So what's a good example of a git command that you might reasonably run as part of your $PS1 that runs an external program? It's not like people have git push or git commit in their $PS1.
`git status`. This essentially has a "prompt" mode with `--porcelain`, which can even print branch and stash state, so it features all of the information for a prompt. Prompts have been mentioned in adding the v2 porcelain format[0]
It will call the fsmonitor hook configured in core.fsmonitor - this is supposed to speed up figuring out which files to check.
The official git-prompt.sh calls `git diff`, which will do the same[1].
