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How to Undo and Revert a Git Repository Merge

Introduction

When working with Git, you will likely need to merge branches at some point. However, sometimes a merge may introduce bugs or other issues that you want to undo. Fortunately, Git provides several methods for reverting a merge:

Key methods covered in this guide:

  • Using git reset to undo a local merge
  • Using git revert to reverse a merge commit
  • Handling remote merge reverts after push

Prerequisites

Before undoing a merge, you should:

  • Have a clean working directory with no uncommitted changes
  • Identify the merge commit or parent commit you want to return to
  • Confirm the merge commit has not already been pushed to the remote repository

Using git reset to Undo a Local Merge

To undo a merge that has not yet been pushed remotely:

  • Checkout the branch where the merge commit was made
  • Use git reflog to find the commit ID of the merge
  • Run git reset --hard <commit> using the parent commit’s ID

For example:

git checkout master 
git reflog
# find merge commit id
git reset --hard abc1234

This will move the master branch pointer back to before the merge.

Key notes on using git reset:

  • Resets the branch to the specified commit
  • Discards any changes from later commits
  • Works for local commits only

Using git revert to Reverse a Merge

The git revert command:

  • Creates a new “revert commit” that reverses the changes
  • Keeps commit history and doesn’t discard commits
  • Can be used after push (with some caveats)

To use it:

git revert -m 1 <merge_commit_hash> 
git push

The -m 1 flag specifies the parent commit to revert to.

Key notes on using git revert:

  • Safer alternative to git reset in most cases
  • Preserves existing commits
  • Can handle remote merges in some cases

Handling Remote Merge Reverts

If a merge has already been pushed remotely, resetting or reverting gets more complex:

  • Resetting can cause issues for other developers
  • Pushed reverts require force pushing the branch

In this case it’s best to:

  1. Revert the merge locally
  2. Force push the branch to overwrite history (git push -f)
  3. Ask teammates to reset their remote branch to match (git reset --hard origin/<branch>)

While more disruptive, this will undo the remote merge.

Conclusion

  • Use git reset to undo a local unpushed merge
  • Leverage git revert to reverse merge commits
  • Handle remote merges carefully to avoid issues

Following these best practices will let you safely undo Git merges when needed.

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