Remote version control with Git

Author

Affiliation

Kyle Niemeyer

Oregon State University

Remote version control (i.e., using GitHub) and Software Licenses

Topics for today:

• Backup up code (and any files) online
• Cloning and forking remote repositories
• Managing files in a collaboration
• Merging simultaneous changes
• Downloading open source code

Repositories

We’ll focus on GitHub.

Why GitHub?

• Nice landing page—renders README automatically
• Grabs information about LICENSE, programming language
• Supports issue tracking and wiki
• Network graphs, time history of commits
• User downloads
• Varying permissions (read, write, etc.)
• Nice web interface to browse, view, and edit code

Workflow (with account)

1. Create space for repo on GitHub account
2. Point to that remote repo from local copy
3. Push repository to the remote location
4. Continue working!

Alternatively, if starting new project, you can:

1. Create a new repo on account
2. Copy (clone) empty repo to local computer
3. Prosper!

Creating and working with repositories

Let’s work through creating a repo

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Create and push new repo

Cloning a repo

Terminology

Clone: make local copy of any repository (Git)

Fork: Remote repository connected to/aware of the “upstream” repo it was cloned from (GitHub)

Forking a repo

Collaborative work using GitHub

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How does Fran keep local repo up to date with the original?

Do this yourself:

1. Fork it: click “Fork” at SoftwareDevEngResearch/analysis_code
2. Clone your fork: $ git clone https://github.com/[you]/analysis_code.git
3. Create alias upstream for the remote repo:

$ git remote add upstream \
https://github.com/SoftwareDevEngResearch/analysis_code.git
$ git remote -v

Fetching and merging remote content

1. In your cloned local repo, fetch the upstream repo history
2. Then merge the upstream main branch into your main branch
3. Look at the changes!

$ git fetch upstream
$ git merge upstream/main

Update your fork

After merging upstream history, push your work to origin main:

$ git push

What if you (or someone else) made a change in your fork?

$ git pull

pull = fetch & merge for origin main

Alternatively, use GitHub

What about conflicts?

When fetching, merging, and/or pulling remote changes, you may encounter conflicts.

To solve: just follow the directions!

(In-class example)

Best practices for collaborating

For solo projects:

• push and pull (to/from origin
• use branches, merge into main

For multi-person projects:

• Fork into a personal repo
• Use git fetch/merge to keep updated with upstream
• Push (and pull) to/from origin (your fork on GitHub)
• Contribute changes via pull requests on GitHub

(Some) issues that arise when using GitHub: Pull requests & licences

Pull Requests

Modern, GitHub-based version of emailing someone a patch

Pull Requests (or PRs) consist of sequences of patches, based on a history of Git commits

Example Pull Request on GitHub

How to contribute a change to someone else’s repository

1. Fork the repo
2. Clone your fork locally
3. Create a new branch for your changes/fix
4. Commit and push your changes
5. Submit a Pull Request via GitHub

$ git clone ...
$ git checkout -b newfix

$ git commit -am "fixes problem in upstream project"
$ git push origin newfix

Create Pull Request

Submitting Pull Requests

Try to submit shorter Pull Requests when possible, as they are easier to review and merge

If the project uses testing, make sure to add a new test (or modify an existing one) to reflect your change. More on tests later!

Software Licenses & Copyright

Important notice

I AM NOT A LAWYER!

AKA: IANAL

Copyright

Facts and ideas are not copyrightable.

Expressions of ideas are copyrightable.

Copyright Examples

Game rules are not copyrightable (chess, Go, football, Dungeons & Dragons)

Expressions of game rules are copyrightable.

Basic Copyright

“Right of First Publication”: copyright automatically goes to the first creator of any creative work

(Even if not explicitly specified)

Consequence: if you post software to GitHub without an explicit license, then you own the copyright—even if openly and publicly visible.

By default, no one else is legally allowed to use or modify your work.

Software Licenses

All software codes you make publicly available should be accompanied by a software license describing the terms by which others may use and/or modify your code.

Public Domain

Alternatively, you can put work into the public domain: “This work has been placed in the public domain.”

Free for anyone and everyone to use and modify.

Literature examples: Sherlock Holmes, Frankenstein

(There are some tricky issues internationally, however.)

Software Licenses

Kinds of software licenses: proprietary, and free/open source (FOSS, FLOSS, OSS).

Pick an existing license. Do not create your own.

Software Licenses

FOSS categories: permissive, and “copyleft”

Permissive licenses: BSD 3-clause, MIT; allow further distribution under any license

Copyleft licenses: GPL; require modifications to be shared under the same license (“viral”)

https://choosealicense.com

Open Source Initiative licenses

Which license to use?

When in doubt, use a permissive license like the BSD 3-clause or MIT licenses.

Copyrighting other creative works: Creative Commons

• BY: Attribution
• SA: ShareAlike
• ND: NoDerivatives
• NC: NonCommercial

Licenses: CC BY, CC BY-SA, CC BY-NC, CC BY-NC-NC

Choose a license

Beyond copyright & licenses

Patents: cover ideas and concepts; modern issues with “patent trolls”

Trademarks: symbols that represent a business or organization

Export control: government may forbid the transfer of source code (and data, ideas) to another country or foreign national without permission

HIPAA compliance: software that deals with human patients must be anonymized

Long story short:

Pick a license when creating a project, and put as LICENSE.txt in your repo.