BASH_BUILTINS
Section: User Commands (1)
Updated: 2004 Apr 20
Page Index
NAME
bash, :, ., [, alias, bg, bind, break, builtin, caller,
cd, command, compgen, complete,
compopt, continue, declare, dirs, disown, echo, enable, eval, exec, exit,
export, false, fc, fg, getopts, hash, help, history, jobs, kill,
let, local, logout, mapfile, popd, printf, pushd, pwd, read,
readonly, return, set,
shift, shopt, source, suspend, test, times, trap, true, type, typeset,
ulimit, umask, unalias, unset, wait - bash built-in commands, see
bash(1)
BASH BUILTIN COMMANDS
Unless otherwise noted, each builtin command documented in this
section as accepting options preceded by
-
accepts
--
to signify the end of the options.
The :, true, false, and test/[ builtins
do not accept options and do not treat -- specially.
The exit, logout, return,
break, continue, let,
and shift builtins accept and process arguments beginning with
- without requiring --.
Other builtins that accept arguments but are not specified as accepting
options interpret arguments beginning with - as invalid options and
require -- to prevent this interpretation.
- : [arguments]
-
No effect; the command does nothing beyond expanding
arguments
and performing any specified
redirections.
The return status is zero.
- . filename [arguments]
-
- source filename [arguments]
-
Read and execute commands from
filename
in the current
shell environment and return the exit status of the last command
executed from
filename.
If
filename
does not contain a slash, filenames in
PATH
are used to find the directory containing
filename.
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.
If the -T option is enabled, source inherits any trap on
DEBUG; if it is not, any DEBUG trap string is saved and
restored around the call to source, and source unsets the
DEBUG trap while it executes.
If -T is not set, and the sourced file changes
the DEBUG trap, the new value is retained when source completes.
The return status is the status of the last command exited within
the script (0 if no commands are executed), and false if
filename
is not found or cannot be read.
- alias [-p] [name[=value] ...]
-
Alias with no arguments or with the
-p
option prints the list of aliases in the form
alias name=value on standard output.
When arguments are supplied, an alias is defined for
each name whose value is given.
A trailing space in value causes the next word to be
checked for alias substitution when the alias is expanded.
For each name in the argument list for which no value
is supplied, the name and value of the alias is printed.
Alias returns true unless a name is given for which
no alias has been defined.
- bg [jobspec ...]
-
Resume each suspended job jobspec in the background, as if it
had been started with
&.
If
jobspec
is not present, the shell's notion of the current job is used.
bg
jobspec
returns 0 unless run when job control is disabled or, when run with
job control enabled, any specified jobspec was not found
or was started without job control.
- bind [-m keymap] [-lpsvPSVX]
-
- bind [-m keymap] [-q function] [-u function] [-r keyseq]
-
- bind [-m keymap] -f filename
-
- bind [-m keymap] -x keyseq:shell-command
-
- bind [-m keymap] keyseq:function-name
-
- bind [-m keymap] keyseq:readline-command
-
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 (vi-move is also
a synonym); emacs is
equivalent to emacs-standard.
- -l
-
List the names of all readline functions.
- -p
-
Display readline function names and bindings in such a way
that they can be re-read.
- -P
-
List current readline function names and bindings.
- -s
-
Display readline key sequences bound to macros and the strings
they output in such a way that they can be re-read.
- -S
-
Display readline key sequences bound to macros and the strings
they output.
- -v
-
Display readline variable names and values in such a way that they
can be re-read.
- -V
-
List current readline variable names and values.
- -f filename
-
Read key bindings from filename.
- -q function
-
Query about which keys invoke the named function.
- -u function
-
Unbind all keys bound to the named function.
- -r keyseq
-
Remove any current binding for keyseq.
- -x keyseq:shell-command
-
Cause shell-command to be executed whenever keyseq is
entered.
When shell-command is executed, the shell sets the
READLINE_LINE
variable to the contents of the readline line buffer and the
READLINE_POINT
and
READLINE_MARK
variables to the current location of the insertion point and the saved
insertion point (the mark), respectively.
If the executed command changes the value of any of
READLINE_LINE,
READLINE_POINT,
or
READLINE_MARK,
those new values will be reflected in the editing state.
- -X
-
List all key sequences bound to shell commands and the associated commands
in a format that can be reused as input.
The return value is 0 unless an unrecognized option is given or an
error occurred.
- break [n]
-
Exit from within a
for,
while,
until,
or
select
loop. If n is specified, break n levels.
n
must be ≥ 1. If
n
is greater than the number of enclosing loops, all enclosing loops
are exited.
The return value is 0 unless n is not greater than or equal to 1.
- builtin shell-builtin [arguments]
-
Execute the specified shell builtin, passing it
arguments,
and return its exit status.
This is useful when defining a
function whose name is the same as a shell builtin,
retaining the functionality of the builtin within the function.
The cd builtin is commonly redefined this way.
The return status is false if
shell-builtin
is not a shell builtin command.
- caller [expr]
-
Returns the context of any active subroutine call (a shell function or
a script executed with the . or source builtins).
Without expr, caller displays the line number and source
filename of the current subroutine call.
If a non-negative integer is supplied as expr, caller
displays the line number, subroutine name, and source file corresponding
to that position in the current execution call stack. This extra
information may be used, for example, to print a stack trace. The
current frame is frame 0.
The return value is 0 unless the shell is not executing a subroutine
call or expr does not correspond to a valid position in the
call stack.
- cd [-L|[-P [-e]] [-@]] [dir]
-
Change the current directory to dir.
if dir is not supplied, the value of the
HOME
shell variable is the default.
Any additional arguments following dir are ignored.
The variable
CDPATH
defines the search path for the directory containing
dir:
each directory name in
CDPATH
is searched for dir.
Alternative directory names in
CDPATH
are separated by a colon (:). A null directory name in
CDPATH
is the same as the current directory, i.e., ``.''. If
dir
begins with a slash (/),
then
CDPATH
is not used. The
-P
option causes cd to use the physical directory structure
by resolving symbolic links while traversing dir and
before processing instances of .. in dir (see also the
-P
option to the
set
builtin command); the
-L
option forces symbolic links to be followed by resolving the link
after processing instances of .. in dir.
If .. appears in dir, it is processed by removing the
immediately previous pathname component from dir, back to a slash
or the beginning of dir.
If the
-e
option is supplied with
-P,
and the current working directory cannot be successfully determined
after a successful directory change, cd will return an unsuccessful
status.
On systems that support it, the -@ option presents the extended
attributes associated with a file as a directory.
An argument of
-
is converted to
$OLDPWD
before the directory change is attempted.
If a non-empty directory name from
CDPATH
is used, or if
- is the first argument, and the directory change is
successful, the absolute pathname of the new working directory is
written to the standard output.
The return value is true if the directory was successfully changed;
false otherwise.
- command [-pVv] command [arg ...]
-
Run
command
with
args
suppressing the normal shell function lookup.
Only builtin commands or commands found in the
PATH
are executed. If the
-p
option is given, the search for
command
is performed using a default value for
PATH
that is guaranteed to find all of the standard utilities.
If either the
-V
or
-v
option is supplied, a description of
command
is printed. The
-v
option causes a single word indicating the command or filename
used to invoke
command
to be displayed; the
-V
option produces a more verbose description.
If the
-V
or
-v
option is supplied, the exit status is 0 if
command
was found, and 1 if not. If neither option is supplied and
an error occurred or
command
cannot be found, the exit status is 127. Otherwise, the exit status of the
command
builtin is the exit status of
command.
- compgen [option] [word]
-
Generate possible completion matches for word according to
the options, which may be any option accepted by the
complete
builtin with the exception of -p and -r, and write
the matches to the standard output.
When using the -F or -C options, the various shell variables
set by the programmable completion facilities, while available, will not
have useful values.
The matches will be generated in the same way as if the programmable
completion code had generated them directly from a completion specification
with the same flags.
If word is specified, only those completions matching word
will be displayed.
The return value is true unless an invalid option is supplied, or no
matches were generated.
- complete [-abcdefgjksuv] [-o comp-option] [-DEI] [-A action] [-G globpat] [-W wordlist]
-
[-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix] name [name ...]
- complete -pr [-DEI] [name ...]
-
Specify how arguments to each name should be completed.
If the -p option is supplied, or if no options are supplied,
existing completion specifications are printed in a way that allows
them to be reused as input.
The -r option removes a completion specification for
each name, or, if no names are supplied, all
completion specifications.
The -D option indicates that other supplied options and actions should
apply to the ``default'' command completion; that is, completion attempted
on a command for which no completion has previously been defined.
The -E option indicates that other supplied options and actions should
apply to ``empty'' command completion; that is, completion attempted on a
blank line.
The -I option indicates that other supplied options and actions should
apply to completion on the initial non-assignment word on the line, or after
a command delimiter such as ; or |, which is usually command
name completion.
If multiple options are supplied, the -D option takes precedence
over -E, and both take precedence over -I.
If any of -D, -E, or -I are supplied, any other
name arguments are ignored; these completions only apply to the case
specified by the option.
The process of applying these completion specifications when word completion
is attempted is described above under Programmable Completion.
Other options, if specified, have the following meanings.
The arguments to the -G, -W, and -X options
(and, if necessary, the -P and -S options)
should be quoted to protect them from expansion before the
complete
builtin is invoked.
-
- -o comp-option
-
The comp-option controls several aspects of the compspec's behavior
beyond the simple generation of completions.
comp-option may be one of:
-
- bashdefault
-
Perform the rest of the default bash completions if the compspec
generates no matches.
- default
-
Use readline's default filename completion if the compspec generates
no matches.
- dirnames
-
Perform directory name completion if the compspec generates no matches.
- filenames
-
Tell readline that the compspec generates filenames, so it can perform any
filename-specific processing (like adding a slash to directory names,
quoting special characters, or suppressing trailing spaces).
Intended to be used with shell functions.
- noquote
-
Tell readline not to quote the completed words if they are filenames
(quoting filenames is the default).
- nosort
-
Tell readline not to sort the list of possible completions alphabetically.
- nospace
-
Tell readline not to append a space (the default) to words completed at
the end of the line.
- plusdirs
-
After any matches defined by the compspec are generated,
directory name completion is attempted and any
matches are added to the results of the other actions.
- -A action
-
The action may be one of the following to generate a list of possible
completions:
-
- alias
-
Alias names. May also be specified as -a.
- arrayvar
-
Array variable names.
- binding
-
Readline key binding names.
- builtin
-
Names of shell builtin commands. May also be specified as -b.
- command
-
Command names. May also be specified as -c.
- directory
-
Directory names. May also be specified as -d.
- disabled
-
Names of disabled shell builtins.
- enabled
-
Names of enabled shell builtins.
- export
-
Names of exported shell variables. May also be specified as -e.
- file
-
File names. May also be specified as -f.
- function
-
Names of shell functions.
- group
-
Group names. May also be specified as -g.
- helptopic
-
Help topics as accepted by the help builtin.
- hostname
-
Hostnames, as taken from the file specified by the
HOSTFILE
shell variable.
- job
-
Job names, if job control is active. May also be specified as -j.
- keyword
-
Shell reserved words. May also be specified as -k.
- running
-
Names of running jobs, if job control is active.
- service
-
Service names. May also be specified as -s.
- setopt
-
Valid arguments for the -o option to the set builtin.
- shopt
-
Shell option names as accepted by the shopt builtin.
- signal
-
Signal names.
- stopped
-
Names of stopped jobs, if job control is active.
- user
-
User names. May also be specified as -u.
- variable
-
Names of all shell variables. May also be specified as -v.
- -C command
-
command is executed in a subshell environment, and its output is
used as the possible completions.
- -F function
-
The shell function function is executed in the current shell
environment.
When the function is executed,
the first argument ($1) is the name of the command whose arguments are
being completed,
the second argument ($2) is the word being completed,
and the third argument ($3) is the word preceding the word being
completed on the current command line.
When it finishes, the possible completions are retrieved from the value
of the
COMPREPLY
array variable.
- -G globpat
-
The pathname expansion pattern globpat is expanded to generate
the possible completions.
- -P prefix
-
prefix is added at the beginning of each possible completion
after all other options have been applied.
- -S suffix
-
suffix is appended to each possible completion
after all other options have been applied.
- -W wordlist
-
The wordlist is split using the characters in the
IFS
special variable as delimiters, and each resultant word is expanded.
Shell quoting is honored within wordlist,
in order to provide a
mechanism for the words to contain shell metacharacters or characters
in the value of
IFS.
The possible completions are the members of the resultant list which
match the word being completed.
- -X filterpat
-
filterpat is a pattern as used for pathname expansion.
It is applied to the list of possible completions generated by the
preceding options and arguments, and each completion matching
filterpat is removed from the list.
A leading ! in filterpat negates the pattern; in this
case, any completion not matching filterpat is removed.
The return value is true unless an invalid option is supplied, an option
other than -p or -r is supplied without a name
argument, an attempt is made to remove a completion specification for
a name for which no specification exists, or
an error occurs adding a completion specification.
- compopt [-o option] [-DEI] [+o option] [name]
-
Modify completion options for each name according to the
options, or for the
currently-executing completion if no names are supplied.
If no options are given, display the completion options for each
name or the current completion.
The possible values of option are those valid for the complete
builtin described above.
The -D option indicates that other supplied options should
apply to the ``default'' command completion; that is, completion attempted
on a command for which no completion has previously been defined.
The -E option indicates that other supplied options should
apply to ``empty'' command completion; that is, completion attempted on a
blank line.
The -I option indicates that other supplied options should
apply to completion on the initial non-assignment word on the line,
or after a command delimiter such as ; or |, which is usually
command name completion.
The return value is true unless an invalid option is supplied, an attempt
is made to modify the options for a name for which no completion
specification exists, or an output error occurs.
- continue [n]
-
Resume the next iteration of the enclosing
for,
while,
until,
or
select
loop.
If
n
is specified, resume at the nth enclosing loop.
n
must be ≥ 1. If
n
is greater than the number of enclosing loops, the last enclosing loop
(the ``top-level'' loop) is resumed.
The return value is 0 unless n is not greater than or equal to 1.
- declare [-aAfFgiIlnrtux] [-p] [name[=value] ...]
-
- typeset [-aAfFgiIlnrtux] [-p] [name[=value] ...]
-
Declare variables and/or give them attributes.
If no names are given then display the values of variables.
The
-p
option will display the attributes and values of each
name.
When
-p
is used with name arguments, additional options,
other than -f and -F, are ignored.
When
-p
is supplied without name arguments, it will display the attributes
and values of all variables having the attributes specified by the
additional options.
If no other options are supplied with -p, declare will display
the attributes and values of all shell variables. The -f option
will restrict the display to shell functions.
The
-F
option inhibits the display of function definitions; only the
function name and attributes are printed.
If the extdebug shell option is enabled using shopt,
the source file name and line number where each name
is defined are displayed as well. The
-F
option implies
-f.
The
-g
option forces variables to be created or modified at the global scope,
even when declare is executed in a shell function.
It is ignored in all other cases.
The
-I
option causes local variables to inherit the attributes
(except the nameref attribute)
and value of any existing variable with the same
name at a surrounding scope.
If there is no existing variable, the local variable is initially unset.
The following options can
be used to restrict output to variables with the specified attribute or
to give variables attributes:
-
- -a
-
Each name is an indexed array variable (see
Arrays
above).
- -A
-
Each name is an associative array variable (see
Arrays
above).
- -f
-
Use function names only.
- -i
-
The variable is treated as an integer; arithmetic evaluation (see
ARITHMETIC EVALUATION
above) is performed when the variable is assigned a value.
- -l
-
When the variable is assigned a value, all upper-case characters are
converted to lower-case.
The upper-case attribute is disabled.
- -n
-
Give each name the nameref attribute, making
it a name reference to another variable.
That other variable is defined by the value of name.
All references, assignments, and attribute modifications
to name, except those using or changing the
-n attribute itself, are performed on the variable referenced by
name's value.
The nameref attribute cannot be applied to array variables.
- -r
-
Make names readonly. These names cannot then be assigned values
by subsequent assignment statements or unset.
- -t
-
Give each name the trace attribute.
Traced functions inherit the DEBUG and RETURN traps from
the calling shell.
The trace attribute has no special meaning for variables.
- -u
-
When the variable is assigned a value, all lower-case characters are
converted to upper-case.
The lower-case attribute is disabled.
- -x
-
Mark names for export to subsequent commands via the environment.
Using `+' instead of `-'
turns off the attribute instead,
with the exceptions that +a and +A
may not be used to destroy array variables and +r will not
remove the readonly attribute.
When used in a function,
declare
and
typeset
make each
name local, as with the
local
command,
unless the -g option is supplied.
If a variable name is followed by =value, the value of
the variable is set to value.
When using -a or -A and the compound assignment syntax to
create array variables, additional attributes do not take effect until
subsequent assignments.
The return value is 0 unless an invalid option is encountered,
an attempt is made to define a function using
``-f foo=bar'',
an attempt is made to assign a value to a readonly variable,
an attempt is made to assign a value to an array variable without
using the compound assignment syntax (see
Arrays
above), one of the names is not a valid shell variable name,
an attempt is made to turn off readonly status for a readonly variable,
an attempt is made to turn off array status for an array variable,
or an attempt is made to display a non-existent function with -f.
- dirs [-clpv] [+n] [-n]
-
Without options, displays the list of currently remembered directories.
The default display is on a single line with directory names separated
by spaces.
Directories are added to the list with the
pushd
command; the
popd
command removes entries from the list.
The current directory is always the first directory in the stack.
-
- -c
-
Clears the directory stack by deleting all of the entries.
- -l
-
Produces a listing using full pathnames;
the default listing format uses a tilde to denote the home directory.
- -p
-
Print the directory stack with one entry per line.
- -v
-
Print the directory stack with one entry per line,
prefixing each entry with its index in the stack.
- +n
-
Displays the nth entry counting from the left of the list
shown by
dirs
when invoked without options, starting with zero.
- -n
-
Displays the nth entry counting from the right of the list
shown by
dirs
when invoked without options, starting with zero.
The return value is 0 unless an
invalid option is supplied or n indexes beyond the end
of the directory stack.
- disown [-ar] [-h] [jobspec ... | pid ... ]
-
Without options, remove each
jobspec
from the table of active jobs.
If
jobspec
is not present, and neither the -a nor the -r option
is supplied, the current job is used.
If the -h option is given, each
jobspec
is not removed from the table, but is marked so that
SIGHUP
is not sent to the job if the shell receives a
SIGHUP.
If no
jobspec
is supplied, the
-a
option means to remove or mark all jobs; the
-r
option without a
jobspec
argument restricts operation to running jobs.
The return value is 0 unless a
jobspec
does not specify a valid job.
- echo [-neE] [arg ...]
-
Output the args, separated by spaces, followed by a newline.
The return status is 0 unless a write error occurs.
If -n is specified, the trailing newline is
suppressed. If the -e option is given, interpretation of
the following backslash-escaped characters is enabled. The
-E
option disables the interpretation of these escape characters,
even on systems where they are interpreted by default.
The xpg_echo shell option may be used to
dynamically determine whether or not echo expands these
escape characters by default.
echo
does not interpret -- to mean the end of options.
echo
interprets the following escape sequences:
-
- \a
-
alert (bell)
- \b
-
backspace
- \c
-
suppress further output
- \e
-
- \E
-
an escape character
- \f
-
form feed
- \n
-
new line
- \r
-
carriage return
- \t
-
horizontal tab
- \v
-
vertical tab
- \\
-
backslash
- \0nnn
-
the eight-bit character whose value is the octal value nnn
(zero to three octal digits)
- \xHH
-
the eight-bit character whose value is the hexadecimal value HH
(one or two hex digits)
- \uHHHH
-
the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
HHHH (one to four hex digits)
- \UHHHHHHHH
-
the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value
HHHHHHHH (one to eight hex digits)
- enable [-a] [-dnps] [-f filename] [name ...]
-
Enable and disable builtin shell commands.
Disabling a builtin allows a disk command which has the same name
as a shell builtin to be executed without specifying a full pathname,
even though the shell normally searches for builtins before disk commands.
If -n is used, each name
is disabled; otherwise,
names are enabled. For example, to use the
test
binary found via the
PATH
instead of the shell builtin version, run
``enable -n test''.
The
-f
option means to load the new builtin command
name
from shared object
filename,
on systems that support dynamic loading. 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
execfail
shell option
is enabled. In that case, it returns failure.
An interactive shell returns failure if the file cannot be executed.
A subshell exits unconditionally if exec fails.
If
command
is not specified, any redirections take effect in the current shell,
and the return status is 0. If there is a redirection error, the
return status is 1.
- exit [n]
-
Cause the shell to exit
with a status of n. If
n
is omitted, the exit status
is that of the last command executed.
A trap on
EXIT
is executed before the shell terminates.
- export [-fn] [name[=word]] ...
-
- export -p
-
The supplied
names
are marked for automatic export to the environment of
subsequently executed commands. If the
-f
option is given, the
names
refer to functions.
If no
names
are given, or if the
-p
option is supplied, a list
of names of all exported variables is printed.
The
-n
option causes the export property to be removed from each
name.
If a variable name is followed by =word, the value of
the variable is set to word.
export
returns an exit status of 0 unless an invalid option is
encountered,
one of the names is not a valid shell variable name, or
-f
is supplied with a
name
that is not a function.
- fc [-e ename] [-lnr] [first] [last]
-
- fc -s [pat=rep] [cmd]
-
The first form selects a range of commands from
first
to
last
from the history list and displays or edits and re-executes them.
First
and
last
may be specified as a string (to locate the last command beginning
with that string) or as a number (an index into the history list,
where a negative number is used as an offset from the current
command number).
When listing, a first or last of
0 is equivalent to -1 and -0 is equivalent to the current
command (usually the fc command); otherwise 0 is equivalent to -1
and -0 is invalid.
If
last
is not specified, it is set to
the current command for listing (so that
``fc -l -10''
prints the last 10 commands) and to
first
otherwise.
If
first
is not specified, it is set to the previous
command for editing and -16 for listing.
The
-n
option suppresses
the command numbers when listing. The
-r
option reverses the order of
the commands. If the
-l
option is given,
the commands are listed on
standard output. Otherwise, the editor given by
ename
is invoked
on a file containing those commands. If
ename
is not given, the
value of the
FCEDIT
variable is used, and
the value of
EDITOR
if
FCEDIT
is not set. If neither variable is set,
vi
is used. When editing is complete, the edited commands are
echoed and executed.
In the second form, command is re-executed after each instance
of pat is replaced by rep.
Command is interpreted the same as first above.
A useful alias to use with this is
``r="fc -s"'',
so that typing
``r cc''
runs the last command beginning with
``cc''
and typing
``r''
re-executes the last command.
If the first form is used, the return value is 0 unless an invalid
option is encountered or
first
or
last
specify history lines out of range.
If the
-e
option is supplied, the return value is the value of the last
command executed or failure if an error occurs with the temporary
file of commands. If the second form is used, the return status
is that of the command re-executed, unless
cmd
does not specify a valid history line, in which case
fc
returns failure.
- fg [jobspec]
-
Resume
jobspec
in the foreground, and make it the current job.
If
jobspec
is not present, the shell's notion of the current job is used.
The return value is that of the command placed into the foreground,
or failure if run when job control is disabled or, when run with
job control enabled, if
jobspec
does not specify a valid job or
jobspec
specifies a job that was started without job control.
- getopts optstring name [arg ...]
-
getopts
is used by shell procedures to parse positional parameters.
optstring
contains the option characters to be recognized; if a character
is followed by a colon, the option is expected to have an
argument, which should be separated from it by white space.
The colon and question mark characters may not be used as
option characters.
Each time it is invoked,
getopts
places the next option in the shell variable
name,
initializing
name
if it does not exist,
and the index of the next argument to be processed into the
variable
OPTIND.
OPTIND
is initialized to 1 each time the shell or a shell script
is invoked. When an option requires an argument,
getopts
places that argument into the variable
OPTARG.
The shell does not reset
OPTIND
automatically; it must be manually reset between multiple
calls to
getopts
within the same shell invocation if a new set of parameters
is to be used.
When the end of options is encountered, getopts exits with a
return value greater than zero.
OPTIND
is set to the index of the first non-option argument,
and name is set to ?.
getopts
normally parses the positional parameters, but if more arguments are
supplied as
arg
values,
getopts
parses those instead.
getopts
can report errors in two ways. If the first character of
optstring
is a colon,
silent
error reporting is used. In normal operation, diagnostic messages
are printed when invalid options or missing option arguments are
encountered.
If the variable
OPTERR
is set to 0, no error messages will be displayed, even if the first
character of
optstring
is not a colon.
If an invalid option is seen,
getopts
places ? into
name
and, if not silent,
prints an error message and unsets
OPTARG.
If
getopts
is silent,
the option character found is placed in
OPTARG
and no diagnostic message is printed.
If a required argument is not found, and
getopts
is not silent,
a question mark (?) is placed in
name,
OPTARG
is unset, and a diagnostic message is printed.
If
getopts
is silent, then a colon (:) is placed in
name
and
OPTARG
is set to the option character found.
getopts
returns true if an option, specified or unspecified, is found.
It returns false if the end of options is encountered or an
error occurs.
- hash [-lr] [-p filename] [-dt] [name]
-
Each time hash is invoked,
the full pathname of the command
name
is determined by searching
the directories in
$PATH
and remembered. Any previously-remembered pathname is discarded.
If the
-p
option is supplied, no path search is performed, and
filename
is used as the full filename of the command.
The
-r
option causes the shell to forget all
remembered locations.
The
-d
option causes the shell to forget the remembered location of each name.
If the
-t
option is supplied, the full pathname to which each name corresponds
is printed. If multiple name arguments are supplied with -t,
the name is printed before the hashed full pathname.
The
-l
option causes output to be displayed in a format that may be reused as input.
If no arguments are given, or if only -l is supplied,
information about remembered commands is printed.
The return status is true unless a
name
is not found or an invalid option is supplied.
- help [-dms] [pattern]
-
Display helpful information about builtin commands. If
pattern
is specified,
help
gives detailed help on all commands matching
pattern;
otherwise help for all the builtins and shell control structures
is printed.
-
- -d
-
Display a short description of each pattern
- -m
-
Display the description of each pattern in a manpage-like format
- -s
-
Display only a short usage synopsis for each pattern
The return status is 0 unless no command matches
pattern.
- history [n]
-
- history -c
-
- history -d offset
-
- history -d start-end
-
- history -anrw [filename]
-
- history -p arg [arg ...]
-
- history -s arg [arg ...]
-
With no options, display the command
history list with line numbers. Lines listed
with a
*
have been modified. An argument of
n
lists only the last
n
lines.
If the shell variable
HISTTIMEFORMAT
is set and not null,
it is used as a format string for strftime(3) to display
the time stamp associated with each displayed history entry.
No intervening blank is printed between the formatted time stamp
and the history line.
If filename is supplied, it is used as the
name of the history file; if not, the value of
HISTFILE
is used. Options, if supplied, have the following meanings:
-
- -c
-
Clear the history list by deleting all the entries.
- -d offset
-
Delete the history entry at position offset.
If offset is negative, it is interpreted as relative to one greater
than the last history position, so negative indices count back from the
end of the history, and an index of -1 refers to the current
history -d command.
- -d start-end
-
Delete the history entries between positions start and end,
inclusive. Positive and negative values for start and end
are interpreted as described above.
- -a
-
Append the ``new'' history lines to the history file.
These are history lines entered since the beginning of the current
bash session, but not already appended to the history file.
- -n
-
Read the history lines not already read from the history
file into the current history list. These are lines
appended to the history file since the beginning of the
current bash session.
- -r
-
Read the contents of the history file
and append them to the current history list.
- -w
-
Write the current history list to the history file, overwriting the
history file's contents.
- -p
-
Perform history substitution on the following args and display
the result on the standard output.
Does not store the results in the history list.
Each arg must be quoted to disable normal history expansion.
- -s
-
Store the
args
in the history list as a single entry. The last command in the
history list is removed before the
args
are added.
If the
HISTTIMEFORMAT
variable is set, the time stamp information
associated with each history entry is written to the history file,
marked with the history comment character.
When the history file is read, lines beginning with the history
comment character followed immediately by a digit are interpreted
as timestamps for the following history entry.
The return value is 0 unless an invalid option is encountered, an
error occurs while reading or writing the history file, an invalid
offset is supplied as an argument to -d, or the
history expansion supplied as an argument to -p fails.
- jobs [-lnprs] [ jobspec ... ]
-
- jobs -x command [ args ... ]
-
The first form lists the active jobs. The options have the following
meanings:
-
- -l
-
List process IDs
in addition to the normal information.
- -n
-
Display information only about jobs that have changed status since
the user was last notified of their status.
- -p
-
List only the process ID of the job's process group
leader.
- -r
-
Display only running jobs.
- -s
-
Display only stopped jobs.
If
jobspec
is given, output is restricted to information about that job.
The return status is 0 unless an invalid option is encountered
or an invalid
jobspec
is supplied.
If the
-x
option is supplied,
jobs
replaces any
jobspec
found in
command
or
args
with the corresponding process group ID, and executes
command
passing it
args,
returning its exit status.
- kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
-
- kill -l|-L [sigspec | exit_status]
-
Send the signal named by
sigspec
or
signum
to the processes named by
pid
or
jobspec.
sigspec
is either a case-insensitive signal name such as
SIGKILL
(with or without the
SIG
prefix) or a signal number;
signum
is a signal number.
If
sigspec
is not present, then
SIGTERM
is assumed.
An argument of
-l
lists the signal names.
If any arguments are supplied when
-l
is given, the names of the signals corresponding to the arguments are
listed, and the return status is 0.
The exit_status argument to
-l
is a number specifying either a signal number or the exit status of
a process terminated by a signal.
The
-L
option is equivalent to -l.
kill
returns true if at least one signal was successfully sent, or false
if an error occurs or an invalid option is encountered.
- let arg [arg ...]
-
Each
arg
is an arithmetic expression to be evaluated (see
ARITHMETIC EVALUATION
above).
If the last
arg
evaluates to 0,
let
returns 1; 0 is returned otherwise.
- local [option] [name[=value] ... | - ]
-
For each argument, a local variable named
name
is created, and assigned
value.
The option can be any of the options accepted by declare.
When
local
is used within a function, it causes the variable
name
to have a visible scope restricted to that function and its children.
If name is -, the set of shell options is made local to the function
in which local is invoked: shell options changed using the
set builtin inside the function are restored to their original values
when the function returns.
The restore is effected as if a series of set commands were executed
to restore the values that were in place before the function.
With no operands,
local
writes a list of local variables to the standard output. It is
an error to use
local
when not within a function. The return status is 0 unless
local
is used outside a function, an invalid
name
is supplied, or
name is a readonly variable.
- logout
-
Exit a login shell.
- mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
-
- readarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
-
Read lines from the standard input into the indexed array variable
array,
or from file descriptor
fd
if the
-u
option is supplied.
The variable
MAPFILE
is the default array.
Options, if supplied, have the following meanings:
-
- -d
-
The first character of delim is used to terminate each input line,
rather than newline.
If delim is the empty string, mapfile will terminate a line
when it reads a NUL character.
- -n
-
Copy at most
count
lines. If count is 0, all lines are copied.
- -O
-
Begin assigning to
array
at index
origin.
The default index is 0.
- -s
-
Discard the first count lines read.
- -t
-
Remove a trailing delim (default newline) from each line read.
- -u
-
Read lines from file descriptor fd instead of the standard input.
- -C
-
Evaluate
callback
each time quantum lines are read. The -c option specifies
quantum.
- -c
-
Specify the number of lines read between each call to
callback.
If
-C
is specified without
-c,
the default quantum is 5000.
When callback is evaluated, it is supplied the index of the next
array element to be assigned and the line to be assigned to that element
as additional arguments.
callback is evaluated after the line is read but before the
array element is assigned.
If not supplied with an explicit origin, mapfile will clear array
before assigning to it.
mapfile returns successfully unless an invalid option or option
argument is supplied, array is invalid or unassignable, or if
array is not an indexed array.
- popd [-n] [+n] [-n]
-
Removes entries from the directory stack. 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
in the same way as echo -e.
- %q
-
causes printf to output the corresponding
argument in a format that can be reused as shell input.
- %(datefmt)T
-
causes printf to output the date-time string resulting from using
datefmt as a format string for strftime(3).
The corresponding argument is an integer representing the number of
seconds since the epoch.
Two special argument values may be used: -1 represents the current
time, and -2 represents the time the shell was invoked.
If no argument is specified, conversion behaves as if -1 had been given.
This is an exception to the usual printf behavior.
The %b, %q, and %T directives all use the field width and precision
arguments from the format specification and write that many bytes from
(or use that wide a field for) the expanded argument, which usually
contains more characters than the original.
Arguments to non-string format specifiers are treated as C constants,
except that a leading plus or minus sign is allowed, and if the leading
character is a single or double quote, the value is the ASCII value of
the following character.
The format is reused as necessary to consume all of the arguments.
If the format requires more arguments than are supplied, the
extra format specifications behave as if a zero value or null string, as
appropriate, had been supplied.
The return value is zero on success, non-zero on failure.
- pushd [-n] [+n] [-n]
-
- pushd [-n] [dir]
-
Adds a directory to the top of the directory stack, or rotates
the stack, making the new top of the stack the current working
directory. With no arguments, pushd exchanges the top two 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 rotating or
adding directories to the stack, so that only the stack is manipulated.
- +n
-
Rotates the stack so that the nth directory
(counting from the left of the list shown by
dirs,
starting with zero)
is at the top.
- -n
-
Rotates the stack so that the nth directory
(counting from the right of the list shown by
dirs,
starting with zero) is at the top.
- dir
-
Adds
dir
to the directory stack at the top, making it the
new current working directory as if it had been supplied as the argument
to the cd builtin.
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,
split into words as described above under Word Splitting,
and the first word
is assigned to the first
name,
the second word to the second
name,
and so on.
If there are more words than names, the remaining words and their
intervening delimiters are assigned to the last
name.
If there are fewer words read from the input stream than names,
the remaining names are assigned empty values.
The characters in
IFS
are used to split the line into words using the same rules the shell
uses for expansion (described above under Word Splitting).
The backslash character (\) may be used to remove any special
meaning for the next character read and for line continuation.
Options, if supplied, have the following meanings:
-
- -a aname
-
The words are assigned to sequential indices
of the array variable
aname,
starting at 0.
aname
is unset before any new values are assigned.
Other name arguments are ignored.
- -d delim
-
The first character of delim is used to terminate the input line,
rather than newline.
If delim is the empty string, read will terminate a line
when it reads a NUL character.
- -e
-
If the standard input
is coming from a terminal,
readline
(see
READLINE
above) is used to obtain the line.
Readline uses the current (or default, if line editing was not previously
active) editing settings, but uses Readline's default filename completion.
- -i text
-
If
readline
is being used to read the line, text is placed into the editing
buffer before editing begins.
- -n nchars
-
read returns after reading nchars characters rather than
waiting for a complete line of input, but honors a delimiter if fewer
than nchars characters are read before the delimiter.
- -N nchars
-
read returns after reading exactly nchars characters rather
than waiting for a complete line of input, unless EOF is encountered or
read times out.
Delimiter characters encountered in the input are
not treated specially and do not cause read to return until
nchars characters are read.
The result is not split on the characters in IFS; the intent is
that the variable is assigned exactly the characters read
(with the exception of backslash; see the -r option below).
- -p prompt
-
Display prompt on standard error, without a
trailing newline, before attempting to read any input. The prompt
is displayed only if input is coming from a terminal.
- -r
-
Backslash does not act as an escape character.
The backslash is considered to be part of the line.
In particular, a backslash-newline pair may not then be used as a line
continuation.
- -s
-
Silent mode. If input is coming from a terminal, characters are
not echoed.
- -t timeout
-
Cause read to time out and return failure if a complete line of
input (or a specified number of characters)
is not read within timeout seconds.
timeout may be a decimal number with a fractional portion following
the decimal point.
This option is only effective if read is reading input from a
terminal, pipe, or other special file; it has no effect when reading
from regular files.
If read times out, read saves any partial input read into
the specified variable name.
If timeout is 0, read returns immediately, without trying to
read any data. The exit status is 0 if input is available on
the specified file descriptor, non-zero otherwise.
The exit status is greater than 128 if the timeout is exceeded.
- -u fd
-
Read input from file descriptor fd.
If no
names
are supplied, the line read,
without the ending delimiter but otherwise unmodified,
is assigned to the variable
REPLY.
The exit status is zero, unless end-of-file is encountered, read
times out (in which case the status is greater than 128),
a variable assignment error (such as assigning to a readonly variable) occurs,
or an invalid file descriptor is supplied as the argument to -u.
- readonly [-aAf] [-p] [name[=word] ...]
-
The given
names are marked readonly; the values of these
names
may not be changed by subsequent assignment.
If the
-f
option is supplied, the functions corresponding to the
names are so
marked.
The
-a
option restricts the variables to indexed arrays; the
-A
option restricts the variables to associative arrays.
If both options are supplied,
-A
takes precedence.
If no
name
arguments are given, or if the
-p
option is supplied, a list of all readonly names is printed.
The other options may be used to restrict the output to a subset of
the set of readonly names.
The
-p
option causes output to be displayed in a format that
may be reused as input.
If a variable name is followed by =word, the value of
the variable is set to word.
The return status is 0 unless an invalid option is encountered,
one of the
names
is not a valid shell variable name, or
-f
is supplied with a
name
that is not a function.
- return [n]
-
Causes a function to stop executing and return the value specified by
n
to its caller.
If
n
is omitted, the return status is that of the last command
executed in the function body.
If return is executed by a trap handler, the last command used to
determine the status is the last command executed before the trap handler.
If return is executed during a DEBUG trap, the last command
used to determine the status is the last command executed by the trap
handler before return was invoked.
If
return
is used outside a function,
but during execution of a script by the
.
(source) command, it causes the shell to stop executing
that script and return either
n
or the exit status of the last command executed within the
script as the exit status of the script.
If n is supplied, the return value is its least significant
8 bits.
The return status is non-zero if
return
is supplied a non-numeric argument, or
is used outside a
function and not during execution of a script by . or source.
Any command associated with the RETURN trap is executed
before execution resumes after the function or script.
- set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
-
- set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
-
Without options, 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
-
Each variable or function that is created or modified is given the
export attribute and marked for export to the environment of
subsequent commands.
- -b
-
Report the status of terminated background jobs
immediately, rather than before the next primary prompt. This is
effective only when job control is enabled.
- -e
-
Exit immediately if a
pipeline (which may consist of a single simple command),
a list,
or a compound command
(see
SHELL GRAMMAR
above), exits with a non-zero status.
The shell does not exit if the
command that fails is part of the command list immediately following a
while
or
until
keyword,
part of the test following the
if
or
elif
reserved words, part of any command executed in a
&&
or
||
list except the command following the final && or ||,
any command in a pipeline but the last,
or if the command's return value is
being inverted with
!.
If a compound command other than a subshell
returns a non-zero status because a command failed
while -e was being ignored, the shell does not exit.
A trap on ERR, if set, is executed before the shell exits.
This option applies to the shell environment and each subshell environment
separately (see
COMMAND EXECUTION ENVIRONMENT
above), and may cause
subshells to exit before executing all the commands in the subshell.
If a compound command or shell function executes in a context
where -e is being ignored,
none of the commands executed within the compound command or function body
will be affected by the -e setting, even if -e is set
and a command returns a failure status.
If a compound command or shell function sets -e while executing in
a context where -e is ignored, that setting will not have any
effect until the compound command or the command containing the function
call completes.
- -f
-
Disable pathname expansion.
- -h
-
Remember the location of commands as they are looked up for execution.
This is enabled by default.
- -k
-
All arguments in the form of assignment statements
are placed in the environment for a command, not just
those that precede the command name.
- -m
-
Monitor mode. Job control is enabled. This option is on
by default for interactive shells on systems that support
it (see
JOB CONTROL
above).
All processes run in a separate process group.
When a background job completes, the shell prints a line
containing its exit status.
- -n
-
Read commands but do not execute them.
This may be used to check a shell script for syntax errors.
This is ignored by interactive shells.
- -o option-name
-
The option-name can be one of the following:
-
- allexport
-
Same as
-a.
- braceexpand
-
Same as
-B.
- emacs
-
Use an emacs-style command line editing interface. This is enabled
by default when the shell is interactive, unless the shell is started
with the
--noediting
option.
This also affects the editing interface used for read -e.
- errexit
-
Same as
-e.
- errtrace
-
Same as
-E.
- functrace
-
Same as
-T.
- hashall
-
Same as
-h.
- histexpand
-
Same as
-H.
- history
-
Enable command history, as described above under
HISTORY.
This option is on by default in interactive shells.
- ignoreeof
-
The effect is as if the shell command
``IGNOREEOF=10''
had been executed
(see
Shell Variables
above).
- keyword
-
Same as
-k.
- monitor
-
Same as
-m.
- noclobber
-
Same as
-C.
- noexec
-
Same as
-n.
- noglob
-
Same as
-f.
- nolog
-
Currently ignored.
- notify
-
Same as
-b.
- nounset
-
Same as
-u.
- onecmd
-
Same as
-t.
- physical
-
Same as
-P.
- pipefail
-
If set, the return value of a pipeline is the value of the last
(rightmost) command to exit with a non-zero status, or zero if all
commands in the pipeline exit successfully.
This option is disabled by default.
- posix
-
Change the behavior of
bash
where the default operation differs
from the POSIX standard to match the standard (posix mode).
See
SEE ALSO
below for a reference to a document that details how posix mode affects
bash's behavior.
- privileged
-
Same as
-p.
- verbose
-
Same as
-v.
- vi
-
Use a vi-style command line editing interface.
This also affects the editing interface used for read -e.
- xtrace
-
Same as
-x.
If
-o
is supplied with no option-name, the values of the current options are
printed.
If
+o
is supplied with no option-name, a series of
set
commands to recreate the current option settings is displayed on
the standard output.
- -p
-
Turn on
privileged
mode. In this mode, the
$ENV
and
$BASH_ENV
files are not processed, shell functions are not inherited from the
environment, and the
SHELLOPTS,
BASHOPTS,
CDPATH,
and
GLOBIGNORE
variables, if they appear in the environment, are ignored.
If the shell is started with the effective user (group) id not equal to the
real user (group) id, and the -p option is not supplied, these actions
are taken and the effective user id is set to the real user id.
If the -p option is supplied at startup, the effective user id is
not reset.
Turning this option off causes the effective user
and group ids to be set to the real user and group ids.
- -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 resolve symbolic links when executing
commands such as
cd
that change the current working directory. It uses the
physical directory structure instead. By default,
bash
follows the logical chain of directories when performing commands
which change the current directory.
- -T
-
If set, any traps on DEBUG and RETURN are inherited by shell
functions, command substitutions, and commands executed in a
subshell environment.
The DEBUG and RETURN traps are normally not inherited
in such cases.
- --
-
If no arguments follow this option, then the positional parameters are
unset. Otherwise, the positional parameters are set to the
args, even if some of them begin with a
-.
- -
-
Signal the end of options, cause all remaining args to be
assigned to the positional parameters. The
-x
and
-v
options are turned off.
If there are no args,
the positional parameters remain unchanged.
The options are off by default unless otherwise noted.
Using + rather than - causes these options to be turned off.
The options can also be specified as arguments to an invocation of
the shell.
The current set of options may be found in
$-.
The return status is always true unless an invalid option is encountered.
- shift [n]
-
The positional parameters from n+1 ... are renamed to
$1
....
Parameters represented by the numbers $#
down to $#-n+1 are unset.
n
must be a non-negative number less than or equal to $#.
If
n
is 0, no parameters are changed.
If
n
is not given, it is assumed to be 1.
If
n
is greater than $#, the positional parameters are not changed.
The return status is greater than zero if
n
is greater than
$#
or less than zero; otherwise 0.
- shopt [-pqsu] [-o] [optname ...]
-
Toggle the values of settings controlling optional shell behavior.
The settings can be either those listed below, or, if the
-o
option is used, those available with the
-o
option to the set builtin command.
With no options, or with the
-p
option, a list of all settable options is displayed, with
an indication of whether or not each is set;
if optnames are supplied, the output is restricted to those options.
The -p option causes output to be displayed in a form that
may be reused as input.
Other options have the following meanings:
-
- -s
-
Enable (set) each optname.
- -u
-
Disable (unset) each optname.
- -q
-
Suppresses normal output (quiet mode); the return status indicates
whether the optname is set or unset.
If multiple optname arguments are given with
-q,
the return status is zero if all optnames are enabled; non-zero
otherwise.
- -o
-
Restricts the values of optname to be those defined for the
-o
option to the
set
builtin.
If either
-s
or
-u
is used with no optname arguments,
shopt
shows only those options which are set or unset, respectively.
Unless otherwise noted, the shopt options are disabled (unset)
by default.
The return status when listing options is zero if all optnames
are enabled, non-zero otherwise. When setting or unsetting options,
the return status is zero unless an optname is not a valid shell
option.
The list of shopt options is:
- assoc_expand_once
-
If set, the shell suppresses multiple evaluation of associative array
subscripts during arithmetic expression evaluation, while executing
builtins that can perform variable assignments,
and while executing builtins that perform array dereferencing.
- autocd
-
If set, a command name that is the name of a directory is executed as if
it were the argument to the cd command.
This option is only used by interactive shells.
- cdable_vars
-
If set, an argument to the
cd
builtin command that
is not a directory is assumed to be the name of a variable whose
value is the directory to change to.
- cdspell
-
If set, minor errors in the spelling of a directory component in a
cd
command will be corrected.
The errors checked for are transposed characters,
a missing character, and one character too many.
If a correction is found, the corrected filename is printed,
and the command proceeds.
This option is only used by interactive shells.
- checkhash
-
If set, bash checks that a command found in the hash
table exists before trying to execute it. If a hashed command no
longer exists, a normal path search is performed.
- checkjobs
-
If set, bash lists the status of any stopped and running jobs before
exiting an interactive shell. If any jobs are running, this causes
the exit to be deferred until a second exit is attempted without an
intervening command (see
JOB CONTROL
above). The shell always
postpones exiting if any jobs are stopped.
- checkwinsize
-
If set, bash checks the window size after each external (non-builtin)
command and, if necessary, updates the values of
LINES
and
COLUMNS.
This option is enabled by default.
- cmdhist
-
If set,
bash
attempts to save all lines of a multiple-line
command in the same history entry. This allows
easy re-editing of multi-line commands.
This option is enabled by default, but only has an effect if command
history is enabled, as described above under
HISTORY.
- compat31
-
- compat32
-
- compat40
-
- compat41
-
- compat42
-
- compat43
-
- compat44
-
These control aspects of the shell's compatibility mode
(see
SHELL COMPATIBILITY MODE
below).
- complete_fullquote
-
If set,
bash
quotes all shell metacharacters in filenames and directory names when
performing completion.
If not set,
bash
removes metacharacters such as the dollar sign from the set of
characters that will be quoted in completed filenames
when these metacharacters appear in shell variable references in words to be
completed.
This means that dollar signs in variable names that expand to directories
will not be quoted;
however, any dollar signs appearing in filenames will not be quoted, either.
This is active only when bash is using backslashes to quote completed
filenames.
This variable is set by default, which is the default bash behavior in
versions through 4.2.
- direxpand
-
If set,
bash
replaces directory names with the results of word expansion when performing
filename completion. This changes the contents of the readline editing
buffer.
If not set,
bash
attempts to preserve what the user typed.
- dirspell
-
If set,
bash
attempts spelling correction on directory names during word completion
if the directory name initially supplied does not exist.
- dotglob
-
If set,
bash
includes filenames beginning with a `.' in the results of pathname
expansion.
The filenames
``.''
and
``..''
must always be matched explicitly, even if
dotglob
is set.
- execfail
-
If set, a non-interactive shell will not exit if
it cannot execute the file specified as an argument to the
exec
builtin command. An interactive shell does not exit if
exec
fails.
- expand_aliases
-
If set, aliases are expanded as described above under
ALIASES.
This option is enabled by default for interactive shells.
- extdebug
-
If set at shell invocation,
or in a shell startup file,
arrange to execute the debugger profile
before the shell starts, identical to the --debugger option.
If set after invocation, behavior intended for use by debuggers is enabled:
-
- 1.
-
The -F option to the declare builtin displays the source
file name and line number corresponding to each function name supplied
as an argument.
- 2.
-
If the command run by the DEBUG trap returns a non-zero value, the
next command is skipped and not executed.
- 3.
-
If the command run by the DEBUG trap returns a value of 2, and the
shell is executing in a subroutine (a shell function or a shell script
executed by the . or source builtins), the shell simulates
a call to return.
- 4.
-
BASH_ARGC
and
BASH_ARGV
are updated as described in their descriptions above.
- 5.
-
Function tracing is enabled: command substitution, shell functions, and
subshells invoked with ( command ) inherit the
DEBUG and RETURN traps.
- 6.
-
Error tracing is enabled: command substitution, shell functions, and
subshells invoked with ( command ) inherit the
ERR trap.
- extglob
-
If set, the extended pattern matching features described above under
Pathname Expansion are enabled.
- extquote
-
If set, $'string' and $"string" quoting is
performed within ${parameter} expansions
enclosed in double quotes. This option is enabled by default.
- failglob
-
If set, patterns which fail to match filenames during pathname expansion
result in an expansion error.
- force_fignore
-
If set, the suffixes specified by the
FIGNORE
shell variable
cause words to be ignored when performing word completion even if
the ignored words are the only possible completions.
See
SHELL VARIABLES
above for a description of
FIGNORE.
This option is enabled by default.
- globasciiranges
-
If set, range expressions used in pattern matching bracket expressions (see
Pattern Matching
above) behave as if in the traditional C locale when performing
comparisons. That is, the current locale's collating sequence
is not taken into account, so
b
will not collate between
A
and
B,
and upper-case and lower-case ASCII characters will collate together.
- globstar
-
If set, the pattern ** used in a pathname expansion context will
match all files and zero or more directories and subdirectories.
If the pattern is followed by a /, only directories and
subdirectories match.
- gnu_errfmt
-
If set, shell error messages are written in the standard GNU error
message format.
- histappend
-
If set, the history list is appended to the file named by the value
of the
HISTFILE
variable when the shell exits, rather than overwriting the file.
- histreedit
-
If set, and
readline
is being used, a user is given the opportunity to re-edit a
failed history substitution.
- histverify
-
If set, and
readline
is being used, the results of history substitution are not immediately
passed to the shell parser. Instead, the resulting line is loaded into
the readline editing buffer, allowing further modification.
- hostcomplete
-
If set, and
readline
is being used, bash will attempt to perform hostname completion when a
word containing a @ is being completed (see
Completing
under
READLINE
above).
This is enabled by default.
- huponexit
-
If set, bash will send
SIGHUP
to all jobs when an interactive login shell exits.
- inherit_errexit
-
If set, command substitution inherits the value of the errexit option,
instead of unsetting it in the subshell environment.
This option is enabled when posix mode is enabled.
- interactive_comments
-
If set, allow a word beginning with
#
to cause that word and all remaining characters on that
line to be ignored in an interactive shell (see
COMMENTS
above). This option is enabled by default.
- lastpipe
-
If set, and job control is not active, the shell runs the last command of
a pipeline not executed in the background in the current shell environment.
- lithist
-
If set, and the
cmdhist
option is enabled, multi-line commands are saved to the history with
embedded newlines rather than using semicolon separators where possible.
- localvar_inherit
-
If set, local variables inherit the value and attributes of a variable of
the same name that exists at a previous scope before any new value is
assigned. The nameref attribute is not inherited.
- localvar_unset
-
If set, calling unset on local variables in previous function scopes
marks them so subsequent lookups find them unset until that function
returns. This is identical to the behavior of unsetting local variables
at the current function scope.
- login_shell
-
The shell sets this option if it is started as a login shell (see
INVOCATION
above).
The value may not be changed.
- mailwarn
-
If set, and a file that bash is checking for mail has been
accessed since the last time it was checked, the message ``The mail in
mailfile has been read'' is displayed.
- no_empty_cmd_completion
-
If set, and
readline
is being used,
bash
will not attempt to search the
PATH
for possible completions when
completion is attempted on an empty line.
- nocaseglob
-
If set,
bash
matches filenames in a case-insensitive fashion when performing pathname
expansion (see
Pathname Expansion
above).
- nocasematch
-
If set,
bash
matches patterns in a case-insensitive fashion when performing matching
while executing case or [[ conditional commands,
when performing pattern substitution word expansions,
or when filtering possible completions as part of programmable completion.
- 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.
- progcomp_alias
-
If set, and programmable completion is enabled, bash treats a command
name that doesn't have any completions as a possible alias and attempts
alias expansion. If it has an alias, bash attempts programmable
completion using the command word resulting from the expanded alias.
- promptvars
-
If set, prompt strings undergo
parameter expansion, command substitution, arithmetic
expansion, and quote removal after being expanded as described in
PROMPTING
above. This option is enabled by default.
- restricted_shell
-
The shell sets this option if it is started in restricted mode (see
RESTRICTED SHELL
below).
The value may not be changed.
This is not reset when the startup files are executed, allowing
the startup files to discover whether or not a shell is restricted.
- shift_verbose
-
If set, the
shift
builtin prints an error message when the shift count exceeds the
number of positional parameters.
- sourcepath
-
If set, the
source (.) builtin uses the value of
PATH
to find the directory containing the file supplied as an argument.
This option is enabled by default.
- xpg_echo
-
If set, the echo builtin expands backslash-escape sequences
by default.
- suspend [-f]
-
Suspend the execution of this shell until it receives a
SIGCONT
signal. A login shell cannot be suspended; the
-f
option can be used to override this and force the suspension.
The return status is 0 unless the shell is a login shell and
-f
is not supplied, or if job control is not enabled.
- test expr
-
- [ expr ]
-
Return a status of 0 (true) or 1 (false) depending on
the evaluation of the conditional expression
expr.
Each operator and operand must be a separate argument.
Expressions are composed of the primaries described in the bash manual page under
CONDITIONALEXPRESSIONS.
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
CONDITIONALEXPRESSIONS,
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
CONDITIONALEXPRESSIONS,
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 pipeline (which may consist of a single simple
command), a list, or a compound command returns a
non-zero exit status,
subject to the following conditions.
The
ERR
trap is not executed if the failed
command is part of the command list immediately following a
while
or
until
keyword,
part of the test in an
if
statement, part of a command executed in a
&&
or
||
list except the command following the final && or ||,
any command in a pipeline but the last,
or if the command's return value is
being inverted using
!.
These are the same conditions obeyed by the errexit (-e) option.
Signals ignored upon entry to the shell cannot be trapped, 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, which is not necessarily the file that appears
first in
PATH.
If the
-a
option is used,
type
prints all of the places that contain
an executable named
name.
This includes aliases and functions,
if and only if the
-p
option is not also used.
The table of hashed commands is not consulted
when using
-a.
The
-f
option suppresses shell function lookup, as with the command builtin.
type
returns true if all of the arguments are found, false if
any are not found.
- ulimit [-HS] -a
-
- ulimit [-HS] [-bcdefiklmnpqrstuvxPRT [limit]]
-
Provides control over the resources available to the shell and to
processes started by it, on systems that allow such control.
The -H and -S options specify that the hard or soft limit is
set for the given resource.
A hard limit cannot be increased by a non-root user once it is set;
a soft limit may be increased up to the value of the hard limit.
If neither -H nor -S is specified, both the soft and hard
limits are set.
The value of
limit
can be a number in the unit specified for the resource
or one of the special values
hard,
soft,
or
unlimited,
which stand for the current hard limit, the current soft limit, and
no limit, respectively.
If
limit
is omitted, the current value of the soft limit of the resource is
printed, unless the -H option is given. When more than one
resource is specified, the limit name and unit, if appropriate,
are printed before the value.
Other options are interpreted as follows:
-
- -a
-
All current limits are reported; no limits are set
- -b
-
The maximum socket buffer size
- -c
-
The maximum size of core files created
- -d
-
The maximum size of a process's data segment
- -e
-
The maximum scheduling priority ("nice")
- -f
-
The maximum size of files written by the shell and its children
- -i
-
The maximum number of pending signals
- -k
-
The maximum number of kqueues that may be allocated
- -l
-
The maximum size that may be locked into memory
- -m
-
The maximum resident set size (many systems do not honor this limit)
- -n
-
The maximum number of open file descriptors (most systems do not
allow this value to be set)
- -p
-
The pipe size in 512-byte blocks (this may not be set)
- -q
-
The maximum number of bytes in POSIX message queues
- -r
-
The maximum real-time scheduling priority
- -s
-
The maximum stack size
- -t
-
The maximum amount of cpu time in seconds
- -u
-
The maximum number of processes available to a single user
- -v
-
The maximum amount of virtual memory available to the shell and, on
some systems, to its children
- -x
-
The maximum number of file locks
- -P
-
The maximum number of pseudoterminals
- -R
-
The maximum time a real-time process can run before blocking, in microseconds
- -T
-
The maximum number of threads
If
limit
is given, and the
-a
option is not used,
limit is the new value of the specified resource.
If no option is given, then
-f
is assumed. Values are in 1024-byte increments, except for
-t,
which is in seconds;
-R,
which is in microseconds;
-p,
which is in units of 512-byte blocks;
-P,
-T,
-b,
-k,
-n,
and
-u,
which are unscaled values;
and, when in posix mode,
-c
and
-f,
which are in 512-byte increments.
The return status is 0 unless an invalid option or argument is supplied,
or an error occurs while setting a new limit.
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] [-n] [name ...]
-
For each
name,
remove the corresponding variable or function.
If the
-v
option is given, each
name
refers to a shell variable, and that variable is removed.
Read-only variables may not be unset.
If
-f
is specified, each
name
refers to a shell function, and the function definition
is removed.
If the
-n
option is supplied, and name is a variable with the nameref
attribute, name will be unset rather than the variable it
references.
-n has no effect if the -f option is supplied.
If no options are supplied, each name refers to a variable; if
there is no variable by that name, a function with that name, if any, is
unset.
Each unset variable or function is removed from the environment
passed to subsequent commands.
If any of
BASH_ALIASES,
BASH_ARGV0,
BASH_CMDS,
BASH_COMMAND,
BASH_SUBSHELL,
BASHPID,
COMP_WORDBREAKS,
DIRSTACK,
EPOCHREALTIME,
EPOCHSECONDS,
FUNCNAME,
GROUPS,
HISTCMD,
LINENO,
RANDOM,
SECONDS,
or
SRANDOM
are unset, they lose their special properties, even if they are
subsequently reset. The exit status is true unless a
name
is readonly.
- wait [-fn] [-p varname] [id ...]
-
Wait for each specified child process and return its termination status.
Each
id
may be a process
ID or a job specification; if a job spec is given, all processes
in that job's pipeline are waited for. If
id
is not given,
wait waits for all running background jobs and
the last-executed process substitution, if its process id is the same as
$!,
and the return status is zero.
If the -n option is supplied,
wait waits for a single job
from the list of ids or, if no ids are supplied, any job,
to complete and returns its exit status.
If none of the supplied arguments is a child of the shell, or if no arguments
are supplied and the shell has no unwaited-for children, the exit status
is 127.
If the -p option is supplied, the process or job identifier of the job
for which the exit status is returned is assigned to the variable
varname named by the option argument.
The variable will be unset initially, before any assignment.
This is useful only when the -n option is supplied.
Supplying the -f option, when job control is enabled,
forces wait to wait for id to terminate before returning
its status, instead of returning when it changes status.
If
id
specifies a non-existent process or job, the return status is
127. Otherwise, the return status is the exit status of the last
process or job waited for.
SHELL COMPATIBILITY MODE
Bash-4.0 introduced the concept of a `shell compatibility level', specified
as a set of options to the shopt builtin
compat31,
compat32,
compat40,
compat41,
and so on).
There is only one current
compatibility level -- each option is mutually exclusive.
The compatibility level is intended to allow users to select behavior
from previous versions that is incompatible with newer versions
while they migrate scripts to use current features and
behavior. It's intended to be a temporary solution.
This section does not mention behavior that is standard for a particular
version (e.g., setting compat32 means that quoting the rhs of the regexp
matching operator quotes special regexp characters in the word, which is
default behavior in bash-3.2 and above).
If a user enables, say, compat32, it may affect the behavior of other
compatibility levels up to and including the current compatibility level.
The idea is that each compatibility level controls behavior that changed
in that version of bash,
but that behavior may have been present in earlier versions.
For instance, the change to use locale-based comparisons with the [[
command came in bash-4.1, and earlier versions used ASCII-based comparisons,
so enabling compat32 will enable ASCII-based comparisons as well.
That granularity may not be sufficient for
all uses, and as a result users should employ compatibility levels carefully.
Read the documentation for a particular feature to find out the
current behavior.
Bash-4.3 introduced a new shell variable:
BASH_COMPAT.
The value assigned
to this variable (a decimal version number like 4.2, or an integer
corresponding to the compatNN option, like 42) determines the
compatibility level.
Starting with bash-4.4, Bash has begun deprecating older compatibility
levels.
Eventually, the options will be removed in favor of
BASH_COMPAT.
Bash-5.0 is the final version for which there will be an individual shopt
option for the previous version. Users should use
BASH_COMPAT
on bash-5.0 and later versions.
The following table describes the behavior changes controlled by each
compatibility level setting.
The compatNN tag is used as shorthand for setting the
compatibility level
to NN using one of the following mechanisms.
For versions prior to bash-5.0, the compatibility level may be set using
the corresponding compatNN shopt option.
For bash-4.3 and later versions, the
BASH_COMPAT
variable is preferred,
and it is required for bash-5.1 and later versions.
- compat31
-
-
- •
-
quoting the rhs of the [[ command's regexp matching operator (=~)
has no special effect
- compat32
-
-
- •
-
interrupting a command list such as "a ; b ; c" causes the execution
of the next command in the list (in bash-4.0 and later versions,
the shell acts as if it received the interrupt, so
interrupting one command in a list aborts the execution of the
entire list)
- compat40
-
-
- •
-
the < and > operators to the [[ command do not
consider the current locale when comparing strings; they use ASCII
ordering.
Bash versions prior to bash-4.1 use ASCII collation and
strcmp(3);
bash-4.1 and later use the current locale's collation sequence and
strcoll(3).
- compat41
-
-
- •
-
in posix mode, time may be followed by options and still be
recognized as a reserved word (this is POSIX interpretation 267)
- •
-
in posix mode, the parser requires that an even number of single
quotes occur in the word portion of a double-quoted
parameter expansion and treats them specially, so that characters within
the single quotes are considered quoted
(this is POSIX interpretation 221)
- compat42
-
-
- •
-
the replacement string in double-quoted pattern substitution does not
undergo quote removal, as it does in versions after bash-4.2
- •
-
in posix mode, single quotes are considered special when expanding
the word portion of a double-quoted parameter expansion
and can be used to quote a closing brace or other special character
(this is part of POSIX interpretation 221);
in later versions, single quotes
are not special within double-quoted word expansions
- compat43
-
-
- •
-
the shell does not print a warning message if an attempt is made to
use a quoted compound assignment as an argument to declare
(declare -a foo='(1 2)'). Later versions warn that this usage is
deprecated
- •
-
word expansion errors are considered non-fatal errors that cause the
current command to fail, even in posix mode
(the default behavior is to make them fatal errors that cause the shell
to exit)
- •
-
when executing a shell function, the loop state (while/until/etc.)
is not reset, so break or continue in that function will break
or continue loops in the calling context. Bash-4.4 and later reset
the loop state to prevent this
- compat44
-
-
- •
-
the shell sets up the values used by
BASH_ARGV
and
BASH_ARGC
so they can expand to the shell's positional parameters even if extended
debugging mode is not enabled
- •
-
a subshell inherits loops from its parent context, so break
or continue will cause the subshell to exit.
Bash-5.0 and later reset the loop state to prevent the exit
- •
-
variable assignments preceding builtins like export and readonly
that set attributes continue to affect variables with the same
name in the calling environment even if the shell is not in posix
mode
- compat50
-
-
- •
-
Bash-5.1 changed the way
$RANDOM
is generated to introduce slightly
more randomness. If the shell compatibility level is set to 50 or
lower, it reverts to the method from bash-5.0 and previous versions,
so seeding the random number generator by assigning a value to
RANDOM
will produce the same sequence as in bash-5.0
- •
-
If the command hash table is empty, bash versions prior to bash-5.1
printed an informational message to that effect, even when producing
output that can be reused as input. Bash-5.1 suppresses that message
when the -l option is supplied.
SEE ALSO
bash(1),
sh(1)