pid - Retrieve process id(s)
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