prevent /index.php in link

I am trying to create a link to a product detail page using perch content custom.

In the list template I have

<a href="<perch:content id="_page" />/product.php?s=<perch:content id="slug" type="slug" />"  > Link here </a>

This is creating a link to: www.mywesbite.com/clothing/index.php/product.php?s=my-product-name

How can I stop the "index.php" part from being included?

The listing items are being called in from multiple pages chance why I need the _page part.