sh-posix(1)

NAME

sh, rsh — standard and restricted POSIX.2-conformant command shells

SYNOPSIS

sh [{-|+}aefhikmnprstuvx] [{-|+}o option]... [-c string] arg]...

rsh [{-|+}aefhikmnprstuvx] [{-|+}o option]... [-c string] [arg]...

Remarks

This shell is intended to conform to the shell specification of the POSIX.2 Shell and Utility standards. Check any standards conformance documents shipped with your system for information on the conformance of this shell to any other standards.

List of Subheadings in DESCRIPTION

Shell Invocation	Tilde Substitution	Environment
Options	Command Substitution	Functions
rsh Restrictions	Parameter Substitution	Jobs
Definitions	Blank Interpretation	Signals
Commands	File Name Generation	Execution
Simple Commands	Quoting	Command Reentry
Compound Commands	Arithmetic Evaluation	Command Line Editing
Special Commands	Prompting	emacs Editing Mode
Comments	Conditional Expressions	vi Editing Mode
Aliasing	Input/Output

DESCRIPTION

sh is a command programming language that executes commands read from a terminal or a file.

rsh is a restricted version of sh. See the "rsh Restrictions" subsection below.

Shell Invocation

If the shell is invoked by an exec*() system call and the first character of argument zero (shell parameter 0) is dash (-), the shell is assumed to be a login shell and commands are read first from /etc/profile, then from either .profile in the current directory or $HOME/.profile if either file exists, and finally from the file named by performing parameter substitution on the value of the environment parameter ENV, if the file exists. If the -s option is not present and an arg is, a path search is performed on the first arg to determine the name of the script to execute. When running sh with arg, the script arg must have read permission and any setuid and setgid settings will be ignored. Commands are read as described below.

Shell output, except for the output of some of the commands listed in the "Special Commands" subsection, is written to standard error (file descriptor 2).

Options

The following options are interpreted by the shell when it is invoked.

-c string: Read commands from string.
-i: If -i is present or if the shell input and output are attached to a terminal (as reported by tty()), the shell is interactive. In this case SIGTERM is ignored and SIGINT is caught and ignored (so that wait is interruptible). In all cases, SIGQUIT is ignored by the shell. See signal(5).
-r: The shell is a restricted shell.
-s: If -s is present or if no arguments remain, commands are read from the standard input.

The remaining options and arguments are described under the set command in the "Special Commands" subsection.

rsh Restrictions

rsh is used to set up login names and execution environments where capabilities are more controlled than those of the standard shell. The actions of rsh are identical to those of sh, except that the following are forbidden:

Changing directory (see the cd special command and cd(1))
Setting the value of SHELL, ENV, or PATH
Specifying path or command names containing /
Redirecting output (>, >|, <>, and >>)

The restrictions above are enforced after the .profile and ENV files are interpreted.

When a command to be executed is found to be a shell procedure, rsh invokes sh to execute it. Thus, the end-user is provided with shell procedures accessible to the full power of the standard shell, while being restricted to a limited menu of commands. This scheme assumes that the end-user does not have write and execute permissions in the same directory.

These rules effectively give the writer of the .profile file complete control over user actions, by performing guaranteed set-up actions and leaving the user in an appropriate directory (probably not the login directory).

The system administrator often sets up a directory of commands (usually /usr/rbin) that can be safely invoked by rsh. HP-UX systems provide a restricted editor red (see ed(1)), suitable for restricted users.

Definitions

metacharacter

One of the following characters:

; & ( ) | < > newline space tab

blank

A tab or a space.

identifier

A sequence of letters, digits, or underscores starting with a letter or underscore. Identifiers are used as names for functions and named parameters.

word

A sequence of characters separated by one or more nonquoted metacharacters.

command

A sequence of characters in the syntax of the shell language. The shell reads each command and carries out the desired action, either directly or by invoking separate utilities.

special command

A command that is carried out by the shell without creating a separate process. Except for documented side effects, most special commands can be implemented as separate utilities.

#

Comment delimiter. A word beginning with # and all following characters up to a newline are ignored.

parameter

An identifier, a decimal number, or one of the characters !, #, $, *, -, ?, @, and _. See the "Parameter Substitution" subsection.

named parameter

A parameter that can be assigned a value. See the "Parameter Substitution" subsection.

variable

A parameter.

environment variable

A parameter that is known outside the local shell, usually by means of the export special command.

Commands

A command can be a simple command that executes an executable file, a special command that executes within the shell, or a compound command that provides flow of control for groups of simple, special, and compound commands.

Simple Commands

A simple command is a sequence of blank-separated words that may be preceded by a parameter assignment list. (See the "Environment" subsection). The first word specifies the name of the command to be executed. Except as specified below, the remaining words are passed as arguments to the invoked command. The command name is passed as argument 0 (see exec(2)). The value of a simple-command is its exit status if it terminates normally, or 128+errorstatus if it terminates abnormally (see signal(5) for a list of errorstatus values).

A pipeline is a sequence of one or more commands separated by a bar (|) and optionally preceded by an exclamation mark (!). The standard output of each command but the last is connected by a pipe (see pipe(2)) to the standard input of the next command. Each command is run as a separate process; the shell waits for the last command to terminate. If ! does not precede the pipeline, the exit status of the pipeline is the exit status of the last command in the pipeline. Otherwise, the exit status of the pipeline is the logical negation of the exit status of the last command in the pipeline.

A list is a sequence of one or more pipelines separated by ;, &, &&, or ||, and optionally terminated by ;, &, or |&.

;: Causes sequential execution of the preceding pipeline. An arbitrary number of newlines can appear in a list, instead of semicolons, to delimit commands.
&: Causes asynchronous execution of the preceding pipeline (that is, the shell does not wait for that pipeline to finish).
|&: Causes asynchronous execution of the preceding command or pipeline with a two-way pipe established to the parent shell. The standard input and output of the spawned command can be written to and read from by the parent shell using the -p option of the special commands read and print.
&&: Causes the list following it to be executed only if the preceding pipeline returns a zero value.
||: Causes the list following it to be executed only if the preceding pipeline returns a nonzero value.

Of these five symbols, ;, &, and |& have equal precedence, which is lower than that of && and ||. The symbols && and || also have equal precedence.

Compound Commands

Unless otherwise stated, the value returned by a compound command is that of the last simple command executed in the compound command. The ; segment separator can be replaced by one or more newlines.

The following keywords are recognized only as the first word of a command and when not quoted:

!            }            elif         for          then 
[[           case         else         function     time 
]]           do           esac         if           until 
{            done         fi           select       while 

A compound command is one of the following.

case word in [[;] [(] pattern [| pattern]...) list ;;]... ; esac

Execute the list associated with the first pattern that matches word. The form of the patterns is identical to that used for file name generation (see the "File Name Generation" subsection). The ;; case terminator cannot be replaced by newlines.

for identifier [in word ...] ; do list ; done

Set identifier to each word in sequence and execute the do list. If in word ... is omitted, set identifier to each set positional parameter instead. See the "Parameter Substitution" subsection. Execution ends when there are no more positional parameters or words in the list.

function identifier { list ; }
identifier () { list ; }

Define a function named by identifier. A function is called by executing its identifier as a command. The body of the function is the list of commands between { and }. See the "Functions" subsection.

if list ; then list ; [elif list ; then list ;]... [else list ;] fi

Execute the if list and, if its exit status is zero, execute the first then list. Otherwise, execute the elif list (if any) and, if its exit status is zero, execute the next then list. Failing that, execute the else list (if any). If no else list or then list is executed, if returns a zero exit status.

select identifier [in word ...] ; do list ; done

Print the set of words on standard error (file descriptor 2), each preceded by a number. If in word ... is omitted, print the positional parameters instead (see the "Parameter Substitution" subsection). Print the PS3 prompt and read a line from standard input into the parameter REPLY. If this line consists of the number of one of the listed words, set identifier to the corresponding word, execute list, and repeat the PS3 prompt. If the line is empty, print the selection list again, and repeat the PS3 prompt. Otherwise, set identifier to null, execute list, and repeat the PS3 prompt. The select loop repeats until a break special command or end-of-file is encountered.

time pipeline

Execute the pipeline and print the elapsed time, the user time, and the system time on standard error. Note that the time keyword can appear anywhere in the pipeline to time the entire pipeline. To time a particular command in a pipeline, see time(1).

until list ; do list ; done

Execute the until list. If the exit status of the last command in the list is nonzero, execute the do list and execute the until list again. When the exit status of the last command in the until list is zero, terminate the loop. If no commands in the do list are executed, until returns a zero exit status.

while list ; do list ; done

Execute the while list. If the exit status of the last command in the list is zero, execute the do list and execute the while list again. When the exit status of the last command in the while list is nonzero, terminate the loop. If no commands in the do list are executed, while returns a nonzero exit status.

( list )

Execute list in a separate environment. If two adjacent open parentheses are needed for nesting, a space must be inserted between them to avoid arithmetic evaluation.

{ list ; }

Execute list, but not in a separate environment. Note that { is a keyword and requires a trailing blank to be recognized.

[[ expression ]]

Evaluate expression and return a zero exit status when expression is true. See the "Conditional Expressions" subsection for a description of expression. Note that [[ and ]] are keywords and require blanks between them and expression.

Special Commands

Special commands are simple commands that are executed in the shell process. They permit input/output redirection. Unless otherwise indicated, file descriptor 1 (standard output) is the default output location and the exit status, when there are no syntax errors, is zero.

Commands that are marked with % are treated specially in the following ways:

1.: Variable assignment lists preceding the command remain in effect when the command completes.
2.: I/O redirections are processed after variable assignments.
3.: Certain errors cause a script that contains them to abort.

Words following commands marked with & that are in the format of a variable assignment are expanded with the same rules as a variable assignment. This means that tilde substitution is performed after the = sign and word-splitting and file-name generation are not performed.

% : [arg]...

(colon) Only expand parameters. A zero exit status is returned.

% . file [arg]...

(period) Read and execute commands from file and return. The commands are executed in the current shell environment. The search path specified by PATH is used to find the directory containing file. If any arguments arg are given, they become the positional parameters. Otherwise, the positional parameters are unchanged. The exit status is the exit status of the last command executed.

& alias [-tx] [name[=value]]...

With name=value specified, define name as an alias and assign it the value value. A trailing space in value causes the next word to be checked for alias substitution.
With name=value omitted, print the list of aliases in the form name=value on standard output.
With name specified without =value, print the specified alias.
With -t, set tracked aliases. The value of a tracked alias is the full path name corresponding to the given name. The value of a tracked alias becomes undefined when the value of PATH is reset, but the alias remains tracked. With name=value omitted, print the list of tracked aliases in the form name=pathname on standard output.
With -x, set exported aliases. An exported alias is defined across subshell environments. With name=value omitted, print the list of exported aliases in the form name=value on standard output.
Alias returns true unless a name is given for which no alias has been defined.

bg [job]...

Put the specified jobs into the background. The current job is put in the background if job is unspecified. See the "Jobs" subsection for a description of the format of job.

% break [n]

Exit from the enclosing for, select, until, or while loop, if any. If n is specified, exit from n levels.

cd [-L|-P] [arg]
cd old new

In the first form, change the current working directory (PWD) to arg. If arg is -, the directory is changed to the previous directory (OLDPWD).
With -L (default), preserve logical naming when treating symbolic links. cd -L .. moves the current directory one path component closer to the root directory.
With -P, preserve the physical path when treating symbolic links. cd -P .. changes the working directory to the actual parent directory of the current directory.
The shell parameter HOME is the default arg. The parameter PWD is set to the current directory.
The shell parameter CDPATH defines the search path for the directory containing arg. Alternative directory names are separated by a colon (:). If CDPATH is null or undefined, the default value is the current directory. Note that the current directory is specified by a null path name, which can appear immediately after the equal sign or between the colon delimiters anywhere else in the path list. If arg begins with a /, the search path is not used. Otherwise, each directory in the path is searched for arg. See also cd(1).
The second form of cd substitutes the string new for the string old in the current directory name, PWD, and tries to change to this new directory.

command [arg]...

Treat arg as a command, but disable function lookup on arg. See command(1) for usage and description.

% continue [n]

Resume the next iteration of the enclosing for, select, until, or while loop. If n is specified, resume at the nth enclosing loop.

echo [arg]...

Print arg on standard output. See echo(1) for usage and description. See also the print special command.

% eval [arg]...

Read the arguments as input to the shell and execute the resulting commands. Allows parameter substitution for keywords and characters that would otherwise be unrecognized in the resulting commands.

% exec [arg]...

Parameter assignments remain in effect after the command completes. If arg is given, execute the command specified by the arguments in place of this shell without creating a new process. Input/output arguments may appear and affect the current process. If no arguments are given, modify file descriptors as prescribed by the input/output redirection list. In this case, any file descriptor numbers greater than 2 that are opened with this mechanism are closed when another program is invoked.

% exit [n]

Exit from the shell with the exit status specified by n. If n is omitted, the exit status is that of the last command executed. An end-of-file also causes the shell to exit, except when a shell has the ignoreeof option set. (See the set special command.)

%& export [name[=value]]...
%& export -p

Mark the given variable names for automatic export to the environment of subsequently executed commands. Optionally, assign values to the variables.
With -p, write the names and values of all exported variables to standard output, in a format with the proper use of quoting, so that it is suitable for re-input to the shell as commands that achieve the same exporting results.

fc [-r] [-e ename] [first [last]]
fc -l [-nr] [first [last]]
fc -s [old=new] [first]
fc -e - [old=new] [command]

List, or edit and reexecute, commands previously entered to an interactive shell. A range of commands from first to last is selected from the last HISTSIZE commands typed at the terminal. The arguments first and last can be specified as a number or string. A given string is used to locate the most recent command. A negative number is used to offset the current command number.
With -l, list the commands on standard output. Without -l, invoke the editor program ename on a file containing these keyboard commands. If ename is not supplied, the value of the parameter FCEDIT (default /usr/bin/ed) is used as the editor. Once editing has ended, the commands (if any) are executed. If last is omitted, only the command specified by first is used. If first is not specified, the default is the previous command for editing and -16 for listing.
With -r, reverse the order of the commands.
With -n, suppress command numbers when listing.
With -s, reexecute the command without invoking an editor.
The old=new argument replaces the first occurrence of string old in the command to be reexecuted by the string new.

fg [job]...

Bring each job into the foreground in the order specified. If no job is specified, bring the current job into the foreground. See the "Jobs" subsection for a description of the format of job.

getopts optstring name [arg]...

Parse the argument list, or the positional parameters if no arguments, for valid options. On each execution, return the next option in name. See getopts(1) for usage and description.
An option begins with a + or a -. An argument not beginning with + or -, or the argument --, ends the options. optstring contains the letters that getopts recognizes. If a letter is followed by a :, that option is expected to have an argument. The options can be separated from the argument by blanks.
For an option specified as -letter, name is set to letter. For an option specified as +letter, name is set to +letter. The index of the next arg is stored in OPTIND. The option argument, if any, is stored in OPTARG. If no option argument is found, or the option found does not take an argument, OPTARG is unset.
A leading : in optstring causes getopts to store the letter of an invalid option in OPTARG, and to set name to ? for an unknown option and to : when a required option argument is missing. Otherwise, getopts prints an error message. The exit status is nonzero when there are no more options.

& hash [utility]...
& hash -r

Affect the way the current shell environment remembers the locations of utilities. With utility, add utility locations to a list of remembered locations. With no arguments, print the contents of the list. With -r, forget all previously remembered utility locations.

jobs [-lnp] [job]...

List information about each given job, or all active jobs if job is not specified. With -l, list process IDs in addition to the normal information. With -n, display only jobs that have stopped or exited since last notified. With -p, list only the process group. See the "Jobs" subsection for a description of the format of job.

kill [-s signal] process ...
kill -l
kill [-signal] process ...

Send either signal 15 (SIGTERM, terminate) or the specified signal to the specified jobs or processes. See kill(1) for usage and description.
With -l, list the signal names and numbers.

let arg ...
(( arg ...))

Evaluate each arg as a separate arithmetic expression. See the "Arithmetic Evaluation" subsection for a description of arithmetic expression evaluation. The exit status is 0 if the value of the last expression is nonzero, and 1 otherwise.

% newgrp [-] [group]

Replace the current shell with a new one having group as the user's group. The default group is the user's login group. With -, the user's .profile and $ENV files are also executed. See newgrp(1) for usage and description. Equivalent to exec newgrp arg ....

print [-nprRsu[n]] [arg]...

The shell output mechanism. With no options or with option - or --, print the arguments on standard output as described in echo(1). See also printf(1).
With -n, do not add a newline character to the output.
With -p, write the arguments onto the pipe of the process spawned with |& instead of standard output.
With -R or -r (raw mode), ignore the escape conventions of echo. With -R, print all subsequent arguments and options other than -n.
With -s, write the arguments into the history file instead of to standard output.
With -u, specify a one-digit file descriptor unit number n on which the output will be placed. The default is 1 (standard output).

pwd [-L|-P]

Print the name of the current working directory (equivalent to print -r - $PWD). With -L (the default), preserve the logical meaning of the current directory. With -P, preserve the physical meaning of the current directory if it is a symbolic link. See also the cd special command, cd(1), ln(1), and pwd(1).

read [-prsu[n]] [name?prompt] [name]...

The shell input mechanism. Read one line (by default, from standard input) and break it up into words using the characters in IFS as separators. The first word is assigned to the first name, the second word to the second name, and so on; the remaining words are assigned to the last name. See also read(1). The return code is 0, unless an end-of-file is encountered.
With -p, take the input line from the input pipe of a process spawned by the shell using |&. An end-of-file with -p causes cleanup for this process so that another process can be spawned.
With -r (raw mode), a \ at the end of a line does not signify line continuation.
With -s, save the input as a command in the history file.
With -u, specify a one-digit file descriptor unit to read from. The file descriptor can be opened with the exec special command. The default value of n is 0 (standard input). If name is omitted, REPLY is used as the default name.
If the first argument contains a ?, the remainder of the argument is used as a prompt when the shell is interactive.
If the given file descriptor is open for writing and is a terminal device, the prompt is placed on that unit. Otherwise, the prompt is issued on file descriptor 2 (standard error).

%& readonly [name[=value]]...
%& readonly -p

Mark the given names read only. These names cannot be changed by subsequent assignment.
With -p, write the names and values of all read-only variables to standard output in a format with the proper use of quoting so that it is suitable for re-input to the shell as commands that achieve the same attribute-setting results.

% return [n]

Cause a shell function to return to the invoking script with the return status specified by n. If n is omitted, the return status is that of the last command executed. Only the low 8 bits of n (decimal 0 to 255) are passed back to the caller. If return is invoked while not in a function or a . script (see the . special command), it has the same effect as an exit command.

% set [{-|+}abCefhkmnopstuvx] [{-|+}o option]... [{-|+}A name] [arg]...

Set (-) or clear (+) execution options or perform array assignments (-A, +A). All options except -A and +A can be supplied in a shell invocation (see the SYNOPSIS section and the "Shell Invocation" subsection).
Using + instead of - before an option causes the option to be turned off. These options can also be used when invoking the shell. The current list of set single-letter options is contained in the shell variable -. It can be examined with the command echo $-.
The - and + options can be intermixed in the same command, except that there can be only one -A or +A option.
Unless -A or +A is specified, the remaining arg arguments are assigned consecutively to the positional parameters 1, 2, ....
The set command with neither arguments nor options displays the names and values of all shell parameters on standard output. See also env(1).
The options are defined as follows.
-A
Array assignment. Unset the variable name and assign values sequentially from the list arg. With +A, do not unset the variable name first.
-a
Automatically export subsequently defined parameters.
-b
Cause the shell to notify the user asynchronously of background jobs as they are completed. When the shell notifies the user that a job has been completed, it can remove the job's process ID from the list of those known in the current shell execution environment.
-C
Prevent redirection > from truncating existing files. Requires >| to truncate a file when turned on.
-e
Execute the ERR trap, if set, and exit if a command has a nonzero exit status, and is not part of the compound list following a if, until, or while keyword, and is not part of an AND or OR list, and is not a pipeline preceded by the ! reserved word. This mode is disabled while reading profiles.
-f
Disable file name generation.
-h
Specify that each command whose name is an identifier becomes a tracked alias when first encountered.
-k
Place all parameter assignment arguments (not just those that precede the command name) into the environment for a command.
-m
Run background jobs in a separate process group and print a line upon completion. The exit status of background jobs is reported in a completion message. This option is turned on automatically for interactive shells.
-n
Read commands and check them for syntax errors, but do not execute them. The -n option is ignored for interactive shells.
-o
Set an option argument from the following list. Repeat the -o option to specify additional option arguments.
allexport
Same as -a.
bgnice
Run all background jobs at a lower priority.
errexit
Same as -e.
emacs
Use a emacs-style inline editor for command entry.
gmacs
Use a gmacs-style inline editor for command entry.
ignoreeof
Do not exit from the shell on end-of-file (eof as defined by stty; default is ^D). The exit special command must be used.
keyword
Same as -k.
markdirs
Append a trailing / to all directory names resulting from file name generation.
monitor
Same as -m.
noclobber
Same as -C.
noexec
Same as -n.
noglob
Same as -f.
nolog
Do not save function definitions in history file.
notify
Same as -b.
nounset
Same as -u.
privileged
Same as -p.
verbose
Same as -v.
trackall
Same as -h.
vi
Use a vi-style inline editor for command entry.
viraw
Process each character as it is typed in vi mode (always on).
xtrace
Same as -x.
-p
Disable processing of the $HOME/.profile file and uses the file /etc/suid_profile instead of the ENV file. This mode is on whenever the effective user ID (group ID) is not equal to the real user ID (group ID). Turning this off causes the effective user ID and group ID to be set to the real user ID and group ID.
-s
Sort the positional parameters.
-t
Exit after reading and executing one command.
-u
Treat unset parameters as an error when substituting.
-v
Print shell input lines as they are read.
-x
Print commands and their arguments as they are executed.
-
Turn off -x and -v options and stop examining arguments for options.
--
Do not change any of the options; useful in setting parameter 1 to a value beginning with -. If no arguments follow this option, the positional parameters are unset.

% shift [n]

Rename the positional parameters from n+1 ... to 1 .... The default value of n is 1. n can be any arithmetic expression that evaluates to a nonnegative number less than or equal to $#.

test [expr]

Evaluate conditional expression expr. See test(1) for usage and description. The arithmetic comparison operators are not restricted to integers. They allow any arithmetic expression. The following additional primitive expressions are allowed:
-L file
True if file is a symbolic link.
-e file
True if file exists.
file1 -nt file2
True if file1 is newer than file2.
file1 -ot file2
True if file1 is older than file2.
file1 -ef file2
True if file1 has the same device and i-node number as file2.

% times

Print the accumulated user and system times for the shell and for processes run from the shell.

% trap [arg] [sig]...

Set arg as a command that is read and executed when the shell receives a sig signal. (Note that arg is scanned once when the trap is set and once when the trap is taken.) Each sig can be given as the number or name of a signal. Letter case is ignored. For example, 3, QUIT, quit, and SIGQUIT all specify the same signal. Use kill -l to get a list of signals.
Trap commands are executed in signal number order. Any attempt to set a trap on a signal that was ignored upon entering the current shell is ineffective. Traps remain in effect for a given shell until explicitly changed with another trap command; that is, a trap set within a function will remain in effect even after the function returns.
If arg is - (or if arg is omitted and the first sig is numeric), reset all traps for each sig to their original values.
If arg is the null string ('' or "" ), each sig is ignored by the shell and by the commands it invokes.
If sig is DEBUG, then arg is executed after each command. If sig is ERR, arg is executed whenever a command has a nonzero exit code. If sig is 0 or EXIT, the command arg is executed on exit from the shell.
With no arguments, print a list of commands associated with each signal name.

& typeset [{-|+}LRZfilrtux[n]] [name[=value]]...

name=value [name=value]...

Assign types and a value to a local named parameter name. See also the export special command. Parameter assignments remain in effect after the command completes. When invoked inside a function, create a new instance of the parameter name. The parameter value and type are restored when the function completes.
The following list of attributes can be specified. Use + instead of - to turn the options off.
-L
Left justify and remove leading blanks from value. If n is nonzero, it defines the width of the field; otherwise, it is determined by the width of the value of first assignment. When name is assigned, the value is filled on the right with blanks or truncated, if necessary, to fit into the field. Leading zeros are removed if the -Z option is also set. The -R option is turned off. Flagged as leftjust n.
-R
Right justify and fill with leading blanks. If n is nonzero, it defines the width of the field; otherwise, it is determined by the width of the value of first assignment. The field is left-filled with blanks or truncated from the end if the parameter is reassigned. The -L option is turned off. Flagged as rightjust n.
-Z
Right justify and fill with leading zeros if the first nonblank character is a digit and the -L option has not been set. If n is nonzero it defines the width of the field; otherwise, it is determined by the width of the value of first assignment. Flagged as zerofill n plus the flag for -L or -R.
-f
Cause name to refer to function names rather than parameter names. No assignments can be made to the name declared with the typeset statement. The only other valid options are -t (which turns on execution tracing for this function) and -x (which allows the function to remain in effect across shell procedures executed in the same process environment). Flagged as function.
-i
Parameter is an integer. This makes arithmetic faster. If n is nonzero it defines the output arithmetic base; otherwise, the first assignment determines the output base. Flagged as integer [base n].
-l
Convert all uppercase characters to lowercase. The uppercase -u option is turned off. Flagged as lowercase.
-r
Mark any given name as "read only". The name cannot be changed by subsequent assignment. Flagged as readonly.
-t
Tag the named parameters. Tags are user-definable and have no special meaning to the shell. Flagged as tagged.
-u
Convert all lowercase characters to uppercase characters. The lowercase -l option is turned off. Flagged as uppercase.
-x
Mark any given name for automatic export to the environment of subsequently executed commands. Flagged as export.
typeset alone displays a list of parameter names, prefixed by any flags specified above.
typeset - displays the parameter names followed by their values. Specify one or more of the option letters to restrict the list. Some options are incompatible with others.
typeset + displays the parameter names alone. Specify one or more of the option letters to restrict the list. Some options are incompatible with others.

ulimit [-HSacdfnst] [limit]

Set or display a resource limit. The limit for a specified resource is set when limit is specified. The value of limit can be a number in the unit specified with each resource, or the keyword unlimited.
The -H and -S flags specify whether the hard limit or the soft limit is set for the given resource. A hard limit cannot be increased once it is set. A soft limit can be increased up to the hard limit. If neither -H nor -S is specified, the limit applies to both. The current resource limit is printed when limit is omitted. In this case, the soft limit is printed unless -H is specified. When more than one resource is specified, the limit name and unit are printed before the value.
If no option is given, -f is assumed.
-a
List all of the current resource limits.
-c
The number of 512-byte blocks in the size of core dumps.
-d
The number of kilobytes in the size of the data area.
-f
The number of 512-byte blocks in files written by child processes (files of any size can be read).
-n
The number of file descriptors.
-s
The number of kilobytes in the size of the stack area.
-t
The number of seconds to be used by each process.

umask [-S] [mask]

Set the user file-creation mask mask. mask can be either an octal number or a symbolic value as described in umask(1). A symbolic value shows permissions that are unmasked. An octal value shows permissions that are masked off.
Without mask, print the current value of the mask. With -S, print the value in symbolic format. Without -S, print the value as an octal number. The output from either form can be used as the mask of a subsequent invocation of umask.

unalias name ...
unalias -a

Remove each name from the alias list. With -a, remove all alias definitions from the current shell execution environment.

% unset [-fv] name ...

Remove the named shell parameters from the parameter list. Their values and attributes are erased. Read-only variables cannot be unset. With -f, names refer to function names. With -v, names refer to variable names. Unsetting _, ERRNO, LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM, SECONDS, and TMOUT removes their special meaning, even if they are subsequently assigned to.

wait [job]

Wait for the specified job to terminate or stop, and report its status. This status becomes the return code for the wait command. Without job, wait for all currently active child processes to terminate or stop. The termination status returned is that of the last process. See the "Jobs" subsection for a description of the format of job.

whence [-pv] name ...

For each name, indicate how it would be interpreted if used as a command name. With -v, produce a more verbose report. With -p do a path search for name, disregarding any use as an alias, a function, or a reserved word.

Comments

A word beginning with # causes that word and all the following characters up to a newline to be ignored.

Aliasing

The first word of each command is replaced by the text of an alias, if an alias for this word has been defined. An alias name consists of any number of characters excluding metacharacters, quoting characters, file expansion characters, parameter and command substitution characters, and =. The replacement string can contain any valid shell script, including the metacharacters listed above. The first word of each command in the replaced text, other than any that are in the process of being replaced, will be tested for additional aliases. If the last character of the alias value is a blank, the word following the alias is also checked for alias substitution. Aliases can be used to redefine special commands, but cannot be used to redefine the keywords listed in the "Compound Commands" subsection. Aliases can be created, listed, and exported with the alias command and can be removed with the unalias command. Exported aliases remain in effect for subshells but must be reinitialized for separate invocations of the shell (see the "Shell Invocation" subsection).

Aliasing is performed when scripts are read, not while they are executed. Therefore, for it to take effect, an alias must be executed before the command referring to the alias is read.

Aliases are frequently used as a shorthand for full path names. An option to the aliasing facility allows the value of the alias to be automatically set to the full path name of the corresponding command. These aliases are called tracked aliases. The value of a tracked alias is defined the first time the identifier is read and becomes undefined each time the PATH variable is reset. These aliases remain tracked so that the next reference will redefine the value. Several tracked aliases are compiled into the shell. The -h option of the set command converts each command name that is an identifier into a tracked alias.

The following exported aliases are compiled into the shell but can be unset or redefined:

autoload='typeset -fu' 
command='command ' 
functions='typeset -f' 
history='fc -l' 
integer='typeset -i' 
local=typeset 
nohup='nohup ' 
r='fc -e -' 
stop='kill -STOP' 
suspend='kill -STOP $$' 
type='whence -v' 

Tilde Substitution

After alias substitution is performed, each word is checked to see if it begins with an unquoted tilde (~). If it does, the word up to a / is checked to see if it matches a user name in the /etc/passwd file. If a match is found, the ~ and the matched login name are replaced by the login directory of the matched user. If no match is found, the original text is left unchanged. A ~ alone or before a / is replaced by the value of the HOME parameter. A ~ followed by a + or - is replaced by the value of the parameter PWD and OLDPWD, respectively. In addition, tilde substitution is attempted when the value of a parameter assignment begins with a ~.

Command Substitution

The standard output from a command enclosed in parenthesis preceded by a dollar sign ($(...)) or a pair of grave accents (`...`) can be used as part or all of a word; trailing newlines are removed. In the second (archaic) form, the string between the accents is processed for special quoting characters before the command is executed. See the "Quoting" subsection. The command substitution $(cat file) can be replaced by the equivalent but faster $(<file). Command substitution of most special commands that do not perform input/output redirection are carried out without creating a separate process.

An arithmetic expression enclosed in double parenthesis preceded by a dollar sign ($((...))) is replaced by the value of the arithmetic expression within the double parenthesis. See the "Arithmetic Evaluation" subsection for a description of arithmetic expressions.

Parameter Substitution

A parameter is an identifier, one or more decimal digits, or one of the characters !, #, $, *, -, ?, @, and _. A named parameter (a parameter denoted by an identifier) has a value and zero or more attributes. Named parameters can be assigned values and attributes with the typeset special command. Exported parameters pass values and attributes to the environment.

The shell supports a limited one-dimensional array facility. An element of an array parameter is referenced by a subscript. A subscript is denoted by a [, followed by an arithmetic expression, followed by a ]. See the "Arithmetic Evaluation" subsection. To assign values to an array, use set -A name value .... The value of all subscripts must be in the range of 0 through 1023. Arrays need not be declared. Any reference to a named parameter with a valid subscript is legal and an array is created if necessary. Referencing an array parameter without a subscript is equivalent to referencing the first element.

If the -i integer attribute is set for name, the value is subject to arithmetic evaluation.

Positional parameters, parameters denoted by a number, can be assigned values with the set special command. Parameter 0 is set from argument zero when the shell is invoked.

Use the prefix character $ to specify the value of a parameter for substitution.

$parameter

${parameter}

${parameter[subscript]}

Substitute the value of the parameter, if any. Braces are required when parameter is followed by a letter, digit, or underscore that should not be interpreted as part of its name or when a named parameter is subscripted. If parameter is one or more digits, it is a positional parameter. A positional parameter of more than one digit must be enclosed in braces. The shell reads all the characters from ${ to the matching } as part of the same word, even if it contains braces or metacharacters.

If parameter is * or @, all the positional parameters, starting with 1, are substituted (separated by a field separator character). See the "Quoting" subsection.

If an array parameter with subscript * or @ is used, the value for each element is substituted (separated by a field separator character).

${#parameter}

If parameter is * or @, the number of positional parameters is substituted. Otherwise, the length of the value of the parameter is substituted.

${#parameter[*]}

Substitute the number of elements in the array.

${parameter:-word}

If parameter is set and is nonnull, substitute its value; otherwise, substitute word.

${parameter:=word}

If parameter is not set or is null, set it to word; then substitute the value of the parameter. Positional parameters may not be assigned in this way.

${parameter:?word}

If parameter is set and is nonnull, substitute its value; otherwise, print word and exit from the shell. If word is omitted, a standard message is printed.

${parameter:+word}

If parameter is set and is nonnull, substitute word; otherwise, substitute nothing.

${parameter#pattern}

${parameter##pattern}

If the shell pattern matches the beginning of the value of parameter, the value of this substitution is the value of the parameter with the matched portion deleted; otherwise, the value of this parameter is substituted. In the former case, the smallest matching pattern is deleted; in the latter case, the largest matching pattern is deleted. These characters # or % should be escaped by a backslash (\) or quotes ('').

${parameter%pattern}

${parameter%%pattern}

If the shell pattern matches the end of the value of parameter, the value of parameter with the matched part is deleted; otherwise, substitute the value of parameter. In the former, the smallest matching pattern is deleted; in the latter, the largest matching pattern is deleted. These characters # or % should be escaped by a backslash (\) or quotes ('').

In the above, word is not evaluated unless it is used as the substituted string. Thus, in the following example, pwd is executed only if d is not set or is null:

echo  ${d:-$(pwd)} 

If the colon (:) is omitted from the above expressions, the shell only checks to determine whether or not parameter is set.

• The following parameters are set automatically by the shell:

0: The string used to call the command or script, set from invocation argument zero.
1, 2, ...: The positional parameters.
*, @: All the set positional parameters, separated by a field separator character. See the "Quoting" subsection.
#: The number of set positional parameters in decimal.
-: Flags supplied to the shell on invocation or by the set command.
?: The decimal exit status returned by the last executed command.
$: The process number of this shell.
_: Initially, the absolute path name of the shell or script being executed, as passed in the environment. Subsequently, it is assigned the last argument of the previous command. This parameter is not set for commands which are asynchronous. This parameter is also used to hold the name of the matching MAIL file when checking for mail.
!: The process number of the last background command invoked.
ERRNO: The value of errno as set by the most recently failed system call. This value is system-dependent and is intended for debugging purposes.
LINENO: The line number of the current line within the script or function being executed.
OLDPWD: The previous working directory set by the cd command.
OPTARG: The value of the last option argument processed by the getopts special command.
OPTERR: If set to 0, OPTERR will suppress error messages from the getopts special command. OPTERR is initially set to 1.
OPTIND: The index of the last option argument processed by the getopts special command.
PPID: The process number of the parent of the shell.
PWD: The present working directory set by the cd command.
RANDOM: Each time this parameter is evaluated, a random integer, uniformly distributed between 0 and 32767, is generated. The sequence of random numbers can be initialized by assigning a numeric value to RANDOM.
REPLY: Set by the select compound command, and by the read special command when no name is supplied.
SECONDS: Each time this parameter is referenced, the number of seconds since shell invocation is returned. If this parameter is assigned a value, the value returned upon reference is the value that was assigned plus the number of seconds since the assignment.

• The following parameters are used by the shell:

CDPATH: The search path for the cd command, a list of directories separated by colons.
COLUMNS: If this variable is set, its value is used to define the width of the edit window for the shell edit modes and for printing select lists.
EDITOR: If the value of this variable ends in emacs, gmacs, or vi and the VISUAL variable is not set, the corresponding option is turned on (see the set special command.
ENV: If this parameter is set, parameter substitution is performed on the value to generate the path name of the script to be executed when the shell is invoked (see the "Invocation" subsection). This file is typically used for alias and function definitions.
FCEDIT: The default editor name for the fc command.
FPATH: The search path for function definitions, a list of directories separated by colons. This path is searched when a function with the -u attribute is referenced and when a command is not found. If an executable file is found, then it is read and executed in the current environment.
HISTFILE: If this parameter is set when the shell is invoked, its value is the path name of the file that is used to store the command history. The default value is $HOME/.sh_history. If the user is a superuser and no HISTFILE is given, then no history file is used. See the "Command Reentry" subsection and the WARNINGS section.
HISTSIZE: If this parameter is set when the shell is invoked, the number of previously entered commands accessible to this shell will be greater than or equal to this number. The default is 128.
HOME: The default argument (home directory) for the cd command.
IFS: Internal field separators, normally space, tab, and newline, that are used to separate command words resulting from command or parameter substitution and for separating words with the special command read. The first character of the IFS parameter is used to separate arguments for the $* substitution (see the "Quoting" subsection). If the value of IFS is space, tab, and newline, or if IFS is unset and it is being used to separate the results of command or parameter substitution, any sequence of IFS characters serves to delimit words; otherwise, each occurrence of a character in IFS serves to delimit a word. If the value of IFS is null, no word splitting is done.
LANG: The locale of your system, which is made up of three parts: language, territory, and code set. The default is the C locale. See environ(5).
LC_ALL: The overriding value for LANG and the LC_* variables. See environ(5).
LC_COLLATE: The collating sequence to use when sorting names and when character ranges occur in patterns. See environ(5).
LC_CTYPE: The character classification information to use. Changing the value of LC_CTYPE after the shell has started does not affect the lexical processing of shell commands in the current shell execution environment or its subshells. See environ(5).
LC_MESSAGES: The language in which system messages appear, and the language that the system expects for user input of yes and no strings. See environ(5).
LC_MONETARY: The currency symbol and monetary value format. See environ(5).
LC_NUMERIC: The numeric format. See environ(5).
LC_TIME: The date and time format. See environ(5).
LINES: If this variable is set, the value is used to determine the column length for printing select lists. select lists print vertically until about two-thirds of LINES lines are filled.
MAIL: If this parameter is set to the name of a mail file and the MAILPATH parameter is not set, the shell informs the user of arrival of mail in the specified file.
MAILCHECK: How often (in seconds) the shell checks for changes in the modification time of any of the files specified by the MAILPATH or MAIL parameters. The default value is 600 seconds. When the time has elapsed, the shell checks before issuing the next prompt.
MAILPATH: A list of file names separated by colons. If this parameter is set, the shell informs the user of any modifications to the specified files that have occurred within the last MAILCHECK seconds. Each file name can be followed by a ? and a message to be printed, in which case the message will undergo parameter and command substitution with the parameter $_ defined as the name of the changed file. The default message is you have mail in $_.
NLSPATH: The search path for message catalogs, a list of directories separated by colons.
PATH: The search path for commands, a list of directories separated by colons. See the "Execution" subsection.
PS1: The value of this parameter is expanded for parameter substitution, to define the primary prompt string. The default value is "$ ". The character ! in the primary prompt string is replaced by the command number. See the "Command Reentry" subsection.
PS2: Secondary prompt string for command completion. The default value is "> ".
PS3: Selection prompt string used within a select loop. If unset, it defaults to "#? ".
PS4: Execution trace string that precedes each line of an execution trace. See the set -x special command. If unset, it defaults to "