I tweaked it a bit, setting $depth to -1

Wouldn't your subroutine always return -1? Shouldn't your GetCallStackDepth look more like:

sub GetCallStackDepth {
  my $depth = 1; # 0 is this sub, why bother checking it?
  $depth++ while caller($depth);
  return $depth - 1;
}
[download]

Wouldn't your subroutine always return -1?

Duh. Yes, of course. Returning $depth - 1 is what I actually did, and on my way from the editor to here, I thought, "Hey, I can save a step by just initializing $depth to -1 to begin with!". And I wrote it down before I actually tried it.

Busted...

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A fair fight is a sign of poor planning.