Let’s come to using these useful operations on PHP. We will introduce a few useful functions for this.

With the preg_match function, we can check that the expression we wrote does not match the content we provide. In the example we will check if the input has a valid time format.

$pattern= '/^([01][0-9]|[2][0-3]):[0-5][0-9]:[0-5][0-9]$/';
$content = '23:15:59';
if(preg_match($pattern, $content))
    echo 'A correct time has been entered.';
    echo 'An incorrect time format has been entered.';

Returns true if expression matches in text, otherwise false.

If you are also curious about the explanation of the expression we wrote; First, we denoted the beginning of the text with ^, so it should start exactly as we wanted it to. Finally, we used $, so we stated that we were looking for content that had exactly the beginning and end we wanted.

We then grouped ([01] [0-9] | [2] [0-3]) 2 expressions. Because the time can be either from 01 to 19 or from 20 to 23. If we said match 2 numbers between 0 and 9 in the form [0-9]{2}, it would also match numbers greater than 23, such as 99.