PHP remove BOM document

//remove the utf-8 boms
//by magicbug at gmail dot com

if (isset($_GET['dir'])){ //要去除的文件目录，无参数则为文件当前目录。
    $basedir=$_GET['dir'];
}else{
    $basedir = '.';
}

$auto = 1;

checkdir($basedir);

function checkdir($basedir){
    if ($dh = opendir($basedir)) {
        while (($file = readdir($dh)) !== false) {
            if ($file != '.' && $file != '..'){
                if (!is_dir($basedir."/".$file)) {
                 echo "filename: $basedir/$file ".checkBOM("$basedir/$file")." ";
            }else{
                $dirname = $basedir."/".
          $file;
                checkdir($dirname);
            }
        }
    }
    closedir($dh);
}

function checkBOM ($filename) {
    global $auto;
    $contents = file_get_contents($filename);
    $charset[1] = substr($contents, 0, 1);
    $charset[2] = substr($contents, 1, 1);
    $charset[3] = substr($contents, 2, 1);
    if (ord($charset[1]) == 239 && ord($charset[2]) == 187 &&
    ord($charset[3]) == 191) {
        if ($auto == 1) {
            $rest = substr($contents, 3);
            rewrite ($filename, $rest);
            return ("BOM found,automatically removed.");
        } else {
            return ("BOM found.");
        }
    }
    else return ("BOM Not Found.");
}

function rewrite ($filename, $data) {
    $filenum = fopen($filename, "w");
    flock($filenum, LOCK_EX);
    fwrite($filenum, $data);
    fclose($filenum);
}
?>

PHP, BOM