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Random Talk on Random Thoughts

Undo an Amendment to a Git Commit

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Objective

To undo the command git commit --amend.

Background (TL;DR)

Tonight, I changed something in a Git repository, and wanted to write a Git commit, but I carelessly ran git commit --amend, instead of git commit --all. As a result, I was brought to a Vim buffer which showed the commit message of the latest commit. I quit the editor with :q. Unfortunately, the SHA-1 name of that commit was replaced with another one. The original latest commit had been pushed to GitHub. In other words, I amended a pushed commit—this is an absolutely bad practice!1 Therefore, I need to undo the “amendment” to the commit.

Solution

I googled “undo git commit amend”, and, at the first glance, found three relevant web pages.

  1. A question on Stack Overflow

    At first, I didn’t understand what HEAD@{1} was, and jumped to the next item.

  2. An article on Pivotal Labs

    I just skimmed through the whole essay for commands. I didn’t think that git diff 8751261..9d3a192 | git apply - was helpful. I feared that applying older commits would lead to the failure of rake deploy. What I learnt from this site was the existence of the command git reflog.

  3. A blog post which has a link to a YouTube video on Coderwall (URL)

    By viewing the video fullscreen in HD, I was finally sure what git reflog really did. To save time, I suggest users to look at the terminal at 2:38.

Going back to the first item, I’ve eventually understood the chosen answer.

Lessons learnt

For non-professionals, using multimedia to illustrate abstract ideas is better than just using words.

  1. According to the original version of a GitHub help page, changing a pushed commit will “cause the wrath of Git gods”. However, the quoted phrase has gone, but I can still find it on Stack Overflow. ↩

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