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UNSET(1P) POSIX Programmer's Manual UNSET(1P)
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.
unset — unset values and attributes of variables and functions
unset [−fv] name...
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 "". Also, the variables that can be unset should not be
misinterpreted to include the special parameters (see Section 2.5.2,
Special Parameters).
See the DESCRIPTION.
See the DESCRIPTION.
Not used.
None.
None.
Default.
Not used.
The standard error shall be used only for diagnostic messages.
None.
None.
0 All name operands were successfully unset.
>0 At least one name could not be unset.
Default.
The following sections are informative.
None.
Unset VISUAL variable:
unset −v VISUAL
Unset the functions foo and bar:
unset −f foo bar
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.
None.
Section 2.14, Special Built-In Utilities
The Base Definitions volume of POSIX.1‐2008, Section 12.2, Utility
Syntax Guidelines
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 .
IEEE/The Open Group 2013 UNSET(1P)