clearenv(3) — Linux manual page


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

NAME         top

       clearenv - clear the environment

SYNOPSIS         top

       #include <stdlib.h>

       int clearenv(void);

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

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

DESCRIPTION         top

       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         top

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

VERSIONS         top

       Available since glibc 2.0.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

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

CONFORMING TO         top

       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 §B.4.6.1).  However,
       POSIX.1-2001 adds only putenv(3), and rejected clearenv().

NOTES         top

       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

       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() func‐
       tions, then clearenv() will return an error and the process environ‐
       ment will remain unchanged.

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.08 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

Linux                            2017-09-15                      CLEARENV(3)

Pages that refer to this page: getenv(3)putenv(3)secure_getenv(3)setenv(3)unsetenv(3)environ(7)