preg_replace_callback

<?php     {

        if ('\\' === DIRECTORY_SEPARATOR) {


            $filename = (string) preg_replace_callback('~^(?P<drive>[a-z]+:\\\)~i', static fn (array $match): string => strtolower($match['drive']), $filename);

        }



        $filename = str_replace('\\\\', '\\', addslashes((string) realpath($filename)));

<?php             $startChar = DIRECTORY_SEPARATOR;



            if ('\\' === DIRECTORY_SEPARATOR || preg_match('~\A[A-Z]:(?![^/\\\\])~i', $path) > 0) {

                $path = (string) preg_replace_callback('~^(?P<drive>[a-z]+:\\\)~i', fn (array $match): string => strtolower($match['drive']), $path);



                $startChar = strtolower((string) preg_replace('~^([a-z]+:\\\).*$~i', '$1', __DIR__));

            }