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       putenv - change or add an environment variable


       #include <stdlib.h>

       int putenv(char *string);

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

       putenv(): _SVID_SOURCE || _XOPEN_SOURCE


       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.


       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.


       ENOMEM Insufficient space to allocate new environment.


       SVr4, POSIX.1-2001, 4.3BSD.


       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.


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


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