PHP清除文件BOM数据

function trimUTF8BOM($file){
    $content = file_get_contents($file);
    if(substr($content, 0, 3) == pack('CCC', 239, 187, 191)) {
        $content = substr($content, 3);
        file_put_contents($file, $content);
    }
    return $file;
}