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 (see SB.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 applications 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 4.15 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                                                               2017-09-15                                                         CLEARENV(3)