Argument

context-symbol

   Specifies a symbol that DCL uses to store a pointer into the
   system's list of processes. The F$PID function uses this pointer
   to return a PID.

   Specify the context symbol by using a symbol. The first time you
   use the F$PID function in a command procedure, you should use
   a symbol that is either undefined or equated to the null string
   ("") or a context symbol that has been created by the F$CONTEXT
   function.

   If the context symbol is undefined or equated to a null string,
   the F$PID function returns the first PID in the system's process
   list that it has the privilege to access. That is, if you have
   GROUP privilege and if the context symbol is null or undefined,
   the F$PID function returns the PID of the first process in your
   group. If you have WORLD privilege, the F$PID function returns
   the PID of the first process in the list. If you have neither
   GROUP nor WORLD privilege, the F$PID returns the first process
   that you own. Subsequent calls to F$PID return the rest of the
   processes on the system you are accessing.

   If the context symbol has been created by the F$CONTEXT function,
   the F$PID function returns the first process name in the
   system's process list that fits the criteria specified in the
   F$CONTEXT calls. Subsequent calls to F$PID return only the PIDs
   of those processes that meet the selection criteria set up by
   the F$CONTEXT function and that are accessible to your current
   privileges.