Hmmm... the previous link (below) seems dead. This is the best page i can find for a Tcl ping how-to. Feel free to improve on it.
Stevenaaus
Ping with TCL and multihomed router for quality measurement http://andreystein.blogspot.com/2013/04/ping-with-tcl-and-multihomed-router-for.html Andrew Shtein
Here [L1 ] is a pleasant reminiscence on the original ping.