Convert any Date format in unix

view story

http://stackoverflow.com – How can I convert any user inputted date into yyyy/mm/dd? For example, the user may input date in one of the following formats: 20120121 2012-01-21 01/21/2012 01/21/2012 ... But I need to convert any of the date entered by the user into yyyy/mm/dd (2012/01/2012). Any suggestion? Here's what I've been trying, but it is not working: echo "Please enter the date: " read X a=$X+"%y/%m/%d" echo $a (HowTos)