linux man page for unset

UNSET(P)						     POSIX Programmer's Manual							  UNSET(P)

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  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 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 mis-
       interpreted 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 histori-
       cal 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 Technol-
       ogy -- 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 .

IEEE
/The Open Group						       2003								  UNSET(P)