When git rebasing two branches with some shared history, is there an easy way to have the common history remain common?

Question

Suppose we have the following revision graph:

A-X-Z--B
     \\
      \\-C

with A preceding both B and C. Further suppose I rebase A from up

Answer 1

git rebase --committer-date-is-author-date --preserve-merges --onto A* A C
git rebase --committer-date-is-author-date --preserve-merges --onto A* A B

This should keep the common commits having the same sha1 and any merges preserved. Preserve merges is not required in this case, but will become an issue with a less trivial history.

To do this for all branches that contain A in their history do:

git branch --contains A | xargs -n 1 git rebase --committer-date-is-author-date --preserve-merges --onto A* A 

Hope this helps.

UPDATE:

This may be cleaner syntax:

for branch in $(git branch --contains A); do git rebase --committer-date-is-author-date --preserve-merges --onto A* A $branch; done