我的基本PHP上传和重命名文件脚本不'；行不通

上传后应该重命名文件，对吗

这是完整的脚本，应该是这样的

重命名（$\u FILES.txt，$\u FILES.html）
改为查看此-
重命名（“$\u FILES.txt”，“$\u FILES.html”）看起来不对。
// Check if $uploadOk is set to 0 by an error
if ($uploadOk == 0) {
    echo "Sorry, your file was not uploaded.";
// if everything is ok, try to upload file
} else {
    if (move_uploaded_file($_FILES["fileToUpload"]["tmp_name"], $target_file)) {
        echo "The file ". basename( $_FILES["fileToUpload"]["name"]). " has been uploaded.";
        rename ("$_FILES.txt", "$_FILES.html");
    } else {
        echo "Sorry, there was an error uploading your file.";
    }
}