The Perl Cookbook covers the problem of watching a constantly growing file.

Their suggested solution is along the lines of:

(re-constructed from memory and some of my scripts)

open (FH, "filename") or die "Unable to open file: $!";
$DELAY = 5;

for(;;) {

  while(<FH>) {
     #do stuff here
  }
  sleep $DELAY
  seek(FH, 0, 1);
}
[download]

The PCB also mentions that IO::Handle but I don't have an example of that quickly availible.

I'll leave the display portion for you or another monk as I don't have any TK experience.

Update: Added the seek line that should have always been there...not sure how I missed it in preview.