Git - how to update an old commit

Question

This is my graph:

Branch A    a-->b
                |
                v
Branch B        b-->c

I have branch B that came out of branch A, from commit b.
I did a commit on branch B called c.

Now let's say I update commit b of branch A with git commit --amend to b'

Branch A    a-->b'
                |
                v
Branch B        b-->c

How do I update comit b on branch B to be the exact b' ?

Thanks

score 3 · Accepted Answer · edited May 23 '17 at 11:48

3

Actually, the grap is

a--b (A)
    \
     c (B)

After amend, you would have a new b' (marking b as tmp):

a--b' (A)
 \
  b--c (B)
(tmp)

You would need to rebase B onto A:

git rebase --onto A tmp B

a--b' (A)
    \
     c' (B)

As divyum comments, you can also merge, but that would add to A, and duplicate b commit between, resulting in possible conflicts:

a--b'--M (A)
 \    /
  b--c (B)

I prefer cherry-picking or rebasing.

edited May 23 '17 at 11:48

Community

answered Sep 17 '16 at 05:41

VonC

won't merge A into B or cherry-pick commits from A to B help? – divyum Sep 17 '16 at 05:46
@divyum `rebase --onto` is cherry-picking every commit after `tmp` up to `B` HEAD and replay them onto `A`: see http://stackoverflow.com/a/1994491/6309. – VonC Sep 17 '16 at 05:52
ohk, makes sense or rather merge A into B. @VonC – divyum Sep 17 '16 at 05:55
@divyum if you have only one commit on B, yes a merge is possible to. – VonC Sep 17 '16 at 05:58
I guess number of commits don't matter, you can merge it anyway. – divyum Sep 17 '16 at 06:01

1 Answers1