Ruby script to extract the TLD from a URL. This can be useful for validating a URL.

extract_tld_from_url.rb

urls = ["http://brigade.codeforamerica.org/index.html", "brigade.codeforamerica.org", "http://codeforamerica.org", "codeforamerica.org/index.html", "brigade.codeforamerica.org/index.html"]

urls.each do |url|
  # clean up the URLs so they all start off with the same format
  if url.include?("http://")
		url.gsub!("http://","")
	end
  # we're only interested in the part that comes before the first slash,
  # so we split the string into the part before the slash, and the part after the slash
	a = url.split("/")
  # the part before the first slash is the first element of the a array, i.e a[0]
  # we then break up that string into the parts to the left and right of each period (split("."))
  # this results in a new array that contains either 2 or 3 strings, but the TLD is always
  # the last element of the array, which can be accessed via [-1]
	tld = a[0].split(".")[-1]
	puts tld
end

# the tld string can be checked for validity by comparing it to this list: http://data.iana.org/TLD/tlds-alpha-by-domain.txt 
# you can create an array that contains all the TLDs, then check if the array includes the string you're validating.
# for example if the array is called "valid_tlds", and the string you're validating is called "tld", you would do:
# valid_tlds.include?(tld)