How to get USPS Shipping API (Shipping price) with PHP

<?php
function USPSParcelRate($weight,$dest_zip,$origin_zip ,$pack_size="REGULAR",$userName,$servicecode) {
// =============== DON'T CHANGE BELOW THIS LINE API CALL===============
$url = "http://Production.ShippingAPIs.com/ShippingAPI.dll";
$ch = curl_init();
// set the target url
curl_setopt($ch, CURLOPT_URL,$url);
curl_setopt($ch, CURLOPT_HEADER, 1);
curl_setopt($ch,CURLOPT_RETURNTRANSFER,1);
// parameters to post
curl_setopt($ch, CURLOPT_POST, 1);
$data = "API=RateV4&XML=<RateV4Request USERID=\"$userName\"><Package ID=\"1ST\"><Service>ALL</Service><ZipOrigination>$orig_zip</ZipOrigination><ZipDestination>$dest_zip</ZipDestination><Pounds>$weight</Pounds><Ounces>0</Ounces><Container/><Size>$pack_size</Size><Machinable>FALSE</Machinable></Package>
</RateV4Request>";
// send the POST values to USPS
curl_setopt($ch, CURLOPT_POSTFIELDS,$data);
$result=curl_exec ($ch);
$data = strstr($result, '<?');
// echo '<!-- '. $data. ' -->'; // Uncomment to show XML in comments
$xml_parser = xml_parser_create();
xml_parse_into_struct($xml_parser, $data, $vals, $index);
xml_parser_free($xml_parser);
$params = array();
$level = array();
foreach ($vals as $xml_elem) {
if ($xml_elem['type'] == 'open') {
if (array_key_exists('attributes',$xml_elem)) {
list($level[$xml_elem['level']],$extra) = array_values($xml_elem['attributes']);
} else {
$level[$xml_elem['level']] = $xml_elem['tag'];
}
}
if ($xml_elem['type'] == 'complete') {
$start_level = 1;
$php_stmt = '$params';
while($start_level < $xml_elem['level']) {
$php_stmt .= '[$level['.$start_level.']]';
$start_level++;
}
$php_stmt .= '[$xml_elem[\'tag\']] = $xml_elem[\'value\'];';
eval($php_stmt);
}
}
curl_close($ch);
// echo '<pre>'; print_r($params); echo'</pre>'; // Uncomment to see the full array
return $params['RATEV3RESPONSE']['1ST'][$servicecode]['RATE'];
}

$res = USPSParcelRate($weight,$dest_zip,$origin_zip ,"REGULAR",$userName,$servicecode);

echo "Price ".$res;
?>