Question

I am attempting to configure a regular expression that matches anything numerical value but 1211 so it will still match variations such as 1212 121 1122, 3411, etc

I am unable to test the below at http://regexpal.com/ as it does not seem to support ?

(1(?!2)|1(?!2)|(?<!1)2|(?<!2)1|[^1211])+|[0-9]{1,4})

Am I doing it right and also where can I test it?

EDIT

Please note that I need to implement in a rewrite module/filter.

Answer 1

You can simplify that regex a lot:

^(?!1211)[1-9]\d{0,3}$

As for regexpal, it’s not working because your regex is invalid. You can tell right away because it as one more closing parenthesis than opening.