UNSETENV(3P)                                        POSIX Programmer's Manual                                       UNSETENV(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       unsetenv - remove an environment variable

SYNOPSIS
       #include <stdlib.h>

       int unsetenv(const char *name);


DESCRIPTION
       The  unsetenv() function shall remove an environment variable from the environment of the calling process. The name argu-
       ment points to a string, which is the name of the variable to be removed. The named argument shall  not  contain  an  '='
       character.  If  the  named variable does not exist in the current environment, the environment shall be unchanged and the
       function is considered to have completed successfully.

       If the application modifies environ or the pointers to which it points, the behavior of  unsetenv()  is  undefined.   The
       unsetenv() function shall update the list of pointers to which environ points.

       The  unsetenv()  function  need  not  be reentrant. A function that is not required to be reentrant is not required to be
       thread-safe.

RETURN VALUE
       Upon successful completion, zero shall be returned. Otherwise, -1 shall be returned, errno set to indicate the error, and
       the environment shall be unchanged.

ERRORS
       The unsetenv() function shall fail if:

       EINVAL The name argument is a null pointer, points to an empty string, or points to a string containing an '=' character.


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       Refer to the RATIONALE section in setenv().

FUTURE DIRECTIONS
       None.

SEE ALSO
       getenv(), setenv(), the Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h>, <sys/types.h>, <unistd.h>

COPYRIGHT
       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,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                  UNSETENV(3P)