3v4l.org

run code in 500+ PHP versions simultaneously
<?php preg_match('/(?<foo>y)?x(?<bar>y)?/', 'x', $matches); print_r($matches); preg_match('/(?<foo>y)?()x(?<bar>y)?/', 'x', $matches); print_r($matches);
Output for 8.0.1 - 8.0.30, 8.1.0 - 8.1.34, 8.2.0 - 8.2.32, 8.3.0 - 8.3.33, 8.4.1 - 8.4.24, 8.5.0 - 8.5.9
Array ( [0] => x ) Array ( [0] => x [foo] => [1] => [2] => )

preferences:
90.25 ms | 1153 KiB | 4 Q