title: shell scripting time difference in variables
body: <p>How can i get the time difference in 2 variables in shell</p>
  
  <pre><code>say i have 4 variables-
  
      t1=07:50:19:612
      t2=07:52:14:697
      t3=10:20:54:201
      t4=11:02:09:716
  
   and i want to find difference in times
   result=(t2-t1)+(t4-t3)
  </code></pre>