Git and GitHub

Using Git Locally

Now let’s learn how to use Git locally from our computer. While there are GUIs (graphical user interfaces) for Git on your computer like GitHub Desktop, we’re going to use the command line to learn Git. That’s because this is a key transferrable skill that applies to any kind of coding.

Learning objective: Build a “mental model” of what your computer is doing.

Some Vocabulary

Git - version control software
Repository - a folder containing your files and also containing a structure that helps keep track of changes in those files. When you intialize a repository, git creates a hidden folder (.git folder) that stores the changes to those files.
GitHub - a place to host git repositories and collaborate
Local Repository - the version of a git repository on your local computer
Remote Repository - the version of a git repository stored somewhere else that your local repository is connected to (frequently on GitHub)
Commit - the basic unit of a git repository is a commit. It is a set of changes to a file. A commit usually comes with an id as well as a commit message that describes the change.

Within a Repository you have

Untracked Changes - files that are in your folder but that git doesn’t pay attention to.
Staging Area - a place where you can put files before you commit them. Once files are in the staging area, git is paying attention to them.
Commit Log (aka Git History) - all of the commits (previous changes) to all of the files in your repository.

Components of a Git Repository

The working directory

git init creates a git repo inside current working directory. This means that this command can turn a regular folder into a git repository by generating a hidden .git folder that starts to keep track of changes.
git clone takes a git repo from somewhere else and makes a copy of that repo into your current working directory. We will frequently be cloning repos from GitHub.

The staging area

git add . adds changes from the working directory to the staging area
git add <filename> adds changes to filenames specified from the working directory to the staging area

The commit

git commit -m "commit message" adds changes in staging area to the repository
git log shows

Protip: Run git status after each command in the beginning because it allows you to visualize what just happaned.

Pushing to GitHub

Key Terms

github - a service that hosts git remote repositories, and provides a web app to interact / collaborate on them
remote - another repository that can be syncronized with a remote
upstream - the name for a remote read-only repository
origin - the name for a remote read-and-write repository
clone - download an entire remote repository, to be used as a local repository
fetch - downloading the set of changes (commits) from a remote repository
pull - fetching changes and merging them into the current branch

In order to show your remotes, you can run git remote -v show. The default remote is named “origin”
In order to push, you run git push. By default this will push from the branch you are on to a remote branch with the same name. (If you’d like to specify a branch, you can do that. The full formulation of this command is git push <remote> <branch>. So, for example you might say git push origin main to push to the “main” branch of the “origin” remote.)

❇️ Example: simple-rscript

Let’s give it a try! We’re going to clone a repository for a simple R script from GitHub down to our computer where we can work with it locally. We will make some edits to the code, commit those changes and then push the changes back up to the remote repository in GitHub.

https://github.com/PolicyCompFoundations/simple-rscript

Next Page (Git from the Command Line)