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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
   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 4.09 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/.



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