3v4l.org

run code in 500+ PHP versions simultaneously
<?php $str = "1111 2222 3333 4444 5555 6666"; if (preg_match_all('~(?:\G(?!^)\s?|\A(?=(?:\d{4}\s?)+\z))(\d{4})~', $str, $m)) { print_r($m[1]); }

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115.65 ms | 1450 KiB | 5 Q