Git Version Control Introduction¶
A more in-depth guide on Git is available on the Git website.
Git is a Distributed Version Control System (VCS) created by Linus Torvalds, also known for creating and maintaining the linux kernel. Version Control is a system for tracking changes of code for developers. The advantages of Git Version Control are:
Separate testing environments into branches
Ability to navigate to a particular commit without removing history
Ability to manage commits in various ways, including combining them
Various other features, see here
This tutorial uses the Windows operating system
You have to download and install Git from the following links:
You may need to add Git to your path
Git revolves around several core commands:
Repository: the data structure of your code, including a
.gitfolder in the root directory
Commit: a particular saved state of the repository, this includes all files and additions
Branch: a means of separating various commits, having a unique history. This is primarily used for separating development and stable branches.
Push: update the remote repository with your local changes
Pull: update your local repository with the remote changes
Clone: retrieving a local copy of a repository to modify
Fork: duplicating a pre-existing repository to modify, and to compare against the original
Merge: combining various changes from different branches/commits/forks into a single history
A Git repository is a data structure containing the structure, history, and files of a project.
Git repositories usually consist of:
.gitfolder. This folder contains the various information about the repository.
.gitignorefile. This file contains the files or directories that you do not want included when you commit.
Files and folders. This is the main content of the repository.
Creating the repository¶
You can store the repository locally, or through a remote. A remote being the cloud, or possibly another storage medium that hosts your repository. Github is a popular free hosting service. Numerous developers use it, and that’s what this tutorial will use.
Creating a Github Account¶
Go ahead and create a Github account by visiting the website and following the own screen prompts.
After creating and verifying your account, you’ll want to visit the homepage. It’ll look similar to the shown image.
Click the plus icon in the top right.
Then click “New Repository”
Fill out the appropriate information, and then click “Create repository”
You should see a screen similar to this
The keyboard shortcut
~ can be used to open a terminal in Visual Studio Code.
Now you’ll want to open a powershell window and navigate to your project directory. An excellent tutorial on powershell can be found here. Please consult your search engine on how to open a terminal on alternative operating systems.
In the below example, we created a file called
README.md with the contents of
# Example Repo. More details on the various commands can be found in the subsequent sections.
Replace the filepath (“C:UsersExampleUser9007DocumentsExample Folder”) with the one you want to create the repo in, and replace the remote URL (https://github.com/ExampleUser9007/ExampleRepo.git) with the URL for the repo you created in the previous steps.
> cd "C:\Users\ExampleUser9007\Documents\Example Folder" > git init Initialized empty Git repository in C:/Users/ExampleUser9007/Documents/Example Folder/.git/ > echo "# ExampleRepo" >> README.md > git add README.md > git commit -m "First commit" [master (root-commit) fafafa] First commit 1 file changed, 1 insertions(+), 0 deletions(-) create mode 100644 README.md > git remote add origin https://github.com/ExampleUser9007/ExampleRepo.git > git push -u origin master
For FRC Robot projects, the above commands should be run in the root of a project created by the VS Code WPILib Project Creator.
Repositories are primarily composed of commits. Commits are saved states or versions of code.
In the previous example, we created a file called README.md. Open that file in your favorite text editor and edit a few lines. After tinkering with the file for a bit, simply save and close. Navigate to powershell and type the following commands.
> git add README.md > git commit -m "Adds a description to the repository" [master bcbcbc] Adds a description to the repository 1 file changed, 2 insertions(+), 0 deletions(-) > git push
Writing good commit messages is a key part of a maintainable project. A guide on writing commit messages can be found here.
git fetch can be used when the user does not wish to automatically merge into the current working branch
This command retrieves the history or commits from the remote repository. When the remote contains work you do not have, it will attempt to automatically merge. See Merging.
This command adds a selected file(s) to a commit. To commit every file/folder that isn’t excluded via gitignore.
git add FILENAME.txt where FILENAME.txt is the name and extension of the file to add to a commit.
git add . will add every untracked, unexcluded file when ran in the root of the repository.
This command creates the commit and stores it locally. This saves the state and adds it to the repositories history.
git commit -m "type message here"
Upload (Push) your local changes to the remote (Cloud)
Branches are a similar to parallel worlds to Git. They start off the same, and then they can “branch” out into different varying paths. Consider the Git control flow to look similar to this.
In the above example, Master was branched (or duplicated) into the branch Feature 1 and someone checked out the branch, creating a local copy. Then, someone committed (or uploaded) their changes, merging them into the branch Feature 1. You are “merging” the changes from one branch into another.
Creating a Branch¶
git branch branch-name where branch-name is the name of the branch to create. The new branch history will be created from the current active branch.
Entering a Branch¶
Once a branch is created, you have to then enter the branch.
git checkout branch-name where branch-name is the branch that was previously created.
In scenarios where you want to copy one branches history into another, you can merge them. A merge is done by calling
git merge branch-name with branch-name being the name of the branch to merge from. It is automatically merged in the current active branch.
It’s common for a remote repository to contain work (history) that you do not have. Whenever you run
git pull, it will attempt to automatically merge those commits. That merge may look like the below.
However, in the above example, what if File 1 was modified by both branch FeatureA and FeatureB? This is called a merge conflict. A merge conflict will can be resolved by editing the conflicting file. In the example, we would need to edit File 1 to keep the history or changes that we want. After that has been done. Simply re-add, re-commit, and then push your changes.
Sometimes history needs to be reset, or a commit needs to be undone. This can be done multiple ways.
Reverting the Commit¶
You cannot revert a merge, as git does not know which branch or origin it should choose.
To revert history leading up to a commit run
git revert commit-id. The commit IDs can be shown using the
git log command.
Resetting the Head¶
Forcibly resetting the head is a dangerous command. It permanently erases all history past the target. You have been warned!
git reset --hard commit-id.
Forks can be treated similarly to branches. You can merge the upstream (original repository) into the origin (forked repository).
Updating a Fork¶
Add the upstream:
git remote add upstream https://github.com/ORIGINAL_OWNER/ORIGINAL_REPOSITORY.git
Confirm it was added via:
git remote -v
Pull changes from upstream:
git fetch upstream
Merge the changes into head:
git merge upstream/upstream-branch-name
It is extremely important that teams do not modify the .gitignore file that is included with their robot project. This can lead to offline deployment not working.
A .gitignore file is commonly used as a list of files to not automatically commit with
git add. Any files or directory listed in this file will not be committed. They will also not show up with git status.
Additional Information can be found here
Hiding a Folder¶
Simply add a new line containing the folder to hide, with a forward slash at the end
Hiding a File¶
Add a new line with the name of the file to hide, including any prepending directory relative to the root of the repository.