bash, :, ., alias, bg, bind, break, builtin, bye, case, cd, command, continue, declare, dirs, echo, enable, eval, exec, exit, export, fc, fg, for, getopts, hash, help, history, if, jobs, kill, let, local, logout, popd, pushd, pwd, read, readonly, return, set, shift, source, suspend, test, times, trap, type, typeset, ulimit, umask, unalias, unset, until, wait, while - bash built-in commands, see bash(1)
: [arguments]
No effect; the command does nothing beyond expanding arguments and performing any specified redirections. A zero exit code is returned.
. filename
[arguments]
source filename [arguments]
Read and execute commands from filename in the current shell environment and return the exit status of the last command executed from filename. If filename does not contain a slash, pathnames in PATH are used to find the directory containing filename. The file searched for in PATH need not be executable. The current directory is searched if no file is found in PATH. If any arguments are supplied, they become the positional parameters when file 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.
alias [name[=value] ...]
Alias with no arguments prints the list of aliases in the form 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]
Place 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] [-lvd] [-q name]
bind [-m keymap] -f filename
bind [-m keymap]
keyseq:function-name
Display current readline
key and function bindings, or bind a key sequence to a
readline function or macro. The binding syntax
accepted is identical to that of .inputrc, but each
binding must be passed as a separate argument; e.g.,
’"\C-x\C-r": re-read-init-file’.
Options, if supplied, have the following meanings:
-m keymap
Use keymap as the keymap to be affected by the subsequent bindings. Acceptable keymap names are emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command, and vi-insert. vi is equivalent to vi-command; emacs is equivalent to emacs-standard.
|
-l |
List the names of all readline functions | ||
|
-v |
List current function names and bindings | ||
|
-d |
Dump function names and bindings in such a way that they can be re-read |
-f filename
Read key bindings from filename
-q function
Query about which keys invoke the named function
The return value is 0 unless an unrecognized option is given or an error occurred.
break [n]
Exit from within a for, while, or until 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 executing 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 you wish to define a function whose name is the same as a shell builtin, but need the functionality of the builtin within the function itself. The cd builtin is commonly redefined this way. The return status is false if shell-builtin is not a shell builtin command.
cd [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 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. 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 pathname used to invoke command to be printed; the -V option produces a more verbose description. An argument of -- disables option checking for the rest of the arguments. 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.
continue [n]
Resume the next iteration of the enclosing for, while, or until 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 [-frxi]
[name[=value]]
typeset [-frxi] [name[=value]]
Declare variables and/or give them attributes. If no names are given, then display the values of variables instead. The options can be used to restrict output to variables with the specified attribute.
|
-f |
Use function names only | ||
|
-r |
Make names readonly. These names cannot then be assigned values by subsequent assignment statements. | ||
|
-x |
Mark names for export to subsequent commands via the environment. | ||
|
-i |
The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC EVALUATION ) is performed when the variable is assigned a value. |
Using ‘+’ instead of ‘-’ turns off the attribute instead. When used in a function, makes names local, as with the local command. The return value is 0 unless an illegal option is encountered, an attempt is made to define a function using "-f foo=bar", one of the names is not a legal shell variable name, an attempt is made to turn off readonly status for a readonly variable, or an attempt is made to display a non-existant function with -f.
dirs [-l] [+/-n]
Display the list of currently remembered directories. Directories are added to the list with the pushd command; the popd command moves back up through the list.
|
+n |
displays the nth entry counting from the left of the list shown by dirs when invoked without options, starting with zero. | ||
|
-n |
displays the nth entry counting from the right of the list shown by dirs when invoked without options, starting with zero. | ||
|
-l |
produces a longer listing; the default listing format uses a tilde to denote the home directory. |
The return value is 0 unless an illegal option is supplied or n indexes beyond the end of the directory stack.
echo [-neE] [arg ...]
Output the args, separated by spaces. The return status is always 0. If -n is specified, the trailing newline is suppressed. If the -e option is given, interpretation of the following backslash-escaped characters is enabled. The -E option disables the interpretation of these escape characters, even on systems where they are interpreted by default.
|
\a |
alert (bell) | ||
|
\b |
backspace | ||
|
\c |
suppress trailing newline | ||
|
\f |
form feed | ||
|
\n |
new line | ||
|
\r |
carriage return | ||
|
\t |
horizontal tab | ||
|
\v |
vertical tab | ||
|
\\ |
backslash | ||
|
\nnn |
the character whose ASCII code is nnn (octal) |
enable [-n] [-all] [name ...]
Enable and disable builtin shell commands. This allows the execution of a disk command which has the same name as a shell builtin without specifying a full pathname. 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, type ‘‘enable -n test’’. If no arguments are given, a list of all enabled shell builtins is printed. If only -n is supplied, a list of all disabled builtins is printed. If only -all is supplied, the list printed includes all builtins, with an indication of whether or not each is enabled. enable accepts -a as a synonym for -all. The return value is 0 unless a name is not a shell builtin.
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 the eval command. If there are no args, or only null arguments, eval returns true.
exec [[-] command [arguments]]
If command is specified, it replaces the shell. No new process is created. The arguments become the arguments to command. If the first argument is -, the shell places a dash in the zeroth arg passed to command. This is what login does. If the file cannot be executed for some reason, a non-interactive shell exits, unless the shell variable no_exit_on_failed_exec exists, 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.
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 [-nf]
[name[=word]] ...
export -p
The supplied names are marked for automatic export to the environment of subsequently executed commands. If the -f option is given, the names refer to functions. If no names are given, or if the -p option is supplied, a list of all names that are exported in this shell is printed. The -n option causes the export property to be removed from the named variables. An argument of -- disables option checking for the rest of the arguments. export returns an exit status of 0 unless an illegal option is encountered, one of the names is not a legal 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 flag suppresses the command numbers when listing. The -r flag reverses the order of the commands. If the -l flag 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, 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 illegal 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]
Place jobspec in the foreground, and make it the current job. If jobspec is not present, the shell’s notion of the current job is used. The return value is that of the command placed into the foreground, or failure if run when job control is disabled or, when run with job control enabled, if jobspec does not specify a valid job or jobspec specifies a job that was started without job control.
getopts optstring name [args]
getopts is used by shell procedures to parse positional parameters. optstring contains the option letters to be recognized; if a letter is followed by a colon, the option is expected to have an argument, which should be separated from it by white space. 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.
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 illegal options or missing option arguments are encountered. If the variable OPTERR is set to 0, no error message will be displayed, even if the first character of optstring is not a colon.
If an illegal 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 normally parses the positional parameters, but if more arguments are given in args, getopts parses those instead. 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 [-r] [name]
For each name, the full pathname of the command is determined and remembered. The -r option causes the shell to forget all remembered locations. If no arguments are given, information about remembered commands is printed. An argument of -- disables option checking for the rest of the arguments. The return status is true unless a name is not found or an illegal option is supplied.
help [pattern]
Display helpful information about builtin commands. If pattern is specified, help gives detailed help on all commands matching pattern; otherwise a list of the builtins is printed. The return status is 0 unless no command matches pattern.
history [n]
history -rwan [filename]
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 a non-option argument 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:
|
-a |
Append the ‘‘new’’ history lines (history lines entered since the beginning of the current bash session) to the history file | ||
|
-n |
Read the history lines not already read from the history file into the current history list. These are lines appended to the history file since the beginning of the current bash session. | ||
|
-r |
Read the contents of the history file and use them as the current history | ||
|
-w |
Write the current history to the history file, overwriting the history file’s contents. |
The return value is 0 unless an illegal option is encountered or an error occurs while reading or writing the history file.
jobs [-lnp] [
jobspec ... ]
jobs -x command [ args ... ]
The first form lists the active jobs. The -l option lists process IDs in addition to the normal information; the -p option lists only the process ID of the job’s process group leader. The -n option displays only jobs that have changed status since last notified. If jobspec is given, output is restricted to information about that job. The return status is 0 unless an illegal option is encountered or an illegal 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
| -sigspec] [pid | jobspec] ...
kill -l [signum]
Send the signal named by sigspec to the processes named by pid or jobspec. sigspec is either a signal name such as SIGKILL or a signal number. If sigspec is a signal name, the name is case insensitive and 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 specified signals are listed, and the return status is 0. An argument of -- disables option checking for the rest of the arguments. kill returns true if at least one signal was successfully sent, or false if an error occurs or an illegal 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 [name[=value] ...]
For each argument, create a local variable named name, and assign it value. 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, or an illegal name is supplied.
|
logout |
Exit a login shell. |
popd [+/-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.
|
+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 illegal option is encountered, the directory stack is empty, a non-existent directory stack entry is specified, or the directory change fails.
pushd [dir]
pushd +/-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 directories and returns 0, unless the directory stack is empty.
|
+n |
Rotates the stack so that the nth directory (counting from the left of the list shown by dirs) is at the top. | ||
|
-n |
Rotates the stack so that the nth directory (counting from the right) is at the top. | ||
|
dir |
adds dir to the directory stack at the top, making it the new current working directory. |
If the pushd command is successful, a dirs is performed as well. If the first form is used, pushd returns 0 unless the cd to dir fails. With the second form, pushd returns 0 unless the directory stack is empty, a non-existant directory stack element is specified, or the directory change to the specified new current directory fails.
|
pwd |
Print the absolute pathname of the current working directory. The path printed contains no symbolic links if the -P option to the set builtin command is set. See also the description of nolinks under Shell Variables above). The return status is 0 unless an error occurs while reading the pathname of the current directory. |
read [-r] [name ...]
One line is read from the standard input, and the first word is assigned to the first name, the second word to the second name, and so on, with leftover words assigned to the last name. Only the characters in IFS are recognized as word delimiters. 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. If the -r option is given, a backslash-newline pair is not ignored, and the backslash is considered to be part of the line.
readonly [-f]
[name ...]
readonly -p
The given names are marked readonly and 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. If no arguments are given, or if the -p option is supplied, a list of all readonly names is printed. An argument of -- disables option checking for the rest of the arguments. The return status is 0 unless an illegal option is encountered, one of the names is not a legal 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 [--abefhkmnptuvxldCHP] [-o option] [arg ...]
|
-a |
Automatically mark variables which are modified or created for export to the environment of subsequent commands. | ||
|
-b |
Cause the status of terminated background jobs to be reported immediately, rather than before the next primary prompt. (Also see notify under Shell Variables above). | ||
|
-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 !. | ||
|
-f |
Disable pathname expansion. | ||
|
-h |
Locate and remember function commands as functions are defined. Function commands are normally looked up when the function is executed. | ||
|
-k |
All keyword arguments are placed in the environment for a command, not just those that precede the command name. | ||
|
-m |
Monitor mode. Job control is enabled. This flag is on by default for interactive shells on systems that support it (see JOB CONTROL above). Background processes run in a separate process group and a line containing their exit status is printed upon their completion. | ||
|
-n |
Read commands but do not execute them. This may be used to check a shell script for syntax errors. This is ignored for interactive shells. |
-o option-name
The option-name can be
one of the following:
allexport
Same as -a.
braceexpand
The shell performs brace expansion (see Brace Expansion above). This is on by default.
|
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 -nolineediting option. | ||
|
errexit |
Same as -e. |
histexpand
Same as -H.
ignoreeof
The effect is as if the shell command ‘IGNOREEOF=10’ had been executed (see Shell Variables above).
interactive-comments
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).
|
monitor |
Same as -m. |
noclobber
Same as -C.
|
noexec |
Same as -n. |
|||
|
noglob |
Same as -f. |
|||
|
nohash |
Same as -d. |
|||
|
notify |
Same as -b. |
|||
|
nounset |
Same as -u. |
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. |
privileged
Same as -p.
|
verbose |
Same as -v. | ||
|
vi |
Use a vi-style command line editing interface. | ||
|
xtrace |
Same as -x. |
If no option-name is supplied, the values of the current options are printed.
|
-p |
Turn on privileged mode. In this mode, the $ENV file is not processed, and shell functions are not inherited from the environment. This is enabled automatically on startup if the effective user (group) id is not equal to the real user (group) id. 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, bash displays the expanded value of PS4, followed by the command and its expanded arguments. | ||
|
-l |
Save and restore the binding of name in a for name [in word] command (see SHELL GRAMMAR above). | ||
|
-d |
Disable the hashing of commands that are looked up for execution. Normally, commands are remembered in a hash table, and once found, do not have to be looked up again. | ||
|
-C |
The effect is as if the shell command ‘noclobber=’ had been executed (see Shell Variables above). | ||
|
-H |
Enable ! style history substitution. This flag is on by default when the shell is interactive. | ||
|
-P |
If set, do not follow symbolic links when performing commands such as cd which change the current directory. The physical directory is used instead. | ||
|
-- |
If no arguments follow this flag, 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 flags are off by default unless otherwise noted. Using + rather than - causes these flags to be turned off. The flags can also be specified as options to an invocation of the shell. The current set of flags may be found in $-. After the option arguments are processed, the remaining n args are treated as values for the positional parameters and are assigned, in order, to $1, $2, ... $n. If no options or args are supplied, all shell variables are printed. The return status is always true unless an illegal 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. If n is 0, no parameters are changed. If n is not given, it is assumed to be 1. n must be a non-negative number less than or equal to $#. If n is greater than $#, the positional parameters are not changed. The return status is greater than 0 if n is greater than $# or less than 0; otherwise 0.
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 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. Expressions may be unary or binary.
Unary expressions are often used to examine the status of a
file. There are string operators and numeric comparison
operators as well. Each operator and operand must be a
separate argument. If file is of the form
/dev/fd/n, then file descriptor n is checked.
-b file
True if file exists and is block special.
-c file
True if file exists and is character special.
-d file
True if file exists and is a directory.
-e file
True if file exists.
-f file
True if file exists and is a regular file.
-g file
True if file exists and is set-group-id.
-k file
True if file has its ‘‘sticky’’ bit set.
-L file
True if file exists and is a symbolic link.
-p file
True if file exists and is a named pipe.
-r file
True if file exists and is readable.
-s file
True if file exists and has a size greater than zero.
-S file
True if file exists and is a socket.
|
-t fd |
True if fd is opened on a terminal. |
-u file
True if file exists and its set-user-id bit is set.
-w file
True if file exists and is writable.
-x file
True if file exists and is executable.
-O file
True if file exists and is owned by the effective user id.
-G file
True if file exists and is owned by the effective group id.
file1 -nt file2
True if file1 is newer (according to modification date) than file2.
file1 -ot file2
True if file1 is older than file2.
file1 -ef file
True if file1 and file2 have the same device and inode numbers.
-z string
True if the length of string is zero.
-n string
|
string |
True if the length of string is non-zero. |
string1 = string2
True if the strings are equal.
string1 != string2
True if the strings are not equal.
|
! expr |
True if expr is false. |
expr1 -a expr2
True if both expr1 AND expr2 are true.
expr1 -o expr2
True if either expr1 OR expr2 is true.
arg1 OP arg2
OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arithmetic binary operators return true if arg1 is equal, not-equal, less-than, less-than-or-equal, greater-than, or greater-than-or-equal than arg2, respectively. Arg1 and arg2 may be positive integers, negative integers, or the special expression -l string, which evaluates to the length of string.
|
times |
Print the accumulated user and system times for the shell and for processes run from the shell. The return status is 0. |
trap [-l] [arg] [sigspec]
The command arg is to be read and executed when the shell receives signal(s) sigspec. If arg is absent or -, all specified signals are reset to their original values (the values they had upon entrance to the shell). If arg is the null string this signal is ignored by the shell and by the commands it invokes. sigspec is either a signal name defined in <signal.h>, or a signal number. If sigspec is EXIT (0) the command arg is executed on exit from the shell. With no arguments, trap prints the list of commands associated with each signal number. The -l option causes the shell to print a list of signal names and their corresponding numbers. An argument of -- disables option checking for the rest of the arguments. 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 either the trap name or number is invalid; otherwise trap returns true.
type [-all] [-type | -path] name [name ...]
With no options, indicate how each name would be interpreted if used as a command name. If the -type flag is used, type prints a phrase 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 -path flag 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 would not return file. If a command is hashed, -path prints the hashed value, not necessarily the file that appears first in PATH. If the -all flag is used, type prints all of the places that contain an executable named name. This includes aliases and functions, if and only if the -path flag is not also used. The table of hashed commands is not consulted when using -all. type accepts -a, -t, and -p in place of -all, -type, and -path, respectively. An argument of -- disables option checking for the rest of the arguments. type returns true if any of the arguments are found, false if none are found.
ulimit [-SHacdfmstpnuv [limit]]
Ulimit provides control over the resources available to the shell and to processes started by it, on systems that allow such control. The value of limit can be a number in the unit specified for the resource, or the value unlimited. 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, the command applies to the soft limit. 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 is printed before the value. Other options are interpreted as follows:
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-a |
all current limits are reported | ||
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-c |
the maximum size of core files created | ||
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-d |
the maximum size of a process’s data segment | ||
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-f |
the maximum size of files created by the shell | ||
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-m |
the maximum resident set size | ||
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-s |
the maximum stack size | ||
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-t |
the maximum amount of cpu time in seconds | ||
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-p |
the pipe size in 512-byte blocks (this may not be set) | ||
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-n |
the maximum number of open file descriptors (most systems do not allow this value to be set, only displayed) | ||
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-u |
the maximum number of processes available to a single user | ||
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-v |
The maximum amount of virtual memory available to the shell |
An argument of -- disables option checking for the rest of the arguments. 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 illegal option is encountered, a non-numeric argument other than unlimited is supplied as limit, or an error occurs while setting a new limit.
umask [-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, or if the -S option is supplied, 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. An argument of -- disables option checking for the rest of the arguments. 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 names 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, given the -f option, function. An argument of -- disables option checking for the rest of the arguments. Note that PATH, IFS, PPID, PS1, PS2, UID, and EUID cannot be unset. If any of RANDOM, SECONDS, LINENO, or HISTCMD are unset, they lose their special properties, even if they are subsequently reset. The exit status is true unless a name does not exist or is non-unsettable.
wait [n]
Wait for the specified process and return its termination status. 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-existant process or job, the return status is 127. Otherwise, the return status is the exit status of the last process or job waited for.
bash(1), sh(1)