As fuel for the fire, here's a regex that does match against itself, and only a small number of other cases besides itself. I know it doesn't satisify the "only itself" bit, but it could help get others thinking in the right direction: 

#Note that even with single quotes, '\\' is 
#interpolated to '\'; this doesn't break the regex, 
#as both sides of =~ will see only '\'.

$regex = '^[24\\\\\[\]\{\}\^\$]{24}$';

$text = '2' x 24; # will also match, for example.

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Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain

In reply to Re: japhy has met his match by Masem
in thread japhy has met his match by japhy

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