UNSET(P) POSIX Programmer's Manual UNSET(P)
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 defi-
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.
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 param-
eters (see Special Parameters ).
See the DESCRIPTION.
See the DESCRIPTION.
The standard error shall be used only for diagnostic messages.
0 All name operands were successfully unset.
>0 At least one name could not be unset.
CONSEQUENCES OF ERRORS
The following sections are informative.
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.
Special Built-In Utilities
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 UNSET(P)