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This regex matches and shouldn't. Why is it?

Answer 1

+9 A:

"google" might not fit in [a-z]{2}, but it does fit in [a-z]{2}([a-zA-Z0-9\?\=\&\%\/]*)? - you forgot to require a / after the TLD if the URL extends beyond the domain. So it's interpreting it with "www.go" as the domain and then "ogle" following it, with no slash in between. You can fix it by adding a [?/] to the front of that last group to require one of those two symbols between the TLD and any further portion of the URL.

Amber 2009-10-27 09:09:43

tsilb 2009-10-27 09:20:09

@tslib: it is as in fact not a valid url.

Residuum 2009-10-27 09:46:25

@Residuum: Then why does C#'s Request.Querystring[] pick it up? :)

tsilb 2009-10-27 09:58:03

@tsilb: Your example is in fact a valid URL. There was a question regarding that exact case here on SO a few days ago, but since it's essentially impossible to search for "com?" I'm afraid I can't find a link to it.

Greg Hewgill 2009-10-27 10:18:56

tsilb: there's a reason why I recommended adding `[?/]` and not just `/` - because either would be valid.

Amber 2009-10-28 02:01:52

Answer 2

+2 A:

Your TLD clause matches "go" in google and the querystring support part matches "ogle" afterwards. Try changing the querystring part to this:

([?/][a-zA-Z0-9\?\=\&\%\/]*)?

Kaivosukeltaja 2009-10-27 09:12:19

Bah, that's right, when I removed the specifically-formatted querystring stuff (Failures, figured I'd fix it after the rest of it works), I forgot it no longer delimits on the question mark!

tsilb 2009-10-27 09:16:18

Answer 3

+2 A:

google" doesn't fit into the "[a-z]{2}" clause.

But "go" does and then "ogle" matches "([a-zA-Z0-9\?\=\&\%\/]*)?"

AnthonyWJones 2009-10-27 09:14:02

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This regex matches and shouldn't. Why is it?

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