Get Operating System

// returns a class based on the OS
function get_os() {
  $oses = array(
  'Win' => 'Win16',
  'Win' => '(Windows 95)|(Win95)|(Windows_95)',
  'Win' => '(Windows 98)|(Win 9x 4.90)|(Windows ME)',
  'Win' => '(Windows 98)|(Win98)',
  'Win' => '(Windows NT 5.0)|(Windows 2000)',
  'Win' => '(Windows NT 5.1)|(Windows XP)',
  'Win' => '(Windows NT 5.2)',
  'Win' => '(Windows NT 6.0)',
  'Win' => '(Windows NT 6.1)',
  'Win' => '(Windows NT 4.0)|(WinNT4.0)|(WinNT)|(Windows NT)',
  'OpenBSD' => 'OpenBSD',
  'SunOS' => 'SunOS',
  'Linux' => '(Linux)|(X11)',
  'MacOS' => '(Mac_PowerPC)|(Macintosh)',
  'QNX' => 'QNX',
  'BeOS' => 'BeOS',
  'OS2' => 'OS/2',
  'SearchBot'=>'(nuhk)|(Googlebot)|(Yammybot)|(Openbot)|(Slurp)|(MSNBot)|(Ask Jeeves/Teoma)|(ia_archiver)'
  );
 
  $agent = strtolower($agent ? $agent : $_SERVER['HTTP_USER_AGENT']);
  foreach($oses as $os=>$pattern) {
    if (preg_match('/'.$pattern.'/i', $agent)) {
      return " ".$os;
    }
  }
  return "";
}