Re^6: This regexp made simpler

I prefer a correct solution that contains some repetition to an incorrect solution any time. There are ways to make .*? work correctly, but ...

I agree that an incorrect solution doesn't make sense, but is it incorrect? .*?Zwould match the shortest possible sequence of characters up to, but not including, the letter Z. Could you give an example where this would fail?

--
Ronald Fischer <ynnor@mm.st>

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Re^7: This regexp made simpler by moritz (Cardinal) on Apr 26, 2010 at 11:36 UTC
I haven't really thought about whether the solutions with .? are actually incorrect, but most of them will almost certainly go wrong if you extend the regex latern on with something that might force backtracking on the preceeding construct. Example: `$ perl -wE 'say "yes" if "A BCZD ZA" =~ /^A(\s.?)?ZA/' yes` [download] Here I added an A to the end, which causes backtracking when there's no A after the first Z. Which in turn allows a match that was forbidden by your rules. (Update: This is a general problem when translating "may not occur inbetween" to "minimum match": it's only the same under certain very fixed conditions. You can "rescue" such a solution by putting it in `(?>...)` non-backtracking groups, but I still recommend against it). So maybe your example wasn't actually wrong (and I apologize for having called it so without any proof), but it's surely not very maintainable, because a very simple, innocent change can break it.	[reply] [d/l] [select]
Re^8: This regexp made simpler by rovf (Priest) on Apr 26, 2010 at 12:06 UTC
I see the problem. Thanks for pointing this out! -- Ronald Fischer <ynnor@mm.st>	[reply] [d/l]
Re^8: This regexp made simpler by rubasov (Friar) on Apr 26, 2010 at 14:31 UTC
To satisfy my curiosity I wrote the backtracking control version you mentioned and I was surprised how simple it is: `while (<DATA>) { print; s[ ^ (START) ( \| \s.? ) (END) (COMMIT) $ ] [ $1 . $2 . 'insert' . $3 ]ex; print; } __DATA__ STARTEND STARTENDEND START SOMETHING END STARTSOMETHINGEND START END START ENDEND STARTSTARTENDEND STARTSTART ENDEND` [download] For comparison here's the other form: `s[ ^ (START) ( \| \s (?:(?!END).)* ) (END) $ ] [ $1 . $2 . 'insert' . $3 ]ex;` [download]	[reply] [d/l] [select]