Regex username for codeigniter route

Question

I am trying to get my regex to not allow the following words:

• create
• Forum

I also would like to allow only 1 underscore..

Here is what I have so far:

$route['(^[A-Za-z][A-Za-z0-9]{3,20}+$)'] = "users/index";

Answer 1

Put the routes you don't want to match before that one (it will stop at the first matched route):

$route['create(/.*)?'] = "create$1";
$route['forum(/.*)?']  = "forum$1";
$route['(^[A-Za-z][A-Za-z0-9]{3,20}+$)'] = "users/index";

Answer 2

Hmm, this is the closest I can get:

^((?:(?!create|Forum)[A-Za-z0-9]){3,20})$

Example

Gotta leave now. Good luck with this!