You committed many times with the wrong email or name - maybe you forgot to configure Git on a new machine. Now you need to fix the author information across multiple commits. Git provides several methods to batch update commit metadata. **TLDR:** To change author for multiple commits, use `git rebase -i` and mark commits as "edit", or use `git filter-branch` for extensive changes across all history. For modern Git, use `git filter-repo` with a mailmap file. These commands rewrite history, so coordinate with your team before force pushing. In this guide, you'll learn how to safely change author information for many commits. ## Prerequisites You'll need Git installed on your system and commits with incorrect author information. Basic familiarity with Git rebase and history rewriting will be helpful. Always backup your repository before rewriting history. ## Understanding Author vs Committer Each commit stores two identities: ```bash # View full commit info git log --format=fuller -1 # Author: Jane Developer # AuthorDate: Mon Jan 15 14:30:00 2024 # Commit: John Smith # CommitDate: Mon Jan 15 14:35:00 2024 ``` - **Author**: Original creator of the changes - **Committer**: Person who committed to the repository Usually you want to change both to match. ## Using Interactive Rebase for Recent Commits For a manageable number of recent commits: ```bash # Rebase last 10 commits git rebase -i HEAD~10 ``` Git opens your editor: ``` pick abc123 Commit 1 pick def456 Commit 2 pick ghi789 Commit 3 ... ``` Change `pick` to `edit` for commits to modify: ``` edit abc123 Commit 1 edit def456 Commit 2 edit ghi789 Commit 3 ``` Save and close. Git stops at each marked commit: ```bash # At each stop, change the author git commit --amend --author="Jane Developer " --no-edit git rebase --continue # Repeat for each 'edit' stop ``` ## Automated Rebase Script To avoid manual intervention at each commit: ```bash #!/bin/bash # fix-author.sh git rebase -i HEAD~20 --exec 'git commit --amend --author="Jane Developer " --no-edit --allow-empty' ``` This automatically changes the author for all commits in the rebase. ## Using Filter-Branch for Extensive Changes For many commits or complex patterns, use filter-branch: ```bash git filter-branch --env-filter ' OLD_EMAIL="wrong@email.com" CORRECT_NAME="Jane Developer" CORRECT_EMAIL="jane@example.com" if [ "$GIT_COMMITTER_EMAIL" = "$OLD_EMAIL" ] then export GIT_COMMITTER_NAME="$CORRECT_NAME" export GIT_COMMITTER_EMAIL="$CORRECT_EMAIL" fi if [ "$GIT_AUTHOR_EMAIL" = "$OLD_EMAIL" ] then export GIT_AUTHOR_NAME="$CORRECT_NAME" export GIT_AUTHOR_EMAIL="$CORRECT_EMAIL" fi ' --tag-name-filter cat -- --branches --tags ``` This changes all commits where the author or committer matches the old email. ## Using Multiple Conditions To handle several wrong emails: ```bash git filter-branch --env-filter ' # Define mappings case "$GIT_AUTHOR_EMAIL" in "old1@email.com") GIT_AUTHOR_NAME="Jane Developer" GIT_AUTHOR_EMAIL="jane@example.com" ;; "old2@email.com") GIT_AUTHOR_NAME="Jane Developer" GIT_AUTHOR_EMAIL="jane@example.com" ;; esac case "$GIT_COMMITTER_EMAIL" in "old1@email.com") GIT_COMMITTER_NAME="Jane Developer" GIT_COMMITTER_EMAIL="jane@example.com" ;; "old2@email.com") GIT_COMMITTER_NAME="Jane Developer" GIT_COMMITTER_EMAIL="jane@example.com" ;; esac export GIT_AUTHOR_NAME GIT_AUTHOR_EMAIL export GIT_COMMITTER_NAME GIT_COMMITTER_EMAIL ' --tag-name-filter cat -- --branches --tags ``` ## Using git-filter-repo (Modern Approach) The recommended modern tool for rewriting history: ```bash # Install git-filter-repo # pip install git-filter-repo # Create a mailmap file cat > mailmap.txt << EOF Correct Name Correct Name Correct Name Old Name EOF # Apply the changes git filter-repo --mailmap mailmap.txt # Filter-repo is faster and safer than filter-branch ``` ## Mailmap Format The mailmap syntax: ``` Proper Name Proper Name Commit Name ``` Examples: ``` # Just email change Jane Developer # Name and email change Jane Developer Jane D # Multiple old emails to one new Jane Developer Jane Developer ``` ## Changing Only Specific Commits To target commits by date or other criteria: ```bash git filter-branch --env-filter ' # Only change commits after specific date COMMIT_DATE=$(git log -1 --format=%at $GIT_COMMIT) CUTOFF_DATE=$(date -d "2024-01-01" +%s) if [ "$COMMIT_DATE" -gt "$CUTOFF_DATE" ] && [ "$GIT_AUTHOR_EMAIL" = "old@email.com" ] then export GIT_AUTHOR_NAME="Jane Developer" export GIT_AUTHOR_EMAIL="jane@example.com" export GIT_COMMITTER_NAME="Jane Developer" export GIT_COMMITTER_EMAIL="jane@example.com" fi ' --tag-name-filter cat -- --branches ``` ## Verifying Changes After rewriting history, verify the changes: ```bash # Check recent commits git log --format="%h %an <%ae> | %cn <%ce>" -10 # Check all unique authors git log --format='%an <%ae>' | sort -u # Check specific commit git show --format=fuller abc123 ``` ## Handling Remote Repository After changing history locally: ```bash # Backup first! git branch backup-before-push # Force push (coordinate with team!) git push --force-with-lease origin main # Or to all branches git push --force-with-lease origin --all ``` **Warning:** Force pushing rewrites remote history. Only do this on branches you own or after team coordination. ## Changing Author in Specific Branch To only change commits in one branch: ```bash # Rewrite only feature-branch git filter-branch --env-filter '...' feature-branch # Or with filter-repo git filter-repo --mailmap mailmap.txt --refs refs/heads/feature-branch ``` ## Preserving Merge Commits When rewriting, preserve merge structure: ```bash # With filter-branch git filter-branch --env-filter '...' --tag-name-filter cat -- --branches # With rebase (use --rebase-merges) git rebase -i --rebase-merges HEAD~20 ``` ## Fixing Partial History To change commits only in a date range: ```bash # Change commits between two dates git filter-branch --env-filter ' COMMIT_TIMESTAMP=$(git log -1 --format=%at $GIT_COMMIT) START=$(date -d "2024-01-01" +%s) END=$(date -d "2024-06-30" +%s) if [ "$COMMIT_TIMESTAMP" -ge "$START" ] && [ "$COMMIT_TIMESTAMP" -le "$END" ] then # Apply author changes export GIT_AUTHOR_NAME="Jane Developer" export GIT_AUTHOR_EMAIL="jane@example.com" fi ' HEAD~100..HEAD ``` ## Handling Multiple Contributors When fixing a team repository: ```bash # Create comprehensive mailmap cat > .mailmap << EOF Jane Developer

Jane Developer John Smith Alice Johnson EOF # Apply with filter-repo git filter-repo --mailmap .mailmap # Commit the mailmap for future reference git add .mailmap git commit -m "Add mailmap for author corrections" ``` ## Testing Before Force Push Test the rewrite on a copy: ```bash # Create test branch git branch test-rewrite # Rewrite the test branch git filter-branch --env-filter '...' test-rewrite # Verify it looks good git log --format="%an <%ae>" test-rewrite | sort -u # If good, apply to main branch git filter-branch --env-filter '...' main # Delete test branch git branch -D test-rewrite ``` ## Recovering from Mistakes If rewrite goes wrong: ```bash # View reflog to find pre-rewrite state git reflog # Reset to before rewrite git reset --hard HEAD@{5} # Or use backup branch git reset --hard backup-before-rewrite ``` ## Cleaning Up After Filter-Branch Filter-branch leaves backup refs: ```bash # Remove backup refs git for-each-ref --format="%(refname)" refs/original/ | xargs -n 1 git update-ref -d # Force garbage collection git reflog expire --expire=now --all git gc --prune=now --aggressive ``` ## Communicating with Team Before force pushing: ```bash # Notify team echo "Team: I need to fix author info in main branch. Please do not push to main for the next hour. After I'm done, you'll need to: 1. git fetch origin 2. git reset --hard origin/main 3. Reapply any local commits" ``` ## Alternative: Using Mailmap Without Rewriting To fix how Git displays authors without rewriting history: ```bash # Create .mailmap in repository root cat > .mailmap << EOF Jane Developer EOF # Commit mailmap git add .mailmap git commit -m "Add mailmap for author display" # Git now displays Jane Developer instead of old name # But commits are not rewritten git log # Shows corrected names ``` This is safer but does not actually change commit data. ## Best Practices Always create a backup: ```bash git branch backup-$(date +%Y%m%d) git push origin backup-$(date +%Y%m%d) ``` Test on a single branch first: ```bash # Test on feature branch git checkout -b test-branch git filter-branch --env-filter '...' test-branch # Verify # If good, apply to other branches ``` Use filter-repo instead of filter-branch: ```bash # Modern, faster, safer git filter-repo --mailmap mailmap.txt # vs old method git filter-branch --env-filter '...' ``` Document the change: ```bash # After fixing git tag -a author-fix-2024 -m "Fixed author information for commits before this point" git push origin author-fix-2024 ``` Coordinate force pushes: ```bash # Before force push # 1. Announce to team # 2. Pick low-activity time # 3. Verify everyone is aware git push --force-with-lease origin --all ``` Now you know how to change author information for multiple commits in Git. Use interactive rebase for recent commits, filter-branch or filter-repo for extensive changes, and always backup before rewriting history. Coordinate with your team when force pushing changes to shared repositories.

Tag: History Rewriting

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How to Change Author and Committer for Multiple Commits in Git