GitHub

Prerequisites: Intro to Git

Setup

Create an account on GitHub.

Create SSH key pair

ssh-keygen -t rsa -b 4096 -C "your_email@youremail.com"

See this for more.

Add public key to GitHub

cat ~/.ssh/id_rsa.pub

Copy the entire block, then follow the instructions here to add it to your account.

Usage

To push an updated commit, it's best to use this command to not overwrite a teammates commit. If you cannot push by running this command then update your local repo by pulling and rebasing, then run this command again.

git push --force-with-lease

New patchset

Make sure new patchsets are created with git commit. Using git commit --amend will change a commit already merged upstream and lead to conflicts. Commit messages should have a format like this:

Implement a thing

Optional extended description that should be complete sentences.

Fixes #42.

where 42 would be the issue number being closed by this PR. The last line ensures the issue is automatically closed when the PR is merged. Make sure each issue resolution is a separate branch and PR.

Revisions to patchset

Any changes should be incorporated into the commit previously pushed by either amending or rebasing (not pushing a new commit on top of the old one). Gerrit tracks the revisions using the "Change-Id" line at the bottom of the commit message. Make sure this line does not change and remains the last line during commit message modifications. Otherwise, a new patchset will be created instead.

Verify this was done correctly by inspecting the output of git log main..HEAD. There should be only one commit listed and its Change-Id should match the old one.

Uncommitted changes

git commit --amend

Squashing committed changes

If a new commit or commits were made while working, they should be squashed into the first before submitting it all as a new revision. To do so, run

git rebase -i <commit hash before your commits>

The first commit in the resulting generated file should be set to "r" for "reword" if the commit message needs to be altered to include parts of the other two commits. The other commits should be set to "f" for "fixup" so their contents are squashed into the first commit. git rebase descriptions for other options are in the file comment.

Git (advanced usage) lecture notes

• Git (advanced usage) lecture slides

Versioning

• Easily get commit later? (tag)
• Getting to tagged commit later? (switch)
• now in detached head state
• can git switch main to get back to tip of main
• can make commits
• make sure commits are saved?
• git branch temp
• git switch temp
• Update main to temp... WARNING: destructive!
• git branch -f main temp (fine if changes on main were bad)
• git switch main
• Or... merge it with HEAD
• Find commit from git reflog
• git switch main
• git merge HEAD@{1} (where HEAD{1} is commit in temp branch from reflog)
• Remove temp branch since it's reachable by main at HEAD now
• git branch -d temp
• IF you just want to edit the commit checked out and not make a new one
• git rebase -i with edit mentioned next to commit
• triggers commmit --amend scenario -> git rebase --continue

Messing with history

• Changing last commit
• Messed up commit message? (git commit --amend)
• Forgot to add files or added wrong ones? (add/rm then git commit --amend)
• Want to change a bunch of commits? rebase!
• git rebase -i is a fantastic tool
• Clean up a billion local commits that don't make sense apart?
• Compress commits w/ squash
• Reorder commits
• Remove commits
• WARNING: Only do this with commits that aren't public yet!

Nuclear option for binary files

• git filter-branch --tree-filter 'rm -f largeFile.out' HEAD

Useful Git features

• End-of-line conversion (crlf or eol)
• Custom diff/merge driver
• textconv gitattribute (converting to text for performing a diff)
• Other gitattributes (e.g. clean/smudge filter)
• Word diff: git diff --color-words
• Merge strategy options (e.g. -Xrenormalize)
• Submodules (subprojects) with git submodule
• Subtree merge (e.g. git subtree, git stree)
• Partial (sparse) switch
• Shallow clone: git clone --depth=
• Multiple worktrees: git worktree
• Searching history for commit message and metadata: git log --grep
• Searching changes in history, pickaxe search: git log -S and git log -G
• Finding errors in history with bisect (also git bisect run
• Tracking code movement with git blame (git blame -M, git gui blame, etc.)
• History of lines: git log -L
• Detaching HEAD: git switch --detach, git switch
• Orphan branches with disconnected history (gh-pages, todo, man, etc.)
• Merging independent histories, joining different projects together (outside subtree merge)
• Alternates mechanism (sharing object database), including git clone --reference
• Stash and autostash (also git stash --keep-index
• Commit message templates, and/or commit-related hooks
• Interactive commit / per-hunk comitting / partial commit / splitting commits
• Interactive rebase, fixup commits (small scale history editing)
• git filter-branch or equivalent, like BFG Repo Cleaner (large history rewriting)
• Committing with dirty tree (keeping some changes uncommitted)
• reflog (including @{1}, @{yesterday}, @{-1} / -, git log -g)
• Include mechanism for configuration files
• Client-side hooks (e.g. post-update, pre-push)
• Server-side hooks (e.g. pre-receive, update, post-receive)
• git-aware shell prompt
• Git aliases, shell aliases for git, or own git scripts
• One-way interaction with other SCMs (from SCM to git)
• Two-way interaction with other SCMs (from SCM to git, and from git to SCM)
• Object overlays (git replace or grafts)
• Object annotation: git notes