Git

Description

Git is a distributed, fast and secure source code management tool. The official Git website is gitscm.org. The Git software was initially created by Linus Torvalds for the Linux project and the current maintainer is Junio Hamano. The development of Git itself is performed on the kernel.org platform.

Operating principle

Contrary to older source code management tools, Git works in a distributed way. This means that developers do not depend on a central repository to commit their changes. Each Git repository contains the full history of the project. Each Git object (changeset, file, directory) is the leaf of a tree with multiple branches. Developing a project with Git is based on a model in which one branch corresponds to one feature. Many revisions of the feature may be archived before the branch gets merged with the main trunk. For a detailed explanation of branch development, we recommend reading this page.

One especially interesting technique is cherry-picking, which is essentially taking part of a branch and merging it with another one.

Basic usage

Generally, a project developer must be able to:

1. clone or create the repository;
2. make changes;
3. commit changes;
4. push changes toward the original repository.

Since Git is distributed, there may not be an authoritative repository.

Summary of commands

Basic commands

Command	Description
git config	Configures git
git init	Creates a new repository
git clone	Clones an existing repository
git add	Adds a file or directory to a repository
git rm	Deletes a file or directory from the repository
git commit	Commits changes to the repository
git push	Pushes commited changes to a different repository
git pull	Pulls changes from a different repository and merges them with your own repository
git fetch	Fetches changes from a different repository without merging them to yours
git merge	Merges changes to the repository

Commands to explore changes

Command	Description
git blame	Gives the origin of each change
git log	Displays changes history
git diff	Compares two versions
git status	Displays status of the current files
git show	Displays various git objects
git cat-file	Displays the content, type or size of objects

Commands for branches, tags and remote repositories

Command	Description
git branch	Manages development branches
git tag	Manages version tags
git remote	Manages remote repositories
git checkout	Checks out a branch or a path
git reset	Changes the head of a branch

Commands for patches

Command	Description
git format-patch	Creates a patch
git am	Applies a patch
git send-email	Sends a patch by email

Other commands

Command	Description
git bisect	Used to diagnose problems
git gc	Collects garbage objects
git rebase	Rebases history of the repository
git grep	Searches for content

Creating or cloning a repository

The first step is usually to create your own repository, or to clone an existing one.

To create a repository:

[name@server ~]$  git init my-project

To clone a repository:

[name@server ~]$  git clone git://github.com/git/git.git

Commiting a change

When the repository is ready, you change directory and edit the file.

[name@server ~]$ cd my-project
[name@server ~]$ nano file.txt

When work is done, you add the file

[name@server ~]$  git add file.txt

and commit the change

[name@server ~]$  git commit

It is then possible to push changes to the origin repository with

[name@server ~]$  git push origin main

In the above command, origin is the remote repository and main is the current branch that will be pushed.

You might have to use git push origin master for older git repositories.

Hosting Git repositories

GitHub and Bitbucket are two of the main Git repository hosting services. They are both available for commercial projects as well as free projects.