Regular expression to find and replace @ mentions like twitter

Question

I am developing a PHP application which needs a regular expression to replace the @ mentions like twitter. Also the regular expression should satisfy the following needs.

Answer 1

Wow. I found the answer myself guys.

$tweet = preg_replace('/(^|[^a-z0-9_])@([a-z0-9_]+)/i', '$1@$2', $tweet);

Thanks for your help guys.