Regular expression to match (, but not \(

Question

I am trying to create a regular expression to match every ( and ) in a string, but exclude \( and \). This is so that I can replace every parentheses but keep the ones with the slash in front of them.

Example String: (,)(5)(5)( )(\()(9)(1)(87x)(100 )(ASP\)( )(5)

Edit: Desired Result after replace: ,55 \(9187x100 ASP\) 5 Then i can remove the \ and get my desired string ,55 (9187x100 ASP) 5

Edit: I am using VB.NET

What language are you using? Some languages will allow you to use a [lookbehind](http://stackoverflow.com/a/546265/1721527) or [lookahead](http://stackoverflow.com/q/9440084/1721527). — Joshua Dwire, Mar 06 '13 at 22:53

score 2 · Answer 1 · answered Mar 06 '13 at 22:51

2

This will match parenthesis without slashes in front of them (and the character before them):

[^\\]\(

answered Mar 06 '13 at 22:51

alestanis

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This would fail to match an open parenthesis at the beginning of a string, as he has in his example. – Kevin Richardson Mar 06 '13 at 23:25

wsdookadr · Answer 2 · 2013-03-06T22:58:45.060

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Well, you have to take context into account. So first you want to not have a \ and then you want a ( or a ).

[^\\]\(
[^\\]\)

But you can put both paranthesis in a character class

[^\\][\)\(]

edited Mar 06 '13 at 22:58

answered Mar 06 '13 at 22:51

wsdookadr

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score 0 · Accepted Answer · answered Mar 06 '13 at 23:18

0

Using a look-behind you can match only "(" or ")" that are not immediately proceeded by a "\":

/(?<!\\)[\(\)]/

answered Mar 06 '13 at 23:18

Daedalus

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Does using a look-behind offer an advantage over a negated character class ? – wsdookadr Mar 06 '13 at 23:43
A look-behind doesn't consume a character, so you don't have the issue of matching more than you want to replace. – Daedalus Mar 07 '13 at 00:06

Regular expression to match (, but not \(

3 Answers3