title: how to convert a date HH: MM: SS in second with bash?
body: <p>How to convert a date HH: MM: SS in second with bash?</p>
  
  <p>Knowing that this is a date that I recovered in a file so I can't take it in another format.</p>
  
  <p>I have two variables $DateStart and $DateEnd and i would like the difference between both.</p>