Git and GitHub

Stephen P Levitt

School of Electrical and Information EngineeringUniversity of the Witwatersrand

2019

Outline

1 Key Git ConceptsSnapshotsTime TravelBranchesParallel Universes

2 GitHub

Git and GitHub 1 / 10

Snapshots

git commit // take a snapshotgit log // view IDs and descriptions of past snapshots

Snapshots of the codebase are created on demand with a commitA commit stores:

the changes to all the files under version controlthe date and time the snapshot was taken, and the authora message describing the work that is contained in the snapshota reference to the parent commit object

Each commit has a unique ID generated by a cryptographic hash function

Git and GitHub : Key Git Concepts : Snapshots 2 / 10

Snapshots continued

commit f0032b7b2a549c6b6d5cd84e0258e3c54711dcaa (HEAD -> master,origin/master)

Author: Stephen Levitt <stephen.levitt@wits.ac.za>Commit: Stephen Levitt <stephen.levitt@wits.ac.za>

Added some videos, comments to slides, new google car image

Included some video content. At the moment videos are not embeddedin the slides. Added comments to slides about talking points.These should be converted into proper notes.

Code in a snapshot can never be changed — immutable

Git and GitHub : Key Git Concepts : Snapshots 3 / 10

Time Travel

git checkout <abbreviated commit hash> // go back to an earliersnapshot

Resurrect the codebase at an earlier point in time — work is never lostSuitable for code inspection; branching required for storing any changes made tothe checked-out commit

Git and GitHub : Key Git Concepts : Time Travel 4 / 10

Branches

git branch <branch name> // create a new branchgit checkout <branch name> // move to the tip of the new branchgit merge <branch name> // merge the named branch into the branch

you are on

Short-lived branches are used forexperimentation and feature developmentEventually will be merged back intomaster or another dev branchMerges take place between two local branches or two remote branchesRemote branch merge required for code review on GitHub, via a pull requestFast-forward merging will occur if the branches being merged have not diverged

Git and GitHub : Key Git Concepts : Branches 5 / 10

Parallel Universes

Enables collaboration

git push // push local branch toremote

git pull // fetch remote branch andmerge into local; you pull codetowards you

Often each developer has a local repo which is synced with a shared remote repo(on GitHub for example); local branches track upstream (remote) branchesMain branch in local repo is called master; main branch in remote repo is calledorigin / master

Git and GitHub : Key Git Concepts : Parallel Universes 6 / 10

GitHub

Web-based Git hosting serviceWorld’s largest host of open-source code - 57 million repositories; used extensivelyin industry as wellProvides additional features such as code review, repo analytics, and lightweightproject management tools

Git and GitHub : GitHub 7 / 10

Apollo 11 Command and Lunar Module Guidance Systems

https://github.com/chrislgarry/Apollo-11

Git and GitHub : GitHub 8 / 10

Quine Relay

https://github.com/mame/quine-relay

Git and GitHub : GitHub 9 / 10

D3

https://github.com/d3

Git and GitHub : GitHub 10 / 10