3v4l.org

run code in 300+ PHP versions simultaneously
<?php $match = 'today'; $n = 2; for ($pos = strlen($match) - $n; $pos >= 0; --$pos) { $nGrams[] = substr($match, $pos, $n); } var_export($nGrams);
Output for 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.33, 8.2.0 - 8.2.29, 8.3.0 - 8.3.26, 8.4.1 - 8.4.13
array ( 0 => 'ay', 1 => 'da', 2 => 'od', 3 => 'to', )

preferences:
139.77 ms | 407 KiB | 5 Q