Question

what will be the regular expression of date format like '01-Aug-12'.

I have the date format of dd-M-y in asp.net application and want to validate it from asp.net regular expression validator control.

Answer 1

This won’t be too elegant, but if you want to use regex to validate dates, it is here:

The regex with explanation

(
  (
    31-(Jan|Mar|May|Jul|Aug|Oct|Dec)|                                   # months with 31 days
    (0[1-9]|[12]\d|30)-(Jan|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)|   # months with 30 or 31 days
    (0[1-9]|1\d|2[0-8])-Feb                                             # February up to 28th
  )
  -\d\d                                                                 # any two digits represent the year
)|
(
    29-Feb-([02468][048]|[13579][26])                                   # February 29th
)

This regex doesn’t accept invalid dates like 00-Aug-00, 32-Aug-00 and 29-Feb-01 while accepting valid dates including leap days (29-Feb-04). Note that we assume 00 stands for year 2000, not 1900. So, we accepted 29-Feb-00 as leap day!

In one line:

See it in action:

((31-(Jan|Mar|May|Jul|Aug|Oct|Dec)|(0[1-9]|[12]\d|30)-(Jan|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)|(0[1-9]|1\d|2[0-8])-Feb)-\d\d)|(29-Feb-([02468][048]|[13579][26]))

Case-insensitivity

In Javascript, add an i as second parameter:

var re = new RegExp(regexStr, "i");

In ASP.NET, use RegexOptions.IgnoreCase:

Regex re = new Regex(regexStr,RegexOptions.IgnoreCase);