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 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).

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 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.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Section 2.14, Special Built-In Utilities

       The Base Definitions volume of POSIX.1‐2008, Section 12.2, Utility Syntax 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 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 .