How to split up a git commit

Quick steps

1. git rebase -i -> mark your commit with edit
2. git reset HEAD~ (remove the marked commit, but keep its changes)
3. Make several commits (optionally setting the previous author manually)
4. git rebase --continue

Detailed instructions

Basically, you will review the last n commits and stop at the splittable commit. Then you'll undo that commit and put its changes into new commits at your liking.

1. Review commits (rebase)

   Copygit rebase -i HEAD~3
   # or
   git rebase -i origin/master
   

   Git will give you a list of commits, youngest at the bottom. It will look like this:

   Copypick 27f2769 Do something
   pick b891fd1 Do many things
   pick da3c35c Do something else
   

2. Mark the splittable commit: replace pick with edit. Save/:wq/exit.

   Git will now re-apply the commits one by one. Once it has applied the splittable commit (say, b891fd1), it will stop and wait for you to make changes

3. Unwrap the commit, i.e. drop the commit, but keep all its file changes:

   Copygit reset HEAD~
   

4. Prepare the first new commit by adding files or parts of files:

   Copy# Examples:
   git add vendor
   # or
   git add config/database.yml
   # or
   git add -p
   

5. Once you're done, commit:

   Copygit commit -m 'My commit message'
   

   If you're modifying the commit of someone else, please re-set them as author as described here.

6. Repeat steps 4 & 5 until no changes are left.

7. Finish by telling git to continue the rebase:

   Copygit rebase --continue
   

Also see Git: Splitting up changes into several commits