I had a tough time reproducing it in Perl, although I think I managed to get it.

  % perl -v
  This is perl 5, version 18, subversion 2 (v5.18.2) built for x86_64-linux-gnu-thread-multi
  % ls -l testfile
  125380092 Jul 20 16:41 testfile
  % time ./regextest testfile
  ./regextest testfile  0.36s user 0.03s system 99% cpu 0.398 total
  (Remove the a at the end)
  % time ./regextest testfile
  ./regextest testfile  0.13s user 0.03s system 99% cpu 0.156 total

I had to make a much larger input file than I expected before I was able to really see the difference. Given the O(n^2) nature of the bug, I was expecting it to take much longer.