Git-Mastery: Lessons

T4L6. Reverting a Specific Commit


Git can add a new commit to reverse the changes made in a specific past commit. This is called reverting a commit.

This lesson covers that part.

When a past commit introduced a bug or an unwanted change, but you do not want to modify that commit (because rewriting history can cause problems if others have already based work on it), you can instead revert that commit.

Reverting creates a new commit that cancels out the changes of the earlier one, i.e., Git computes the opposite of the changes introduced by that commit (essentially a reverse diff) and applies it as a new commit on top of the current branch. This way, the problematic changes are reversed while preserving the full history, including the "bad" commit and the "fix".

C3
|
C2
|
C1

→
[revert C2]

R2(This commit is the reverse of C2)
|
C3
|
C2
|
C1

HANDS-ON: Revert a commit

Scenario You are working with a repo named pioneers, which contains information about computer science pioneers. You discovered that one of the earlier commits mistakenly added information about a fictional character instead of a real CS pioneer.

C3←HEADAdd Hopper
|
C2Add Turing
|
C1Add Neo

Target Correct the mistake without rewriting past commits. That is, add a new commit that reverts the offending commit.

C4←HEADRevert "Add Neo"
|
C3Add Hopper
|
C2Add Turing
|
C1Add Neo

Preparation

Option 1: Create a fresh sandbox using the Git-Mastery app

  • Navigate inside the gitmastery-exercises folder.
  • Run the gitmastery download hp-revert-commit command.

The sandbox will be set up inside the gitmastery-exercises/hp-revert-commit folder.

Git-Mastery commands list | Report Git-Mastery bugs | How to update Git-Mastery

Option 2: Manually set up a sandbox

Run the following commands to create the pioneers repo:

mkdir pioneers
cd pioneers
git init -b main

echo "hacked the matrix" >> neo.txt
git add .
git commit -m "Add Neo"

echo "father of theoretical computing" >> alan-turing.txt
git add .
git commit -m "Add Turing"

echo "created COBOL, compiler pioneer" >> grace-hopper.txt
git add .
git commit -m "Add Hopper"

1 Revert the commit Add Neo.

 CLI

You can use the git revert <commit> command to revert a commit. In this case, we want to revert the commit that is two commits behind the HEAD.

git revert HEAD~2

What happens next:

  1. Git prepares a new commit that reverses the target commit
  2. Git opens your default text editor with a proposed commit message. You can edit it or accept the proposed text.
  3. Once you close the editor, Git will create the new commit.
 Sourcetree

In the revision graph, right-click on the commit you want to revert, and choose Reverse commit...

2 Verify the revert commit has been added, e.g.,

git log --oneline --decorate
⤷
604b770 (HEAD -> main) Revert "Add Neo"
682fc8d Add Hopper
268ceb1 Add Turing
6fb6bd8 Add Neo

done!

A revert can result in a conflict if the new changes that reverse the previous commit conflict with later changes. You then need to resolve the conflict before the revert operation can proceed. Conflict resolution is covered in a later topic.

EXERCISE: sensors-revert