sh-posix(1)

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 >>)

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.

See also the unalias special command.

In the first form, change the current working directory (PWD) to arg. If arg is -, the directory is changed to the previous directory (OLDPWD). The shell parameter HOME is the default arg. After the cd, the PWD and OLDPWD environment variables are set to the new current directory and the former directory respectively.

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 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.

Mark the given variable names for automatic export to the environment of subsequently executed commands. Optionally, assign values to the variables.

With no arguments, write the names and values of all exported variables to standard output,

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.

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.

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.

Send either signal 15 (SIGTERM, terminate) or the specified signal to the specified jobs or processes. If the signal being sent is TERM (terminate) or HUP (hangup), the job or process is sent a CONT (continue) signal when stopped. See kill(1) for usage and description.

With -l, list the signal names and numbers.

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).

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).

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.

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.

Evaluate conditional expression expr. See test(1) for usage and description. See also the Conditional Expressions subsection.

The arithmetic comparison operators are not restricted to integers. They allow any arithmetic expression. The following additional primitive expressions are allowed:

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.

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.

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.

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.