3v4l.org

run code in 300+ PHP versions simultaneously
<?php $txt = <<<TXT jkDDDJJJJjjjjJJlk jhlkj_sdHHhhHhhHHHHHHH kjhlkjh_JJJjjkkkkIIIIiiii TXT; echo preg_replace('/(.)(.*)/', '\u\1\L\2\E', $txt);

preferences:
34.22 ms | 402 KiB | 5 Q