Catching Keywords from Search Engines

<?php
class keywords
{
 private $referer;
 private $_e;
 public $keywords;

 public function __construct()
 {
   if($_SERVER['HTTP_REFERER'])
   {
     if(preg_match("#\.google|search\.yahoo|\.bing#", $_SERVER['HTTP_REFERER']))
     {
       $this->referer = urldecode($_SERVER['HTTP_REFERER']);
     }
     else
     {
       return;
     }    
   }
   else
   {
     return;
   }    
 }

 private function getSeparators()
 {
   $this->_e = (preg_match("#\?q=|\?p=#", $this->referer)) ? "\?" : "&";
 }

 public function getKeywords()
 {
   if(!empty($this->referer))
   {
     $this->getSeparators();
     //google
     if(preg_match("#\.google#", $this->referer))
     {
       $m_ = preg_match("#{$this->_e}q=(.+?)&#si", $this->referer, $this->keywords);

       if($m_ == 0)
       {
         return false;
       }
     }
     //yahoo
     elseif(preg_match("#search\.yahoo#", $this->referer))
     {
       $m_ = preg_match("#{$this->_e}p=(.+?)\&#si", $this->referer, $this->keywords);

       if($m_ == 0)
       {
         return false;
       }
     }
     //bing
     elseif(preg_match("#\.bing#", $this->referer))
     {
       $m_ = preg_match("#{$this->_e}q=(.+?)\&#si", $this->referer, $this->keywords);

       if($m_ == 0)
       {
         return false;
       }
     }
     else
     {
       return false;
     }

     return $this->keywords[1];
   }
   else
   {
     return false;
   }
  }
}
?>

<?php
require_once('keywords_class.php');
$keywordsObj = new keywords();
$keys = $keywordsObj->getKeywords();

if($keys)
{
 print $keys;
}
else
{
 print "ooops";
}
?>