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       putenv - change or add an environment variable


       #include <stdlib.h>

       int putenv(const char *string);


       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 -1 if an error occurs.


       ENOMEM Insufficient space to allocate new environment.


       The  putenv()  function  is  not required to be reentrant, and the one in libc4, libc5 and
       glibc2.0 is not, but the glibc2.1 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 glibc2.1.2.

       The BSD4.4 version, like glibc 2.0, uses a copy.

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


       SVID 3, POSIX, BSD 4.3


       getenv(3), setenv(3), unsetenv(3), environ(5)