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Re^3: Problem with regex is a bug? or my regex (updated)

by haukex (Bishop)
on Nov 20, 2021 at 14:45 UTC ( #11138980=note: print w/replies, xml ) Need Help??


in reply to Re^2: Problem with regex is a bug? or my regex (updated)
in thread Problem with regex is a bug? or my regex

Thanks for posting the details. Expect 1.21 is about ten years older than 1.35 (2007 vs 2017). Since I'm unable to reproduce your issue with Expect 1.35 on both versions of Perl, I am guessing that the issue lies with one of the bugs that was fixed in Expect over those 10 years. I'd say your best course of action is to upgrade the module.

Update: Sorry, I see now that you're getting your expected behavior on the older version of the module instead of the newer version. The Changelog does mention "Eliminate $` and $' from the code. part of (RT #61395) This fix might break some existing code n some extreme cases when the regex being matched has a lookbehind or a lookahead at the edges." which could potentially be a hint, but finding out if this actually is the issue will take a bit more digging.

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Re^4: Problem with regex is a bug? or my regex (updated)
by hanspr (Sexton) on Nov 20, 2021 at 15:05 UTC
    Strange, I can reproduce in my machine, I upgraded to 1.35 and now its broken.
    hans@hans-desktop ~ perl -MExpect -e 'print $Expect::VERSION ."\n";' 1.35 hans@hans-desktop ~ perl test.pl Match before : ####################################################### +#######################\r\n# This system is a restricted access syste +m. Match : # Match after : \r\n# If collected security information reveals possibl +e criminal activity that #\r\n# exceeds privileges, evidence of such + activity may be provided to the rele- #\r\n# vantauthorities for fur +ther action. By continuing past this point, you #\r\n# expressly cons +ent to this security monitoring. #\r\n################## +############################################################\r\n\r\nh +ostname: ~#

      I checked and can now confirm that the version where the behavior of your test script changes is Expect v1.26, which is where I quoted the Changelog entry from above. Specifically, it's commits 7ee4816 and d9e0365 that each change the behavior of your script.

      The problem actually turns out to be fairly simple: The position of a capturing group was changed. Previously, the module did /$pattern->[2]()/ where it now does /($pattern->[2])/, which changes the ordering of the capture groups and which breaks your \2 backreference. Change the backreference to \g-1 and your regex should work even on the newest version of Expect (at least my testing shows that it does).

        Thank you very much, it does work perfect.

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