Ruby DNS CNAME check

cname_check.rb

require 'resolv'

url = 'mail.bocistudio.com'
begin
  r = Resolv::DNS.open do |dns|
    dns.getresource(url, Resolv::DNS::Resource::IN::CNAME)
  end
  r.name.to_s # => return alias domain
rescue Resolv::ResolvError => e
  # handle error
end