title: Check the date and time entered by user in UNIX
body: <p>I have a Shell script which uses the date and time parameters entered by the user.
  Date  as mm/dd/yyyy  and Time as HH:MM .
  What would be the easiest means to check the user had entered the proper date [ like month should be less than 12.... for time MM should be less than 60...
  Do we have any built in functions in UNIX for checking the timestamp?</p>