How to discover user's browser

<html>
    <head>
        <title>Example</title>
    </head>

    <body> 
        <?php 
        $useragent = $HTTP_SERVER_VARS["HTTP_USER_AGENT"];
	echo $useragent; 
        ?>

    </body>
</html>

Output:
Mozilla/4.5 [en]C-CCK-MCD {Sony} (Win98; U)

Variables in PHP always begin with a $
Types of variables are not set by the programmer, but are determined at runtime by the context in which a variable is used
PHP has predefined variables which are automatically set by PHP