title: How to delete lines containing only numbers in BASH?
body: <p>I have a TXT file. How can I delete only those lines which only contain numbers. For e.g.:</p>
  
  <pre><code>This has some text.
  1300
  This has some more text.
  1210
  This has a text and some numbers. 12
  </code></pre>
  
  <p>In the sample above, only lines 2 and 4 would be deleted as they are the ones that contain no other symbols besides numbers.</p>