Recursive PHP function to list folders and subforlders of a directory and returned a PHP Array.

listfolders.php

<?php
function getFolders($dir = false) {
    $server_sign = filter_input(INPUT_SERVER, 'SERVER_SIGNATURE', FILTER_SANITIZE_STRING);
    $unix_server = (stristr($server_sign, "win")) ? false : true;
    $slash = ($unix_server) ? "/" : "\\";
    $dir = (!$dir) ? getcwd() : $dir;
    $open_dir = opendir($dir);
    $folders = [];
    while ($item = readdir($open_dir)) {
        if ($item != "." && $item != "..") {
            $path = filetype(realpath($dir . $slash . $item));
            if ($path == "dir") {
                $folders[] = $item;
                foreach (getFolders(realpath($dir . $slash . $item)) as $folder) {
                    $folders[] = $item . $slash . $folder;
                }
            }
        }
    }
    return $folders;
}

//TEST
echo "<pre>";
print_r(getFolders());
echo "</pre>";
?>