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man: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  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 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 4.16 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)

/data/webs/external/dokuwiki/data/pages/man/clearenv.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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