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UNSET
Section: POSIX Programmer's Manual (1P)
Updated: 2003
Index
Return to Main Contents
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 IEEE Std 1003.1-2001, 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 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
Special Built-In Utilities
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .
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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