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 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 previous array was also allocated by putenv(), then it will be freed.  In no case
       will the old storage associated to the environment 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  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
       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 3.54 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/.