Regular Expression Replace in All Files and Subdirs

<?php
    function recursiveFileReplace ($directory, $search, $replace, $valid_ext = '') {

        // directory is the starting point of the search
        // search is a regular expression
        // replace is the replacement string

        // example: replace <? with <?php
        // recursiveFileReplace('/path-to-files/', '|<\?\s+|', '<?php ', array('php'));
        if (substr($directory, -1, 1) == '/') {
            $directory = substr($directory, 0, strlen($directory) - 1);
        }

        // recursively scan directory and retrieve files
        if ($handle = opendir($directory)) {

            while (false !== ($file = readdir($handle))) {

                if ($file != '..' && $file != '.') {

                    if (is_file($directory. '/' .$file)) {

                        if (is_array($valid_ext)) {

                            $file_ext = strtolower(substr($file, strrpos($file, '.') + 1));
                            if (!in_array($file_ext, $valid_ext)) {
                                continue;
                            }

                        }

                        $contents = file_get_contents($directory. '/' .$file);
                        $contents = preg_replace($search, $replace, $contents);
                        file_put_contents($directory. '/' .$file, $contents);

                    }

                    if (is_dir($directory. '/' .$file)) {

                        recursiveFileReplace($directory. '/' .$file, $search, $replace, $valid_ext);

                    }

                }

            }

            return true;

        }

    }
?>