module ActionDispatch::Http::URL

def subdomain(tld_length = @@tld_length)

in "www.rubyonrails.co.uk".
such as 2 to catch "www" instead of "www.rubyonrails"
returned for "dev.www.rubyonrails.org". You can specify a different tld_length,
Returns all the \subdomains as a string, so "dev.www" would be 
def subdomain(tld_length = @@tld_length)
  ActionDispatch::Http::URL.extract_subdomain(host, tld_length)
end