3v4l.org

run code in 300+ PHP versions simultaneously
<?php $sentence = strtolower('Jumpy Qbert grawlix'); $usage = count_chars($sentence, 3); $alphabet = range('a', 'z'); var_export([ 'Sentence' => $sentence, 'Total Length' => strlen($sentence), 'Alphabetical Length' => preg_match_all('~[a-z]~', $sentence, $letters), 'Unused Letters' => array_diff($alphabet, $letters[0]), 'Duplicated Letters' => array_diff(array_count_values($letters[0]), [1]), ]);
based on rCU6J
Output for 7.2.0 - 7.2.31, 7.3.0 - 7.3.19, 7.4.0 - 7.4.7, 8.0.0alpha1 - alpha2
array ( 'Sentence' => 'jumpy qbert grawlix', 'Total Length' => 19, 'Alphabetical Length' => 17, 'Unused Letters' => array ( 2 => 'c', 3 => 'd', 5 => 'f', 7 => 'h', 10 => 'k', 13 => 'n', 14 => 'o', 18 => 's', 21 => 'v', 25 => 'z', ), 'Duplicated Letters' => array ( 'r' => 2, ), )