Do you know the basics of Git but wonder what all the hype is about? Do you want the ultimate control over your Git history? This tutorial will walk you through the basics of committing changes before diving into the more advanced and "dangerous" Git commands. Git is an open source, distributed version control system used to track many different projects. You can use it to manage anything from a personal notes directory to a multi-programmer project. This tutorial provides a short walk through of basic git commands and the Git philosophy to project management. Then we’ll dive into an exploration of the more advanced and “dangerous” Git commands. Watch as we rewrite our repository history, track bugs down to a specific commit, and untangle commits into an LKML-worthy patchset.

1. Advanced Git Tutorial
by Sarah Sharp

2. WARNING:
I am a unique snowflake

3. WARNING:
This tutorial may make you lazy

4. WARNING:
Some Git features are
dangerous!

5. What is Git?
● Distributed
● Fast
● Flexible

6. Git Basics
● See Everyday Git Tutorial:
– http://www.kernel.org/pub/software/scm/git/doc
s/everyday.html
● My git commands:
– git add - git commit
– git diff - git log - git show
– git push - git pull
– git fetch - git rebase

7. Naming commits
<Commitish>
● (Indirect) hash of repo files, current
commit message, and ancestor commits.
● HEAD refers to the last commit
● ~ at the end means commit before that
– e.g. HEAD~
– ^ is roughly equivalent to ~
● A branch points to a specific commit
● see git rev-parse

8. Git Philosophy

9. Git Philosophy
● Commit early, commit often
● One commit represents one idea or one
change.
– Makes it easy to read patches
– Easy to revert unwanted changes later
● Your working directory, index, and local
repo are your scratch pads.

10. Frequent Use Infrequent Use

11. The Index, the staging area
Front stage: Back stage:
Changes to be committed Uncommited changes
and unadded files

12. Staging Changes
● git add <file> – adds a file to the Index
● git commit – commits added changes to
the local repo
● But what about files not added to the
Index?

13. Staging Changes
● git add <file> – adds a file to the Index
● git commit – commits added changes to
the local repo
● But what about files not added to the
Index?
– Answer: they aren't included in the commit.
● Key idea: You can add and commit files
separately from other files.
– This makes separating changes into small
patches easier.

14. What changed?
● git status
● git diff
git diff HEAD
local
workspace
repository
git diff index git diff --cached

15. Advanced Staging

16. Advanced Staging
● git add --patch
– try the "split" option to split across hunks
● git add -i
– Very powerful tool with lots of options
● Key idea: You can add and commit
different parts of a file separately.

17. Unstaging changes
● Revert to the last commit
– git reset --hard HEAD
● Remove all added changes from the index
– git reset --mixed HEAD
● Remove some files added to index
– git add -i and choose revert, or
– git reset HEAD filename(s)

18. Viewing History

19. Viewing History
● git log
● git log <commit A>..<commit B>
– shows history after commit A, up to commit B
– can omit either commit
– e.g. `git log` `git log origin..` `git log ..v2.6.30`
● git log -p
– shows log as a series of patches
● git log --pretty=oneline –abbrev-commit

21. Viewing old files
● Contents of a file at a particular commit
– git show <commitish>:<path to file>
● Contents of a directory
– git show <commitish>:<directory>

22. Pointing Fingers:
git blame

23. Pointing Fingers
● git blame <file>
– show who committed each line
● git blame <commit ID> <file>
– show the line history before that commit

24. Branches

25. Branches
● Only one branch can be checked out
– trunk ~= master
● show all branches
– git branch -a
● switching branches
– git checkout name
● creating new branches
– git checkout -b name <commit>

26. Advanced Branching
● Merge branches with git merge
– creates a "merge commit"
● Rebase current branch against branch B
– find a common ancestor commit
– apply commits from branch B
– apply commits from current branch
● Apply a commit from one branch
– git cherry-pick

27. Interacting with other people

28. Interacting with other people
● Creating a patchset, starting at commitA
– git format-patch -o directory commitA^
--cc=<cced-email>
– use git send-email or `mutt -H <gitpatch>`
● Applying a patch
– git am patchfile
– can also take a mailbox or maildir or stdin
● Pushing a new branch
– git push remote branch

29. Changing History

30. Changing History:
DANGER, WILL ROBINSON!
● After a commit, often you will find bugs
– could make a new bug fix commit
– or you could "amend" the previous commit
● Fix your code
● git add <file>
– This adds your code to the index
● git commit --amend
– This modifies the commit in the local repo
– useful to have vim git-commit script installed

31. Changing History:
DANGER, WILL ROBINSON!
● A total history rewrite:
– git rebase -i <commit ID>
● Can reorder commits
● Can edit commits
● Can "squash" one commit into another
● May have merge conflicts
– edit files, resolve conflicts surrounded by
<<<< and >>>>
– git add files, git rebase --continue

32. git rebase -i --dontscrewme
● No such command
● git rebase -i the safe way:
– git checkout -b master-rebase
– use `git rebase -i` to move one patch
– resolve any merge conflicts
– squash that patch using `git rebase -i`
– git diff master master-rebase
– git branch -M master master-old
– git branch -M master-rebase master

33. Git Hooks

34. Git Hooks
● Hooks are scripts found in .git/hooks/
● Enable them with chmod a+x <file>
● Triggered by various git commands
– e.g. git commit, git push
– pre-commit, post-update
● Examples
– shipped pre-commit hook checks for white
space at the end of line, long lines, etc.
– Checking for swear words?

35. Git Hooks
● Example post-update hook on remote repo:
#!/bin/sh
cd /home/sarah/blog
unset GIT_DIR
git-fetch origin
git-reset --hard origin/master
● Whenever I push to the remote repository, this
goes into the server's checkout of my blog git
repo and updates it unconditionally.

36. Setting up a
remote repository

37. Setting up a
remote repository
● Server needs git and sshd installed to use
git+ssh to push to your repo
● Server needs webDAV installed to allow
push to your repo over https
● http://github.com/ will host your repo
● Next directions assume you have your
own server with git installed

38. Setting up a
remote repository
1. Make local repo, commit stuff, etc.
2. ssh to the server:
GIT_DIR=/path/to/repo git init --shared
3. Next, tell the local repo about the server:
git remote add origin git+ssh://hostname/path/to/repo
4. Push to the server from the local repo:
git push origin master
5. Clean up the local repo so that you can pull from the
remote server:
git config branch.master.remote origin
git config branch.master.merge refs/heads/master

39. Resources
● Git work flow diagrams:
http://osteele.com/archives/2008/05/my-git-workflow
● The Tangled Working Copy:
http://tomayko.com/writings/the-thing-about-git
● http://github.com/
● Kernel module examples at http://lwn.net/Kernel/LDD3/
● vim git-commit script will display commit messages in a
more useful manner. Script kept at vim.sourceforge.net.
– sudo aptitude install vim-scripts vim-addon-manager
– vim-addons install git-commit

40. Creative Commons
Image Attributions
● GIT picture:
http://flickr.com/photos/29862082@N06/2908889599/
● Snowflake:
http://commons.wikimedia.org/wiki/Image:SnowflakesWilson
Bentley.jpg
● Danger:http://flickr.com/photos/dawvon/32305882/
● Cat: http://flickr.com/photos/jamilsoni/118499378/
● Remote: http://flickr.com/photos/markkelley/957631507/
● Philosophy: http://flickr.com/photos/paullew/2442045767/
● Branches: http://flickr.com/photos/shapeshift/136184752/
● Interacting with other people:
http://www.flickr.com/photos/exlibris/3222440467/

41. Creative Commons
Image Attributions
● Front stage:
http://flickr.com/photos/69108241@N00/118040089/
● Back stage: http://flickr.com/photos/piotramigo/2561391320/
● Hooks:http://www.flickr.com/photos/yabanji/3175297773/
● Blame: http://flickr.com/photos/iandesign/1205496024/
● Ballet: http://www.flickr.com/photos/oudeschool/3553416511/
● Papyrus: http://flickr.com/photos/charlestilford/2548991271/

42. Thank you!
● Sarah Sharp
● @sarahsharp
● http://sarah.thesharps.us