pid - Retrieve process identifiers

       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 elements 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  is  not a process pipeline.  If no fileId argument is given then pid returns the process identifier
       of the current process.  All process identifiers are returned as decimal strings.

       Print process information about the processes in a pipeline using the SysV ps program before reading  the
       output of that pipeline:

              set pipeline [open "| zcat somefile.gz | grep foobar | sort -u"]
              # Print process information
              exec ps -fp [pid $pipeline] >@stdout
              # Print a separator and then the output of the pipeline
              puts [string repeat - 70]
              puts [read $pipeline]
              close $pipeline

       file, pipeline, process identifier

Tcl                                                    7.0                                             pid(3tcl)

       pid - Retrieve process identifiers

exec(3tcl), open(3tcl)

pid ?fileId?
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