#!/usr/bin/ruby -w
require 'socket'
require 'uri'
require 'net/http'
class Domain
	def read_file(dns_file,url)
		pra = URI(url)
		counter = 1
		file = File.new(dns_file, "r")
		while (line = file.gets)
			full_url = (line+"."+pra.host)
			puts(full_url)
			counter = counter + 1
		end
		file.close
	end
end

dns = Domain.new
dns.read_file("test.txt","http://example.com")

-----------
result
test
.example.com
mail
.example.com
cpanel
.example.com
file
.example.com
gallery
.example.com
one
.example.com