Validating date format using regular expression

Question

Using regular expression, how would I validate a date to make sure it is only entered in this format: mm/dd/yyyy?

If anyone is interested, I'm using validates_format_of :date_field, :with => // in a Ruby model.

A regex really isn't the right tool for this job, [`DateTime.strptime`](http://ruby-doc.org/stdlib-1.9.3/libdoc/date/rdoc/DateTime.html#method-c-strptime) with the appropriate format string and an exception handler would be much better. — mu is too short, Nov 17 '11 at 20:40
What I need to do is validate a string that should be formatted like : (2 numbers)/(2 numbers)/(4 numbers). — Artem Kalinchuk, Nov 17 '11 at 20:44
You're right. But I don't mind, as long as it's entered in that format. — Artem Kalinchuk, Nov 17 '11 at 21:01

hsz · Answer 1 · 2011-11-17T21:28:17.587

5

Regex for this format can looks like:

^\d{2}\/\d{2}\/\d{4}$

edited Nov 17 '11 at 21:28

answered Nov 17 '11 at 20:08

hsz

I think you made a mistake in the regular expression. You need to remove the extra `\\`. I tried to fix the mistake but the changes were reset back to what it was. – Artem Kalinchuk Nov 17 '11 at 21:16
The main mistake is related to line endings: http://homakov.blogspot.ru/2012/05/saferweb-injects-in-various-ruby.html – denis.peplin Dec 28 '15 at 07:37

FailedDev · Accepted Answer · 2011-11-17T21:18:59.163

3

@hsz answer is correct. Should you need to also validate the date itself you can use this :

/^(?:0?[1-9]|1[0-2])/(?:0?[1-9]|[1-2]\d|3[01])/\d{4}$/

Edit :

As @Tim said this will is not a 100% regex validator. See his linked answer for that.

if subject =~ /\A(?:0?[1-9]|1[0-2])\/(?:0?[1-9]|[1-2]\d|3[01])\/\d{4}\Z/
    # Successful match

Edit #2 : Ruby specific version above.

edited Nov 17 '11 at 21:18

answered Nov 17 '11 at 20:13

FailedDev

2

This only gets you halfway there - 02/31/1234 would pass and many other invalid dates - for a true date validation that takes leap years into account, you'd need a huge regex (which is [possible, but not a good idea](http://stackoverflow.com/questions/4290433/regular-expression-for-aspregularexpressionvalidator-with-format-mmddyy-leap-y/4291747#4291747)). Better leave validation to a specialized function. – Tim Pietzcker Nov 17 '11 at 20:23
@TimPietzcker I wouldn't do this with regex. I am sure there are modules for this, or other better ways. – FailedDev Nov 17 '11 at 20:36
You might need to escape the `/` characters. – Artem Kalinchuk Nov 17 '11 at 21:17

2 Answers2