title: How to find a double quoted string using grep and regex?
body: <p>I'm trying to find all the occurrences of the string "5.1" in all files under a certain directory.
  I've tried using the following command but it finds none:</p>
  
  <pre><code>#grep -Re[5]+\.+[1] .
  </code></pre>
  
  <p>What am I doing wrong?</p>