Description

   The system function spawns a subprocess and executes the command
   specified by string in that subprocess. The system function waits
   for the subprocess to complete before returning the subprocess
   status as the return value of the function.

   The subprocess is spawned within the system call by a call to
   vfork. Because of this, a call to system should not be made after
   a call to vfork and before the corresponding call to an exec
   function.

   For OpenVMS Version 7.0 and higher systems, if you include
   <stdlib.h> and compile with the _POSIX_EXIT feature-test macro
   set, then the system function returns the status as if it called
   waitpid to wait for the child. Therefore, use the WIFEXITED and
   WEXITSTATUS macros (described in the wait* routines) to retrieve
   the exit status in the range of 0 to 255.

   You set the _POSIX_EXIT feature-test macro by using /DEFINE=_
   POSIX_EXIT or #define _POSIX_EXIT at the top of your file, before
   any file inclusions.