• Download from https://git-scm.com/downloads.
• Or install via your favorite package manager.

								% brew install git # macOS
								% apt install git # Ubuntu
							

• Setup user information, so git knowns who is making changes.

								% git config --global user.name "JohnDoe"
								% git config --global user.email "JohnDoe@unknown.com"
								% git config --global core.editor "code --wait"
								% git config --global init.defaultBranch main # Github
								% git config --global core.autocrlf true # Windows
							

								% git config --global core.editor "atom --wait"
								% git config --global core.editor "'c:/program files/Notepad++/notepad++.exe' -multiInst -notabbar -nosession -noPlugin"
								% git config --global core.editor "emacs"
								% git config --global core.editor "vim"
								% git config --global core.editor "gedit --wait --new-window"
								% git config --global core.editor "open -W -n" # TextEdit on mac
							

• Let us first create a folder that will serve as a container for our new repository.

								% mkdir beer # create folder
								% cd beer # move into folder
								% git init # init a repository
							

• Check that the .git folder was actually created.

								% ls -a # list all files/folders
								. .. .git
							

• Let us create a document called volta_brau.txt.

								% code volta_brau.txt
							

								% git status
							

• git tells us that there are untracked changes. So let us add them to the staging area.

								% git add volta_brau.txt # adds one file at a time
								% git add . # use . to add all changes
							

• Check the status again. This time git tells us that it has added our file to the staging area.

								% git commit -m "Adding volta_brau.txt"
							

• Try checking the status once more. This time git tells us that there isn't any new changes.

									On branch main
									nothing to commit, working tree clean
								

• Let us review what we have done so far.

• git keeps a nice log for each branch in a repository.

								% git log # prints the log
								% git log -n 2 # prints the last 2 commit logs
							

• The log cotains a block for each of our commits.

								commit 0123456789abcdef0123456789abcdef01234567
								Author: JohnDoe JohnDoe@unknown.com
								Date: Thu Jan 1 00:00:00 1970 -0000

									Adding volta_brau.txt
							

• Going back through the repository is easy. We can use the wildcard HEAD.

								% git checkout HEAD~1 # going back one step
								% git checkout 0123456 # using the SHA1 hash
							

• We can move forward using HEAD.
• To get out of the detached HEAD state, use one of two options:

								% git checkout - # only works for a fully detached HEAD
								% git checkout main # always works
							

• We can also directly compare the differences between commits, using diff.

								% git diff HEAD~1 volta_brau.txt
								% git difftool HEAD~1 volta_brau.txt # opens in a diff tool
							

• git should print both lines in our document, but notice that the second line is green. git tells us that the second line is added compared to previous commit.

• What if we realize that our last commit was full of spelling mistakes? Can we take it back.

								% git revert HEAD # or some older commit
							

• git will open a file in your prefered editor and ask you to type a commit comment. Close the file when done.
• Open the file and check what happend. Next check the log, there should be a new commit reverting our second commit.

Branches is mostly used when more than one person is collaborating in a repository. All past commits are carried over when a new branch is created.

Our three past commits along the main branch. And a new branch in magenta.

• We can create a new branch at any point along the tree. We could go back through our tree using checkout and branch off.
• But let's branch off right here.

								% git branch more_beer # create new branch
								% git checkout more_beer # move to new branch
								% git checkout -b more_beer # doing both commands in one go
							

• Try looking at the log once again, what do you see?

• Let us add some more text to volta_brau.txt.
• Let us also create a new text file called bbb.txt and add some content to that one.

									% code volta_brau.txt # open and add more text
									% code bbb.txt # create new file
									% git add . # add everyting to the staging area
									% git commit -em "Adding new file bbb.txt"
								

• Notice the extra "e" in the last line. This opens your editor and allows you to futher edit your comment.

• Now that we have added some more content, let's merge more_beer back into main.

								% git checkout main # move back to main
								% git merge more_beer
							

• Now that we have merged more_beer into main, we don't need that branch anymore.

								% git branch -d more_beer # -d only remove if fully merged
							

• It is time to publish our repository on Github. Sooo exciting:)
• First we have to create a repository on Github.
• No need at make a README.md file, we will do that on the commandline.

• Create a new file called README.md. Add lines 2 & 3 to the README file.

								% code README.md # Markdown format
								% # beer <-- use hashtag for headline
								% Some description of the repo
							

• Commit your README file to the main branch.

								% git add .
								% git commit -m "Adding a README"
							

• We are now ready to publish our repository. Use the second line if you are using a ssh key.

								% git remote add origin https://github.com/<username>/beer.git
								% git remote add origin git@github.com:<username>/beer.git
								% git remote -v # check that it worked
								origin	https://github.com/<username>/beer.git (fetch)
								origin	https://github.com/<username>/beer.git (push)
							

• And now push the main branch to your remote repository.

								% git push origin main
							

• The frist rule of git is: Don't push directly to the main branch!
• The second rule of git is: Seriously, don't push directly to the main branch.
• Make a new branch, make sure everyting works and then make a Pull request on Github.
• Let us go through the required steps.

• Use clone to get a local copy of a remote repository.
• If you are contributing to other peoples projects, you should fork their repository first.

• Let us pretent that you want to contribute to my very cool repository "gitr".
• Find it on Github and fork it, so you have your own copy. My username is chrede88.
• Once you have forked it, clone it so you can work on it locally.

								% git clone https://github.com/<username>/gitr.git
								% git clone git@github.com:<username>/gitr.git
							

• Make a new branch, make some changes etc. & commit to the new branch.
• Push the chages to your remote repository. The push command will create a new branch in the remote repository automatically.

In case you forgot 😉

									% git checkout -b <newbranch> # make new branch
									# make your changes
									% git add . # add to staging area
									% git commit -m "Made some changes" # commit to local repo
									% git push origin <newbranch> # push to remote repo
								

• Now your changes are incorporated into your version of gitr on Github.
• Make a pull request (from your repo) to the main branch of my repository.
• You have now successfully contributed to a project 😁

It's a good idea to add a second "git remote" when contributing to other peoples repositories. Add a remote called upstream to the original repository. This way you can easily pull recent changes to your own repository.

								% git remote add upstream https://github.com/<original-user>/somerepo.git
								% git pull upstream main # pull upstream changes to original repo
							

• Conflicts can happen if two people are trying to add changes to the same line.
• git will refuse to overwrite anything and open your editor so you can fix the conflict.

								Here is some text about Mars.
								Mars is red.
								<<<<<<< HEAD
								I think Elon Musk will land there.
								=======
								Elon Musk will never land there.
								>>>>>>> dabb4c8c450e8475aee9b14b4383acc99f42af1d
							

• Pick the "correct" line and delete the rest. Save the document and try again.

								Here is some text about Mars.
								Mars is red.
								Elon Musk will never land there.