PHP通过CURL上传文件

<?php
$url = 'http://test/upload_file';
$file_name = 'test.jpg';
$real_name = realpath($file_name);
$data = array(
'file' => '@' . $real_name;
);

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $data);

$res = curl_exec($ch);
curl_close($ch);