[Richard Suchenwirth] 2002-08-16 - This little script checks periodically for the existance of a file at well-specified location ("todo"), and if it exists, 
   * executes it in a sh (hence Unix only, for now)
   * deletes it
   * writes the result to another file ("done")
Very simple, but seems to work also with non-trivial tasks...

 proc every {ms body} {eval $body; after $ms [info level 0]}

 set filename /home/suchenwi/todo
 every 5000 {
	if [file exists $::filename] {
		catch {exec sh $::filename} res
		set fp [open /home/suchenwi/done w]
		puts $fp $res
		close $fp
		file delete $::filename
	}
 }

To feed this demon, I only have to type at the shell prompt
  echo "grep fff t" > ~/todo   
and 5 sec or so later, the file ~/done contains the result of this demonery...
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[Arts and crafts of Tcl-Tk programming]