Overview

What is git?

Summary of basic commands

• add, commit
• status, diff, show

Handling branches

• switch
• merge

Using git with other people

• pull
• push

Handling small mistakes

• commit --amend
• reset HEAD^

Visualizing: seeing what is the current state of things

$ git status
On branch main

No commits yet

Changes to be committed:
  (use "git rm --cached <file>..." to unstage)
        new file:   hello-world.py

Create a commit

(if you don't use -m, you will be put in a text editor to write the message)

What is a commit?

A commit is when you “save” a version of your files

• you might think of it as a “savepoint”
• you might think of it as a “snapshot”
• you might think of it as a “version”

Some theory about commits

A commit is the unit of change. It roughly contains:

• the changes of the files
• the author
• the identifier (hash) of the parent commit(s)

The value of all these fields will give to your commit its hash, which is used to identify the commit.

Visualizing: seeing the last commit

$ git show
commit 6a195fc8a9ce6059e5db4b51303bde0334473687 (HEAD -> main)
Author: Antoine Fontaine <antoine.fontaine@epfl.ch>
Date:   Sun Feb 20 18:03:47 2022 +0100

    Add hello-world.py

diff --git a/hello-world.py b/hello-world.py
new file mode 100644
index 0000000..e94acca
--- /dev/null
+++ b/hello-world.py
@@ -0,0 +1 @@
+print("hello, world!")

It's time to work on your project and make changes

(here we'll add a line to our file)

Visualizing: seeing the changes made since the last commit

$ git diff
diff --git a/hello-world.py b/hello-world.py
index e94acca..0672c0c 100644
--- a/hello-world.py
+++ b/hello-world.py
@@ -1 +1,2 @@
 print("hello, world!")
+print("this is a simple python program")

A story of trees

blackboard time!

Remember the git logo? that's a tree with branches.

Switching branch or creating one

or, if it doesn't exist already

Visualizing: listing branches

$ git branch
* dev
  main

Integrating changes

You typically switch to master before doing this

(This will be covered in detail in the next talk)

Visualizing: the killer tool

2022-03-02 11:52 +0100 Antoine Fontaine M─┐ [main] Merge branch 'some-feature'
2022-03-02 11:50 +0100 Antoine Fontaine │ o [some-feature] checking the comput
2022-03-02 11:51 +0100 Antoine Fontaine o │ some changes on main
2022-03-02 10:53 +0100 Antoine Fontaine o─┘ [dev] My other message
2022-03-02 10:48 +0100 Antoine Fontaine I Initial commit

Collaborating

Here we'll introduce GitLab as the hosting platform

• Go to https://gitlab.epfl.ch
• Login with your EPFL account
• Create a project for your group

Add your SSH key

Here, I won't post steps, raise your hand and ask for help, or look it up on the internet

You only have to do this once

Get your copy of the repository

Updating a branch to the latest remote version

You typically use git switch main before running it

Sending your branch to the remote

Recommandation for collaborating

• Don't commit on main
• Have one person responsible for main
• That one person will merge stuff
• Before working on a new feature, switch to master, pull and create a new branch from that