Scriptable mode for git bisect

Dear Git maintainers,

I have looked at the manpage of git bisect but have not found what I need: I would like git bisect not just to report the 'bad' revision within a bunch of text but instead either stop at the first bad revision (the last good will then be HEAD~1) or report it in a scriptable way, i.e.

  BADHEAD=$(git bisect run --shut-up-and-report-the-bad)

Have I overlooked anything?

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The pourpose is to keep the source trees of two different projects that share a few files synchronous. My good/bad-script is a script that checks whether these files are similar. I want git to stop at the first change in source tree A so that I can update source tree B with the same commit message, then proceed to the next change in A that changes one of those files.

Regards,

Cluas