UVA workshop!

-Last updated 28-Jan-2020

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git-intro

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UVA Library Workshop on Introduction to Git and GitHub/GitLab.

This file exists here: https://github.com/rjp0i/git-intro (or visit here for a prettified view)

About Me

• Ricky Patterson: I am the Associate Director, Research Data Services, UVA Library
• I was a research astronomer for 20+ years here at UVA

Data Resources in the UVA Library

• Research Data Services
• Workshop Series

First, our goals

1. Everyone has a GitHub and GitLab account, and has GitHub Desktop running on their computer
2. Create a repository and fork it
3. Feel comfortable with git/github workflows
4. Know how to get help

Second, some terms

• git - version control software.
• GitHub - a for profit company recently purchased by Microsoft. It provides cloud-based hosting of repositories.
• GitLab - an alternative to GitHub, not owned by Microsoft (why you might want to switch). “Free software deserves free tools.”
• repository (repo) - Basic unit in git: a record of all changes to specified files.
• fork - personal copy of another users repo.
• branch - a parallel version of a repo (main branch is called “master”).

Git Glossary

You can look at GitHub’s Git Handbook

Getting Git

• To play along you will need a GitHub account –> https://github.com/

• If on mac/linux you probably already have git, but we also want GitHub Desktop.
  • go to http://desktop.github.com and download.
• If on windows, the latest version of GitHub desktop http://desktop.github.com is fine for today, but it won’t include the git “command line tools.” They are available:
  • Go to https://gitforwindows.org/ and download.

Outline

1. Some background
2. Work on the GitHub browser interface
3. Look at the GitHub Desktop interface
4. Tips on getting help

Reference for Git

The book Computing Skills for Biologists: A Toolbox contains a useful introduction to Git with practice data and code. Members of the UVA community can access the book online. The examples, data, code, and solutions are hosted on a github repo.

A brief history of Version Control

• CVS (1990s) Centralized (client-server)
• SVN (2000s) Centralized (client-server)
• git (2005) Distributed. Developed by Linus Torvalds for Linux development.

Getting Started: Hello World

• Let’s walk through GitHub’s Hello World Guide in the steps below.

Using Github

Step 0 - Inspect this Current Repo

• In a web browser, visit this repo: https://github.com/rjp0i/git-intro
• We are in the github interface:
  1. upper left corner: notebook icon next to rjp0i/git-intro (a repo)
  2. big green button on the right hand side (down a little) says “Clone or Download” (how to get the files)
  3. list of files (how to browse the files)
  4. readme.md is rendered as Markdown (github automatically shows the readme file, very handy)

Step 1 - Create your own Repo

https://guides.github.com/activities/hello-world/#repository

• Not so obvious, but in the upper right hand corner, click the ‘+’ button, pull down: select ‘new repository’
  1. name (this will be the address of the repo…)
  2. description
  3. public v private
  4. initialize with readme (alway say yes)
  5. license

Step 2 - Create a Branch (for Direct Collaborators)

https://guides.github.com/activities/hello-world/#branch

• Let’s leave the master branch alone and create a new branch
  1. Click the drop down at the top of the file list that says branch: master.
  2. Type a branch name, readme-edits, into the new branch text box.
  3. Select the blue Create branch box or just hit “Enter” on your keyboard.

Now we have two branches: master and readme-edits

Step 3 - Edit a File and Commit Changes

https://guides.github.com/activities/hello-world/#commit

• You should now be in the readme-edits branch.
• Click on README.md in the list and then click the pencil to edit the file
  1. now type in the editor
  2. when done click green button at bottom ‘commit changes’
     • commits can/should(?) be done early and often
     • no change is too small to commit, but you’ll get a feel for how often you should commit after some time
     • but always write a commit message that describes your changes
• Now the master and readme-edits branches differ

Step 4 - Making Pull Requests

https://guides.github.com/activities/hello-world/#pr

• Indirect Collaboration - pull requests
  1. Click the “Pull Request” tab, then “New pull request”
  2. In the Example Comparisons box, select the branch you made, readme-edits, to compare with master (the original).
  3. Proofread your changes in the diffs on the Compare page
  4. When ready to submit, click the Create Pull Request Button
  5. Write a title and a brief description of your changes
  6. Click Create Pull Request

  Step 5 - Merging Pull Requests

  https://guides.github.com/activities/hello-world/#merge

  • Now, let’s merge the Pull Request, to bring the changes from readme-edits into the master branch.
    1. Click the green Merge pull request button to merge the changes into master.
    2. Click Confirm merge.
    3. Now we can delete the readme-edits branch, since its changes have been incorporated into master. You’ll be prompted to do so inside the purple box.

  Step 5.1 - Resolving Conflicts when Merging Pull Requests

  https://help.github.com/en/articles/resolving-a-merge-conflict-on-github

  • Any time a merge is attempted when changes have been made to both versions of the same line of a file (in the master and in a fork, say), then you will have to resolve the conflicts in the merge.
  • Often, you can just use the github interface to do this. If this is the case (i.e., the conflict isn’t too complex), a Resolve Conflicts button will appear (and not be greyed-out).
  • Clicking on “Resolve Conflicts” will show you the conflict and use symbols to indicate the location of the conflict (<<<<<<<branch1-name, =======, >>>>>>>branch2-name), and the two versions of the conflicting line.
  • Choose the correct version of the line (or edit one version), then remove the other version and remove the symbols and the branch/fork names, leaving only the text you want in the final version.
  • Resolve any other marked conflicts in the file.
  • Click on Mark as Resolved.
  • Resolve conflicts in any other files.
  • Click on Commit Merge (and click on the I understand pop-up).
  • Finally, click on Merge Pull Request, and then confirm the merge.

GitHub Flow

https://guides.github.com/introduction/flow/

Forks - Indirect Collaboration

If you are not a collaborator in a repo, you can’t branch that repo. However, you can “fork” it, which is just creates a clone of the repo on the GitHub server.

1. You can’t push changes directly back to the original repo.
2. You’ll want to work on keeping your fork in sync with the project
   • add it to the original project as a remote, or
   • fetching regularly from the original repo

Try forking from my repo, and make changes to the resulting fork, and then submit a pull request to me!

Additional Items

• Command Line Interface (CLI) cheat sheet
• Create your own Webpage (such as https://rjp0i.github.io/intro.html)

Getting Help

• Please, feel free to email me: ricky@virginia.edu
• The book Computing Skills for Biologists: A Toolbox contains a very useful introduction to Git, with practice data and code. Members of the UVA community can access the book online
  • The examples, data, code and solutions are hosted on a github repo
• Lots of git/GitHub/GitLab resources from the source, as well as free training through a number of github sites
• StackOverflow is another good resource (e.g., for questions concerning git (or GitHub/GitLab): https://stackoverflow.com/questions/tagged/git

How to compare revisions

• use the following style of URL with two commit hashes (Rev A and Rev B)
  • of the form: github.com/$USER/$REPO/compare/$REV_A…$REV_B
• $REV_A and B are the commit hashes for the versions you want to compare. You can get these by examining the Commit history of a file on Github

Ways to Practice

1. Write some code, or some text
2. Do the version control in github
3. Edit it yourself
4. Have a friend do some edits as well

# This is an additional edit for practice. Hopefully this works