
select loop. If n is specified, break n levels.
n must be ≥ 1. If n is greater than the number of
enclosing loops, all enclosing loops are exited. The return value is
non-zero when n is ≤ 0; Otherwise, break returns 0
value.
- builtin shell-builtin [arguments]
- Execute the specified shell builtin, passing it 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. The variable HOME is
the default dir. The variable CDPATH defines the search path
for the directory containing 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 says to use the physical directory structure instead of
following symbolic links (see also the -P option to the set
builtin command); the -L option forces symbolic links to be
followed. 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.
An argument of - is equivalent to $OLDPWD. If a non-empty
directory name from CDPATH is used, or if - is the first
argument, and the directory change is successful, the absolute pathname of
the new working directory is written to the standard output. The return
value is true if the directory was successfully changed; false
otherwise.
- command [-pVv] command [arg ...]
- Run command with args suppressing the normal shell 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 file name
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]
[-DE] [ -A action] [-G globpat]
[-W wordlist] [-F function] [-C
command]
-
[ -X filterpat] [-P prefix] [-S
suffix] name [name ...]
- complete -pr [-DE] [name ...]
- Specify how arguments to each name should be completed. If the
-p option is supplied, or if no options are 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 the remaining 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 the remaining options
and actions should apply to ``empty'' command completion; that is,
completion attempted on a blank line.
The process of applying these completion specifications when word completion
is attempted is described above under Programmable Completion.
Other options, if specified, have the following meanings. The arguments to
the -G, -W, and -X options (and, if 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.
- 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.
- -F function
- The shell function function is executed in the current shell
environment. When it finishes, the possible completions are retrieved from
the value of the COMPREPLY array variable.
- -G globpat
- The pathname expansion pattern globpat is expanded to generate the
possible completions.
- -P prefix
- prefix is added at the beginning of each possible completion after
all other options have been applied.
- -S suffix
- suffix is appended to each possible completion after all other
options have been applied.
- -W wordlist
- The wordlist is split using the characters in the IFS
special variable as delimiters, and each resultant word is expanded. The
possible 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] [-DE] [+o
option] [ name]
- Modify completion options for each name according to the
options, or for the currently-executing completion if no
names are supplied. If no options are given, display the
completion options for each name or the current completion. The
possible values of option are those valid for the complete
builtin described above. The -D option indicates that the remaining
options should apply to the ``default'' command completion; that is,
completion attempted on a command for which no completion has previously
been defined. The -E option indicates that the remaining options
should apply to ``empty'' command completion; that is, completion
attempted on a blank line.
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. When continue is executed inside of
loop, the return value is non-zero when n is ≤ 0; Otherwise,
continue returns 0 value. When continue is executed outside
of loop, the return value is 0.
- declare [-aAfFgilrtux] [-p]
[name[=value] ...]
- typeset [-aAfFgilrtux] [-p]
[name[=value] ...]
- Declare variables and/or give them attributes. If no names are
given then display the values of variables. The -p option will
display the attributes and values of each name. When -p is
used with name arguments, additional options are ignored. When
-p is supplied without name arguments, it will display the
attributes and values of all variables having the attributes specified by
the additional options. If no other options are supplied with -p,
declare will display the attributes and values of all shell
variables. The -f option will restrict the display to shell
functions. The -F option inhibits the display of function
definitions; only the function name and attributes are printed. If the
extdebug shell option is enabled using shopt, the source
file name and line number where the function is defined are displayed as
well. The -F option implies -f. The -g option forces
variables to be created or modified at the global scope, even when
declare is executed in a shell function. It is ignored in all other
cases. The following options can be used to restrict output to variables
with the specified attribute or to give variables attributes:
- -a
- Each name is an indexed array variable (see Arrays
above).
- -A
- Each name is an associative array variable (see Arrays
above).
- -f
- Use function names only.
- -i
- The variable is treated as an integer; arithmetic evaluation (see
ARITHMETIC EVALUATION above) is performed when the variable is
assigned a value.
- -l
- When the variable is assigned a value, all upper-case characters are
converted to lower-case. The upper-case attribute is disabled.
- -r
- Make names readonly. These names cannot then be assigned values by
subsequent assignment 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 may not be used to destroy an array variable and
+r will
not remove the readonly attribute. When used in a function, makes each
name local, as with the
local command, unless the
-g
option is supplied, If a variable name is followed by =
value, the
value of the variable is set to
value. The return value is 0 unless an
invalid option is encountered, an attempt is made to define a function using
``-f foo=bar'', an attempt is made to assign a value to a readonly variable,
an attempt is made to assign a value to an array variable without using the
compound assignment syntax (see
Arrays above), one of the
names
is not a valid shell variable name, an attempt is made to turn off readonly
status for a readonly variable, an attempt is made to turn off array status
for an array variable, or an attempt is made to display a non-existent
function with
-f.
- dirs [+n] [-n] [-clpv]
- Without options, displays the list of currently 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.
- +n
- Displays the nth entry counting from the left of the list shown by
dirs when invoked without options, starting with zero.
- -n
- Displays the nth entry counting from the right of the list shown by
dirs when invoked without options, starting with zero.
- -c
- Clears the directory stack by deleting all of the entries.
- -l
- Produces a longer listing; the default listing format uses a tilde to
denote the home directory.
- -p
- Print the directory stack with one entry per line.
- -v
- Print the directory stack with one entry per line, prefixing each entry
with its index in the stack.
The return value is 0 unless an invalid option is supplied or
n indexes
beyond the end of the directory stack.
- disown [-ar] [-h] [jobspec ...]
- Without options, each jobspec is removed from the table of active
jobs. If jobspec is not present, and neither -a nor
-r is supplied, the shell's notion of the current job is
used. If the -h option is given, each jobspec is not removed
from the table, but is marked so that SIGHUP is not sent to the job
if the shell receives a SIGHUP. If no jobspec is present,
and neither the -a nor the -r option is supplied, the
current job is used. If no 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 always 0. If -n is specified, the trailing newline
is suppressed. If the -e option is given, interpretation of the
following backslash-escaped characters is enabled. The -E option
disables the interpretation of these escape characters, even on systems
where they are interpreted by default. The xpg_echo shell option
may be used to dynamically determine whether or not echo expands
these escape characters by default. echo 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. 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. 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 shell option execfail is enabled, in which case
it returns failure. An interactive shell returns failure if the file
cannot be executed. 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 all names that are
exported in this shell is printed. The -n option causes the export
property to be removed from each name. If a variable name is
followed by = word, the value of the variable is set to
word. export returns an exit status of 0 unless an invalid
option is 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]
- Fix Command. In the first form, a range of commands from first to
last is selected from the history list. First and
last may be specified as a string (to locate the last command
beginning with that string) or as a number (an index into the history
list, where a negative number is used as an offset from the current
command number). If last is not specified it is set to the current
command for listing (so that ``fc -l -10'' prints the last 10 commands)
and to first otherwise. If first is not 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. 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 [args]
- getopts is used by shell procedures to parse positional parameters.
optstring contains the option characters to be recognized; if a
character is followed by a colon, the option is expected to have an
argument, which should be separated from it by white space. The colon and
question mark characters may not be used as option characters. Each time
it is invoked, getopts places the next option in the shell variable
name, initializing name if it does not exist, and the index
of the next argument to be processed into the variable OPTIND.
OPTIND is initialized to 1 each time the shell or a shell script is
invoked. When an option requires an argument, getopts places that
argument into the variable OPTARG. The shell does not reset
OPTIND automatically; it must be manually reset between multiple
calls to getopts within the same shell invocation if a new set of
parameters is to be used.
When the end of options is encountered, getopts exits with a return
value greater than zero. OPTIND is set to the index of the first
non-option argument, and name is set to ?.
getopts normally parses the positional parameters, but if more
arguments are given in args, getopts parses those instead.
getopts can report errors in two ways. If the first character of
optstring is a colon, silent error reporting is used. In
normal operation diagnostic messages are printed when invalid options or
missing option arguments are encountered. If the variable OPTERR is
set to 0, no error messages will be displayed, even if the first character
of optstring is not a colon.
If an invalid option is seen, getopts places ? into name and,
if not silent, prints an error message and unsets OPTARG. If
getopts is silent, the option character found is placed in
OPTARG and no diagnostic message is printed.
If a required argument is not found, and getopts is not silent, a
question mark ( ?) is placed in name, OPTARG is
unset, and a diagnostic message is printed. If getopts is silent,
then a colon ( :) is placed in name and OPTARG is set
to the option character found.
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 file name of the command. The
-r option causes the shell to forget all remembered locations. The
-d option causes the shell to forget the remembered location of
each name. If the -t option is supplied, the full pathname
to which each name corresponds is printed. If multiple name
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 -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.
- -a
- Append the ``new'' history lines (history lines entered since the
beginning of the current bash session) to the history file.
- -n
- Read the history lines not already read from the history file into the
current history list. These are lines appended to the history file since
the beginning of the current bash session.
- -r
- Read the contents of the history file and use them as the current
history.
- -w
- Write the current history to the history file, overwriting the history
file's contents.
- -p
- Perform history substitution on the following args and display the
result on the standard output. Does not store the results in the history
list. Each arg must be quoted to disable normal history
expansion.
- -s
- Store the args in the history list as a single entry. The last
command in the history list is removed before the args are
added.
If the
HISTTIMEFORMAT variable is set, the time stamp information
associated with each history entry is written to the history file, marked with
the history comment character. When the history file is read, lines beginning
with the history comment character followed immediately by a digit are
interpreted as timestamps for the previous history line. The return value is 0
unless an invalid option is encountered, an error occurs while reading or
writing the history file, an invalid
offset is supplied as an argument
to
-d, or the history expansion supplied as an argument to
-p
fails.
- jobs [-lnprs] [ jobspec ... ]
- jobs -x command [ args ... ]
- The first form lists the active jobs. The options have the following
meanings:
- -l
- List process IDs in addition to the normal information.
- -n
- Display information only about jobs that have changed status since the
user was last notified of their status.
- -p
- List only the process ID of the job's process group leader.
- -r
- Restrict output to running jobs.
- -s
- Restrict output to stopped jobs.
If
jobspec is given, output is restricted to information about that job.
The return status is 0 unless an invalid option is encountered or an invalid
jobspec is supplied.
If the
-x option is supplied,
jobs replaces any
jobspec
found in
command or
args with the corresponding process group
ID, and executes
command passing it
args, returning its exit
status.
- kill [-s sigspec | -n signum |
-sigspec] [pid | jobspec] ...
- kill -l [sigspec | exit_status]
- Send the signal named by sigspec or signum to the 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.
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. 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 [-n count] [-O origin]
[-s count] [-t] [-u fd] [-C
callback] [ -c quantum] [array]
- readarray [-n count] [-O origin]
[-s count] [-t] [-u fd] [-C
callback] [ -c quantum] [array]
- Read lines from the standard input into the indexed array variable
array, or from file descriptor fd if the -u option is
supplied. The variable MAPFILE is the default array.
Options, if supplied, have the following meanings:
- -n
- Copy at most count lines. If count is 0, all lines are
copied.
- -O
- Begin assigning to array at index origin. The default index
is 0.
- -s
- Discard the first count lines read.
- -t
- Remove a trailing newline from each line read.
- -u
- Read lines from file descriptor fd instead of the standard
input.
- -C
- Evaluate callback each time quantum lines are read. The
-c option specifies quantum.
- -c
- Specify the number of lines read between each call to
callback.
If
-C is specified without
-c, the default quantum is 5000. When
callback is evaluated, it is supplied the index of the next array
element to be assigned and the line to be assigned to that element as
additional 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. With no arguments, removes the
top directory from the stack, and performs a cd 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. For example: ``popd +0'' removes the
first directory, ``popd +1'' the second.
- -n
- Removes the nth entry counting from the right of the list shown by
dirs, starting with zero. For example: ``popd -0'' removes the last
directory, ``popd -1'' the next to last.
If the
popd command is successful, a
dirs is performed as well,
and the return status is 0.
popd returns false if an invalid option is
encountered, the directory stack is empty, a non-existent directory stack
entry is specified, or the directory change fails.
- printf [-v var] format [arguments]
- Write the formatted arguments to the standard output under the
control of the format. The -v option causes the output to be
assigned to the variable var rather than being printed to the
standard output.
The format is a character string which contains three types of
objects: plain characters, which are simply copied to standard output,
character escape sequences, which are converted and copied to the standard
output, and format specifications, each of which causes printing of the
next successive argument. In addition to the standard
printf(1) format specifications, printf interprets the
following extensions:
- %b
- causes printf to expand backslash escape sequences in the
corresponding argument (except that \c terminates output,
backslashes in \', \", and \? are not removed,
and octal escapes beginning with \0 may contain up to four
digits).
- %q
- causes printf to output the corresponding argument in a
format that can be reused as shell input.
- %(datefmt)T
- causes printf to output the date-time string resulting from using
datefmt as a format string for strftime(3). The
corresponding argument is an integer representing the number of
seconds since the epoch. Two special argument values may be used: -1
represents the current time, and -2 represents the time the shell was
invoked.
Arguments to non-string format specifiers are treated as C constants, except
that a leading plus or minus sign is allowed, and if the leading character is
a single or 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, exchanges the top two directories and returns 0, unless the
directory stack is empty. Arguments, if supplied, have the following
meanings:
- -n
- Suppresses the normal change of directory when adding directories to the
stack, so that only the stack is manipulated.
- +n
- Rotates the stack so that the nth directory (counting from the left
of the list shown by dirs, starting with zero) is at the top.
- -n
- Rotates the stack so that the nth directory (counting from the
right of the list shown by dirs, starting with zero) is at the
top.
- dir
- Adds dir to the directory stack at the top, making it the new
current working directory.
If the
pushd command is successful, a
dirs is performed as well.
If the first form is used,
pushd returns 0 unless the cd to
dir
fails. With the second form,
pushd returns 0 unless the directory stack
is empty, a non-existent directory stack element is specified, or the
directory change to the specified new current directory fails.
- pwd [-LP]
- Print the absolute pathname of the current working 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, and the first
word is assigned to the first name, the second word to the second
name, and so on, with leftover words and their intervening
separators assigned to the last name. If there are fewer words read
from the input stream than names, the remaining names are assigned empty
values. The characters in IFS are used to split the line into
words. The backslash character ( \) may be used to remove any
special meaning for the next character read and for line continuation.
Options, if supplied, have the following meanings:
- -a aname
- The words are assigned to sequential indices of the array variable
aname, starting at 0. aname is unset before any new values
are assigned. Other name arguments are ignored.
- -d delim
- The first character of delim is used to terminate the input line,
rather than newline.
- -e
- If the standard input is coming from a terminal, readline (see
READLINE above) is used to obtain the line. Readline uses the
current (or default, if line editing was not previously active) editing
settings.
- -i text
- If readline is being used to read the line, text is placed
into the editing buffer before editing begins.
- -n nchars
- read returns after reading nchars characters rather than
waiting for a complete line of input, but honor a delimiter if fewer than
nchars 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.
- -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 be
used as a line continuation.
- -s
- Silent mode. If input is coming from a terminal, characters are not
echoed.
- -t timeout
- Cause read to time out and return failure if a complete line of
input is not read within timeout seconds. timeout may be a
decimal number with a fractional portion following the decimal point. This
option is only effective if read is reading input from a terminal,
pipe, or other special file; it has no effect when reading from regular
files. If timeout is 0, read returns success if input is
available on the specified file descriptor, failure otherwise. The exit
status is greater than 128 if the timeout is exceeded.
- -u fd
- Read input from file descriptor fd.
If no
names are supplied, the line read is assigned to the variable
REPLY. The return code is zero, unless end-of-file is encountered,
read times out (in which case the return code is greater than 128), or
an invalid file descriptor is supplied as the argument to
-u.
- readonly [-aAf] [-p] [name[=word]
...]
- The given names are marked readonly; the values of these
names may not be changed by subsequent assignment. If the -f
option is supplied, the functions corresponding to the names are so
marked. The -a option restricts the variables to indexed arrays;
the -A option restricts the variables to associative arrays. If
both options are supplied, -A takes precedence. If no name
arguments are given, or if the -p option is supplied, a list of all
readonly names is printed. The other options may be used to restrict the
output to a subset of the set of readonly names. The -p option
causes output to be displayed in a format that may be reused as input. If
a variable name is followed by = word, the value of the variable is
set to word. The return status is 0 unless an invalid option is
encountered, one of the names is not a valid shell variable name,
or -f is supplied with a name that is not a function.
- return [n]
- Causes a function to exit with the return value specified by n. If
n is omitted, the return status is that of the last command
executed in the function body. If used 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 used outside a function and not during execution
of a script by ., the return status is false. Any command
associated with the RETURN trap is executed before execution
resumes after the function or script.
- set [--abefhkmnptuvxBCEHPT] [-o option-name]
[arg ...]
- set [+abefhkmnptuvxBCEHPT] [+o option-name]
[arg ...]
- Without options, the name and value of each shell variable are displayed
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
- Automatically mark variables and functions which are modified or created
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 subshell command enclosed in parentheses,
or one of the commands executed as part of a command list enclosed by
braces (see SHELL GRAMMAR above) exits with a non-zero status. The
shell does not exit if the command that fails is part of the command list
immediately following a while or until keyword, part of the
test following the if or elif reserved words, part of any
command executed in a && or || list except the
command following the final && or ||, any command in
a pipeline but the last, or if the command's return value is being
inverted with !. A trap on ERR, if set, is 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.
- -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). Background processes run in a separate process group and a line
containing their exit status is printed upon their completion.
- -n
- Read commands but do not execute them. This may be used to check a shell
script for syntax errors. This is ignored by interactive shells.
- -o option-name
- The option-name can be one of the following:
- allexport
- Same as -a.
- braceexpand
- Same as -B.
- emacs
- Use an emacs-style command line editing interface. This is enabled by
default when the shell is interactive, unless the shell is started with
the --noediting option. This also affects the editing interface
used for read -e.
- errexit
- Same as -e.
- errtrace
- Same as -E.
- functrace
- Same as -T.
- hashall
- Same as -h.
- histexpand
- Same as -H.
- history
- Enable command history, as described above under HISTORY. This
option is on by default in interactive shells.
- ignoreeof
- The effect is as if the shell command ``IGNOREEOF=10'' had been executed
(see Shell Variables above).
- keyword
- Same as -k.
- monitor
- Same as -m.
- noclobber
- Same as -C.
- noexec
- Same as -n.
- noglob
- Same as -f.
- nolog
- Currently ignored.
- notify
- Same as -b.
- nounset
- Same as -u.
- onecmd
- Same as -t.
- physical
- Same as -P.
- pipefail
- If set, the return value of a pipeline is the value of the last
(rightmost) command to exit with a non-zero status, or zero if all
commands in the pipeline exit 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).
- 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.
- -t
- Exit after reading and executing one command.
- -u
- Treat unset variables and parameters other than the special parameters
"@" and "*" as an error when performing parameter
expansion. If 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 follow 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 variables controlling optional shell behavior. With
no options, or with the -p option, a list of all settable options
is displayed, with an indication of whether or not each is set. The
-p option causes output to be displayed in a form that may be
reused as input. Other options have the following meanings:
- -s
- Enable (set) each optname.
- -u
- Disable (unset) each optname.
- -q
- Suppresses normal output (quiet mode); the return status indicates whether
the optname is set or unset. If multiple optname arguments
are given with -q, the return status is zero if all optnames
are enabled; non-zero otherwise.
- -o
- Restricts the values of optname to be those defined for the
-o option to the set builtin.
If either
-s or
-u is used with no
optname arguments, the
display is limited to those options which are set or unset, respectively.
Unless otherwise noted, the
shopt options are disabled (unset) by
default.
The return status when listing options is zero if all
optnames are
enabled, non-zero otherwise. When setting or unsetting options, the return
status is zero unless an
optname is not a valid shell option.
The list of
shopt options is:
- autocd
- If set, a command name that is the name of a directory is executed as if
it were the argument to the cd command. This option is only used by
interactive shells.
- cdable_vars
- If set, an argument to the cd builtin command that is not a
directory is assumed to be the name of a variable whose value is the
directory to change to.
- cdspell
- If set, minor errors in the spelling of a 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 file name is printed, and the command
proceeds. This option is only used by interactive shells.
- checkhash
- If set, bash checks that a command found in the hash table exists
before trying to execute it. If a hashed command no longer exists, a
normal path search is performed.
- checkjobs
- If set, bash lists the status of any stopped and running jobs
before exiting an interactive shell. If any jobs are running, this causes
the exit to be deferred until a second exit is attempted without an
intervening command (see JOB CONTROL above). The shell always
postpones exiting if any jobs are stopped.
- checkwinsize
- If set, bash checks the window size after each command and, if
necessary, updates the values of LINES and COLUMNS.
- cmdhist
- If set, bash attempts to save all lines of a multiple-line command
in the same history entry. This allows easy re-editing of multi-line
commands.
- compat31
- If set, bash changes its behavior to that of version 3.1 with
respect to quoted arguments to the [[ conditional command's
=~ operator.
- compat32
- If set, bash changes its behavior to that of version 3.2 with
respect to locale-specific string comparison when using the [[
conditional command's < and > operators. Bash versions
prior to bash-4.1 use ASCII collation and strcmp(3); bash-4.1 and
later use the current locale's collation sequence and
strcoll(3).
- compat40
- If set, bash changes its behavior to that of version 4.0 with
respect to locale-specific string comparison when using the [[
conditional command's < and > operators (see previous
item) and the effect of interrupting a command list.
- compat41
- If set, bash, when in posix mode, treats a single quote in a
double-quoted parameter expansion as a special character. The single
quotes must match (an even number) and the characters between the single
quotes are considered quoted. This is the behavior of posix mode through
version 4.1. The default bash behavior remains as in previous
versions.
- 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.
- 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, 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), a call to
return is simulated.
- 4.
- BASH_ARGC and BASH_ARGV are updated as described in their
descriptions above.
- 5.
- Function tracing is enabled: command 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.
- 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.
- 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.
- 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.
- nullglob
- If set, bash allows patterns which match no files (see Pathname
Expansion above) to expand to a null string, rather than
themselves.
- progcomp
- If set, the programmable completion facilities (see Programmable
Completion above) are enabled. This option is enabled by default.
- promptvars
- If set, prompt strings undergo parameter 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.
- xpg_echo
- If set, the echo builtin expands backslash-escape sequences by
default.
- suspend [-f]
- Suspend the execution of this shell until it receives a SIGCONT
signal. When the suspended shell is a background process, it can be
restarted by the fg command. For more information, read the JOB
CONTROL section. The suspend command can not suspend the login
shell. However, when -f option is specified, suspend command
can suspend even login shell. The return status is 0 unless the shell is a
login shell and -f is not supplied, or if job control is not
enabled.
- test expr
- [ expr ]
- Return a status of 0 or 1 depending on the evaluation of the conditional
expression expr. Each operator and 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
- If the first argument is !, the result is the negation of the
three-argument expression composed of the remaining arguments. Otherwise,
the expression is parsed and evaluated according to precedence using the
rules listed above.
- 5 or more arguments
- The expression is parsed and evaluated according to precedence using the
rules listed above.
When used with
test or
[, the
< and
>
operators sort 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 simple command has a non-zero exit status, subject to the
following conditions. The ERR trap is not executed if the failed
command is part of the command list immediately following a while
or until keyword, part of the test in an if statement, part
of a command executed in a && or || list, or if the
command's return value is being inverted via !. These are the same
conditions obeyed by the errexit option.
Signals ignored upon entry to the shell cannot be trapped, reset or listed.
Trapped signals that are not being ignored are reset to their original
values in a subshell or subshell environment when one is created. The
return status is false if any sigspec is invalid; otherwise
trap returns true.
- type [-aftpP] name [name ...]
- With no options, indicate how each name would be 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, not necessarily the file that appears first in
PATH. If the -a option is used, type prints all of
the places that contain an executable named name. This includes
aliases and functions, if and only if the -p option is not also
used. The table of hashed commands is not consulted when using -a.
The -f option suppresses shell function lookup, as with the
command builtin. type returns true if all of the arguments
are found, false if any are not found.
- ulimit [-HSTabcdefilmnpqrstuvx [limit]]
- Provides control over the resources available to the shell and to
processes started by it, on systems that allow such control. The -H
and -S options specify that the hard or soft limit is set for the
given resource. A hard limit cannot be increased by a non-root user once
it is set; a soft limit may be increased up to the value of the hard
limit. If neither -H nor -S is specified, both the soft and
hard limits are set. The value of limit can be a number in the unit
specified for the resource or one of the special values hard,
soft, or unlimited, which stand for the current hard limit,
the current soft limit, and no limit, respectively. If limit is
omitted, the current value of the soft limit of the resource is printed,
unless the -H option is given. When more than one resource is
specified, the limit name and unit are printed before the value. Other
options are interpreted as follows:
- -a
- All current limits are reported
- -b
- The maximum socket buffer size
- -c
- The maximum size of core files created
- -d
- The maximum size of a process's data segment
- -e
- The maximum scheduling priority ("nice")
- -f
- The maximum size of files written by the shell and its children
- -i
- The maximum number of pending signals
- -l
- The maximum size that may be locked into memory
- -m
- The maximum resident set size (many systems do not honor this limit)
- -n
- The maximum number of open file descriptors (most systems do not allow
this value to be set)
- -p
- The pipe size in 512-byte blocks (this may not be set)
- -q
- The maximum number of bytes in POSIX message queues
- -r
- The maximum real-time scheduling priority
- -s
- The maximum stack size
- -t
- The maximum amount of cpu time in seconds
- -u
- The maximum number of processes available to a single user
- -v
- The maximum amount of virtual memory available to the shell and, on some
systems, to its children
- -x
- The maximum number of file locks
- -T
- The maximum number of threads
If
limit is given, it is the new value of the specified resource (the
-a option is display only). If no option is given, then
-f is
assumed. Values are in 1024-byte increments, except for
-t, which is in
seconds,
-p, which is in units of 512-byte blocks, and
-T,
-b,
-n, and
-u, which are unscaled values. The return
status is 0 unless an invalid option or argument is supplied, or an error
occurs while setting a new limit. In POSIX Mode 512-byte blocks are used for
the `-c' and `-f' options.
- umask [-p] [-S] [mode]
- The user file-creation mask is set to mode. If mode begins
with a digit, it is interpreted as an octal 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] [name ...]
- For each name, remove the corresponding variable or function. If no
options are supplied, or the -v option is given, each name
refers to a shell variable. Read-only variables may not be unset. If
-f is specified, each name refers to a shell function, and
the function definition is removed. Each unset variable or function is
removed from the environment passed to subsequent commands. If any of
COMP_WORDBREAKS, RANDOM, SECONDS, LINENO,
HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are
unset, they lose their special properties, even if they are subsequently
reset. The exit status is true unless a name is readonly.
- wait [n ...]
- Wait for each specified process and return its termination status. Each
n 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 n is
not given, all currently active child processes are waited for, and the
return status is zero. If n specifies a non-existent process or
job, the return status is 127. Otherwise, the return status is the exit
status of the last process or job waited for.
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, ENV,
or BASH_ENV
- •
- specifying command names containing /
- •
- specifying a file name containing a / as an argument to the
. builtin command
- •
- specifying a filename containing a slash as an argument to the -p
option to the hash builtin command
- •
- importing function definitions from the shell environment at startup
- •
- parsing the value of SHELLOPTS from the shell environment at
startup
- •
- redirecting output using the >, >|, <>, >&, &>,
and >> redirection operators
- •
- using the exec builtin command to replace the shell with another
command
- •
- adding or deleting builtin commands with the -f and -d
options to the enable builtin command
- •
- using the enable builtin command to enable disabled shell
builtins
- •
- specifying the -p option to the command builtin command
- •
- turning off restricted mode with set +r or set +o
restricted.
These restrictions are enforced after any startup files are read.
When a command that is found to be a shell script is executed (see
COMMAND
EXECUTION above),
rbash turns off any restrictions in the shell
spawned to execute the script.
- Bash Reference Manual, Brian Fox and Chet Ramey
- The Gnu Readline Library, Brian Fox and Chet Ramey
- The Gnu History Library, Brian Fox and Chet Ramey
- Portable Operating System Interface (POSIX) Part 2: Shell and
Utilities, IEEE
- sh(1), ksh(1), csh(1)
- emacs(1), vi(1)
- readline(3)
- /bin/bash
- The bash executable
- /etc/profile
- The systemwide initialization file, executed for login shells
- /etc/bash.bash_logout
- The systemwide login shell cleanup file, executed when a login shell
exits
- ~/.bash_profile
- The personal initialization file, executed for login shells
- ~/.bashrc
- The individual per-interactive-shell startup file
- ~/.bash_logout
- The individual login shell cleanup file, executed when a login shell
exits
- ~/.inputrc
- Individual readline initialization file
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/.
Once you have determined that a bug actually exists, use the
bashbug
command (from the source package) to submit a bug report. If you have a fix,
you are encouraged to mail that as well! Suggestions and `philosophical' bug
reports may be mailed to
bug-bash@gnu.org or posted to the Usenet
newsgroup
gnu.bash.bug.
ALL bug reports should include:
- The version number of bash
- The hardware and operating system
- The compiler used to compile
- A description of the bug behaviour
- A short script or `recipe' which exercises the bug
Comments and bug reports concerning this manual page should be directed to
chet.ramey@case.edu.
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.