pid - Retrieve process id(s)


       pid ?fileId?


       If  the  fileId  argument is given then it should normally
       refer to a process pipeline created with the open command.
       In this case the pid command will return a list whose ele-
       ments are the process identifiers of all the processes  in
       the  pipeline, in order.  The list will be empty if fileId
       refers to an open file that isn't a process pipeline.   If
       no  fileId  argument is given then pid returns the process
       identifier of the current process.   All  process  identi-
       fiers are returned as decimal strings.


       file, pipeline, process identifier