Online PHP editor | refs for 7Nb7D

<?php $re = '/(?:"\K([^_\r\n]+)|\G(?!^))(?=[^":\r\n]*")(?=[^:\r\n]*:)_?([a-zA-Z])([^"_\r\n]*)/'; $str = '"aa_bb" : "foo" "pp_Qq" : "bar" "Xx_yY_zz" : "foobar" "Xx_yYyyyyyYyY_zz_a" : "foobar"'; $result = preg_replace_callback($re, function($matches) { return strtolower($matches[1]) . strtoupper($matches[2]) . strtolower($matches[3]); }, $str); echo $result;