Regex lookaround with special characters is invalid?

Question

I am trying this regex

(?<!(John|Joe)) (Taylor)

On this text John James Taylor

but I am getting "invalid pattern in lookbehind" here http://www.rubular.com/r/TjD2d4oG5z

I am trying to match "Taylor" that does not have John or Joe before it.

Any tips please?

Is your regex flavor accept variable length lookbehind? Most of them don't. — Toto, Sep 24 '12 at 09:58
Thanks! Just found out that variable length does not work in lookaround by this comment: http://stackoverflow.com/questions/3479131/problem-with-quantifiers-and-look-behind In addition both of the answers are working with the proposed changes, but not if I add sg like \w+ because that is a variable length quantifier as I understand now :). — giorgio79, Sep 24 '12 at 10:02

João Silva · Accepted Answer · 2012-09-24T10:01:16.430

3

Try the following:

(?<!(?:John|Joe)) (Taylor)

(?:) is a non-capturing group, which makes sense in a lookaround, since you are merely doing an assertion, not actually matching anything. Or just remove the capturing group all together, that is, (?<!John|Joe).

edited Sep 24 '12 at 10:01

answered Sep 24 '12 at 09:55

João Silva

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The non-capturing group is not necessary I think. – xdazz Sep 24 '12 at 10:00
@xdazz: It's not, yes. I was just trying to point out that using a capturing group was the reason why the original regex was invalid. – João Silva Sep 24 '12 at 10:01

score 2 · Answer 2 · answered Sep 24 '12 at 09:56

2

Try:

/(?<!John|Joe) (Taylor)/

answered Sep 24 '12 at 09:56

xdazz

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Regex lookaround with special characters is invalid?

2 Answers2