Git and GitHub

45 min Foundations Needs: a terminal, a GitHub account

Git saves snapshots of your work. GitHub stores those snapshots online so you do not lose them and other people can see them. In this tutorial you set both up, then push your first project to GitHub.

Why this matters

You will write a lot of code in the next nine months. Some of it will work and then stop working, and you will want the version from yesterday back. Git gives you that.

There is a second reason. When you apply for a job, your GitHub profile is the first thing a hiring manager opens. Every project you finish here should end up there. Start building that history on day one.

How Git works

Four places hold your work. Three of them are on your computer, one is on GitHub. Each command below moves your work from one place to the next.

Keep this picture in your head. Most Git confusion comes from not knowing which of the four boxes your work is sitting in right now.

Step 1: Tell Git who you are

Git writes your name on every snapshot you save. Set it once and you never think about it again.

git config --global user.name "Your Full Name"
git config --global user.email "your-email@example.com"

Use the same email address as your GitHub account. If the two do not match, your commits show up on GitHub without your name attached to them.

Nothing prints when this works. Check it like this:

git config --global --list

Step 2: Let your computer talk to GitHub

GitHub stopped accepting passwords in the terminal. You need a token instead. There are two ways to set this up. The first is easier, so try it first.

GitHub CLI (easier)Personal access token

The gh tool does the whole login for you and stores the token safely.

sudo apt update && sudo apt install gh    # Ubuntu or WSL
gh auth login

Answer the questions like this: GitHub.com, HTTPS, yes authenticate Git with your GitHub credentials, login with a web browser. Copy the one time code it shows you, press Enter, and finish in the browser that opens.

Check it worked:

gh auth status

Use this if gh will not install on your machine.

1. On GitHub, open Settings, then Developer settings, then Personal access tokens, then Fine-grained tokens.
2. Click Generate new token. Give it a name and an expiry of 90 days.
3. Under Repository access, choose All repositories. Under Permissions, set Contents to Read and write.
4. Click generate, then copy the token. GitHub shows it once and never again, so paste it somewhere safe right now.

Then tell Git to remember it:

git config --global credential.helper store

The first time you push, Git asks for a username and password. Type your GitHub username, then paste the token as the password. Git saves it and stops asking.

Do not put your token in a URL

You will find advice online that says to clone like this: git clone https://username:token@github.com/.... It works, and it is a bad habit. Git writes that URL into a file inside your project, and your shell saves it in your command history. One screenshot in a chat channel and someone else has full access to your account. Use one of the two methods above instead.

Step 3: Make the repository on GitHub first

A repository, or repo, is one project folder that Git is tracking. It is easier to create it on GitHub and copy it down than to create it locally and connect it afterwards.

1. On GitHub, click the green New button.
2. Name it my-ml-project.
3. Leave it public.
4. Leave Add a README file unchecked.
5. Click Create repository.

You now have an empty repo and GitHub shows you its address.

Step 4: Copy it to your computer

Cloning downloads the repo and connects your local folder to the GitHub one.

git clone https://github.com/your-username/my-ml-project.git
cd my-ml-project

You should see something like this:

Cloning into 'my-ml-project'...
warning: You appear to have cloned an empty repository.

The warning is fine. The repo is empty because you have not put anything in it yet.

Step 5: The four commands you will use every day

Make a file, check what changed, save it, send it to GitHub. That is the whole loop, and you will run it hundreds of times.

echo "# My ML Project" > README.md

See what Git noticed. Run this whenever you are unsure what state you are in. It is the most useful command in Git.

git status

Git reports README.md as untracked. It can see the file but is not saving it yet.

Pick what to save.

git add README.md

Save it. The message says what you changed. Write it for the version of you who reads it in three months.

git commit -m "Add project README"

Send it to GitHub.

git push origin main

Refresh the repo page in your browser. Your file is there.

Write commit messages in the present tense

Say "Add data loader", not "Added data loader". Git's own messages are written that way, so your history reads consistently. Also, if your message needs the word "and", you are probably saving two things at once. Make two commits.

When something goes wrong

fatal: not a git repository

You are in the wrong folder. Run pwd to see where you are, then cd into the project folder you cloned.

Authentication failed when you push

Your token is wrong, expired, or you typed your GitHub password instead of the token. Generate a new token and run gh auth login again, or delete the saved credentials with rm ~/.git-credentials and push again.

Updates were rejected because the remote contains work

Someone changed the repo on GitHub after you last downloaded it. Run git pull, deal with any conflicts, then push again.

Please tell me who you are

You skipped Step 1. Set your name and email, then commit again.

Check yourself

Do this now, before moving on. It takes five minutes and proves the whole setup works.

1. Add a line to your README.md describing what you plan to build this year.
2. Run git status and read what it tells you.
3. Stage, commit, and push the change.
4. Open the repo on GitHub and find your commit under the commits link.
5. Post the repository link in the cohort channel.

If step 3 fails, the problem is almost always authentication. Go back to Step 2.

Quick reference

Command	What it does	When you run it
git status	Shows what changed and what is staged	Any time you are unsure
git add file.py	Stages one file	After editing
git add .	Stages everything you changed	When all of it belongs together
git commit -m "message"	Saves a snapshot on your machine	After staging
git push	Sends your snapshots to GitHub	After committing
git pull	Brings down other people's work	Before you start working
git log --oneline	Lists your past snapshots	When looking for an old version

Next

You have version control working. Next you need somewhere to run code and see results straight away.

Jupyter notebook setup

Want to go deeper on Git later: the Pro Git book is free and thorough, and Learn Git Branching lets you practise branching visually.