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 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/.