Git plumbing command to find out which files have been changed in a given revision

I've created a hook that sends out notification emails when a developer pushes an update to his shared repository. This email includes a list of changed files, example: ``` A __classes/Page/Activity.php M __config/Scheme.php ``` that I generate using the following bit of bash: ``` $(git diff "$newrev"^ "$newrev" --name-status) ``` This works fine. However, I'm trying to port all this now to the well-known post-receive-email hook. This hook does have a `hooks.showrev` configuration directive, but this I think this only allows for the revision number (`%s`) to be used once in the command. So this doesn't work: ``` showrev = "git diff %s^ %s --name-status" ``` There must be a 'plumbing' command that does just this. Can anyone point me in the right direction? :)