Simple PHP script required

Require php script to determine a variable that changes based on the current date. This variable is passed via a hidden field once a user clicks on the link to access a particular website page. The variable is 8 characters (4 are alpha, 4 are numeric). The alpha characters are static and the numeric value (determined by the current date) is interspersed with the alpha characters. I can provide an example and the method that the value is derived to the successful coder. This should be an easy and quick project for a coder experienced in php.