Regex to extract subdomain from URL?

Question

I have a bunch of domain names coming in like this:

http://subdomain.example.com (example.com is always example.com, but the subdomain varies).

I need \"subd

Answer 1

Purely the subdomain string (result is $1):

^http://([^.]+)\.domain\.com

Making http:// optional (result is $2):

^(http://)?([^.]+)\.domain\.com

Making the http:// and the subdomain optional (result is $3):

(http://)?(([^.]+)\.)?domain\.com