A script to modify custom field names in a URL and redirect to new url

I'm guessing I need a PHP script. Something short and simple. I want to pass data from a webform to my shopping cart by sending the data from the form when the user clicks the submit button (the cart url is that thank you page). The cart needs url in this format with these name values to work: [login to view URL] Product&qty=10&price=1.00 The userid and price is static. The webform can append userdata to the url as seen here: &contactId=591&screenResolution=1440x900 &inf_custom_FanFavorite=xxxxx+&inf_form_xid=a54b09858deb1b2ba88fcacaf39606ea&infusionsoft_version=1.27.7.27 &inf_custom_NumberOfVotes=5&inf_field_LastName=xxxxx&inf_form_name=Sign+up+for+newsletter&inf_field_FirstName=xxxxx&javaEnabled=true&inf_field_Email=xxxxx%40xxxxxxxx.com&pluginList=Shockwave+Flash%2CChrome+Remote+Desktop+Viewer%2CNative+Client%2CChrome+PDF+Viewer%2CMicrosoft%C2%AE+Windows+Media+Player+Firefox+Plugin%2CAdobe+Acrobat%2CJava+Deployment+Toolkit+6.0.270.7%2CJava%28TM%29+Platform+SE+6+U27%2CMicrosoft+Office+2013%2CQuickTime+Plug-in+7.1.6%2CQuickTime+Plug-in+7.1.6%2CQuickTime+Plug-in+7.1.6%2CQuickTime+Plug-in+7.1.6%2CQuickTime+Plug-in+7.1.6%2CQuickTime+Plug-in+7.1.6%2CQuickTime+Plug-in+7.1.6%2CActiveTouch+General+Plugin+Container%2CGoogle+Talk+Plugin%2CGoogle+Talk+Plugin+Video+Accelerator%2CMicrosoft+Office+2010%2CMicrosoft+Office+2013%2CPicasa%2CSilverlight+Plug-In%2CRealPlayer%28tm%29+G2+LiveConnect-Enabled+Plug-In+%2832-bit%29+%2CRealJukebox+NS+Plugin%2CRealPlayer+Download+Plugin%2CWindows+Live%C2%99+Photo+Gallery%2CiTunes+Application+Detector%2CRealNetworks%28tm%29+Chrome+Background+Extension+Plug-In+%2832-bit%29+%2CRealPlayer%28tm%29+HTML5VideoShim+Plug-In+%2832-bit%29+%2CGoogle+Update%2CHulu+Desktop%2CShockwave+Flash What I need is for when the user clicks submit to submit the webform - the thank you page is a php script that will convert the custom field names from the webform to the name values required by the cart to function and redirect them to the cart via the new url. Example: inf_custom_FanFavorite needs to become product inf_custom_NumberOfVotes needs to become qty it should send userid and price as static values. and the user ends up at: [login to view URL] Product&qty=10&price=1.00 with the proper values from the webform for product and qty ---- I can send the actual URL and userid to the selected coder.