Rebase

Rationale

• Change the base of a branch;

• After rebasing, there are still two branches, similar to a fast-forward merge situation;

• Rebasing is creating new commits, hence the SHA will be different even though it's the same change set;

Notes

• Rebase re-assigns the common ancestor of a branch to a different commit, i.e. changing the base of a branch.

• By default, a rebase will drop merge commits, and place the rebased commits into a single, linear branch. To try include merged commits, use the --rebase-merges option.

• It's similar to merge, but

  • meerge maintains the branching history;

  • rebase puts one branch at the end of another.

• Rebase is suitable if you want to maintain a single-branch paradigm.

• It will interfere with the commit history, so only apply it locally with caution.

Command

Use the current branch as base

• Checkout the branch to be rebased

• git rebase <new-base>

Use any two branches

• git rebase <b1> <b2> will rebase b2 on b1 (equiv. to checkout b2, then rebase on b1)

Check divergence

• git merge-base <b1> <b2> returns commit where b2 diverges from b1

Onto other branches

• git rebase --onto master ecommerce new_feature will gather the commits from new_feature diverged from ecommerce and put them onto master.

Undo

• git reset --hard ORIG_HEAD

  • ORIG_HEAD is the previous state of HEAD so that dangerous operations can be reverted.

  • This assumes no other destructive operations are done after the rebase.

• Alternatively, rebase again to restore the original structure, but the SHA value will be changed.

Conflicts

If conflicts occur

• Modified the files to the final state you want. Then add the files to the staging tree (git add). Instead of commit, use git rebase --continue to finish rebasing.

• You might need to do this multiple times if more than one conflict is found.

Manually resolve the conflict

• git add <file>, then

  • git rebase --continue to continue

  • No commit required as the commit history is in the branch

• git rebase --abort to cancel

• git rebase --skip to skip the conflict