以下实例我们使用php curl 来获取远程文件大小，返回文件大小单位为字节：

<?php
// 获取远程文件大小函数
function remote_filesize($url, $user = "", $pw = "")
{
    ob_start();
    $ch = curl_init($url);
    curl_setopt($ch, CURLOPT_HEADER, 1);
    curl_setopt($ch, CURLOPT_NOBODY, 1);
 
    if(!empty($user) && !empty($pw))
    {
        $headers = array('Authorization: Basic ' .  base64_encode("$user:$pw"));
        curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
    }
 
    $ok = curl_exec($ch);
    curl_close($ch);
    $head = ob_get_contents();
    ob_end_clean();
 
    $regex = '/Content-Length:\s([0-9].+?)\s/';
    $count = preg_match($regex, $head, $matches);
 
    return isset($matches[1]) ? $matches[1] . " 字节" : "unknown";
}

// 实例测试
echo remote_filesize("https://www.cdsy.xyz/d/file/computer/programme/html_div_css/2022-02-13/2e41a242eba7796dbc88ca6fff66d0ae.png");
?>

以上实例输出结果为：

8416 字节