php won't pass variable to php rss function -

i have http://communitychessclub.com/test.php

i have php function named "getposts" want send url form:

<form action="#" method = "post">  <input type="hidden" name="sub" value="1" />  <select name="url" id="url"> <option value="http://www.chess.com/rss/articles">chess.com</option> <option value="http://chesscafe.com/feed/">chess cafe</option> <option value="http://www.chessdom.com/rss">chessdom</option> <option value="http://chess-news.ru/rss-eng">chess-news</option>  </select> </form> 

for reason, php code below doesn't grab option selected , pass function. why that?

<?php $sub = intval( $_post["sub"]);   if ($sub == 1){  $url= $_post["url"]; } else{ $url = "http://www.theweekinchess.com/twic-rss-feed";  }  getposts($url); ?> 

its because there no submit button. if want auto-submit form on change need like

<form name="myform" action="#" method = "post"> <select name="url" id="url" onchange="document.forms['myform'].submit()"> 

i checked , looks works fine.

also don't need $sub thing, can do

<?php  if(isset($_post["url")){ $url = $_post["url"]; } else{ $url = "http://www.theweekinchess.com/twic-rss-feed";  }  getposts($url); ?>