NAME

unset — unset values and attributes of variables and functions

SYNOPSIS

DESCRIPTION

Each variable or function specified by name shall be unset.

If -v is specified, name refers to a variable name and the shell shall unset it and remove it from the environment. Read-only variables cannot be unset.

If -f is specified, name refers to a function and the shell shall unset the function definition.

If neither -f nor -v is specified, name refers to a variable; if a variable by that name does not exist, it is unspecified whether a function by that name, if any, shall be unset.

Unsetting a variable or function that was not previously set shall not be considered an error and does not cause the shell to abort.

The unset special built-in shall support the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), xbd_chap12(7).

Note that:

VARIABLE=

is not equivalent to an unset of VARIABLE; in the example, VARIABLE is set to "". Also, the variables that can be unset should not be misinterpreted to include the special parameters (see xcu_chap02(1)).

OPTIONS

See the DESCRIPTION.

OPERANDS

See the DESCRIPTION.

STDIN

Not used.

INPUT FILES

None.

ENVIRONMENT VARIABLES

None.

ASYNCHRONOUS EVENTS

Default.

STDOUT

Not used.

STDERR

The standard error shall be used only for diagnostic messages.

OUTPUT FILES

None.

EXTENDED DESCRIPTION

None.

EXIT STATUS

0

All name operands were successfully unset.

>0

At least one name could not be unset.

CONSEQUENCES OF ERRORS

Default.

The following sections are informative.

APPLICATION USAGE

None.

EXAMPLES

Unset VISUAL variable:

unset -v VISUAL

Unset the functions foo and bar:

unset -f foo bar

RATIONALE

Consideration was given to omitting the -f option in favor of an unfunction utility, but the standard developers decided to retain historical practice.

The -v option was introduced because System V historically used one name space for both variables and functions. When unset is used without options, System V historically unset either a function or a variable, and there was no confusion about which one was intended. A portable POSIX application can use unset without an option to unset a variable, but not a function; the -f option must be used.

FUTURE DIRECTIONS

None.

SEE ALSO

xcu_chap02(1)

CHANGE HISTORY

Issue 6

IEEE Std 1003.1-2001 (“POSIX.1”)/Cor 1-2002, item XCU/TC1/D6/5 is applied so that the reference page sections use terms as described in the Utility Description Defaults ( xcu_chap01(1)). No change in behavior is intended.

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