Using_SYS$COMMAND

   The SYS$COMMAND of a subprocess is normally the same as its
   SYS$INPUT (if no command procedures are involved). In a
   pipeline, however, the SYS$COMMAND of a subprocess is set to
   the SYS$COMMAND of the parent process instead of to the preceding
   pipe (which is the SYS$INPUT of the pipeline-segment command).