php获取客户端IP

function ip()
{
if(getenv('HTTP_CLIENT_IP') && strcasecmp(getenv('HTTP_CLIENT_IP'), 'unknown'))
{
$ip = getenv('HTTP_CLIENT_IP');
}
elseif(getenv('HTTP_X_FORWARDED_FOR') && strcasecmp(getenv('HTTP_X_FORWARDED_FOR'), 'unknown'))
{
$ip = getenv('HTTP_X_FORWARDED_FOR');
}
elseif(getenv('REMOTE_ADDR') && strcasecmp(getenv('REMOTE_ADDR'), 'unknown'))
{
$ip = getenv('REMOTE_ADDR');
}
elseif(isset($_SERVER['REMOTE_ADDR']) && $_SERVER['REMOTE_ADDR'] && strcasecmp($_SERVER['REMOTE_ADDR'], 'unknown'))
{
$ip = $_SERVER['REMOTE_ADDR'];
}
return preg_match("/[\d\.]{7,15}/", $ip, $matches) ? $matches[0] : 'unknown';
}