From: Justin Collins <justincollins@...>
Date: 2009-06-23T17:11:05+09:00
Subject: Re: how to extract domain name without sub domain from url

Chem Leakhina wrote:
> Hi everyone,
>
> Does anyone know how to extract domain name without sub domain from url?
>
> Example: http://test.domain.com => http://domain.com
>
> Please give me an example code in ruby.
>
> Thanks,
> Leakhina
>   

This is actually quite difficult, because there is a multitude of 
possible second-level domains which can be used (such as .co.uk), and 
they are not really standardized. Just picking one at random, the 
country of Jordan has .com.jo, .net.jo, .gov.jo, .edu.jo, .org.jo, 
.mil.jo, .name.jo, and .sch.jo.

If one were to ignore such things, then it becomes easier:

$ irb
irb(main):001:0> require 'uri'
=> true
irb(main):002:0> u = URI.parse "http://test.domain.com/"
=> #<URI::HTTP:0xb7bbf848 URL:http://test.domain.com/>
irb(main):003:0> u.host
=> "test.domain.com"
irb(main):004:0> u.host.split(".")[-2,2]
=> ["domain", "com"]
irb(main):005:0> u.host.split(".")[-2,2].join(".")
=> "domain.com"


However, as mentioned above, there are a lot of domains this will not 
work for.

-Justin