grepurls.rb

require 'nokogiri'
require 'open-uri'
require_relative 'lib/thing'

pattern = ARGV[0]
urls = ARGV[1..-1]

thing = Thing.new

urls.each do |url|
  doc = Nokogiri::HTML(open(url))
  doc.css("a").each do |link|
    if thing.match pattern, link
      puts link["href"]
    end
  end
end

thing.rb

class Thing
  def match pattern, link
    begin
      link["href"].include? pattern
    rescue NoMethodError
      false
    end
  end
end

thing_spec.rb

require_relative '../lib/thing.rb'

describe Thing do
  describe 'match' do
    it 'matches if the href matches' do
      link = { "href" => "/goose/gander" }
      thing = Thing.new
      expect(thing.match("goose", link)).to be(true)
    end

    it 'does not match if the anchor has no href' do
      link = {}
      thing = Thing.new
      expect(thing.match("banana", link)).to be(false)
    end
  end
end