title: regex: return characters inside parenthensis
body: <p>I can't seem to get the values inside a parenthesis using grep.</p>
  
  <pre><code>echo "(this is a string)" | grep -Eo '[a-z ]*'
  </code></pre>
  
  <p>Ideally that should return the value inside the parenthesis, "this is a astring", instead it is not returning anything. Does anyone know the explanation?</p>