How to pre-empt git pull merge error?

[Pete Forman <petef4+usenet@gmail.com>]

I am looking for a way of detecting up front whether a git pull or git
merge would fail. The sort of script I want to perform is to update a
server.

    git fetch
    git okay
    stop server
    backup data
    git merge
    start server

Here git okay is a place holder for the command I am asking for.

If a file has been changed outside of a commit then git pull fails with
the following error.

error: Your local changes to '...' would be overwritten by merge.
Aborting. Please, commit your changes or stash them before you can
merge.

I would like git okay to perform the pre-merge checks described in git
merge and return non-zero status so that the script aborts before the
server is stopped.

Possibilities I have looked for and not found include git merge
--dry-run. My best line of thought is git status --porcelain |
pre-merge-okay. That seems like a lot of work to make a pre-merge-okay
that deals with things like benign untracked files.

I have also asked this question on Stack Overflow but received no
answers.

http://stackoverflow.com/questions/20221383/

-- 
Pete Forman