title: Subtraction of two dates to give age
body: <p>I need to subtract two dates in the form 'yyyymmdd' (Study date - Date of birth) to find the age of a patient, how can I do this in C shell? </p>
  
  <p>I've looked online but all I can find are bash &amp; korn scripts, I'm not really familiar enough with either to change them.</p>