LinuxSysAdminsDoc/Git/readme.md

# Git

## Description

Git is a free and open source distributed version control system designed to handle everything from small to very large projects with speed and efficiency. 

## Useful links

- a very handy [cheat sheet](https://gitea.86thumbs.net/waldek/LinuxSysAdminsDoc/raw/branch/master/Git/SWTM-2088_Atlassian-Git-Cheatsheet.pdf) in pdf outlines the basic Git commands to help you learn git, as well as more advanced concepts such as Git branches, remote repositories, undoing changes, and much much more
- the main git [documentation](https://git-scm.com/book/en/v2) is an excellent reference manual

## Git System

The diagram below outlines the main gt commands and how they relate to the version control system.
In our classes the **local** is the repository on your own computer and the **remote** is the corresponding repository you create on our [gitea](https://gitea.86thumbs.net/) server.
Nothing is stopping you from hosting your own gitea server or pushing your local repository to a third party server such as [gitlab](https://about.gitlab.com/).

![Git System](img/Git_Guide.png)

A remote repository is often referenced by the name **origin** but this naming is fully up to you.
If you would push to multiple remote locations you could for example add one named gitea for our own and gitlab for your gitlab account.

```bash
git remote add gitea https://gitea.86thumbs.net/USER/REPOSITORY.git
git remote add gitlab https://gitlab.com/USER/REPOSITORY.git
```

# Basic commands

## Git clone

Clone repo located at **\<repo>** onto local machine. Original repo can be located on the local file system or on a remote machine via **HTTPS** or **SSH**.
Throughout the classes you'll first clone via HTTPS but once we'll learn about [RSA](https://en.wikipedia.org/wiki/RSA_(cryptosystem)) you'll be able to clone, push and pull over SSH.

```bash
git clone $REPOSITORY_URL

```

## Git config --global name & email 

Before you can use git you **need** to identity yourself.
Git uses this information in each commit so we can keep track of **who** did **what** **when**.

```bash
git config --global user.name "$FISTNAME $LASTNAME"
git config --global user.email "$EMAIL"
```

Name and email are **required** configuration settings but there are a lot more settings you can change to your liking.
For example you can set the user interface to have colors by default by setting the following configuration.

```bash
git config --global color.ui auto
```

All of the possible configuration settings can be seen my running:

```bash
man git-config
```

Additionally you can read up on all of these settings a bit more on the [documentation page](https://www.git-scm.com/book/en/v2/Customizing-Git-Git-Configuration) online.

## Git init

To initialize an existing directory as a Git repository you have to input the following command into a shell.
On windows your best bet is to launch a **git bash** shell by right clicking in the folder.
On linux you can just open a terminal, navigate to the desired directory and execute the command.

```bash
git init
```

If you want to create a new directory with git version control inside it you run the following command.

```bash
git init $DIR_NAME
```

## Git status

List which files are staged, unstaged, and untracked.
This gives you a good overview of the current state of you repository and hints towards which files you can or should stage.

```bash
git status
```

## Git add 

By staging files you put them in the list to be added to the next commit.
You can add one or more files at the same time.
Complete directories can also be added.

```bash
git add readme.md image.jpg
```

## Git rm 

Delete the file from project and stage the removal for commit.
Do keep in mind that this removes the file from the next commit but the file will still exist in the previous commits.This makes it very difficult to *lose* files for ever.

```bash
git rm $FILENAME
```

Change an existing file path and stage the move.

```bash
git mv $OLDPATH $NEWPATH
```

Show all commit logs with indication of any paths that moved.

```bash
git log --stat -M
```

If you ever *lose* a file you can use the following command to locate when files got deleted.
Remember that *when* is tied to a commit.
Once you find the commit you can check out only that file to bring it back to your working directory.

```bash
git log --all --full-history -- "**/$FILENAME*"
git log --all --full-history -- $PATH_TO_FILE
git show $SHA -- $PATH_TO_FILE
git checkout $SHA^ -- $PATH_TO_FILE
```

## Git commit 

You commit your staged content as a new commit snapshot with the following command.
The message you include in the commit is fully up to you but as a general rule of thumb it should explain what the commit does.
For example: this commit *"adds pictures to the asset folder"*
Some projects have serious commit message [guidelines](https://www.datree.io/resources/git-commit-message), others not.

```bash
git commit -m "$YOUR_COMMIT_MESSAGE"
```

If the identity is not correct you can fix this this the following command.

```bash
git commit --amend --reset-author
```

## Git diff

Show unstaged changes between your index and working directory.
Unstaged changes are files that have changes to them and have not been added with the *git add $FILENAME* command.

```bash
git diff
```

## Git log

Show all commits in the current branch’s history.
This can be very handy, especially if the commit messages give a clean idea of *what* the commit does.

```bash
git log
```

More elaborate log view can be accieved with optional argument.
Some handy ones are listed below.
 
### Graphs

The --graph option draws an ASCII graph representing the branch structure of the commit history.
This is commonly used in conjunction with the --oneline and --decorate commands to make it easier to see which commit belongs to which branch:


```bash
git log --graph --oneline --decorate
```

The image below visualizes this output.

![git log with graph option](img/git_log.PNG)

## Tig

Tig is an additional program that can be used to inspect and visualize the commit history.
It uses the underlying Git commands to present the user with various views, such as summarized commit log and showing the commit with the log message, diffstat, and the diff.
As it's a command line program wherein you can navigate, select, etc, we can call it a [tui](https://itsfoss.com/gui-cli-tui/).
It comes installed by default with git in windows but on debian you have to install it manually.

```bash
sudo apt install tig
```

Tig allows you to browse changes in a Git repository and can additionally act as a pager for output of various Git commands.
When used as a pager, it will display input from stdin and colorize it.
To use tig you have to be inside a git repository and invoke the following command.

```bash
tig
```

![tig](img/tig.PNG)

#
# SHARE & UPDATE
#
### Retrieving updates from another repository and updating local repos
=================================

add a git URL as an alias

>git remote add [alias] [url]

fetch down all the branches from that Git remote

>git fetch [alias]

merge a remote branch into your current branch to bring it up to date
>git merge [alias]/[branch]


Transmit local branch commits to the remote repository branch

>git push [alias] [branch]

>git pull

fetch and merge any commits from the tracking remote branch

## BRANCH & MERGE
### Isolating work in branches, changing context, and integrating changes

![Remote Execution](img/Branching.png)

>git branch

list your branches. a * will appear next to the currently active branch

>git branch [branch-name]

create a new branch at the current commit

>git checkout

switch to another branch and check it out into your working directory

>git checkout -b|-B <new_branch> [<start point>]

Specifying -b causes a new branch to be created as if git-branch(1) were called and then checked out. 

If -B is given, <new_branch> is created if it doesn’t exist; otherwise, it is reset. This is the transactional equivalent of

>git merge [branch]

merge the specified branch’s history into the current one

>git log

show all commits in the current branch’s history

## TRACKING PATH CHANGES

### Checker le satus
> git status

Ajouter un element dans la branche
> git add Readme.md

Commit les changement
> git commit -m "First commit"

Show all commit
>git checkout

Merge 
>git merge

## Saving your uncommitted work for a quick fix then getting it back

>git stash

temporarily stash your work since your last commit

>git stash pop

fetch your stashed work to continue it

$ git stash pop stash@{2}

in case you want to apply a specific Stash item (not the most recent one), you can provide the index name of that item in the "pop" option

## Rewriting history 

>git commit --amend -m "New commit message"

replace the last commit

>git commit --amend --no-edit

replace the last commit without changing the commit message

>git rebase -i {branch}

take the precedent commit and add it to your branch

## Ignoring files

>touch .gitignore && echo {what you want to ignore} >> .gitignore

create a file and specify what (extensions, directories, files) to ignore in it

>git rm --cached {fileignored}

remove from the tracking index a file that should be ignored but wasnt because already tracked when the ignore rule was created