Can I use a regular expression to extract the domain from a URL? - ruby-on-rails

Question

Suppose I want to turn this :
http://en.wikipedia.org/wiki/Anarchy
into this :
en.wikipedia.org
or even better, this :
wikipedia.org
Is this even possible in regex?

Answer 1

Why use a regex when Ruby has a library for it? The URI library:
ruby-1.9.1-p378 > require 'uri'
=> true
ruby-1.9.1-p378 > uri = URI.parse("http://en.wikipedia.org/wiki/Anarchy")
=> #<URI::HTTP:0x000001010a2270 URL:http://en.wikipedia.org/wiki/Anarchy>
ruby-1.9.1-p378 > uri.host
=> "en.wikipedia.org"
ruby-1.9.1-p378 > uri.host.split('.')
=> ["en", "wikipedia", "org"]
Splitting the host is one way to separate the domains, but I'm not aware of a reliable way to get the base domain -- you can't just count, in the event of a URL like "http://somedomain.otherdomain.school.ac.uk" vs "www.google.com".

Answer 2

/http:\/\/([^\/]*).*/ will produce en.wikipedia.org from the string you provided.
/http:\/\/.{0,3}\.([^\/]*).*/ will produce wikipedia.org.

Answer 3

yes
Now I know you haven't asked for how, and you haven't specified a language, but I'll answer anyway... (note, this works for all language subsites, not just en.wikipedia...)
perl:
$url =~ s,http://[a-z]{2}\.(wikipedia\.org)/.*,$1,;
ruby:
url = url.sub(/http:\/\/[a-z]{2}\.(wikipedia\.org)\/.*/, '\1')
php:
$url = preg_replace('|http://[a-z]{2}.(wikipedia.org)/.*|, '$1', $url);
Of course, for this particular example, you don't even need a regex, just this will do:
url = 'wikipedia.org'
but I jest...
you probably want to handle any URL and pull out the domain part, and it should also work for domains in different countries, eg: foo.co.uk.
In which case, I'd use Mark Rushakoff's solution to get the hostname and then a regex to pull out the domain:
domain = host.sub(/^.*\.([^.]+\.[^.]+(\.[a-z]{2})?)$/, '\1')
Hope this helps
Also, if you want to learn more, I have a regex tute online: http://tech.bluesmoon.info/2006/04/beginning-regular-expressions.html

Answer 4

Sure all you would have to do is search on http://(.*)/wiki/Anarchy
In Perl (Sorry I don't know Ruby, but I expect it's similar)
$string_to_search =~ s/http:////(.)//. should give you wikipedia.org
to get rid of the en, you can simply search on http:////en(.)//......
That should do it.
Update: In case you're not familiar with Regex, I would recommend picking up a Regex book, this one really rocks and I like it: REGEX BOOK,Mastering Regular Expressions, I saw it on half.com the other day for 14.99 used, but to clarify what i suggested above, is to look for the string http://en, then for anything until you find a / this is all captured in $1 (in perl, not sure if it's the same in ruby), a simple print $1 will print the string.
Update: #2 sorry the star in the regex is not showing up for some reason, so where you see the . in the () and after the // just imagine a *, oh and I forgot for the en part add a /. at the end that way you don't end up with .wikipedia.org