single-command git commits

[Eric Abrahamsen <eric@ericabrahamsen.net>]

I know one of you has a recipe for this...

I'm working on a long document in a single-file git repository (I know
there are probably better solutions). What I'd like to do is have a
single command that prompts me for a git commit message, and then
commits. The in-Emacs equivalent of:

git commit -a -m "(read-string \"Commit message: \")"

Yes, I could probably write a shell script, but I'd like to do it in
Emacs! The vc-* commands don't provide an immediately-obvious way to do
this. I have magit and projectile installed, and would be happy to use
their commands, but again haven't found anything obvious. I'll write
something myself, but does anyone have a nice foundation for building
this on?

Free beers in return...

E