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”. !ref icon=“rocket” text=“How to stage a folder/file”

• 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#

:icon-arrow-up: Go to the desired directory, for example: cd ~/myproject

• Initialize a local repository:

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

• Or initialize a remote repository:

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

The git clone command will directly import the project and its source files into a folder with its name.

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

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git pull origin mybranch

NOTE

“Pull” and “fetch” allow you to request a repository

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

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.

:icon-unverified: More information is available here

NOTE

git status allows you to see the changes of folders/files compared to the last saved version (commit).

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.

NOTE

These changes are applied from the “working directory” and are no longer in “Stage”, they are moved to the “repository”.

TIP

It is recommended to name commits with a different name for each modification step.
git commit -m step1 allows you to name (indicate concisely the content of the commit, max. 60 characters).
git commit --amend -m "step2" allows you to change the name of an existing commit!

Installation of Git#

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

NOTE

Thanks to the --global option, you will only need to do this once.

CAUTION

If you want to change your username for a specific project, you will need to pass this line again without the --global option.

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

TIP

It is recommended to activate colors for better visibility:

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

Push the repository#

• First add the origin (the remote location of the repository):

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.

• Select the branch where you want to upload the repository:

git branch -M mybranch

• Upload 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.

ℹ️ 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:

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  list
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* master

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

NOTE

The -d option deletes a branch (git branch -d mybranch) The -b option creates a new branch (git checkout -b mybranch)

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

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Switched to branch 'mybranch'

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

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git checkout -b mynewbranch <commit_sha>

TIP

Note that git checkout <sha> also allows you to return to a commit.

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

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

The sha is made up of the hexadecimal characters after the ”*” :icon-arrow-right: 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

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* mynewbranch
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master

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git stash apply

Git reset#

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

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

git reset --hard HEAD^

Github authentication#

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

To generate this pair of keys, I use the following command:

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)).

Then, I get the public key which will be used to prove my identity to github:

ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAKC91uWop9DhfNh23i6u0yUlhEkGv0IOQKzhU5ltKBkAG contact@contactit.fr

I can now enter it in: Settings>SSH and GPG keys, in the title section I can put any name and in the key section I paste ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAKC91uWop9DhfNh23i6u0yUlhEkGv0IOQKzhU5ltKBkAG contact@contactit.fr, validate with Add SSH key.

Summary of Git/Github#