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Basics and motivation

- What is version control and why?
- What are commits and branches?
- What are forks and clones?

- Get a mental representation for commits and branches.
- Understand the difference between forks and clones.
- Understand the difference between Git and GitHub.

What we will not cover

  • Command line interface
  • Cloning using SSH protocol and SSH keys
  • Rebasing and squashing
  • Many Git tricks which can be explored later {: .discussion}

Version control

Why version control?

Version control is the answer to these questions:

  • "It broke ... hopefully I have a working version somewhere?"
  • "Can you please send me the latest version?"
  • "Where is the latest version?"
  • "Which version are you using?"
  • "Which version have the authors used in the paper I am trying to reproduce?"
  • "Found a bug! Since when was it there?"
  • "I am sure it used to work. When did it change?"

What are version control tools?

  • Version control is a tool that can record snapshots of a project.
  • You can think of version control like regularly taking a photo of your work (movie sets take regular polaroids to be able to recreate a scene the next day).
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Snapshots (**commits**) in the [EHT-imaging](https://github.com/achael/eht-imaging) repository.

What we typically like to version control (or "snapshot")?

  • Software (this is how it started but Git/GitHub can track a lot more)
  • Scripts
  • Documents (plain text file much better suitable than Word documents)
  • Manuscripts (Git is great for collaborating/sharing LaTeX manuscripts)
  • Configuration files
  • Website sources
  • Data

Why are snapshots valuable? Reproducibility!

:alt: Research comic
:width: 100%
  • We can always go back if we make a mistake.
  • We can test new ideas without editing the working version
  • If we discover a problem, we can find out when it was introduced.
  • We have the means to refer to a well-defined version of a project when sharing, collaborating, and publishing.

Difference between Git and GitHub

Git

  • Tool that can record and synchronize snapshots.
  • Not the only tool that can record snapshots (other popular tools are Subversion and Mercurial).
  • Not only a tool but also a format that can be read by many different tools.

GitHub

  • Service that provides hosting for Git repositories with a nice web interface.
  • Not the only service that provides this (other popular services are GitLab and Bitbucket).

GitHub Desktop

  • Graphical user interface to Git and GitHub which runs locally on your computer.
  • There are other tools that can do this, too (e.g. Sourcetree).

Commits, branches, repositories, forks, clones

  • repository: The project, contains all data and history (commits, branches, tags).
  • branch: Independent development line, often we call the main development line master.
  • commit: Snapshot of the project, gets a unique identifier (e.g. c7f0e8bfc718be04525847fc7ac237f470add76e).
  • tag: A pointer to one commit, to be able to refer to it later. Like a sticky note that you attach to a particular commit (e.g. phd-printed or paper-submitted).
  • cloning: Copying the whole repository to your laptop - the first time. It is not necessary to download each file one by one.
  • forking: Taking a copy of a repository (which is typically not yours) - your copy (fork) stays on GitHub and you can make changes to your copy.
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GitHub file view of the
[EHT-imaging](https://github.com/achael/eht-imaging)
repository.  This is the version of all files at a single point in
time.

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Github history view of the
[EHT-imaging](https://github.com/achael/eht-imaging)
repository.  This is the progression of the repository (with the
**commit message** over time).

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Network graph of all commits in the
[EHT-imaging](https://github.com/achael/eht-imaging/network)
repository.  This shows the relationship between different **forks**
of people who are contributing and sharing code.

Interesting repositories to explore these concepts

Why use repositories? Think of your usecases for the following:

  • All changes are recorded.
  • We do not have to send changes via email.
  • We can experiment with several ideas which might not work out (using branches).
  • Several people can work on the same project at the same time (using branches).
  • We do not have to wait for others to send us "the latest version" over email.
  • We do not have to merge parallel developments by hand.
  • Group-based access model where shared access is the default, instead of everything fundamentally owned by individuals who manage sharing as-needed: with Git you can easily have collaboration be the default.
  • It is possible to serve websites directly from a repository. {: .discussion}

Discussion: workflows without version control

  • How have you solved these in the past without version control? {: .discussion}