title: How to grep files that contains ONLY numbers?
body: <p>Im trying to grep names of txt files containing numbers and numbers only, but I have no idea if grep is even suitable for that job. </p>
  
  <p>if I have files like below... </p>
  
  <pre><code>FILE1: 12324
  FILE2: 12345q
  FILE3: qqerxv
  </code></pre>
  
  <p>It should give me only the name of <code>FILE1</code>.</p>
  
  <p>I've tried <code>grep -r -l [a-zA-Z]</code> but that gives me the opposite.</p>
  
  <p>What pattern should I use? What should I do to grep everything but files containing anything but numbers </p>
  
  <p>How do I grep files that contains ONLY numbers?</p>