Git

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Git

What is Git?

The modern de facto standard in version control is Git. Version control software allows you to manage and track changes to files over time in a project. It is especially beneficial for keeping track of source code as it is being developed and debugged. You may not use it in all of your classes but it is extremely helpful to use for many reasons:

  • If you properly version your software, it is much easier to undo mistakes. For example, reverting to an earlier version of the code before you implemented a feature that introduced a bug, or restoring the files you just accidentally deleted. You can also view differences between different versions of the code, so if you do introduce a bug, you can more easily identify what change caused it.
  • It makes it simple to transfer your code to your instructor. If you need feedback during office hours, instructors can simply pull up the most recent version of your code from your project repository. Similarly, when it is due, your professor or TA can just grade the latest version of your code.
  • Version control is great and important technology to be familiar with. You'll almost certainly use it later in the major and in your career. Why not get a head start?

In the Computer Science department, we use git for version control. This page will introduce you to the basic functionality of git.

One-Time Git Setup

One time only, before you use git the first time, you need to tell it a little bit about yourself and your account. This configures git to know you are part of the department's GitLab. Run the following commands in your terminal, supplying your full name and email address:

git config --global user.name "${your name}"
git config --global user.email ${username}@wwu.edu

If you'll recall from previous pages, SSH allows you to remotely connect to another machine using your account on that computer (if you haven't gotten there, please read this page). In this case, git uses the SSH connection to interact with your remote repository. As noted in the SSH page, you should never give out your private key to anybody. That is yours and yours alone. You will, however, need to give GitLab your public SSH key. You can add your public key in your user settings on GitLab by accessing the SSH Keys tab on your profile and copy the public portion of your key into the text box.

Gitsshkeys.png

Using Git

Git Terminology

The setup you will most likely encounter throughout the major will include three main components:

  1. the main or remote repository - The online master copy of your code repository. If you use git properly, it will contain a record of all versions of your code as you develop it. This is the location instructors go to find your current code during office hours and for grading.
  2. the local working copy - The current version of files you are editing stored on a local machine. This can be put anywhere you like, e.g. ~/schoolWorkingCopy/. As the name suggests, the local working copy is where you will develop your project.
  3. the local repository - Contains a record of all current and previous versions of your code as you develop it, but it is stored locally to compare itself against the remote repository. This is stored in the .git hidden subdirectory of your working copy. If you use git properly, this version will stay in sync with your remote repository. Do not directly edit any files in your local repository! That is git's job, using the following commands will update this repository using the changes in your local repo.

Repo Setup

The easiest way to create and start working on a project repo is to create a New Project on GitLab and then "clone" it onto your machine. To do this, find the new project button on the home page of GitLab, give your project a name, and click "Create Project"

After you first create a repository you will need to choose a local location to clone your working copy. Let's assume you choose ~/schoolWorkingCopy. To clone your repository, use the git clone <url> <local location> command:

git clone ${ssh url} ~/schoolWorkingCopy

Where ${ssh url} is found here:

Gitssh.png

Note: If you click the drop down location just to the left of the repository url, you'll notice you have an option between SSH and HTTPS. While HTTPS can be easier to configure for a beginner, as a student in this department you will need to familiarize yourself with the capabilities and the added security of SSH. If you're curious about other options of interacting with your repository, feel free to read documentation provided by GitLab and GitHub on their respective websites.

Individual Work Flow

Now that you've set up your local repository, you are ready to work on developing your code. There is a basic flow of work when using git in your local working repository (~/studentWorkingCopy in our case).

  1. If you use multiple computers to work on a project, you'll want to make sure that your local and remote repositories are synced up before you start working. The command you'll need is git pull --all.
  2. As you add, delete, or change files in your program, you will have to add these changes to keep track of them in your repository:
    • git status will tell you which files you have changed.
      Here there are two files that are not staged. README.md was modified and main.py is a new file.
    • git add <filename> will stage any new file or changed files to be committed to your local repository (.git directory).
      Those two files are now ready to be committed.
  3. Repeat step 2 until you get to a good stopping point to commit your changes.
  4. When you are ready, you will need to finalize your staged changes to the repository with git commit:
    • Using git commit by itself without the -m will open a text editor in your terminal, Vim by default (See this section if you are unfamiliar with terminal text editors). If you save and exit the editor with no uncommented text, it will abort the commit.
      Editing the commit message with Vim. If you save and exit the editor with no uncommented text, it will abort the commit.
    • Side note: you can specify your default text editor by using the command git config --global core.editor "$EDITOR"
    • Using git commit with the -m flag, you can specify a short commit message quickly.
      Committing with the git commit command with a short commit message.
  5. The last step is to push your commit(s) to your remote repository with git push. This will update your remote repo to the current version of your project.
    Example of running git push --all.
  6. Repeat steps 2 through 5 as necessary!

Conventions on Commit

The use of commit messages are to summarize recent changes you have made and relay that back to your remote repository. It all depends on how you use git. For personal usage, you can do anything. If you're with a team, its good to talk about conventions so everyone knows the work flow everyone would like to see. You can use the -m flag you to fit what you did in one quick line. In some cases, you'll want to use the command git commit to explain what's getting you changed with some context and reasoning.

Here's an article that will give you perspective on the power of commit messages: https://chris.beams.io/posts/git-commit/

Group Work and Version Control

You may have heard that you can use version control to work on group projects. If you simply have a group project in a class, it's easiest to have one person create a repository and have the rest of the team added as developers on the project. You'll find under settings for projects you create the members section and you can decide what roles should be given to each new member there. Feel free to look up the documentation by GitLab for the different roles in a project in order to assign as you see fit. Generally, you'll be looking to add people as developers at most. Below is what the website will look like when you get there.

Member.png

Another form of group work through version control you may encounter in the department is forking. This is generally done when you come across a project that you haven't worked directly on but would like to make an addition to. Instructors may choose to create a project where they ask you to fork from their own repository and grade work submitted to your own copy of the master repository they create. The process of forking is really powerful and probably the one that gets confused over the most. Let's go through the process beginning to end of a team on GitLab called groupteamthing creating a repository for a project and user billieSmith coming across something they want to change.

  1. billieSmith forks the master repository from groupteamthing.
  2. billieSmith clones their forked repository to their working machine. This happens on the GitLab website and the fork button is found underneath the name of the project you want to change.
    • The fork button.
  3. billieSmith creates a branch on their machine. The command to do this is git checkout -b ${name of branch}. The purpose of this is to specify exactly what from another project you want to change and so the name should reflect that. It is invalid to include spaces in your branch names.
    • By the command git branch, billieSmith can see all the branches at their disposal.
      How to view all your branches.
  4. When you create a new branch you automatically get switched onto that branch. Now, billieSmith is on the new branch so they can work on their change. This step follows a lot of the individual steps as mentioned in the section above.
  5. To let groupteamthing know that someone fixed something on their project, billieSmith needs to commit their work and push to their remote repository.
    • These two commands are the same as you do for your individual work.
      Committing and viewing status of git.
      Finding the merge button.
  6. At this point, billieSmith would submit a merge request to groupteamthing on GitLab and depending on what they think, the merge request could get accepted or denied.
    • Creating the merge request. Be sure to describe what you did and why.
      Merge request form.

Branch Names

As mentioned before, commit messages are to describe changes you want to update to your remote repository. Branch names on the other hand should say why you forked the project in the first place. Could this project use a new feature? Did you notice a bug? Are you testing out some changes you think you'd want to see? What are you working on?

GitLab vs. Github

Throughout this section of the survival guide, we've been talking about GitLab and bringing back the importance of the use of SSH. There are other services that use git including a similar one you may recognize as GitHub. We have a server that runs GitLab for the department and that's why there's been an emphasis on GitLab throughout this section. The major difference between the two is what you get out of those services. We use GitLab because it's made to be used by organizations for remote hosting of repositories. GitHub is a free service that promotes open source projects, meaning when you create an account there, you agree to leave your code publicly available so anyone can comment and/or suggest changes. Neither GitHub nor GitLab created git and neither did BitBucket or other forms of remote hosting of repositories. git is an open source form of version control.

A thank you

Special thanks to Brian Hutchinson for the git tutorial provided in his Spring 2017 241 class, where the template of this page originated.