/sys$common/syshlp/helplib.hlb CC, Run-time functions, setenv  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Inserts or resets the environment variable name in the current
  environment list.

  Syntax:

        #include <stdlib.h>

        int setenv (const char *name,
                    const char *value,
                    int overwrite);