Abort a Git Merge Operation

1. Overview

Git is a powerful version control system that enables developers to collaborate on projects efficiently. One of the most common operations in Git is merging branches to integrate changes from one branch into another.

However, sometimes during the merge process, we may encounter conflicts that we need to resolve. In such cases, we might decide to abort the merge operation altogether.

In this article, we’ll explore different methods we can use to abort a Git merge operation.

2. Understanding Git Merge Conflicts

Before moving on to how we can abort a merge conflict, let’s briefly discuss what merge conflicts are.

A merge conflict occurs when Git is unable to merge changes from different branches automatically. This usually happens when the same line of codes has been modified in both branches being merged. Git marks the conflicting lines in the affected files, and it’s up to the operator to resolve the conflicts manually.

Let’s look at what a merge conflict message might look like:

<<<<<<< HEAD
This is the content from the current branch.
=======
This is the content from the branch being merged.
>>>>>>> branch-name

Git uses such markers to indicate the conflicting lines.

The content between <<<<<<< HEAD and ======= represents the changes in the current branch. On the other hand, the content between ======= and >>>>>>> represents the changes from the branch being merged.

However, to resolve the conflict, we might need to manually edit the file, remove the conflict markers, and decide which changes to keep. Once we’ve resolved all the conflicts, we can stage the changes and commit the merge.

3. Aborting a Git Merge

If we find ourselves in a situation where we want to abort a merge operation, Git provides several ways to do so. Let’s explore different methods.

3.1. Using the git merge –abort Command

The most straightforward way to abort a merge is the git merge –abort command. This command aborts all the merge processes and restores the repository to its original state before the merge begins:

$ git merge --abort

After we run this command, Git cleans up any temporary files created during the merge process and resets the working tree to its version before the merge.

For example, let’s suppose we have two branches:

• main
• feature

We’re currently on the main branch, and we want to merge the changes from the feature branch:

$ git merge feature
Auto-merging index.html
CONFLICT (content): Merge conflict in index.html
Automatic merge failed; fix conflicts and then commit the result.
$ git merge --abort

In the code snippet above, when we run git merge feature, Git attempts to automatically merge the changes from the feature branch into the current main branch. However, it encounters a merge conflict in the index.html file.

In this case, the conflict arises because both the main branch and the feature branch have made conflicting changes to the same part of the index.html file. Git is unable to resolve the conflicts automatically and requires manual intervention.

However, we run git merge –abort, and Git aborts the merge process and restores the whole repository to the state it was in before the merge began. Thus, the index.html file reverts to its original state on the main branch, and the feature branch remains unchanged.

3.2. Using the git reset Command

Another way to abort a merge is to use the git reset command. This command enables us to reset a repository to a previous state, effectively undoing the merge attempt.

Before aborting a merge using reset, we first use the git log command to find the commit hash of the state we want to return to, which is usually the commit before the merge attempt. Once we know the desired commit identifier, we use the git reset command followed by that ID to reset the repository to that version.

Notably, the command discards any changes we made during the merge attempt. So, we should ensure we don’t have any uncommitted changes we want to keep.

For example, let’s suppose we’re on the main branch, and we start a merge process with the feature branch. During the merge, we encounter conflicts and decide to abort the merge:

$ git log --oneline
abcd123 (HEAD -> main) Update README
ef45678 Add new feature
...
$ git reset abcd123

The command git log –online displays a condensed version of our commit history, showing each commit on a single line along with its hash and commit message. After that, we identify the commit hash abcd123 as the state we want to return to. Then, we abort with the git reset abcd123 command, which resets the repository to the state at commit abcd123, effectively undoing the merge attempt.

Additionally, any changes made during the merge are discarded.

3.3. Removing Merge Artifacts Manually

In some cases, we might have started a merge without committing any changes. In such situations, we can manually remove the merge artifacts to abort the merge.

To abort a merge manually, we remove several filesystem objects:

• .git/MERGE_HEAD file: information about the merge in progress
• .git/MERGE_MSG file: commit message for the merge commit
• *.orig files: backup files created by Git during the merge process

After we remove these files, the repository should return to its state before the merge started.

For example, we start a merge operation between two branches, and during the merge, we realize we want to abort it without committing any changes.

Next, we navigate to the .git directory:

$ cd .git

of the repository and remove the MERGE_HEAD:

$ rm MERGE_HEAD

Now, we delete the MERGE_MSG file:

$ rm MERGE_HEAD

At this point, we’ve successfully removed MERGE_HEAD and MERGE_MSG.

Finally, we search for any file with the .orig extension and delete them:

$ find . -name "*.orig" -delete

After removing these files, the repository should be back to its state before the merge. We can continue working on the branch as if the merge never happened.

4. Conclusion

In this article, we looked at what a Git merge conflict is and how we can abort a merge using different commands.

In conclusion, aborting a Git merge operation is a useful skill when we encounter conflicts or decide not to proceed with a given operation.