Automatic Rebase of Last Commit in Git

Introduction

I often find myself in the situation where I have just pushed a branch with my changes and created a pull request, only to later realize that I forgot to add a file or made a typo in my code. In such cases, my goal is to make a small change while maintaining a clean Git history, so I opt to rebase the last commit to essentially hide it. Of course this wouldn’t work if there was a chance that someone already used my branch or I cooperated with someone on it. But usually the branch is just mine and I make the changes almost immediately after pushing it so I think it’s worth it to keep the history clean.

Manual Procedure

Over the years, I’ve developed a manual procedure that I can execute quite swiftly. Essentially, it involves creating a commit with any message, running a rebase on HEAD~2, marking the commit as fixup in Vim, and finally performing a force push. It was just a matter of few seconds. However, once I wondered whether I could save myself a few keystrokes and automate it.

Automated Procedure

In fact, you can. While there might be other methods, I decided to strictly automate my procedure, and I was surprised to discover that I could automate Vim 🤯:

function git_rebase_last_and_push
    set -lx GIT_EDITOR "vim +2 -c 'normal cwf' -c 'wq'"
    git commit -a -m "wip"
    git rebase -i HEAD~2
    git push -f origin HEAD
end

The trick is in setting the GIT_EDITOR environment variable. It tells Git to use Vim as the editor and to open the file at line 2 (which is exactly the line with my last commit). Then it runs 2 Vim commands. First normal cwf which is to change the word under the cursor to f (as in fixup). And second wq which is to write the file and quit Vim. And that’s it.

So when you run git_rebase_last_and_push in your shell (Fish shell in my case) it will commit everything with “wip” message, it will start the rebase process with the last two commits which will trigger Vim, it will fixup the last commit and quit and finally everything is force pushed to the remote repository. The force push is necessary because the commit history was changed. This is the part that’s a bit dangerous and does not work if you cooperate on the code with others but as long as the branch is just yours I encourage you to keep the history clean.

Conclusion

It’s quite satisfying to see it in action. I hope you will find it useful as well.

Edit August 30th, 2023

Of course there is an easier way even though I wasn’t able to find it. It was pointed out to me that you can just do git commit --amend --no-edit instead of the rebase and it will do the same thing.