title: Grep a particular length of characters
body: <p>Let's say I have a file, foo.txt with certain contents:</p>
  
  <pre><code>abcds9912:        8c b2           1e12
  asddb221          jj 7u 9i         e2e1
  </code></pre>
  
  <p>Now I want to <code>grep</code> only <code>8c, b2, jj, 7u, 9i</code>
  i.e characters coming in pairs</p>
  
  <p>So far I have tried</p>
  
  <pre><code>cat foo.txt | grep -Eo '[a-z0-9]{2}'
  </code></pre>
  
  <p>but it didn't work</p>