Regex for string not containing multiple specific words

Question

I\'m trying to put together a regex to find when specific words don\'t exist in a string. Specifically, I want to know when \"trunk\", \"tags\" or \"branches\" does

Answer 1

Use a negative look-ahead that asserts the absence of any of the three words somewhere in the input:

^(?!.*(trunk|tags|branches)).*$

I also slightly rearranged your regex to correct minor errors.

Answer 2

Use a "standard" match and look for !IsMatch

var exp = new Regex(@"trunk|tags|branches");
var result = !exp.IsMatch("trunk/blah/blah");

Why persons love to make their life difficult?

Ah... And remember the ass principle! http://www.codinghorror.com/blog/2008/10/obscenity-filters-bad-idea-or-incredibly-intercoursing-bad-idea.html

So it would be better to write

var exp = new Regex(@"\b(trunk|tags|branches)\b");

But if you really need a negative lookahed expression, and keeping up with the ass principle

var exp = new Regex(@"^(?!.*\b(trunk|tags|branches)\b)";

Tester: http://gskinner.com/RegExr/?2uv1g

I'll note that if you are looking for full paths (words separated by / or \) then

var exp = new Regex(@"^(?!.*(^|\\|/)(trunk|tags|branches)(/|\\|$))";

Tester: http://gskinner.com/RegExr/?2uv1p