osx man page for pid

pid(n)							       Tcl Built-In Commands							    pid(n)

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NAME
       pid - Retrieve process identifiers

SYNOPSIS
       pid ?fileId?
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DESCRIPTION
       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 identi-
       fier of the current process.  All process identifiers are returned as decimal strings.

EXAMPLE
       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

SEE ALSO
       exec(n), open(n)

KEYWORDS
       file, pipeline, process identifier

Tcl									7.0								    pid(n)