Edit a regular expression

Question

I have some kind of problems with regular expressions, this one checks if my date is in mm/dd/yyyy format:

/^(0[1-9]|1[012])[- /.](0[1-9]|[12][0-9]|3[01])[- /.](19|20)\d\d+$/

I need the same one but checking if the date is like dd/mm/yyyy (european date)

I got no clue about how this stuff work, I've checked some guides but I can't figure out how to edit this one.

Any help would be appreciated =)

Is't it easier to split the string by `'/'` then check the value of each component? — axiac, Feb 09 '15 at 11:26

score 1 · Accepted Answer · edited May 23 '17 at 10:25

Have a careful look at your expression: you will see that it is divided into three parts: the first part (0[1-9]|1[012]) matches months (from 01 to 12), the second part (0[1-9]|[12][0-9]|3[01]) matches days (from 01 to 31), while a last part (19|20)\d\d+ matches years (from 1900 up). Finally, [- /.] matches your separators (- or .) and ^ and $ match string beginning and string end, respectively.

I want to add two more observations:

Usually (in my experience, mainly web) the escape character (used in your expression before . is \ rather than /
At the end of your expression you have (19|20)\d\d+: this will maths 1900 but will also match 190000 (because of the + sign).

Given this, I would change your regexp as follows:

^(0[1-9]|[12][0-9]|3[01])[- \.](0[1-9]|1[012])[- \.](19|20)\d{2}$

note however that this regexp will match also non-valid dates as for example 30th of February.

If you need something more accurate have a look here: Regex to validate date format dd/mm/yyyy

Take my +1 sir. Thank you for the detailed explaination – Gino Perla Feb 09 '15 at 11:43 — Gino Perla, Feb 09 '15 at 11:43

websky · Answer 2 · 2015-02-09T11:36:57.870

Example for php

09-02-2015

/**
         * Validates the date
         * @param string $date
         * @return boolean
         */
        protected function checkDate($date)
        {
            if (preg_match('@^[0-9]{2}-[0-9]{2}-[0-9]{4}$@', $date)) {
                return true;
            } else {
                return false;
            }
        }

for 09/02/2015

/**
         * Validates the date
         * @param string $date
         * @return boolean
         */
        protected function checkDate($date)
        {
            if (preg_match('@^[0-9]{2}\/[0-9]{2}\/[0-9]{4}$@', $date)) {
                return true;
            } else {
                return false;
            }
        }

it doesn't work. what does that function expects? it returns false for my date 09/02/2015 — Gino Perla, Feb 09 '15 at 11:31

score 0 · Answer 3 · answered Feb 09 '15 at 11:41

^(0[1-9]|1[012]) matches the month component
(0[1-9]|[12][0-9]|3[01]) matches the day of month component
(19|20)\d\d matches the year component
[- /.] just matches a -, space, /, or .

This means that your regex will also match e.g. 12-31/2013

I think that the + at the end of the regex doesn't belong there - it would allow for additional digits after the year component.

The same regex restructured to match dd/mm/yyyy would look like this:

^(0[1-9]|[12][0-9]|3[01])[- \/.](0[1-9]|1[012])[- \/.](19|20)\d\d$

Edit a regular expression

3 Answers3