Re-writing previous git commits to change committer author/email

If you’ve committed a number of git commits using a wrong user.name or user.email value, you can re-write previous commits with:

git filter-branch --commit-filter '
        if [ "$GIT_COMMITTER_NAME" = "Old Name" ];
        then
                GIT_COMMITTER_NAME="new-name";
                GIT_AUTHOR_NAME="new-name";
                GIT_COMMITTER_EMAIL="new-email";
                GIT_AUTHOR_EMAIL="new-email";
                git commit-tree "$@";
        else
                git commit-tree "$@";
        fi' HEAD

Note that this will re-write all commits on the current branch matching the if condition which may or may not be what you’re looking for, so be careful. push the changes back to your remote origin as needed.

This is based on answers to this question here.

Moving a git ‘master’ branch to ‘main’

By default, the git install on my MacOS 11.5 creates new projects with a ‘master’ branch, but GitHub which I push to for my remote projects has been creating new projects with a default branch of ‘main’ for some time now.

To move a master branch to main locally, set it as the default branch and then push to GitHub I use the following steps (taken from multiple places but mainly from this article):

Create a new main branch from master locally:

git branch -m master main

Add remote GitHub repo:

git remote add github https://your-repo-url

Pull remote changes from remote main branch

git pull github main

Set upstream branch to track main

git branch  --set-upstream-to github/main

Push local to github main

git push github main

If you have changes in the new remote project (like a readme) that don’t exist locally yet and you get the error: “fatal: refusing to merge unrelated histories” then pull with the allow unrelated histories option:

git pull github master --allow-unrelated-histories

Now:’git push’ and you should be good.

For my local development these steps are enough for what I need, but if you have a master in your remote repo too and want to delete it there are additional steps in the article linked above.

git tags and pushing to a remote repo

Tags are useful to mark specific versions or releases of your code in a repo on a given branch. To tag everything on the current branch, use:

git tag new-tag-name

To push a new tag to a remote repo, you can either push all tags (which is not recommended):

git push remote-name --tags

or push a specific tag:

git push remote-name tag-name

More example in this SO question.

Removing commit history in Git

To avoid committing files to version control you can add their names to a .gitignore file, and to committing local changes to an already version controlled file you can use the git command described in my previous post here.

How can you remove history if you’ve already committed a file? For example, let’s say you have a properties file with some environment specific values that you’ve committed, but you want to remove the history of those committed values?

This FAQ walks through the steps needed, which in summary are:

    • Remove all history from the repo:
git filter-branch --force --index-filter 'git rm --cached --ignore-unmatch path/to/your_file_name' 
  --prune-empty --tag-name-filter cat -- --all
  • on Windows, replace the ‘ with “
  • add the filename to .gitignore if you want to avoid future commits (and commit .gitignore: git commit -m “updated gitignore” )
  • push changes back to your remotes: git push remotename master –force

If you need to make local changes to a tracked file and then not commit them in future commit, use the ‘git update-index -skip-worktree’ as described here.