git-fixup

Creates a git fixup commit that is amended automatically to the target commit.

'fzf' is used to improve the user experience by providing a selectable list of usable commits. If 'fzf' is not found in the PATH user must provide the commit hash to the 'git-fixup' command.

This command is intended to be used as a git alias. Aliases can be added to '.gitconfig' file. Add an alias to the '.gitconfig' file called 'fixup' (or some other preferred name) and point it to the location of this script.

[alias]
	fixup = git-fixup

Problem statement

Applying changes to the last commit with git is trivial, but when applying changes to older commits we need to run cumbersome commands to make the changes and to keep the git history pristine.

I'm quite certain that many developers will face the issue of wanting to edit a previous commit, especially when relying on rebase mechanics (as one should). However, fixups are a great way to keep the context of the commit knowledge within a single commit by directly modifying the existing commit and rebasing the history.

If you are not familiar with rebasing, I highly recommend reading the following chapter from the Pro Git book 3.6 Git Branching - Rebasing.

The usual flow for applying fixups is as follows:

# Stage changes for older commit in the branch
git add file.txt

# Find the commit hash by using the log command and copy the commit hash
git log --oneline origin..

# Create a fixup
git commit --fixup <commit_hash>

# Interactive rebase with autosquash and autostash
git rebase -i --autosquash --autostash

As we can see, the process itself is quite cumbersome and requires a better approach, especially since this is a recurring operation that happens multiple times a day.

Solution

The solution is simple:

Create a git alias called fixup that will run a POSIX-compatible shell script, which automates the cumbersome parts of the fixup operation.

The same example as above, but with the fixup command:

# Stage changes for older commit in the branch
git add file.txt

# Prompts fzf to select commit hash the fixup should be applied to.
# After selection creates a fixup that is rebased to the original commit.
git fixup

As we can see, the solution is vastly simpler than the original way of creating fixup commits.

The one caveat is the requirement of the external dependency fzf, but I'd imagine this is one of the 'default' tools developers have on their machines anyway.

Installation

Easiest way to install git-fixup is with shm.

To install shm run either one of these one-liners:

curl:

curl -sSL https://raw.githubusercontent.com/erikjuhani/shm/main/shm.sh | sh

wget:

wget -qO- https://raw.githubusercontent.com/erikjuhani/shm/main/shm.sh | sh

then run:

shm get erikjuhani/git-fixup

to get the latest version of git-fixup.

git-fixup uses fzf which can be installed by following the instructions here.

Usage

git-fixup [<commit_hash>]

When commit hash is not provided git-fixup will use 'fzf' to provide a list of selectable commits in the branch, however, if 'fzf' is not found in the PATH, user must provide a commit hash.

Examples

Amend to older commit behind 2 commits in the current branch

git add file.txt
git-fixup HEAD~2

Amend to older commit in the current branch using git alias

git add file.txt
git fixup HEAD~2

Amend to selected commit with 'fzf'

git add file.txt
git-fixup