3v4l.org

run code in 300+ PHP versions simultaneously
<?php $str = '12345678'; $head = substr($str, 0, strlen($str)%3); $str = substr($str, strlen($head)); $str = preg_replace( '/(.{3})/', ' $1', $str ); echo trim($head . $str); //string(10) "12 345 678"
Output for 5.6.0 - 5.6.28, 7.0.0 - 7.0.20, 7.1.0 - 7.1.33, 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 - 8.1.28, 8.2.0 - 8.2.19, 8.3.0 - 8.3.7
12 345 678
preferences:
189.94 ms | 404 KiB | 223 Q