huschi.net

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 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 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
       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  misin-
       terpreted to include the special parameters (see Section 2.5.2, 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 his-
       torical 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
       Section 2.14, Special Built-In Utilities
       The Base Definitions volume of POSIX.1-2008, Section 12.2, Utility Syn-
       tax Guidelines
COPYRIGHT
       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 Electri-
       cal 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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                            UNSET(1P)