Update previously installed product from the command line by ibdavidc

I write a lot of scripts to install SQL Server, mainly for desktop tools. Due to company policy, we do not do direct downloads from Microsoft (or any other company) to the desktop; all updates must be staged in a common area and consumed from there. This would be similar to the update tool from IBM when patching things like DB2 or WebSphere.

The one thing that I don't see is an obvious way to check the current installed version and apply updates from the update depot. When installing, setup.exe does a great job of searching to see if the files in the update depot shoule be installed. If there are multiple updates required, it will apply them as needed. If an update is superceded, it will apply the later one (CU4 rather than CU2 and 3, for example)

In short, the goal is to patch an existing install. With as many installs as I have throughout the company, this would be very nice.