Introduction to Git & Github

This tool has three main functions:

• Return to a previous version of your code in case of problems
• Track the evolution of your code step by step
• Work collaboratively without risking deletion of other contributors’ changes

How it works

Git works similarly to incremental backup, where a set of folders/files will be added to the project. Subsequently, a complete history of project changes will be available - these changes can be ignored, added, deleted or merged.

Git offers a branch system, which allows for example, to develop content on the main branch without altering it. This is because Git will have previously made a kind of secondary clone of the branch (using the command git checkout -b mybranch).

• The Working directory corresponds to the project folder on the machine.

• The Stage or Index is the intermediate stage representing all modified files that have been “staged”. See how to add folders and files to the repository.

• The repository is the entire project with its commits.

Local repository

• A repository is the set of folders/files that make up a Git-initiated project.
• In online documentation or professional settings, we often talk about repositories.
• The local repository is stored directly on the machine.

Remote repository

• The remote repository is hosted on a remote server

Initialize a repository

Go to the desired directory, for example: cd ~/myproject

tip: Using 'master' as the name of the initial branch. This default branch name
tip: is subject to change. To configure the initial branch name for all new
tip: repositories, and suppress this warning, run:
tip:
tip:         git config --global init.defaultBranch <name>
tip:
tip: Names commonly chosen instead of 'master' are 'main', 'trunk' and
tip: 'development'. The newly created branch can be renamed with:
tip:
tip:         git branch -m <name>
Empty Git repository initialized in /home/contact/contactit.fr/.git/

Cloning into 'myproject.git'...
remote: Enumerating objects: 11779, done.
remote: Counting objects: 100% (82/82), done.
remote: Compressing objects: 100% (66/66), done.
remote: Total 11779 (delta 52), reused 33 (delta 16), pack-reused 11697
Receiving objects: 100% (11779/11779), 23.50 MiB | 11.34 MiB/s, done.
Resolving deltas: 100% (7047/7047), done.

• It may be necessary to update the repository following a change made by another project contributor, use the command:

git pull origin mybranch

Verification

total 12
drwxr-xr-x  3 contact contact 4096 Sept.  5 15:26 .
drwxr-x--- 14 contact contact 4096 Sept.  5 15:23 ..
drwxrwxr-x  7 contact contact 4096 Sept.  5 15:26 .git

The .git repository is present in the directory in the form of a hidden folder.

Adding folders/files to repository:

The git add command allows you to index files to Git.

• Once the folders/files are indexed, it is possible to make a commit after modifying an element.

Some examples:

• git add README adds the README file
• git add . adds all folders and files in the directory where .git is located.

.gitignore

• .gitignore is a file that lists the folders/files ignored by Git.
• It follows a defined syntax.

Some examples:

• *.log ignores all files with the .log extension
• /folder ignores the folder recursively.

More information is available here

Commits

A “commit” is a version of the previously indexed folders/files, which is different from the subsequent version.

• The git commit command allows you to validate the changes made to the indexed or “staged” files by Git.

Installation of Git

[sudo] Password for contact:
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
git is already the newest version (1:2.34.1-1ubuntu1.4).
git set as "manually installed"
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
1 partially installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n]

• Validate the installation: Y or add the -y option at the end of the command.

Identity

Identity in Git is simply your name and your email address.

These two pieces of information are necessary for Git validation:

• git config --global user.name "John Doe"

• git config --global user.email contact@contactit.fr

• To check that your settings have been taken into account, simply pass the command: git config --list

git config --global color.diff auto
git config --global color.status auto
git config --global color.branch auto

Push the repository

1. Add the remote origin

   git remote add origin https://github.com/username/project/myproject.git

   Note

   git remote add name https://github.com/username/project/myproject.git allows you to shorten the name (url > “name”) to call the repository later.

2. Select the branch

   git branch -M mybranch

3. Push the repository

   git push -u origin mybranch

Branches

• A branch is a copy of the project at a given time T, all modifications made to it will only affect that one. This allows you to have multiple states of the project at the same time.

• The main branch is the main branch (previously called master before October 2020). This branch is often the production branch, therefore stable, of the project.

• There may be other branch names like: dev or staging, these are non-stable development branches, tests and verifications will be made on them once the development is finished.

• If the result is conclusive, it may be possible to merge these branches to the main or master branch. Branches are often used to recreate a test / preproduction and production environment.

Git can be compared to a tree:

• The trunk of the tree is the main branch of the project (most of the time: main or master)

• The branches are elements that come from the trunk but go in different directions

• The leaves are one on top of the other, more or less numerous and fall or remain on the branches like commits.

• Conclusion: in winter there are more commits

• The git branch command allows you to list the branches of the repository:

  list
* master

• Here there are two branches: list and master now main. The * indicates that I am currently in the master branch.

• The git checkout mybranch command allows you to change branches:

Switched to branch 'mybranch'

• It is possible to create a branch from a commit with one of the following commands:

git checkout -b mynewbranch <commit_sha>

• To get the sha (hash) of the commit, we can use the command:

* 5aaf865 Deletion of README
* 6746dbc Adding test text
* 931dc0f Creation of README

The sha is made up of the hexadecimal characters after the ”*” 931dc0f, for example.

Git stash

• The git stash command allows you to put a commit aside so that the current branch becomes clean, therefore without data in the stage area. This situation is suitable when a commit has not been made and the modifications are still in the stage.

• In practice, the git status command returns that there are several changes (in the stage area) that have not been committed.

• Stash allows you to put them aside, to be able to insert them into another branch, which can be useful when you have made a mistake in the branch!

• After executing the git stash command if you run the git status command again, it returns that the working directory is clean (stage empty).

• Now I can go to a new branch or an existing one before inserting the changes made:

git branch mynewbranch

git checkout mynewbranch

* mynewbranch
master

git stash apply

Git reset

• Git reset allows you to undo changes in three different ways: soft, mixed and hard

Delete the last commit

• First, look at the logs and therefore the last commit made and its identifier:

ca83a6dff817ec66f443420071545390a954664949 Author: contact
<contactit[.]yarka(at)slmail.me> Date: Mon Mar 19 21:52:11 2022 -0700

• Note the identifier: ca83a6dff817ec66f443420071545390a954664949 if you need to assign it to another branch after deleting it.

• Now I can delete the last commit with the command:

git reset --hard HEAD^

Github authentication

Github relies on authentication with SSH, therefore a pair of keys.

1. Generate an SSH key pair

   Generating public/private ed25519 key pair.
   Enter file in which to save the key (/home/contact/.ssh/id_ed25519):
   Created directory '/home/contact/.ssh'.
   Enter passphrase (empty for no passphrase):
   Enter same passphrase again:
   Your identification has been saved in /home/contact/.ssh/id_ed25519
   Your public key has been saved in /home/contact/.ssh/id_ed25519.pub
   The key fingerprint is:
   SHA256:myhash contact@mydomain
   The key's randomart image is:
   +--[ED25519 256]--+
   |%@+.             |
   |EBCVB.             |
   |+=Bo.            |
   |+.o* .           |
   |oo..o . S S       |
   |=+oo   o         |
   |B++ o . .        |
   |+=.. o .         |
   |o.    . .         |
   +----[SHA256]-----+

   Tip

   ed25519 is the current recommended standard in terms of security, RSA is compatible with more systems (but less secure (-4096 minimum)).

2. Get the public key

   ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAKC91uWop9DhfNh23i6u0yUlhEkGv0IOQKzhU5ltKBkAG contact@contactit.fr

3. Add the key to GitHub

   Go to Settings > SSH and GPG keys, in the title section put any name and in the key section paste your public key, then validate with Add SSH key.

Summary of Git/Github