Question

I try to find string that doesn’t contains the same substring. This is my code:

var regex = new Regex(@"aaa(?!.*aaa).*aaa");
var str1 = @"aaa aaa aaa";
var match = regex.Match(str1); // no
var str1 = @"aaa bbb aaa";
var match = regex.Match(str1); // yes

But this code doesn’t work… What I do wrong?

Thanks!

Answer 1

You want an expression like this:

aaa(?:(?!aaa).)*aaa

(?:(?!aaa).)* matches strings that do not contain aaa (in whole or part).

You could also write it like this:

aaa(?:[^a]+|a(?!aa))*aaa