Question

Is it possible to ignore a specific match in a regular expression?

For example:

I have the following regular expression:

^[0-9]{2}$

But I don’t want to match a specific string, let’s say “12”.

I think I’m looking for something like an and operator for regular expressions, but haven’t been able to find anything like this in .NET / C#.

I would prefer to do this in the regular expression itself.
Any advice or suggestion?

Answer 1

^[0-9]{2}(?<!12)$

Or the reverse:

^(?!12)[0-9]{2}$

Note that in this specific case, negating 1 specific match was easy. Sometimes it isn’t, an sometimes it’s (nigh) impossible, depends on the regex.