Extract a YYYmmDD in PHP

I have images and videos from my camera which are uploaded to my server. In order to properly organize them I need to extract the year month and day. But I cant seem to get this pregmatch right..

Input would be 20211215_083437.jpg Output would be Year2021 Month11 Day15

if (preg_match('/^(d{4})(d{2})(d{2})$/', $value, $matches)) {
    $year = $matches[0];
    $month = $matches[2];
    $day = $matches[3];

Answer

You need to remove the $ anchor in your RegEx to make it work: it matches the end of the string but yours has content after the date. Also, the year is the 1st capture group. The index 0 contains the complete matching string.

if (preg_match('/^(d{4})(d{2})(d{2})/', $value, $matches)) {
    $year = $matches[1];
    $month = $matches[2];
    $day = $matches[3];
}

But, using a regex for this is overkill. You could sustract the date part of the filename and create a DateTime object from it:

$date_string = substr($value, 0, 8);

$date = DateTime::createFromFormat('Ymd', $date_string);

// Format the date as you want
echo $date->format('Y-m-d');