UNSET
Section: POSIX Programmer's Manual (1P)
Updated: 2013
Index
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PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
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.1-2008,
Section 12.2,
Utility Syntax Guidelines.
Note that:
-
VARIABLE=
is not equivalent to an
unset
of
VARIABLE;
in the example,
VARIABLE
is set to
dqdq.
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.1-2008,
Section 12.2,
Utility Syntax 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
Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- OPERANDS
-
- STDIN
-
- INPUT FILES
-
- ENVIRONMENT VARIABLES
-
- ASYNCHRONOUS EVENTS
-
- STDOUT
-
- STDERR
-
- OUTPUT FILES
-
- EXTENDED DESCRIPTION
-
- EXIT STATUS
-
- CONSEQUENCES OF ERRORS
-
- APPLICATION USAGE
-
- EXAMPLES
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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