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



NAME
       putenv - change or add an environment variable

SYNOPSIS
       #include <stdlib.h>

       int putenv(char *string);

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

       putenv(): _SVID_SOURCE || _XOPEN_SOURCE

DESCRIPTION
       The  putenv()  function  adds or changes the value of environment variables.  The argument
       string is of the form name=value.  If name does not already exist in the environment, then
       string  is  added  to  the environment.  If name does exist, then the value of name in the
       environment is changed to value.  The string pointed to by  string  becomes  part  of  the
       environment, so altering the string changes the environment.

RETURN VALUE
       The  putenv()  function  returns  zero  on success, or nonzero if an error occurs.  In the
       event of an error, errno is set to indicate the cause.

ERRORS
       ENOMEM Insufficient space to allocate new environment.

CONFORMING TO
       SVr4, POSIX.1-2001, 4.3BSD.

NOTES
       The putenv() function is not required to be reentrant, and the one in glibc  2.0  is  not,
       but the glibc 2.1 version is.

       Since  version 2.1.2, the glibc implementation conforms to SUSv2: the pointer string given
       to putenv() is used.  In particular, this string becomes part of the environment; changing
       it  later  will change the environment.  (Thus, it is an error is to call putenv() with an
       automatic variable as the argument, then return from the calling function while string  is
       still  part  of  the environment.)  However, glibc versions 2.0 to 2.1.1 differ: a copy of
       the string is used.  On the one hand this causes a memory leak, and on the other  hand  it
       violates SUSv2.

       The 4.4BSD version, like glibc 2.0, uses a copy.

       SUSv2 removes the const from the prototype, and so does glibc 2.1.3.

SEE ALSO
       clearenv(3), getenv(3), setenv(3), unsetenv(3), environ(7)

COLOPHON
       This  page  is  part of release 3.74 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 http://www.kernel.org/doc/man-pages/.



GNU                                         2014-08-19                                  PUTENV(3)