Re: Find the starting point of a local branch

[Kevin <ikke@ikke.info>]

On Mon, Dec 24, 2012 at 8:31 AM, Woody Wu <narkewoody@gmail.com> wrote:
> But thanks anyway, I see you guys's discussions and it's a little hard
> to understand to me at the moment. Currently, I still have to use gitk
> with narrowed outputs.

Each commit refers to it's parent. If you take a branch, and keep
following the first parent of the commits, you will finally reach the
root commit (the first commit made). You don't see any branches, it's
just one straight line. That's why git can't tell you where a branch
started, because it all looks like a single branch to git.

With merge-base, you basically give git two branches, and git finds
the first ancestor that is common to both branches.

See [1] for an example. If you follow the arrows from branch a, you
get from E to A (note that commit C doesn't know about commit F
pointing to it). So it looks like there is only a single branch.

If you do git merge-base a b, git sees both branches have commit C in
common, and reports that as the merge-base.

[1]: http://g.jk.gs/9W.png