Description

   The putenv function sets the value of an environment variable
   by altering an existing variable or by creating a new one. The
   string argument points to a string of the form name=value, where
   name is the environment variable and value is the new value for
   it.

   The string pointed to by string becomes part of the environment,
   so altering the string changes the environment. When a new
   string-defining name is passed to putenv, the space used by
   string is no longer used.

                                 NOTES

      o  The putenv function manipulates the environment pointed
         to by the environ external variable, and can be used with
         getenv. However, the third argument to the main function
         (the environment pointer), is not changed.

         The putenv function uses the malloc function to enlarge
         the environment.

         A potential error is to call putenv with an automatic
         variable as the argument, then exit the calling function
         while string is still part of the environment.

      o  Do not use the setenv, getenv, and putenv functions
         to manipulate symbols and logicals. Instead, use the
         OpenVMS library calls lib$set_logical, lib$get_logical,
         lib$set_symbol, and lib$get_symbol. The *env functions
         deliberately provide UNIX behavior, and are not a
         substitute for these OpenVMS runtime library calls.

         OpenVMS DCL symbols, not logical names, are the closest
         analog to environment variables on UNIX systems. While
         getenv is a mechanism to retrieve either a logical name
         or a symbol, it maintains an internal cache of values for
         use with setenv and subsequent getenv calls. The setenv
         function does not write or create DCL symbols or OpenVMS
         logical names.

         This is consistent with UNIX behavior. On UNIX systems,
         setenv does not change or create any symbols that will be
         visible in the shell after the program exits.