set(1p)

NAME

set - set or unset options and positional parameters

SYNOPSIS

set [-abCefmnuvx][-h][-o option][argument...]
set [+abCefmnuvx][+h][+o option][argument...]
set -- [argument...]
set -o
set +o

DESCRIPTION

If no options or arguments are specified, set shall write the names and values of all shell variables in the collation sequence of the current locale. Each name shall start on a separate line, using the format:

"%s=%s\n", <name>, <value>

The value string shall be written with appropriate quoting; see the description of shell quoting in Quoting . The output shall be suitable for reinput to the shell, setting or resetting, as far as possible, the variables that are currently set; read-only variables cannot be reset.

When options are specified, they shall set or unset attributes of the shell, as described below. When arguments are specified, they cause positional parameters to be set or unset, as described below. Setting or unsetting attributes and positional parameters are not necessarily related actions, but they can be combined in a single invocation of set.

The set special built-in shall support the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines except that options can be specified with either a leading hyphen (meaning enable the option) or plus sign (meaning disable it) unless otherwise specified.

Implementations shall support the options in the following list in both their hyphen and plus-sign forms. These options can also be specified as options to sh.

-a When this option is on, the export attribute shall be set for

each variable to which an assignment is performed; see the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.21, Variable Assignment. If the assignment precedes a utility name in a command, the export attribute shall not persist in the current execution environment after the utility completes, with the exception that preceding one of the special built-in utilities causes the export attribute to persist after the built-in has completed. If the assignment does not precede a utility name in the command, or if the assignment is a result of the operation of the getopts or read utilities, the export attribute shall persist until the variable is unset.

-b This option shall be supported if the implementation supports

the User Portability Utilities option. It shall cause the shell to notify the user asynchronously of background job completions. The following message is written to standard error:

"[%d]%c %s%s\n", <job-number>, <current>, <status>, <job-name>

where the fields shall be as follows:

<current>

The character '+' identifies the job that would be used as a default for the fg or bg utilities; this job can also be specified using the job_id "%+" or "%%" . The character '-' identifies the job that would become the default if the current default job were to exit; this job can also be specified using the job_id "%-" . For other jobs, this field is a <space>. At most one job can be identified with '+' and at most one job can be identified with '-' . If there is any suspended job, then the current job shall be a suspended job. If there are at least two suspended jobs, then the previous job also shall be a suspended job.

<job-number>

A number that can be used to identify the process group to the wait, fg, bg, and kill utilities. Using these utilities, the job can be identified by prefixing the job number with '%' .

<status>

Unspecified.

<job-name>

Unspecified.

When the shell notifies the user a job has been completed, it may remove the job's process ID from the list of those known in the current shell execution environment; see Asynchronous Lists . Asynchronous notification shall not be enabled by default.

-C (Uppercase C.) Prevent existing files from being overwritten by

the shell's '>' redirection operator (see Redirecting Output );
the ">|" redirection operator shall override this noclobber option for an individual file.

-e When this option is on, if a simple command fails for any of the

reasons listed in Consequences of Shell Errors or returns an exit status value >0, and is not part of the compound list following a while, until, or if keyword, and is not a part of an AND or OR list, and is not a pipeline preceded by the ! reserved word, then the shell shall immediately exit.

-f The shell shall disable pathname expansion.

-h Locate and remember utilities invoked by functions as those

functions are defined (the utilities are normally located when the function is executed).

-m This option shall be supported if the implementation supports

the User Portability Utilities option. All jobs shall be run in their own process groups. Immediately before the shell issues a prompt after completion of the background job, a message reporting the exit status of the background job shall be written to standard error. If a foreground job stops, the shell shall write a message to standard error to that effect, formatted as described by the jobs utility. In addition, if a job changes status other than exiting (for example, if it stops for input or output or is stopped by a SIGSTOP signal), the shell shall write a similar message immediately prior to writing the next prompt. This option is enabled by default for interactive shells.

-n The shell shall read commands but does not execute them; this

can be used to check for shell script syntax errors. An interactive shell may ignore this option.

-o Write the current settings of the options to standard output in

an unspecified format.

+o Write the current option settings to standard output in a format

that is suitable for reinput to the shell as commands that achieve the same options settings.

-o option

This option is supported if the system supports the User Portability Utilities option. It shall set various options, many of which shall be equivalent to the single option letters. The following values of option shall be supported:

allexport

Equivalent to -a.

errexit

Equivalent to -e.

ignoreeof

Prevent an interactive shell from exiting on end-of-file. This setting prevents accidental logouts when <control>-D is entered. A user shall explicitly exit to leave the interactive shell.

monitor

Equivalent to -m. This option is supported if the system supports the User Portability Utilities option.

noclobber

Equivalent to -C (uppercase C).

noglob

Equivalent to -f.

noexec

Equivalent to -n.

nolog

Prevent the entry of function definitions into the command history; see Command History List .

notify

Equivalent to -b.

nounset

Equivalent to -u.

verbose

Equivalent to -v.

vi

Allow shell command line editing using the built-in vi editor. Enabling vi mode shall disable any other command line editing mode provided as an implementation extension.

It need not be possible to set vi mode on for certain block-mode terminals.

xtrace

Equivalent to -x.

-u The shell shall write a message to standard error when it tries

to expand a variable that is not set and immediately exit. An interactive shell shall not exit.

-v The shell shall write its input to standard error as it is read.

-x The shell shall write to standard error a trace for each command

after it expands the command and before it executes it. It is unspecified whether the command that turns tracing off is traced.

The default for all these options shall be off (unset) unless stated otherwise in the description of the option or unless the shell was invoked with them on; see sh.

The remaining arguments shall be assigned in order to the positional parameters. The special parameter '#' shall be set to reflect the number of positional parameters. All positional parameters shall be unset before any new values are assigned.

The special argument "--" immediately following the set command name can be used to delimit the arguments if the first argument begins with '+' or '-' , or to prevent inadvertent listing of all shell variables when there are no arguments. The command set -- without argument shall unset all positional parameters and set the special parameter '#' to zero.

OPTIONS

See the DESCRIPTION.

OPERANDS

See the DESCRIPTION.

STDIN

Not used.

INPUT FILES

None.

ENVIRONMENT VARIABLES

None.

ASYNCHRONOUS EVENTS

Default.

STDOUT

See the DESCRIPTION.

STDERR

The standard error shall be used only for diagnostic messages.

OUTPUT FILES

None.

EXTENDED DESCRIPTION

None.

EXIT STATUS

Zero.

CONSEQUENCES OF ERRORS

Default.

The following sections are informative.

APPLICATION USAGE

None.

EXAMPLES

Write out all variables and their values:

set

Set $1, $2, and $3 and set "$#" to 3:

set c a b

Turn on the -x and -v options:

set -xv

Unset all positional parameters:

set -

Set $1 to the value of x, even if it begins with '-' or '+' :

set -- "$x"

Set the positional parameters to the expansion of x, even if x expands with a leading '-' or '+' :

set -- $x