Git cheatsheet

Undo pushed merge cos I meant to rebase

1. checkout (detached) the last commit before the merge commit. (I don’t know how to do it in bash yet—I use VS Code GUI)
2. create new branch from it

   git checkout -b <new branch name>

3. checkout my main branch (in this case v4 not main (yes I was fixing this repo—turns out I don’t like npx quartz sync, I want to commit granularly)) and reset to the last commit I still want to include

   git reset --hard <the commit I want to go back to> # or usually `HEAD~2`

4. rebase the new branch onto the main branch

   git checkout main
   git rebase <new branch name>

5. force push to origin

   git push --force origin v4

I’m still not sure about the reset in step 3. It might not be generally applicable. Well, I will know more next time this happens.

Rebase to main

git checkout main
git rebase <new changes branch>

I need to write this down because I never remember whether it’s that or the other way around

Delete local branch

git branch -D <branch name> # -D means --delete --force
git branch -d <branch name> # will error if branch hasn't been merged

Multi-account Git config essentials

a.k.a. what I do when setting up multiple git accounts on a new OS

1. generate an ssh key for each account following this GitHub tutorial. give it a name that represents the associated account, not just ”id_ed25519“

2. create ssh config file:

   ~/.ssh/config

   # study
   Host study.github.com
       Hostname github.com
       PreferredAuthentications publickey
       IdentityFile ~/.ssh/id_ed25519-study
   # play
   Host play.github.com
       Hostname github.com
       PreferredAuthentications publickey
       IdentityFile ~/.ssh/id_ed25519-play

3. create folder for each account, create separate config files for each account

   ~/.gitconfig-study

   [user]
     name = student
     email = student@users.noreply.github.com
     signingkey = ~/.ssh/id_ed25519-study.pub
   [url "git@study.github.com"]
     insteadOf = git@github.com

   ~/.gitconfig-play

   [user]
     name = fun
     email = fun@users.noreply.github.com
     signingkey = ~/.ssh/id_ed25519-play.pub
   [url "git@play.github.com"]
     insteadOf = git@github.com

4. assign each config to its respective directory

   ~/.gitconfig

   [includeIf "gitdir:~/study/"]
     path = ~/.gitconfig-study
   [includeIf "gitdir:~/play/"]
     path = ~/.gitconfig-play
   [gpg]
     format = ssh
   [init]
     defaultBranch = main
   [core]
     editor = code --wait
     autocrlf = input
   [pull]
     rebase = true

Change commit author name and email on past commits

Sometimes, for some reason, I have my config email set to automation@github.io or whatever and forget to change that for the new project I’m working on. This can change commit author name and email on past commits with certain email without modifying the timestamp. (Source)

$ git filter-branch --commit-filter '
	if [ "$GIT_AUTHOR_EMAIL" = "automation@whatever.io" ];
	then
		GIT_AUTHOR_NAME="Correct Name";
		GIT_AUTHOR_EMAIL="correctemail@example.com";
		git commit-tree "$@";
	else
		git commit-tree "$@";
	fi' HEAD