That's a great tool, and here's something I discovered by playing around. There's a difference between executing:
  perl -Mre=debug -le'"lahblahblahblah" =~ /(.?lah)$1{2}/'

[download]
and
  perl -Mre=debug -le'"lahblahblahblah" =~ /(.?lah)\1{2}/'

[download]

The first one matches on "lahblahblah", and the second one matches on "blahblahblah". Why do you suppose that is?

The debugging engine appears to see the $1 as an almost literal copy of the regexp in the brackets. Whereas the \1 seems to be looking for whatever was matched by the regexp in the brackets..

Update: Thanks to Aristotle for pointing out the error in the $1 interpretation.

In reply to Re^2: Regex, capturing variables vs. speed by monarch
in thread Regex, capturing variables vs. speed by albert

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