Regular Expression to match a valid day in a date

Question

I need help coming up with a regex to make sure the user enters a valid date The string will be in the format of mm/dd/yyyy

Here is what I have come up

Answer 1

Simpler regex:

([12]\d|3[01]|0?[1-9])

Consider the accepted answer and this expression:

(0[1-9]|[12]\d|3[01])

This matches 01 but not 1

The other expression in the accepted answer:

([1-9]|[12]\d|3[01])

This matches 1 but not 01

It is not possible to add an OR clause to get them both working.

The one I suggested matches both. Hope this helps.