how to get user agent use in codeigniter code example

Example: codeigniter device

$this->load->library('user_agent');

if ($this->agent->is_browser())
{
        $agent = $this->agent->browser().' '.$this->agent->version();
}
elseif ($this->agent->is_robot())
{
        $agent = $this->agent->robot();
}
elseif ($this->agent->is_mobile())
{
        $agent = $this->agent->mobile();
}
else
{
        $agent = 'Unidentified User Agent';
}

echo $agent;

echo $this->agent->platform(); // Platform info (Windows, Linux, Mac, etc.)