Updated 2012-12-01 04:47:19 by RLE

http://www.purl.org/tcl/home/man/tcl8.4/TclCmd/pid.htm
pid ?channel?

Returns the process ID of the current process, or the process IDs of the programs running in the pipeline (created by open) that channel “names”.

This command can be very useful when you have used open to open a pipeline command - you can then get the process id to do a kill, etc.