你的正则表达式没有工作，因为你有>未转义 / 分隔符。

Your regex didn't work because you had unescaped / delimiter.

正则表达式将以 YYYY-MM-DD 如下：

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

它将验证年份以 19开始或 20 ，该月份不超过 12 而不等于 0 而且该日期不大于 31 并且不等于 0 。

It will validate that the year starts with 19 or 20, that the month is not greater than 12 and doesn't equal 0 and that the day is not greater than 31 and doesn't equal 0.

在线示例

使用您的初始示例，您可以这样测试：

Using your initial example, you could test it like this:

$date_regex = '/^(19|20)\d\d[\-\/.](0[1-9]|1[012])[\-\/.](0[1-9]|[12][0-9]|3[01])$/';
$hiredate = '2013-14-04';

if (!preg_match($date_regex, $hiredate)) {
    echo '<br>Your hire date entry does not match the YYYY-MM-DD required format.<br>';
} else {
    echo '<br>Your date is set correctly<br>';      
}

在线示例