How to Undo and Revert Git Commits

Introduction

This tutorial will guide you through the essential techniques for undoing and reverting Git commits. You'll learn how to safely undo local changes, revert committed changes, reset the branch history, and recover lost or deleted commits. Mastering these git commit revert skills will help you maintain a clean and organized Git repository.

Skills Graph

Understanding Git Commits and Revisions

Git is a distributed version control system that tracks changes in your codebase over time. At the core of Git are commits, which are snapshots of your project's state at a specific point in time. Each commit has a unique identifier, known as a SHA-1 hash, which allows you to reference and navigate through the commit history.

Anatomy of a Git Commit

A Git commit contains the following key elements:

1. Author: The person who made the changes and created the commit.
2. Committer: The person who finalized and recorded the commit.
3. Commit Message: A brief description of the changes made in the commit.
4. Timestamp: The date and time when the commit was created.
5. Diff: The changes made to the files, including additions, modifications, and deletions.
6. Parent Commit(s): The previous commit(s) that this commit is based on.

Visualizing Commit History

You can visualize the commit history using a Git commit graph. This graph represents the branching and merging of your project's development over time. Here's an example of a commit graph:

In this example, the commit history shows the creation of a develop branch, a feature/new-functionality branch, and a bugfix/critical-issue branch, with merges back into the develop branch.

Understanding Revisions

In Git, a revision refers to a specific point in the commit history. Revisions can be specified using various methods, such as:

1. Commit Hash: The unique SHA-1 hash of a commit, e.g., a1b2c3d4.
2. Branch Name: The name of a branch, e.g., main or develop.
3. Tag: A named reference to a specific commit, e.g., v1.0.
4. Relative References: Relative references to a commit, such as HEAD~2 (two commits before the current HEAD), or HEAD@{1} (the state of the repository one operation ago).

Understanding how to specify revisions is crucial for navigating and manipulating the commit history in Git.

Undoing Local Commits and Changes

Amending the Last Commit

If you've made a mistake in your last commit, you can easily fix it using the git commit --amend command. This command allows you to modify the previous commit, including the commit message and the changes included in the commit.

## Modify the previous commit
git commit --amend -m "Updated commit message"

Unstaging Files

If you've added files to the staging area (using git add) but you don't want to commit them yet, you can unstage them using the git restore --staged command.

## Unstage a file
git restore --staged file.txt

## Unstage all files
git restore --staged .

Discarding Local Changes

To discard all local changes in your working directory, you can use the git restore command.

## Discard all local changes
git restore .

## Discard changes in a specific file
git restore file.txt

Resetting to a Previous Commit

If you want to undo multiple commits and reset your branch to a specific point in the commit history, you can use the git reset command.

## Reset the branch to a previous commit (soft reset)
git reset HEAD~2

## Reset the branch and discard all changes (hard reset)
git reset --hard HEAD~2

Be careful when using git reset --hard, as it will permanently discard all local changes.

Recovering Lost Commits

If you've accidentally deleted a commit or it's no longer visible in your branch history, you can use the git reflog command to find and recover it.

## View the reflog
git reflog

## Restore a lost commit
git reset --hard HEAD@{n}

The git reflog command keeps track of all the changes made to the HEAD pointer, allowing you to recover lost commits.

Reverting Committed Changes Safely

Understanding the git revert Command

The git revert command is a safe way to undo committed changes without rewriting the commit history. Instead of deleting the commit, it creates a new commit that undoes the changes introduced by the target commit.

## Revert the last commit
git revert HEAD

## Revert a specific commit
git revert a1b2c3d4

Handling Merge Conflicts During Revert

When you revert a commit that has been merged into another branch, Git may encounter merge conflicts. In this case, you'll need to resolve the conflicts manually before completing the revert operation.

## Revert a merged commit
git revert a1b2c3d4

## Resolve the merge conflicts
## (Edit the conflicting files, choose the desired changes)
git add .
git revert --continue

Reverting a Range of Commits

You can also revert a range of commits using the git revert command with a commit range.

## Revert the last 3 commits
git revert HEAD~2..HEAD

## Revert a specific range of commits
git revert a1b2c3d4..x9y8z7w6

This will create a new commit that undoes the changes introduced by the specified range of commits.

Reverting Merge Commits

Reverting a merge commit is a special case, as it can be more complex to resolve the conflicts. Git provides the --mainline option to specify which parent commit should be used as the "main" branch when reverting the merge.

## Revert a merge commit, using the first parent as the mainline
git revert -m 1 a1b2c3d4

In this example, the -m 1 option tells Git to use the first parent commit as the mainline when reverting the merge.

By understanding the git revert command and how to handle merge conflicts, you can safely undo committed changes without rewriting the commit history.

Resetting the Branch History Selectively

Understanding git reset

The git reset command is a powerful tool for selectively resetting the branch history. It allows you to move the branch pointer to a specific commit, effectively undoing commits and changes up to that point.

There are three main modes for git reset:

1. --soft: Moves the branch pointer to the specified commit, but leaves the working directory and staging area unchanged.
2. --mixed (default): Moves the branch pointer and resets the staging area to match the specified commit, but leaves the working directory unchanged.
3. --hard: Moves the branch pointer, resets the staging area, and discards all changes in the working directory.

Resetting to a Specific Commit

You can use git reset to move the branch pointer to a specific commit, effectively undoing all commits after that point.

## Reset the branch to a previous commit (soft reset)
git reset HEAD~2

## Reset the branch and discard all changes (hard reset)
git reset --hard HEAD~2

In the above examples, HEAD~2 refers to the commit two steps before the current HEAD.

Selective Resetting

You can also use git reset to selectively reset the staging area or the working directory, without affecting the branch pointer.

## Reset the staging area to the last commit
git reset HEAD file.txt

## Reset the working directory to the last commit
git reset --hard HEAD file.txt

This allows you to undo changes in the staging area or working directory without affecting the overall branch history.

Recovering from Resets

If you accidentally reset your branch too far back, you can use the git reflog command to find and recover the lost commits.

## View the reflog
git reflog

## Restore a lost commit
git reset --hard HEAD@{n}

The git reflog keeps track of all the changes made to the HEAD pointer, allowing you to recover from accidental resets.

By understanding the different modes of git reset and how to use it selectively, you can effectively manage and manipulate your branch history without losing important commits.

Recovering Lost or Deleted Commits

Understanding the Git Reflog

The Git reflog is a powerful tool that can help you recover lost or deleted commits. The reflog keeps track of all the changes made to the HEAD pointer, including when branches are checked out, commits are made, and commits are undone.

## View the reflog
git reflog

The reflog will display a list of all the changes to the HEAD pointer, with the most recent changes at the top.

Recovering Deleted Commits

If you've accidentally deleted a commit, you can use the reflog to find and restore it.

## Restore a deleted commit
git reset --hard HEAD@{n}

Replace n with the index of the commit you want to restore, as shown in the reflog output.

Recovering Dangling Commits

Sometimes, commits can become "dangling" in the Git repository, meaning they are no longer referenced by any branch or tag. This can happen when you've used git reset or git rebase to remove commits from the branch history.

You can use the git fsck command to find and recover these dangling commits.

## Find dangling commits
git fsck --lost-found

## Restore a dangling commit
git branch recovered-branch HEAD@{n}

The git fsck command will list any dangling commits, and you can then use git branch to create a new branch pointing to the recovered commit.

Recovering from Rebase Mistakes

If you've made a mistake during a rebase operation, you can use the reflog to recover the original branch state.

## Abort an ongoing rebase
git rebase --abort

## Return to the original branch state
git reset --hard HEAD@{n}

Replace n with the index of the commit you want to restore, as shown in the reflog output.

By understanding the Git reflog and how to use it to recover lost or deleted commits, you can ensure that your important work is never truly lost, even in the face of accidental or complex Git operations.

Handling Merge Conflicts During Revert

Understanding Merge Conflicts in Revert

When you revert a commit that has been merged into another branch, Git may encounter merge conflicts. This happens when the changes introduced by the reverted commit conflict with the changes made in the target branch.

Resolving Merge Conflicts

To resolve the merge conflicts during a revert, follow these steps:

1. Initiate the revert operation:

   git revert a1b2c3d4

2. Git will pause the revert process and present you with the conflicting files.

3. Open the conflicting files and resolve the conflicts manually. You'll see markers like <<<<<<< HEAD, =======, and >>>>>>> a1b2c3d4 indicating the conflicting changes.

4. Edit the files to keep the desired changes and remove the conflict markers.

5. Add the resolved files to the staging area:

   git add .

6. Continue the revert operation:

   git revert --continue

   This will create a new commit that reverts the original changes, while incorporating the resolved conflicts.

Aborting a Conflicting Revert

If you're unable to resolve the merge conflicts or decide to abandon the revert operation, you can abort the revert process:

git revert --abort

This will cancel the revert operation and leave your branch in its original state.

Handling Merge Conflicts with --no-commit

You can also use the --no-commit option when reverting a commit to avoid the immediate creation of a new commit. This can be helpful when you need to resolve complex merge conflicts.

git revert --no-commit a1b2c3d4
## Resolve conflicts
git revert --continue

By using the --no-commit option, you can take the time to carefully resolve the conflicts before finalizing the revert with a new commit.

Understanding how to handle merge conflicts during revert operations is crucial for maintaining a clean and manageable commit history in your Git repository.

Summary

In this comprehensive tutorial, you've learned various methods to undo and revert Git commits, including undoing local changes, safely reverting committed changes, selectively resetting the branch history, and recovering lost or deleted commits. By understanding these git commit revert techniques, you can confidently manage your Git repository and maintain a clean commit history.