summerschool_simtech_2023/material/2_tue/git/git_basics_demo.md

Git Demo

Recap of Git basics

• Expert level poll on git: ask students to estimate their level.
  • Beginner: I have hardly ever used Git
  • User: pull, commit, push, status, diff
  • Developer: fork, branch, merge, checkout
  • Maintainer: rebase, squash, cherry-pick, bisect
  • Owner: submodules

git overview picture from py-rse

• git --help, git commit --help

• incomplete statement git comm

• There is a difference between Git and hosting services (forges)

  • GitHub
  • GitLab, open-source, hosted e.g. at IPVS
  • Bitbucket
  • SourceForge
  • many more
  • often, more than just hosting, also DevOps

• Give outlook on remainder of Git chapter: How I work with Git, quiz, advanced topics (workflows, rebase, standards), my neat little Git trick

How I work with Git

Starting remarks:

• There is not the one solution how to do things with Git. I simply show what I typically use.

• Don’t use a client if you don’t understand the command line git

• 1. Look at GitHub
  • preCICE repository
  • default branch develop
  • fork -> my fork
• 2. Working directory:
  • ZSH shell shows git branches
  • git remote -v (I have upstream, myfork, …)
  • mention difference between ssh and https (also see GitHub)
  • get newest changes git pull upstream develop
  • git log -> I use special format, see ~/.gitconfig,
  • check log on GitHub; explain short hash
  • git branch
  • git branch add-demo-feature
  • git checkout add-demo-feature
• 3. First commit
  • git status -> always tells you what you can do
  • vi src/action/Action.hpp -> add #include "MagicHeader.hpp"
  • git diff, git diff src/com/Action.hpp, git diff --color-words
  • git status, git add, git status
  • git commit -> “Include MagicHeader in Action.hpp”
  • git status, git log, git log -p, git show
• 4. Change or revert things
  • I forgot to add sth: git reset --soft HEAD~1, git status
  • git diff, git diff HEAD because already staged
  • git log
  • git commit
  • actually all that is nonsense: git reset --hard HEAD~1
  • modify again, all nonsense before committing: git checkout src/action/Action.hpp
• 5. Stash
  • while working on unfinished feature, I need to change / test this other thing quickly, too lazy for commits / branches
  • git stash
  • git stash pop
• 6. Create PR
  • create commit again
  • preview what will be in PR: git diff develop..add-demo-feature
  • git push -u myfork add-demo-feature -> copy link
  • explain PR template
  • explain target branch
  • explain “Allow edits by maintainers”
  • cancel
  • my fork -> branches -> delete
• 7. Check out someone else’s work
  • have a look at an existing PR, look at all tabs, show suggestion feature
  • but sometimes we want to really build and try sth out …
  • git remote -v
  • git remote add alex git@github.com:ajaust/precice.git if I don’t have remote already (or somebody else)
  • git fetch alex
  • git checkout -t alex/[branch-name]
  • I could now also push to ajaust’s remote

Further reading

Quick things

• Video: Git in 15 minutes: basics, branching, no remote
• The GitHub Blog: Commits are snapshots, not diffs
• Chapters 6 and 7 of Research Software Engineering with Python
• Podcast All Things Git: History of VC
• git purr

References

• Official documentation