ENABLE linux command manual
BASH_BUILTINS(1) BASH_BUILTINS(1)
NAME
bash, :, ., [, alias, bg, bind, break, builtin, cd, command, compgen,
complete, continue, declare, dirs, disown, echo, enable, eval, exec,
exit, export, fc, fg, getopts, hash, help, history, jobs, kill, let,
local, logout, popd, printf, pushd, pwd, read, readonly, return, set,
shift, shopt, source, suspend, test, times, trap, 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 sec-
tion as accepting options preceded by - accepts -- to signify the end
of the options.
: [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 exe-
cuted 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 exe-
cutable. 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 the 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, if jobspec was not found or 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 subse-
quent 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-com-
mand; 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.
-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.
-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.
-f filename
Read key bindings from filename.
-q function
Query about which keys invoke the named function.
-u function
Unbind all keys bound to the named function.
-r keyseq
Remove any current binding for keyseq.
-x keyseq:shell-command
Cause shell-command to be executed whenever keyseq is
entered.
The return 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 the shell is not execut-
ing a loop when break is executed.
builtin shell-builtin [arguments]
Execute the specified shell builtin, passing it arguments, and
return its exit status. This is useful when defining a func-
tion 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.
cd [-L|-P] [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. An argument of - is equivalent to $OLDPWD. 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 pro-
duces 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 pro-
grammable completion code had generated them directly from a
completion specification with the same flags. If word is spec-
ified, 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] [-A action] [-G globpat] [-W
wordlist] [-P prefix] [-S suffix]
[-X filterpat] [-F function] [-C command] name [name ...]
complete -pr [name ...]
Specify how arguments to each name should be completed. If the
-p option is supplied, or if no options are supplied, existing
completion specifications are printed in a way that allows them
to be reused as input. The -r option removes a completion
specification for each name, or, if no names are supplied, all
completion specifications.
The process of applying these completion specifications when
word completion is attempted is described above under Pro-
grammable 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 expan-
sion before the complete builtin is invoked.
-o comp-option
The comp-option controls several aspects of the comp-
spec's behavior beyond the simple generation of comple-
tions. comp-option may be one of:
default Use readline's default filename completion if
the compspec generates no matches.
dirnames
Perform directory name completion if the comp-
spec generates no matches.
filenames
Tell readline that the compspec generates file-
names, so it can perform any filename-specific
processing (like adding a slash to directory
names 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.
-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.
-G globpat
The filename expansion pattern globpat is expanded to
generate the possible completions.
-W wordlist
The wordlist is split using the characters in the IFS
special variable as delimiters, and each resultant word
is expanded. The possible completions are the members
of the resultant list which match the word being com-
pleted.
-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 com-
pletions are retrieved from the value of the COMPREPLY
array variable.
-X filterpat
filterpat is a pattern as used for filename expansion.
It is applied to the list of possible completions
generated by the preceding options and arguments, and
each completion matching filterpat is removed from the
list. A leading ! in filterpat negates the pattern; in
this case, any completion not matching filterpat is
removed.
-P prefix
prefix is added at the beginning of each possible com-
pletion after all other options have been applied.
-S suffix
suffix is appended to each possible completion after
all other options have been applied.
The return value is true unless an invalid option is supplied,
an option other than -p or -r is supplied without a name argu-
ment, 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.
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 the shell is
not executing a loop when continue is executed.
declare [-afFirtx] [-p] [name[=value]]
typeset [-afFirtx] [-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, additional options are ignored. The -F option inhibits
the display of function definitions; only the function name and
attributes are printed. The -F option implies -f. The follow-
ing options can be used to restrict output to variables with
the specified attribute or to give variables attributes:
-a Each name is an array variable (see Arrays above).
-f Use function names only.
-i The variable is treated as an integer; arithmetic evalu-
ation (see ARITHMETIC EVALUATION ) is performed when the
variable is assigned a value.
-r Make names readonly. These names cannot then be
assigned values by subsequent assignment statements or
unset.
-t Give each name the trace attribute. Traced functions
inherit the DEBUG trap from the calling shell. The
trace attribute has no special meaning for variables.
-x Mark names for export to subsequent commands via the
environment.
Using '+' instead of '-' turns off the attribute instead, with
the exception that +a may not be used to destroy an array vari-
able. When used in a function, makes each name local, as with
the local command. 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 vari-
able 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.
+n Displays the nth entry counting from the left of the
list shown by dirs when invoked without options, start-
ing with zero.
-n Displays the nth entry counting from the right of the
list shown by dirs when invoked without options, start-
ing 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, pre-
fixing 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 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 trail-
ing newline is suppressed. If the -e option is given, inter-
pretation 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 dynami-
cally determine whether or not echo expands these escape char-
acters 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 trailing newline
\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)
\nnn the eight-bit character whose value is the octal value
nnn (one to three octal digits)
\xHH the eight-bit character whose value is the hexadecimal
value HH (one or two hex digits)
enable [-adnps] [-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 previ-
ously 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 com-
mand. 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 arg 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 com-
mand 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 envi-
ronment 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 the named variables. export
returns an exit status of 0 unless an invalid option is encoun-
tered, one of the names is not a valid shell variable name, or
-f is supplied with a name that is not a function.
fc [-e ename] [-nlr] [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. Other-
wise, 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, 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 dis-
abled 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 parame-
ters. optstring contains the option characters to be recog-
nized; 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 initial-
ized to 1 each time the shell or a shell script is invoked.
When an option requires an argument, getopts places that argu-
ment 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 dis-
played, 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]
For each name, the full file name of the command is determined
by searching the directories in $PATH and remembered. If the
-p option is supplied, no path search is performed, and file-
name 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 loca-
tion of each name. If the -t option is supplied, the full
pathname to which each name corresponds is printed. If multi-
ple 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 sup-
plied.
help [-s] [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. The -s option restricts the information
displayed to a short usage synopsis. 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 argu-
ment of n lists only the last n lines. If filename is sup-
plied, it is used as the name of the history file; if not, the
value of HISTFILE is used. Options, if supplied, have the fol-
lowing 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, overwrit-
ing 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.
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.
-p List only the process ID of the job's process group
leader.
-n Display information only about jobs that have changed
status since the user was last notified of their status.
-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 signal name such
as SIGKILL or a signal number; signum is a signal number. If
sigspec is a signal name, the name may be given with or without
the SIG prefix. 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 sig-
nals corresponding to the arguments are listed, and the return
status is 0. The exit_status argument to -l is a number speci-
fying either a signal number or the exit status of a process
terminated by a signal. kill returns true if at least one sig-
nal 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). 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.
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 fol-
lowing meanings:
+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 sec-
ond.
-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.
-n Suppresses the normal change of directory when removing
directories from the stack, so that only the stack is
manipulated.
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 format [arguments]
Write the formatted arguments to the standard output under the
control of the format. The format is a character string which
contains three types of objects: plain characters, which are
simply copied to standard output, character escape sequences,
which are converted and copied to the standard output, and for-
mat specifications, each of which causes printing of the next
successive argument. In addition to the standard printf(1)
formats, %b causes printf to expand backslash escape sequences
in the corresponding argument, and %q causes printf to output
the corresponding argument in a format that can be reused as
shell input.
The format is reused as necessary to consume all of the argu-
ments. If the format requires more arguments than are sup-
plied, 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] [dir]
pushd [-n] [+n] [-n]
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 directo-
ries and returns 0, unless the directory stack is empty. Argu-
ments, if supplied, have the following meanings:
+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.
-n Suppresses the normal change of directory when adding
directories to the stack, so that only the stack is
manipulated.
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 ele-
ment 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] [-u fd] [-t timeout] [-a aname] [-p prompt] [-n nchars]
[-d delim] [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 remain-
ing 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 charac-
ter 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 argu-
ments 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, read-
line (see READLINE above) is used to obtain the line.
-n nchars
read returns after reading nchars characters rather than
waiting for a complete line of input.
-p prompt
Display prompt on standard error, without a trailing
newline, before attempting to read any input. The
prompt is displayed only if input is coming from a ter-
minal.
-r Backslash does not act as an escape character. The
backslash is considered to be part of the line. In par-
ticular, a backslash-newline pair may not be used as a
line continuation.
-s Silent mode. If input is coming from a terminal, char-
acters are not echoed.
-t timeout
Cause read to time out and return failure if a complete
line of input is not read within timeout seconds. This
option has no effect if read is not reading input from
the terminal or a pipe.
-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, or an invalid file descriptor is
supplied as the argument to -u.
readonly [-apf] [name ...]
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 arrays. If
no name arguments are given, or if the -p option is supplied, a
list of all readonly names is printed. The -p option causes
output to be displayed in a format that may be reused as input.
The return status is 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.
set [--abefhkmnptuvxBCHP] [-o option] [arg ...]
Without options, the name and value of each shell variable are
displayed in a format that can be reused as input. The output
is sorted according to the current locale. When options are
specified, they set or unset shell attributes. Any arguments
remaining after the options are processed 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 immedi-
ately, rather than before the next primary prompt.
This is effective only when job control is enabled.
-e Exit immediately if a simple command (see SHELL GRAMMAR
above) exits with a non-zero status. The shell does
not exit if the command that fails is part of an until
or while loop, part of an if statement, part of a && or
|| list, or if the command's return value is being
inverted via !. A trap on ERR, if set, is executed
before the shell exits.
-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 pro-
cesses run in a separate process group and a line con-
taining their exit status is printed upon their comple-
tion.
-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 inter-
face. This is enabled by default when the
shell is interactive, unless the shell is
started with the --noediting option.
errexit Same as -e.
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.
posix Change the behavior of bash where the default
operation differs from the POSIX 1003.2
standard to match the standard (posix mode).
privileged
Same as -p.
verbose Same as -v.
vi Use a vi-style command line editing interface.
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 recre-
ate 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
variable, if it appears in the environment, is ignored.
If the shell is started with the effective user (group)
id not equal to the real user (group) id, and the -p
option is not supplied, these actions are taken and the
effective user id is set to the real user id. If the
-p option is supplied at startup, the effective user id
is not reset. Turning this option off causes the
effective user and group ids to be set to the real user
and group ids.
-t Exit after reading and executing one command.
-u Treat unset variables as an error when performing
parameter expansion. If expansion is attempted on an
unset variable, 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, display the
expanded value of PS4, followed by the command and its
expanded arguments.
-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 >.
-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 logi-
cal chain of directories when performing commands which
change the current directory.
-- If no arguments follow this option, then the positional
parameters are unset. Otherwise, the positional param-
eters 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 dis-
play 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:
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 interac-
tive 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 per-
formed.
checkwinsize
If set, bash checks the window size after each command
and, if necessary, updates the values of LINES and
COLUMNS.
cmdhist If set, bash attempts to save all lines of a multiple-
line command in the same history entry. This allows
easy re-editing of multi-line commands.
dotglob If set, bash includes filenames beginning with a '.' in
the results of 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 inter-
active shells.
extglob If set, the extended pattern matching features
described above under Pathname Expansion are enabled.
histappend
If set, the history list is appended to the file named
by the value of the HISTFILE variable when the shell
exits, rather than overwriting the file.
histreedit
If set, and readline is being used, a user is given the
opportunity to re-edit a failed history substitution.
histverify
If set, and readline is being used, the results of his-
tory substitution are not immediately passed to the
shell parser. Instead, the resulting line is loaded
into the readline editing buffer, allowing further mod-
ification.
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.
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 dis-
played.
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 Path-
name Expansion above).
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 variable and parameter
expansion after being expanded as described in PROMPT-
ING 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 param-
eters.
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. The -f option says not to complain if this is a login
shell; just suspend anyway. The return status is 0 unless the
shell is a login shell and -f is not supplied, or if job con-
trol 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.
Expressions may be combined using the following operators,
listed in decreasing order of precedence.
! expr True if expr is false.
( expr )
Returns the value of expr. This may be used to override
the normal precedence of operators.
expr1 -a expr2
True if both expr1 and expr2 are true.
expr1 -o expr2
True if either expr1 or expr2 is true.
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 expres-
sion 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
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.
If the first argument is !, the value is the negation of
the two-argument test using the second and third argu-
ments. If the first argument is exactly ( and the third
argument is exactly ), the result is the one-argument
test of the second argument. Otherwise, the expression
is false. The -a and -o operators are considered binary
operators in this case.
4 arguments
If the first argument is !, the result is the negation
of the three-argument expression composed of the remain-
ing arguments. Otherwise, the expression is parsed and
evaluated according to precedence using the rules listed
above.
5 or more arguments
The expression is parsed and evaluated according to
precedence using the rules listed above.
times Print 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 or -, all speci-
fied signals are reset to their original values (the values
they 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 asso-
ciated with each signal number. Each sigspec is either a sig-
nal name defined in , or a signal number. 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
after every simple command (see SHELL GRAMMAR above). If a
sigspec is ERR, the command arg is executed whenever a simple
command has a non-zero exit status. The ERR trap is not exe-
cuted if the failed command is part of an until or while loop,
part of an if statement, part of a && or || list, or if the
command's return value is being inverted via !. The -l option
causes the shell to print a list of signal names and their cor-
responding numbers. Signals ignored upon entry to the shell
cannot be trapped or reset. Trapped signals are reset to their
original values in a child process when it is created. The
return status is 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 spec-
ified 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 neces-
sarily the file that appears first in PATH. If the -a option
is used, type prints all of the places that contain an exe-
cutable 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 any of the arguments are found, false if
none are found.
ulimit [-SHacdflmnpstuv [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
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 num-
ber in the unit specified for the resource or one of the spe-
cial values hard, soft, or unlimited, which stand for the cur-
rent hard limit, the current soft limit, and no limit, respec-
tively. 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
-c The maximum size of core files created
-d The maximum size of a process's data segment
-f The maximum size of files created by the shell
-l The maximum size that may be locked into memory
-m The maximum resident set size
-n The maximum number of open file descriptors (most sys-
tems do not allow this value to be set)
-p The pipe size in 512-byte blocks (this may not be set)
-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
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 -n and -u, which are unscaled values. The
return status is 0 unless an invalid option or argument is sup-
plied, or an error occurs while setting a new limit.
umask [-p] [-S] [mode]
The user file-creation mask is set to mode. If mode begins
with a digit, it is interpreted as an octal number; otherwise
it is interpreted as a symbolic mode mask similar to that
accepted by chmod(1). If mode is omitted, the current value of
the mask is printed. The -S option causes the mask to be
printed in symbolic form; the default output is an octal num-
ber. 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 specifed, each name refers to a shell func-
tion, and the function definition is removed. Each unset vari-
able or function is removed from the environment passed to sub-
sequent commands. If any of RANDOM, SECONDS, LINENO, HISTCMD,
FUNCNAME, GROUPS, or DIRSTACK are unset, they lose their spe-
cial properties, even if they are subsequently reset. The exit
status is true unless a name does not exist or is readonly.
wait [n]
Wait for the specified process and return its termination sta-
tus. 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. Oth-
erwise, the return status is the exit status of the last pro-
cess or job waited for.
SEE ALSO
bash(1), sh(1)
GNU Bash-2.05a 2001 November 27 BASH_BUILTINS(1)