How to extract user from regex in search?

Hello folks, 

I am attempting to extract data for users who have browsed torrents. I've applied a regex query to match users, but it's returning all users instead of only those matching the regex.

Here is a query : "user"=* application=bittorrent | process regex("^"a-zA-Z]\.\a-zA-Z]+\d*\.\d{2}$",user ) 

If anyone know what I am missing, love to hear. 

Thanks