unset(1p) — Linux manual page
UNSET(1P) POSIX Programmer's Manual UNSET(1P)
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NAME
unset — unset values and attributes of variables and functions
SYNOPSIS
unset [-fv] name...
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 POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
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 Section 2.5.2, Special Parameters).
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
Section 2.14, Special Built-In Utilities
The Base Definitions volume of POSIX.1‐2017, Section 12.2,
Utility Syntax Guidelines
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any
discrepancy between this version and the original IEEE and The
Open Group Standard, the original IEEE and The Open Group
Standard is the referee document. The original Standard can be
obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .