Chapter 9 Github
by Stephanie Djajadi and Nolan Pokpongkiat
9.1 Basics
- A detailed tutorial of Git can be found here on the CS61B website.
- If you are already familiar with Git, you can reference the summary at the end of Section B.
- If you have made a mistake in Git, you can refer to this article to undo, fix, or remove commits in git.
9.2 Github Desktop
While knowing how to use Git on the command line will always be useful since the full power of Git and its customizations and flexibilty is designed for use with the command line, Github also provides Github Desktop as an graphical interface to do basic git commands; you can do all of the basic functions of Git using this desktop app. Feel free to use this as an alternative to Git on the command line if you prefer.
9.3 Git Branching
Branches allow you to keep track of multiple versions of your work simultaneously, and you can easily switch between versions and merge branches together once you’ve finished working on a section and want it to join the rest of your code. Here are some cases when it may be a good idea to branch:
- You may want to make a dramatic change to your existing code (called refactoring) but it will break other parts of your project. But you want to be able to simultaneously work on other parts or you are collaborating with others, and you don’t want to break the code for them.
- You want to start working on a new part of the project, but you aren’t sure yet if your changes will work and make it to the final product.
- You are working with others and don’t want to mix up your current work with theirs, even if you want to bring your work together later in the future.
A detailed tutorial on Git Branching can be found here. You can also find instructions on how to handle merge conflicts when joining branches together.
9.4 Example Workflow
A standard workflow when starting on a new project and contributing code looks like this:
| Command | Description |
|---|---|
SETUP: FIRST TIME ONLY: git clone <url> <directory_name> |
Clone the repo. This copies of all the project files in its current state on Github to your local computer. |
1. git pull origin master |
update the state of your files to match the most current version on GitHub |
2. git checkout -b <new_branch_name> |
create new branch that you’ll be working on and go to it |
| 3. Make some file changes | work on your feature/implementation |
4. git add -p |
add changes to stage for commit, going through changes line by line |
5. git commit -m <commit message> |
commit files with a message |
6. git push -u origin <branch_name> |
push branch to remote and set to track (-u only needed if this is first push) |
| 7. Repeat step 4-5. | work and commit often |
8. git push |
push work to remote branch for others to view |
9. Follow the link given from the git push command to submit a pull request (PR) on GitHub online |
PR merges in work from your branch into master |
| (10.) Your changes and PR get approved, your reviewer deletes your remote branch upon merging | |
11. git fetch --all --prune |
clean up your local git by untracking deleted remote branches |
Other helpful commands are listed below.
9.5 Commonly Used Git Commands
| Command | Description |
|---|---|
git clone <url> <directory_name> |
clone a repository, only needs to be done the first time |
git pull origin master |
pull from master before making any changes |
git branch |
check what branch you are on |
git branch -a |
check what branch you are on + all remote branches |
git checkout -b <new_branch_name> |
create new branch and go to it (only necessary when you create a new branch) |
git checkout <branch name> |
switch to branch |
git add <file name> |
add file to stage for commit |
git add -p |
adds changes to commit, showing you changes one by one |
git commit -m <commit message> |
commit file with a message |
git push -u origin <branch_name> |
push branch to remote and set to track (-u only works if this is first push) |
git branch --set-upstream-to origin <branch_name> |
set upstream to origin/<branch_name> (use if you forgot -u on first push) |
git push origin <branch_name> |
push work to branch |
git checkout <branch_name> git merge master |
switch to branch and merge changes from master into <branch_name> (two commands) |
git merge <branch_name> master |
switch to branch and merge changes from master into <branch_name> (one command) |
git checkout --track origin/<branch_name> |
pulls a remote branch and creates a local branch to track it (use when trying to pull someone else’s branch onto your local computer) |
git push --delete <remote_name> <branch_name> |
delete remote branch |
git branch -d <branch_name> |
deletes local branch, -D to force |
git fetch --all --prune |
untrack deleted remote branches |
9.6 How often should I commit?
It is good practice to commit every 15 minutes, or every time you make a significant change. It is better to commit more rather than less.
9.7 What should be pushed to Github?
Never push .Rout files! If someone else runs an R script and creates an .Rout file at the same time and both of you try to push to github, it is incredibly difficult to reconcile these two logs. If you run logs, keep them on your own system or (preferably) set up a shared directory where all logs are name and date timestamped.
There is a standardized .gitignore for R which you can download and add to your project. This ensures you’re not committing log files or things that would otherwise best be left ignored to GitHub. This is a great discussion of project-oriented workflows, extolling the virtues of a self-contained, portable projects, for your reference.