Re: A Regex simple Question

Your regex says "an a, followed by arbitrary characters, followed by arbitrary characters that don't start with ab, then a b".

This means that the (?!ab) will always find a position where the next position is not ab.

Knowing this, the solution is not so hard:

/^a(?!.*ab).*b$/

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Re^2: A Regex simple Question by ikegami (Patriarch) on Sep 06, 2007 at 16:11 UTC
That will fail (false negative) for `a000ab`.	[reply] [d/l]
Re^3: A Regex simple Question by moritz (Cardinal) on Sep 06, 2007 at 16:36 UTC
You are right. That can easily be ammended by changing it to `/^a(?!.ab.).b$/`. Regexes are hard, sometimes. Especially corner cases ;) Perl 6 in German	[reply] [d/l]