title: Getting attribute's value in Nokogiri to extract link URLs
body: <p>I have a document which look like this:</p>
  
  <pre><code>&lt;div id="block"&gt;
      &lt;a href="http://google.com"&gt;link&lt;/a&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>I can't get Nokogiri to get me the value of <code>href</code> attribute. I'd like to store the address in a Ruby variable as a string.</p>