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Re: Re: Re: match and regex

by Shendal (Hermit)
on Aug 13, 2002 at 19:47 UTC ( #189931=note: print w/replies, xml ) Need Help??


in reply to Re: Re: match and regex
in thread match and regex

I could, but I think that perldoc perlre can give a better explanation:
(?!pattern) A zero-width negative lookahead assertion. For example /foo(?!bar)/ matches any occurrence of "foo" that isn't followed by "bar". Note however that lookahead and lookbehind are NOT the same thing. You cannot use this for lookbehind. If you are looking for a "bar" that isn't preceded by a "foo", /(?!foo)bar/ will not do what you want. That's because the (?!foo) is just saying that the next thing cannot be "foo"--and it's not, it's a "bar", so "foobar" will match. You would have to do something like /(?!foo)...bar/ for that. We say "like" because there's the case of your "bar" not having three characters before it. You could cover that this way: /(?:(?!foo)...|^.{0,2})bar/. Sometimes it's still easier just to say: if (/bar/ && $` !~ /foo$/)
Cheers,
Shendal

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