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title Git and GitHub
author UND Association for Computing Machinery
institute https://linktr.ee/UND_ACM
date \today
theme Warsaw
colortheme spruce
fontsize 12pt
aspectratio 169
header-includes \usepackage{hyperref} \hypersetup{colorlinks=true,urlcolor=blue}

What is Git?

Git

Git is a version control system (VCS) created by Linus Torvalds in 2005.

A VCS is a kind of "meta-save" that allows for storing the history of a software project.

They are primarily used for organization and collaboration.

Git Repositories

A software project with its git history and source code is referred to as a repository (repo).

  • .git directory (stores history)
  • working directory (the plaintext source code)

Decentralization

Git is unique from previous version control systems because it's decentralized.

The server/client dynamic is far less rigid (local/remote).

\pagebreak

What is GitHub?

GitHub

GitHub is one example of where git repositories live.

It was founded in 2008 by

  • Tom Preston-Werner
  • Chris Wanstrath
  • P. J. Hyett
  • Scott Chacon

GitHub was acquired by Microsoft in 2018.

GitHub Alternatives

GitHub is not the only git forge, but it is the most popular despite being proprietary.

Alternatives

  • GitLab
  • Gitea
  • Codeberg
  • Sourcehut
  • None (wait until the end)

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Why should I care?

Rollback

Reverting commits

Collaboration

  • Merging branches
  • Merging with upstream/remote

Forking

Fork: Git(Hub) term for a copy (of the source code).

As in a "fork in the road"

  • Soft Fork (pull requests)
  • Hard Fork

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How do I install it?

Installation

Install it via your package management system of choice.

It is in your package management system, whether it's apt, pacman, brew, winget, etc.

For up-to-date install instructions, refer to git-scm.com/downloads

Git Usage

Basic Usage

First, run git help
From then on git status and git log will be your best friends.

Pre-configuration

NAME="Your Name"
EMAIL="[email protected]"

git config --global init.defaultBranch main
git config --global user.name "$NAME"
git config --global user.email "$EMAIL"

Creating a project

git init my-project

cd my-project
ls -la
ls -la .git
git status
git log

First Commit

echo "# My Awesome Project" >> README.md
git status
git log

git add README.md # aka "staging" README.md
git status

git commit -m "Initial Commit"
git log
git status

Second Commit

echo "Description of my awesome project" >> README.md
cat README.md
git status
git diff
git add README.md
echo "It supports both foo and bar" >> README.md
cat README.md
git status
# git restore --staged README.md # unstage
# git restore README.md          # discard
# git add README.md              # update
git restore --staged README.md # unstage
git status

git add README.md              # stage
git status

git diff
git diff --staged

git commit -m "Add project description"
git log

Third Commit

git rm README.md
git status
git commit -m "Remove README"
git log

Reverting the Third Commit

git log
git revert --no-commit HEAD
git status
git log
git revert --continue

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Viewing our Commits

git log
git log -p
git log -p -n 1

git remote -v # outputs nothing

Pushing to GitHub

Create a new repo on GitHub: github.com/new

Fill out the form and click "Create repository"

Click the "SSH" button

git remote add origin "[email protected]:${USERNAME}/my-project.git"
git branch -M main
git push -u origin main

git remote -v

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A Fresh Start

cd ..
rm -rf my-project/

git clone "[email protected]:${USERNAME}/my-project.git"
cd my-project

Push and Pull

# Pull changes from remote
git fetch --all
git merge origin
# git pull  # equiv. to `git fetch && git merge`

# Push changes to remote
echo "Hello" > hello.txt
git add hello.txt
git commit
git push

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Checkout and Branching

Checkout

Git allows users to temporarily view a previous commit by using git checkout and the commit id.

Branching

Git also has a feature called branching, which is used to "split the timeline" so to speak.

Checkout Commits

Notice that after checking out a commit, Git informs us we can create a new branch at this commit.

We may wish to do this to build new features on a known-working previous commit, rather than on main.

git checkout "$COMMIT_ID" # detached HEAD state
git switch -

git checkout "$COMMIT_ID" # detached HEAD state
git switch -c old-branch

git switch main
git branch -d old-branch # delete old-branch

Checkout Branches

git checkout jeff-branch # error: pathspec...
git branch

git branch jeff-branch
git checkout jeff-branch # or `git switch jeff-branch`
git branch

# git checkout -b jeff-branch 
# git switch -c jeff-branch

git branch matt-branch
git branch

\pagebreak

Populating jeff-branch

We'll populate each branch and then merge them, just as we had done earlier with main and origin/main.

git switch jeff-branch
echo "Hello, Jeff!" > hello.txt
git status
git add hello.txt
git commit

Populating matt-branch

git switch matt-branch
echo "Hello, Matt!" > hello.txt
git status
git add hello.txt
git commit

Merging matt-branch and jeff-branch

# git switch matt-branch # currently on matt-branch
git merge jeff-branch

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Conflict!

Merge Conflict

Auto-merging hello.txt
CONFLICT (content): Merge conflict in hello.txt
Automatic merge failed fix conflicts and then commit the result

Finding the Conflict

grep -rl "======="
grep -r  "=======" -C 5
cat hello.txt
# Resolve the merge conflict in your text editor of choice

hello.txt

<<<<<<< HEAD
Hello, Matt!
=======
Hello, Jeff!
>>>>>>> jeff-branch

Post-Conflict

git status
git add hello.txt
git commit

git switch main
git merge matt-branch

Final Push

Push all branches to origin (i.e. GitHub)

git push -u origin --all

\pagebreak

GitHub SSH Keys

Creating an SSH key

EMAIL="[email protected]" # Should match your GitHub account

ssh-keygen -t ed25519 -C "$EMAIL"
eval "$(ssh-agent -s)" # Start the SSH agent

ssh-add "$HOME/.ssh/id_ed25519"

clear
cat "$HOME/.ssh/id_ed25519.pub" # Copy this output

GitHub configuration (SSH keys)

GitHub > Settings > SSH and GPG keys > New SSH key

Title: <Describe the computer>

Key: <The contents of the .pub file>

ssh -T [email protected]

# Hi $USER! You've successfully authenticated, but GitHub
# does not provide shell access.

See also Connecting to GitHub with SSH - GitHub Documentation

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Private Email

GitHub Configuration (noreply emails)

GitHub > Settings > Emails

Check "Keep my email address private"

Check "Block command line pushes that expose my email"

Git Configuration (noreply emails)

EMAIL="[email protected]"
git config --global user.email "$EMAIL"

Parting Thoughts

Commit Messages

Merging and Maintainership

Git Features

\pagebreak

Advanced git clone-ing

# Renamed repo
git clone https://github.com/acm-ndsu/GitHub-Workshop \
GitHub-Workshop-but-cooler

# Bare repo
git clone --bare https://github.com/torvalds/linux linux.git

# Shallow Clones
git clone https://github.com/git/git --depth 2

# Local Clone
git clone ./my-project ./my-project-clone
cd ./my-project-clone
git remote -v

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Recap

What is Git and GitHub?

  • Git is a version control system
  • GitHub is a place where git repos live
  • Git can be used independently of GitHub

Git Commands - Part 1

git status
git log
git diff

git init
git clone

git add
git commit

Git Commands - Part 2

git restore
git revert
git rm

git pull
git push
git merge

git branch
git checkout
git switch

Git Commands In Context

git clone "$URL" # or `git init "$REPO_NAME"`
cd "$REPO_NAME"

git pull
git add "$FILE"
git status
git commit
git push

git log

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Questions?

Additional Resources