PHP Regex to check date is in YYYY-MM-DD format

It's probably better to use another mechanism for this.

The modern solution, with DateTime:

$dt = DateTime::createFromFormat("Y-m-d", $date);
return $dt !== false && !array_sum($dt::getLastErrors());

This validates the input too: $dt !== false ensures that the date can be parsed with the specified format and the array_sum trick is a terse way of ensuring that PHP did not do "month shifting" (e.g. consider that January 32 is February 1). See DateTime::getLastErrors() for more information.

Old-school solution with explode and checkdate:

list($y, $m, $d) = array_pad(explode('-', $date, 3), 3, 0);
return ctype_digit("$y$m$d") && checkdate($m, $d, $y);

This validates that the input is a valid date as well. You can do that with a regex of course, but it's going to be more fuss -- and February 29 cannot be validated with a regex at all.

The drawback of this approach is that you have to be very careful to reject all possible "bad" inputs while not emitting a notice under any circumstances. Here's how:

• explode is limited to return 3 tokens (so that if the input is "1-2-3-4", $d will become "3-4")
• ctype_digit is used to make sure that the input does not contain any non-numeric characters (apart from the dashes)
• array_pad is used (with a default value that will cause checkdate to fail) to make sure that enough elements are returned so that if the input is "1-2" list() will not emit a notice

Try this.

$date="2012-09-12";

if (preg_match("/^[0-9]{4}-(0[1-9]|1[0-2])-(0[1-9]|[1-2][0-9]|3[0-1])$/",$date)) {
    return true;
} else {
    return false;
}

yyyy-mm-dd : /^((((19|[2-9]\d)\d{2})\-(0[13578]|1[02])\-(0[1-9]|[12]\d|3[01]))|(((19|[2-9]\d)\d{2})\-(0[13456789]|1[012])\-(0[1-9]|[12]\d|30))|(((19|[2-9]\d)\d{2})\-02\-(0[1-9]|1\d|2[0-8]))|(((1[6-9]|[2-9]\d)(0[48]|[2468][048]|[13579][26])|((16|[2468][048]|[3579][26])00))\-02\-29))$/g

yyyy/mm/dd : /^((((19|[2-9]\d)\d{2})\/(0[13578]|1[02])\/(0[1-9]|[12]\d|3[01]))|(((19|[2-9]\d)\d{2})\/(0[13456789]|1[012])\/(0[1-9]|[12]\d|30))|(((19|[2-9]\d)\d{2})\/02\/(0[1-9]|1\d|2[0-8]))|(((1[6-9]|[2-9]\d)(0[48]|[2468][048]|[13579][26])|((16|[2468][048]|[3579][26])00))\/02\/29))$/g

mm-dd-yyyy : /^(((0[13578]|1[02])\-(0[1-9]|[12]\d|3[01])\-((19|[2-9]\d)\d{2}))|((0[13456789]|1[012])\-(0[1-9]|[12]\d|30)\-((19|[2-9]\d)\d{2}))|(02\-(0[1-9]|1\d|2[0-8])\-((19|[2-9]\d)\d{2}))|(02\-29\-((1[6-9]|[2-9]\d)(0[48]|[2468][048]|[13579][26])|((16|[2468][048]|[3579][26])00))))$/g

mm/dd/yyyy : /^(((0[13578]|1[02])\/(0[1-9]|[12]\d|3[01])\/((19|[2-9]\d)\d{2}))|((0[13456789]|1[012])\/(0[1-9]|[12]\d|30)\/((19|[2-9]\d)\d{2}))|(02\/(0[1-9]|1\d|2[0-8])\/((19|[2-9]\d)\d{2}))|(02\/29\/((1[6-9]|[2-9]\d)(0[48]|[2468][048]|[13579][26])|((16|[2468][048]|[3579][26])00))))$/g

dd/mm/yyyy : /^(((0[1-9]|[12]\d|3[01])\/(0[13578]|1[02])\/((19|[2-9]\d)\d{2}))|((0[1-9]|[12]\d|30)\/(0[13456789]|1[012])\/((19|[2-9]\d)\d{2}))|((0[1-9]|1\d|2[0-8])\/02\/((19|[2-9]\d)\d{2}))|(29\/02\/((1[6-9]|[2-9]\d)(0[48]|[2468][048]|[13579][26])|((16|[2468][048]|[3579][26])00))))$/g

dd-mm-yyyy : /^(((0[1-9]|[12]\d|3[01])\-(0[13578]|1[02])\-((19|[2-9]\d)\d{2}))|((0[1-9]|[12]\d|30)\-(0[13456789]|1[012])\-((19|[2-9]\d)\d{2}))|((0[1-9]|1\d|2[0-8])\-02\-((19|[2-9]\d)\d{2}))|(29\-02\-((1[6-9]|[2-9]\d)(0[48]|[2468][048]|[13579][26])|((16|[2468][048]|[3579][26])00))))$/g