3v4l.org

run code in 300+ PHP versions simultaneously
<?php $str = 'a,b,c,d,e'; $arr = explode( ',', $str); $arr[] = (array_pop( $arr) . (array_pop( $arr) . "")); echo implode( ',', $arr);

preferences:
62.5 ms | 402 KiB | 5 Q