GIT tutorial

1. Wing Research Group GIT tutorial

2. Introduction • Learn why and how GIT aids software development • The outcome of this tutorial: • Understand the design and phylosophy of GIT • Be able to use GIT for everyday work

3. Agenda • GIT background • GIT design objectives • Everyday work with GIT • QA

4. Overview • Collaboration is ubiquitous in software development. Consequently, you see CVS, SVN, Mercurial, TLA, Mecurial and GIT. • How such a SCM can help many people to work together effectively?

5. Terminology • Repository • Pull / Push / Checkout • Branch • Merge • Conflict • Commit • Revert

7. GIT background • Developed by Linus Torvald • Purpose: to facilitate Linux kernel development • Consider CVS/SVN as the evil

8. Git design objectives • Distributed • No central repo • Everyone is on her own island • Write access class VS. Network of trust • Performance • Branching and merge is cheap • Diff the whole kernel tree in less than 1 second • Store the KDE tree in less than 2GB while SVN takes 8GB

9. Git design objectives • Reliability • File corruption, RAM corruption, Macilious users • GIT tracks the content of the whole repo, not single file, not only filenames • GIT use SHA1 for data integrity: file, commit, repo... • Consequently: • May not check in a single file • May not check out a single file • Break a big project to sub projects smartly :)

10. Everyday tasks with GIT • GIT has many routines: • “git merge” • “git pull” • “git push” • “gitk” • “git init” • “git config” • GIT man page • “man git-merge”

11. Everyday tasks with GIT • Introduce yourself to GIT • “git config –global user.name “Trung”” • “git config –global user.email “u0407784@nus.edu.sg”” • Create a repo • “git init” • Clone a repo • “git clone git://git.kernel.org/scm/git/git.git” • git clone ssh://trunglt@aye.comp.nus.edu.sg/home/min/forecite/

12. Everyday tasks with GIT • Lean a bit about GIT concepts: • Repo: your local repo and remote repos • Reference in history: either commit or merge • Branch: “master” is the default branch name. Do not give name such as test1, test2... but test_login, rel_iteration1 • SHA1 • Tag: a friendly name for a commit (version 1.0 vs e74g64a21...) • Head: you see that branch is a series of commits. A branch name also means the latest commit on that branch

13. Everyday tasks with GIT • HEAD: the commit that you are working on • HEAD^, HEAD^^, HEAD~3 = HEAD^^^, • HEAD^1, HEAD^2

14. Everyday tasks with GIT • Create a branch: • “git branch <name>” • “git branch <name> <commit-id>” • Delete a branch: • “git branch -d <name>” • List branch: • “git branch” • “git branch -r” //remote branch • Jump to a commit: • “git checkout <commit-id>” • “git checkout -b <name> <commit-id>”

15. Everyday tasks with GIT • Give remote repo a nicer name: • “git remote add min ssh://<username>@aye.comp.nus.edu.sg/home/min/parcite” • Fetch changes from Min: • “get fetch min” • Merge with the master branch of Min's repo: • “get merge min/master” • Or in one shot: git pull min

16. Everyday tasks with GIT • View SHA1 of a commit: • Git rev-list HEAD^..HEAD • View logs: • “git log” • “git log HEAD~4..HEAD” • “git log –pretty=oneline v1.0..v2.0 | wc-l • git log --raw -r --abbrev=40 –pretty=oneline origin..HEAD • git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz • “git blame <filename>”

17. Everyday tasks with GIT • Git commit and merge: • Git has its own index database • When you edit your repo, there are 3 things: • HEAD: the reference in history from that you are editing • Cached: whatever you have just added and run git add • The remaining files that you have not ask git to keep track

18. Everyday tasks with GIT • Make a commit: • After you edit some files, • look at the output of “git status” • ask GIT to keep track new files: “git add .” • Create new files • “git diff –cached” • “git add .” • “git diff HEAD” • “git commit”

19. Everyday tasks with GIT • Git merge: • “git pull min” OR (“git fetch min” then “git merge min”) • Conflicts • $ git show :1:file.txt # the file in a common ancestor of both branches • $ git show :2:file.txt # the version from HEAD, but including any • # nonconflicting changes from MERGE_HEAD • $ git show :3:file.txt # the version from MERGE_HEAD, but including any • # nonconflicting changes from HEAD. • Resolve the conflicts / reset and ask others to help

20. Everyday tasks with GIT • Reset the conflicted merge: use git-reset • “git reset –mixed <commit-id> • Reset the index database to the moment before merging • “git reset –hard <commit-id> • Reset the index database and the working data • “git reset –soft <commit-id> • You made a commit and also made some typo mistake. This commands help us fix those errors without touching the working data and index database

21. Everyday tasks with GIT • “git reset” help you to revert the most recent commit only • Revert older commit by hiding is bad • Use “git revert” to introduce a patch to revert the merge/commit done. • This is left as an exercise

22. Everyday tasks with GIT • Last thing: how to ignore files in a repo: • Use .gitignore: list files that you want to ignore • Put .gitignore in the directory containing the files • Example: Ruby on Rails project • Example: C/C++ project

23. Everyday tasks with GIT • Quality Assurance? How Linux developer keep track of bugs: • “git bisect”: binary search for a bug in a series of commits: • git bisect start • git bisect good v2.6.17 • git bisect bad v2.6.18

24. Question and Answer • Question and Answer :)

25. Summary • Git is a great tools for collaboration • New paradigm in SCM • Difficult to master, so learn it through everyday usage • Can always post questions to forum/admin group or :) Trung :)