echo sef($yazi);

   function sef($s) {
        $tr = array('ş','Ş','ı','İ','ğ','Ğ','ü','Ü','ö','Ö','Ç','ç');
        $eng = array('s','s','i','i','g','g','u','u','o','o','c','c');
        $s = str_replace($tr,$eng,$s);
        $s = strtolower($s);
        $s = preg_replace('/[^%a-z0-9 _-]/', '', $s);
        $s = preg_replace('/\s+/', '-', $s);
        $s = preg_replace('|-+|', '-', $s);
        $s = trim($s, '-');
       return $s;
    }