PHP
From Shopify Wiki
You can use PHP to connect to the Shopify API.
For this you need SimpleXML and CURL support.
Example
<?php
//Modify these
$API_KEY = 'your-token-here';
$SECRET = 'your-secret-here';
$TOKEN = 'your-secret-here';
$STORE_URL = 'yourestore.myshopify.com';
$PRODUCT_ID = 'product-id-here';
$url = 'https://' . $API_KEY . ':' . md5($SECRET . $TOKEN) . '@' . $STORE_URL . '/admin/products/' . $PRODUCT_ID . '.xml';
$session = curl_init();
curl_setopt($session, CURLOPT_URL, $url);
curl_setopt($session, CURLOPT_HTTPGET, 1);
curl_setopt($session, CURLOPT_HEADER, false);
curl_setopt($session, CURLOPT_HTTPHEADER, array('Accept: application/xml', 'Content-Type: application/xml'));
curl_setopt($session, CURLOPT_RETURNTRANSFER, true);
if(ereg("^(https)",$url)) curl_setopt($session,CURLOPT_SSL_VERIFYPEER,false);
$response = curl_exec($session);
curl_close($session);
$product_xml = new SimpleXMLElement($response);
echo $product_xml->title;
echo $product_xml->variants->variant->{'inventory-quantity'};
?>
PHP Active Resource
There is a PHP implementation of the active resource style API that Shopify adheres to. This *may* work: