Creating a local repositry

Overview

Teaching: 10 min
Exercises: 10 min

Questions

• How do I create a simple repository?

Objectives

• Remind you how to create a very basic repository

• Add your credentials to CERN’s GitLab

• Push your simple README.md

In this episode we hope to demonstrate that “publishing” anything via CERN GitLab is extremely easy.

Create a base directory

We’ll be working with this repository for the remainder of this workshop, so before doing anything let’s make sure you’re putting your code somewhere where you won’t lose it! For instance, if you drop your laptop down the hill and one of the turkeys steals it!

Code in Docker Containers/Images

Be very careful where you put your code while developing within containers! Nothing in the image is saved when you exit, so make sure you develop within the directories you’ve mounted on your laptop. If you don’t, then ask your instructor.

Start by creating a subdirectory like bootcamp. Personally I keep my ATLAS projects under a directory called ~/work but you can adjust this as you see fit.

mkdir -p ~/work/bootcamp
cd ~/work/bootcamp

We’ll do our work from here. That means we’ll need:

• The pre-workshop material
• The input data file in a path like

  data/DAOD_EXOT27.24604725._000008.pool.root
  

  • If you don’t have this data file, there are instructions to download it a later section

If you didn’t do your homework

You really should set up the pre-workshop material. But we can continue by cloning it now and removing the .git directory.

git clone ssh://git@gitlab.cern.ch:7999/usatlas-computing-bootcamp-2020/v1-prework-finished-code.git pre-workshop
rm -rf pre-workshop/.git/

You can check your working directory with tree .. I get something like

.
├── data
│   └── DAOD_EXOT27.24604725._000008.pool.root
└── pre-workshop
    ├── AnalysisPayload.cxx
    ├── CMakeLists.txt
    └── README.md

Initializing the repository

Now let’s create a git repository. We create this in a subdirectory of the working directory, because not everything we’re working on will be versioned. GitLab only saves the stuff that we put in this subdirectory.

mkdir amber-example
cd amber-example
git init

Where you should replace amber with your name. You should see something like

Initialized empty Git repository in ...

where ... is your working directory. If you try to commit something now git will complain that there is nothing to commit. Git has good intentions here: in general commiting nothing at all is a mistake.

Name your repository carefully

In general you shouldn’t make a repository called amber-example. We’ve chosen this name to make it clear that this should be your example with your unique name. Our reason for this is pedagogical: we want everyone to develop their own code, but we also want you to be able to fork your friend’s code and develop that. This would get very confusing if everyone used the same name.

In a real world setting it would be very silly for everyone to name their code after themselves and rewrite it from scratch. Your repository name should reflect what it does not who wrote it.

Adding a file

So let’s add a file. Use your favorite text editor to create a file called README.md. What you put here is up to you but it will be the first thing everyone sees when they look for your code so make it count!

For now we’ll describe what you’re doing here. Add something like this

ATLAS Software Bootcamp
-----------------------

This is the README file for our bootcamp project.

Let's add some sugar and spice with Cupcake Ipsum!

Cupcake ipsum dolor sit amet gummi bears chocolate bar bear claw cake. Carrot cake pie donut croissant lollipop I love jujubes. Marshmallow I love muffin. Donut lollipop candy canes dragée wafer liquorice chocolate.

and save the file. (ipsum text generated at Cupcake Ipsum) Let’s ask git what is sees now:

git status

On branch master
Untracked files:
  (use "git add <file>..." to include in what will be committed)

	README.md

nothing added to commit but untracked files present (use "git add" to track)

Great, git sees the file but it’s just floating around for now, we’re not properly keeping it under version control. OK, let’s add it to the index:

git add README.md

and check that it’s been properly added

git status

On branch master
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

	new file:   README.md

Turning Red to Green

Git can color its text to make it easier on your brain. If you don’t see untracked files in red and the new file as green, you can run

git config --global color.ui auto

Setting your name and email

In the Git session you had to configure git to add your name and email to every commit, using git config. We’d recommend you use your CERN account email and name so that the names on local commits match the ones you’ll create via GitLab.

To change this you can run

git config --global user.name <your cern name>
git config --global user.email <your cern email>

Great, now our README.md is ready to commit.

git commit -m "Add README file" -m "And a pretty poor README at that"

In general git will force you to create a commit message. You should try to write good commit messages, since this helps everyone understand what you were doing. In this case it’s pretty self-explanitory, but in many real-world examples a commit might just change one line deep inside your code. A commit message is a very good way to explain why you decided to make this change.

Also note that a good commit message might run for several paragraphs to explain the full context of the commit. Each time you call -m it will start a new paragraph, which is convient if you want to write a short (less than 50 characters is recommended) description followed by a longer one. If you need something more verbose, you can use the contents of a text file with git commit -F file.txt.

This all might be review, but next the real fun begins: we’ll push this repository to GitLab.

Key Points

• Always add a README.md file to your repository

• Write verbose and useful commit messages.