/sys$common/syshlp/helplib.hlb Lexicals, F$PID, Example  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  $ CONTEXT = ""
  $ START:
  $     PID = F$PID(CONTEXT)
  $     IF PID .EQS. "" THEN EXIT
  $     SHOW SYMBOL PID
  $     GOTO START

      This command procedure uses the F$PID function to display a
      list of PIDs. The assignment statement declares the symbol
      CONTEXT, which is used as the context-symbol argument for the
      F$PID function. Because CONTEXT is equated to a null string,
      the F$PID function returns the first PID in the process list
      that it has the privilege to access.

      The PIDs displayed by this command procedure depend on the
      privilege of your process. When run with GROUP privilege, the
      PIDs of users in your group are displayed. When run with WORLD
      privilege, the PIDs of all users on the system are displayed.
      Without GROUP or WORLD privilege, only those processes that you
      own are displayed.