module ActionDispatch::Http::URL

def subdomains(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 an array, so ["dev", "www"] would be 
def subdomains(tld_length = @@tld_length)
  ActionDispatch::Http::URL.extract_subdomains(host, tld_length)
end