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UNSET(1P)                  POSIX Programmer's Manual                 UNSET(1P)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (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 environ-
       ment. 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  develop-
       ers decided to retain historical practice.

       The  -v  option  was  introduced because System V historically used one name space for both variables and func-
       tions. 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, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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 Stan-
       dard, 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(1P)