title: Sed expression doesn't allow optional grouped string
body: <p>I'm trying to use the following regex in a <code>sed</code> script but it doesn't work:</p>
  
  <pre><code>sed -n '/\(www\.\)\?teste/p'
  </code></pre>
  
  <p>The regex above doesn't seem to work. <code>sed</code> doesn't seem to apply the <code>?</code> to the grouped <code>www\.</code>.</p>
  
  <p>It works if you use the <code>-E</code> parameter that switches <code>sed</code> to use the Extended Regex, so the syntax becomes:</p>
  
  <pre><code>sed -En '/(www\.)?teste/p'
  </code></pre>
  
  <p>This works fine but I want to run this script on a machine that doesn't support the <code>-E</code> operator. I'm  pretty sure that this is possible and I'm doing something very stupid. </p>