See also, this video: https://youtu.be/sgW9_D0vK5A

Inevitably, you discover as you work in a feature branch, that you made a mistake in an earlier commit.

Of course you can just fix it with a new commit, but then you end up with a commit history like this:

0a89f pc - add students controller to support CRUD operations for students
34s9c pc - add front end React form component for student CRUD operations
3240a pc - fix spelling error in parameter name in students controller
7bd40 pc - add yet another missing HTTP header in controller
d0240 pc - add missing HTTP header in students controller

The last three commits are just fixing errors that are in the controller; the new file added in the first commit.

And those commits are now separated from the original commit by one dealing with a React form; an entirely separate concern.

Wouldn’t it be nice if you just fix up the original commit? Now you can.

The technique is explained in:

• This video by P. Conrad: https://youtu.be/sgW9_D0vK5A
• This web page by Florent Lebreton https://fle.github.io/git-tip-keep-your-branch-clean-with-fixup-and-autosquash.html

But here’s the short version:

1. Use git log to identify sha of commit you want to fix up (call this abcd1234), and the sha of the commit immediately before that one (e.g. dcba5678)

2. Use git add to add the files you want to add to your fixup commit
3. git commit --fixup abcd1234 (sha of commit you want to fix up)
4. git rebase -i --autosquash dcba5678 (sha of commit right before the one you want to fix up)
5. Exit the editor window (you don’t have to change anything; the --autosquash has taken care of that). For vim, it’s type escape key, then :wq
6. force push your branch, e.g. git push origin my-branch-name