php $ FILES是空的

<?php
// 1. 创建一个随机命名的文件
$filename = uniqid();
$filepath = '/path/to/file';
$fileinfo = pathinfo($filename);

// 2. 创建文件并写入内容
$file = fopen($filepath . '/' . $filename, 'w');
fwrite($file, 'Hello, World!');
fclose($file);

// 3. 上传文件到服务器
$tempName = $_FILES['file']['tmp_name'];
$fileType = pathinfo($tempName, PATHINFO_EXTENSION);
$fileName = $fileinfo['filename'] . '.' . $fileType;
if (move_uploaded_file($tempName, $filepath . '/' . $fileName)) {
    echo 'File uploaded successfully.';
} else {
    echo 'Error uploading file.';
}