title: difference between number in the same column using AWK
body: <p>I have a file containing one column of number:</p>
  
  <pre><code>1
  2
  4
  4
  10
  </code></pre>
  
  <p>I would like to calculate the difference between each number using awk. The output should be like this :</p>
  
  <pre><code>1
  2
  0
  6
  </code></pre>
  
  <p>How can I do it ?</p>