random password

jag vill göra en lösenordssnurra...har denna kod:

<?
function ranpass($len = "8"){
 $pass = NULL;
 for($i=0; $i<$len; $i++) {
   $char = chr(rand(48,122));
   while (!ereg("[a-zA-Z0-9]", $char)){
     if($char == $lchar) continue;
     $char = chr(rand(48,90));
   }
   $pass .= $char;
   $lchar = $char;
 }
 return $pass;
}

$password = ranpass(6);

echo $password;
?>

...men emellanåt får jag detta felmeddelande:

Notice: Undefined variable: lchar...