From: Robert Klemme <shortcutter@...>
Date: 2009-06-23T18:11:25+09:00
Subject: Re: how to extract domain name without sub domain from url

2009/6/23 Justin Collins <justincollins@ucla.edu>:
> 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.

We can get better results by ignoring particular known domain prefixes
such as "ftp" and "www":

# this works with 1.8 and 1.9
%w{
  www.google.com
  google.co.uk
  www.google.co.uk
  foo.bar
  }.each do |domain|
  dom = domain.sub(/^(?:www|ftp)\./, '')[/^[^.]+/]
  printf "%p -> %p\n", domain, dom
  # alternative
  dom = domain[/^(?:(?:ftp|www)\.)?([^.]+)/, 1]
  printf "%p -> %p\n", domain, dom
end

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
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