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"

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59.11 ms | 402 KiB | 5 Q