CLEARENV(3)		   Linux Programmer's Manual		   CLEARENV(3)



NAME
       clearenv - clear the environment

SYNOPSIS
       #include <stdlib.h>

       int clearenv(void);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       clearenv():
	   /* Glibc since 2.19: */ _DEFAULT_SOURCE
	       || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

DESCRIPTION
       The  clearenv() function clears the environment of all name-value pairs
       and sets the value of the external variable  environ  to	 NULL.	 After
       this  call,  new	 variables  can	 be  added  to	the  environment using
       putenv(3) and setenv(3).

RETURN VALUE
       The clearenv() function returns zero on success, and a nonzero value on
       failure.

VERSIONS
       Available since glibc 2.0.

ATTRIBUTES
       For   an	  explanation	of   the  terms	 used  in  this	 section,  see
       attributes(7).

       +-----------+---------------+---------------------+
       |Interface  | Attribute	   | Value		 |
       +-----------+---------------+---------------------+
       |clearenv() | Thread safety | MT-Unsafe const:env |
       +-----------+---------------+---------------------+

CONFORMING TO
       Various UNIX variants (DG/UX, HP-UX, QNX, ...).	POSIX.9 (bindings  for
       FORTRAN77).   POSIX.1-1996 did not accept clearenv() and putenv(3), but
       changed its mind and scheduled these functions for some later issue  of
       this   standard	 (cf.	B.4.6.1).   However,  POSIX.1-2001  adds  only
       putenv(3), and rejected clearenv().

NOTES
       On systems where clearenv() is unavailable, the assignment

	   environ = NULL;

       will probably do.

       The clearenv() function may be useful  in  security-conscious  applica-
       tions  that want to precisely control the environment that is passed to
       programs executed using exec(3).	 The  application  would  do  this  by
       first clearing the environment and then adding select environment vari-
       ables.

       Note that the main effect of clearenv() is to adjust the value  of  the
       pointer	environ(7);  this  function does not erase the contents of the
       buffers containing the environment definitions.

       The DG/UX and Tru64 man pages write: If environ has  been  modified  by
       anything	 other than the putenv(3), getenv(3), or clearenv() functions,
       then clearenv() will return an error and the process  environment  will
       remain unchanged.

SEE ALSO
       getenv(3), putenv(3), setenv(3), unsetenv(3), environ(7)

COLOPHON
       This  page  is  part of release 4.10 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest	  version     of     this    page,    can    be	   found    at
       https://www.kernel.org/doc/man-pages/.



Linux				  2016-03-15			   CLEARENV(3)