UNSET(1P) POSIX Programmer's Manual UNSET(1P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
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NAMEunset — unset values and attributes of variables and functions
SYNOPSISunset [−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 func‐
tion 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.1‐2008, 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 misin‐
terpreted 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 his‐
torical 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.1‐2008, Section 12.2, Utility Syn‐
tax Guidelines
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 UNSET(1P)
