title: REGEX: Extract parameter from URL
body: <p>What REGEX should I use to extract the following parameter from a url string:</p>
  
  <pre><code>/?c=135&amp;a=1341
  </code></pre>
  
  <p>I basically want to get the value of the <code>a</code> parameter from this string.</p>
  
  <p>Thanks,</p>