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How to Modify and Update a Git Source Code Commit Message

As a software engineer with over 10 years of experience using Git for version control, I often need to go back and modify commit messages to make them clearer or more descriptive. Updating your commit messages is a best practice that leads to better documentation of your code changes over time. Here are the key things you need to know about modifying Git commit messages both before and after you have pushed the commit to a remote repository.

Before Pushing the Commit

If you have not yet pushed the commit to a central repository, modifying the message is straightforward using Git’s --amend option:

  • Run git commit --amend to bring up the commit message editor for the most recent commit.
  • Edit the commit message to update it or fix any typos.
  • Save and close the editor to complete amending the commit.

This will replace the existing commit with a new one and update the commit message while keeping the same code changes.

Benefits:

  • Quick and easy way to update commit messages locally.
  • Does not require any history rewriting on the remote repository.

Drawbacks:

  • Only works for commits that have not been pushed yet.

After Pushing with git commit --amend

You can also amend commits that have already been pushed up to a remote repository, but it requires forcing an update by rewriting the commit history. Here are the basic steps:

  • Make your changes to the commit message using git commit --amend as shown above.
  • Run git push --force to force push the amended commit to the remote repository. This overwrites history.
  • Any other developers working on the remote repo will need to fetch your changes and reset their local branches to see the new commit message.

Benefits:

  • Works even if the commit has already been published.

Drawbacks:

  • Rewrites history which can confuse other developers working on the same branch.
  • Overwriting shared commit history should usually be avoided in collaborative projects.

Modifying Older Commit Messages with git rebase

To modify commit messages further back in your project’s history, you can use the powerful git rebase tool. This also does a history rewrite but gives you total control over amending old commits.

Here is the basic workflow:

  • Run git rebase -i HEAD~N where N is the number of commits back you want to modify.
  • An interactive rebase editor will open showing a list of commits.
  • Change pick to reword on any commits you want to modify the message for.
  • Save and close the file when you are done.
  • An editor will open for each commit marked for rewording where you can alter the message.
  • When done, run git push --force to force push the rewritten history to the remote repository.

This is very useful for cleaning up old commit messages without losing the context of the history.

Benefits:

  • Complete control over rewriting commit history and messages.

Drawbacks:

  • Requires force pushing rewritten history which can impact other developers.
  • Interactive rebase can be complicated for novice git users.

Additional Tips

Here are some additional tips for managing your commit history and messages:

  • Use descriptive, imperative commit messages – Proper commit messages serve as documentation and help other developers understand the changes.
  • Fix mistakes early before too many dependent commits – It becomes harder to modify history the more subsequent commits that rely on it. Fix issues early.
  • Communicate history rewrites – If working on a team, communicate when you are doing a major history rewrite to avoid confusion.
  • Limit how far back you modify – Don’t amend commits from too far back unless absolutely necessary to limit disruption.
  • Squash minor commits before merging to keep history clean – Use git rebase -i to squash minor commits before merging feature branches.

Conclusion

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