Affiliate link and redirection code(repost)

I need a piece of code that I can place behind a 'buy it now' button on my site. At the moment the client clicks on my button and it takes them to site of the product owner (I am an affiliate) then they have to click on the buy it now button on the second site. I would like a code that I can insert behind this button which simulates this in the background. For example I have a sales page about hernia's, the customer clicks my buy it now button and goes to the purchase page of the other site. i.e <my aff link here [login to view URL] > code here <link for 3rd party payment button here [login to view URL]> I would like this code generic so I can use it for other sites and I can change the affiliate link and the 3rd party payment link. I hope this makes sense!