以下是一个简单的PHP示例，用于检测用户代理（User Agent）。用户代理字符串提供了有关访问者使用什么浏览器、操作系统和设备类型的信息。
```php
function getUserAgent() {
$userAgent = $_SERVER['HTTP_USER_AGENT'];
return $userAgent;
}
function detectBrowser($userAgent) {
$browser = '';
if (strpos($userAgent, 'Firefox') !== false) {
$browser = 'Mozilla Firefox';
} elseif (strpos($userAgent, 'Chrome') !== false) {
$browser = 'Google Chrome';
} elseif (strpos($userAgent, 'Safari') !== false) {
$browser = 'Apple Safari';
} elseif (strpos($userAgent, 'Opera') !== false) {
$browser = 'Opera';
} elseif (strpos($userAgent, 'MSIE') !== false || strpos($userAgent, 'Trident/') !== false) {
$browser = 'Internet Explorer';
}
return $browser;
}
function detectOS($userAgent) {
$os = '';
if (strpos($userAgent, 'Windows NT') !== false) {
$os = 'Windows';
} elseif (strpos($userAgent, 'Macintosh') !== false) {
$os = 'MacOS';
} elseif (strpos($userAgent, 'X11') !== false) {
$os = 'UNIX';
} elseif (strpos($userAgent, 'Linux') !== false) {
$os = 'Linux';
} elseif (strpos($userAgent, 'Android') !== false) {
$os = 'Android';
} elseif (strpos($userAgent, 'iOS') !== false) {
$os = 'iOS';
}
return $os;
}
$userAgent = getUserAgent();
$browser = detectBrowser($userAgent);
$os = detectOS($userAgent);
>
