Online PHP editor | output for 9fqMP

<?php $find = 'place'; // case is irrelevant to processing $replace = 'garden'; // must be declared in all lowercase echo preg_replace_callback( '#\b' . preg_quote($find) . '\b#ui', function ($word) use ($replace) { $i = 0; return preg_replace_callback( '#(\p{Lu})|.#su', function ($char) use (&$i, $replace) { $newChar = mb_substr($replace, $i++, 1); return isset($char[1]) ? mb_strtoupper($newChar) : $newChar; }, $word[0] ); }, 'Place replacements in their proper plACe without being complacent; use word boundaries.' );