Just got bit today (at least for a while) by this: 
# prints "xxx_", instead of "xxx"
print '__xxx__' =~ /\b_+(\w+)_+\b/ ? "$1\n" : "no match\n";

[download]
I've since figured it out, but since it was so much fun, I'll leave the answer for you to figure out :)

-QM
--
Quantum Mechanics: The dreams stuff is made of

In reply to Regex puzzle for you by QM

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