clearenv

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 §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 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 variables.

       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 5.09 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)