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.

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 libc4, libc5 and glibc 2.0 is not,  but  the  glibc
       2.1 version is.

       Description  for  libc4, libc5, glibc: If the argument string is of the form name, and does not contain an '=' character,
       then the variable name is removed from the environment.  If putenv() has to allocate a new array environ, and the  previ-
       ous array was also allocated by putenv(), then it will be freed.  In no case will the old storage associated to the envi-
       ronment variable itself be freed.

       The libc4 and libc5 and glibc 2.1.2 versions conform to SUSv2: the pointer string given to putenv() is used.  In particu-
       lar,  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 2.0-2.1.1 differs: a copy of the string is used.  On the one hand this
       causes a memory leak, and on the other hand it violates SUSv2.  This has been fixed in glibc 2.1.2.

       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 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



GNU                                                        2007-07-26                                                  PUTENV(3)