Changing the author and committer name/email for multiple commits in Git can be a crucial task for developers who need to correct mistakes, anonymize contributions, or standardize the identity associated with commits. The process typically involves using interactive rebase or filter-branch commands, both powerful tools when working with Git history. This article delves into the technical steps required to make these changes, complete with examples and additional considerations.

Technical Explanation

Git identifies changes using commit objects, which include metadata like the author name, author email, committer name, and committer email. To change this metadata across multiple commits, you can employ the following methods.

Using git rebase for Editing Commits

Step-by-Step Process

1. Start an Interactive Rebase
   Begin the rebase process from the commit just before the one you want to change.

   git rebase -i HEAD~n

Replace n with the number of commits you want to go back from the current HEAD.

1. Mark Commits for Edit
   In the interactive editor that opens, change the command from pick to edit for each commit you wish to modify.
2. Modify Author/Committer Information
   For each commit:
   • Stop at the commit by typing:

     git commit --amend --author="New Author Name <[email protected]>"

• Adjust committer details, if necessary:

     export GIT_COMMITTER_NAME="New Committer Name"
     export GIT_COMMITTER_EMAIL="[email protected]"

1. Continue the Rebase
   After modifying each commit:

   git rebase --continue

1. Force Push Changes
   • Since history has changed, force push to update the remote:

    git push origin branch-name --force

Using git filter-branch

If you need to alter author details for a range of commits or an entire branch, git filter-branch is more appropriate.

Step-by-Step Process

1. Backup Current Branch It's essential to create a backup of your current branch before making history alterations.

   git branch backup-branch

1. Run Filter-Branch Command
   The following syntax changes author/committer information across all commits:

1   git filter-branch --env-filter '
2   if [ "$GIT_COMMITTER_EMAIL" = "[email protected]" ]
3   then
4       GIT_COMMITTER_NAME="New Name"
5       GIT_COMMITTER_EMAIL="[email protected]"
6   fi
7   if [ "$GIT_AUTHOR_EMAIL" = "[email protected]" ]
8   then
9       GIT_AUTHOR_NAME="New Name"
10       GIT_AUTHOR_EMAIL="[email protected]"
11   fi
12   ' -- --all

1. Force Push Updated History
   After applying the filters:

   git push origin --force --all

Considerations

• Backup Before You Begin: Before rewriting history, ensure you have backups, as this process is irreversible and sensitive operations might lead to data loss.
• Impact on Collaborators: Changing commit history will affect anyone else using the same branch. Communicate these changes to your team, and coordinate to prevent merge conflicts.
• Checking Updated History: Verify the updated commit history using:

  git log

Key Points Summary

Conclusion

Changing the author and committer information in multiple Git commits can significantly improve codebase consistency and rectify errors. Depending on the required scope of changes, either git rebase or git filter-branch can be employed to achieve the desired outcome. Remember to communicate with the team about any history changes and always ensure adequate backups before performing such operations.