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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.
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Advanced Git Tutorialby Sarah Sharp
WARNING:I am a unique snowflake
WARNING:This tutorial may make you lazy
WARNING:Some Git features are
dangerous!
What is Git?
● Distributed● Fast● Flexible
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
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
Git Philosophy
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.
Infrequent UseFrequent Use
The Index, the staging area
Front stage:Changes to be committed
Back stage:Uncommited changes
and unadded files
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?
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.
What changed?
workspaceindex
localrepository
git diff git diff --cached
git diff HEAD
● git status● git diff
Advanced Staging
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.
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)
Viewing History
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
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>
Pointing Fingers:git blame
Pointing Fingers
● git blame <file>– show who committed each line
● git blame <commit ID> <file>– show the line history before that commit
Branches
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>
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
Interacting with other people
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
Changing History
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
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
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
Git Hooks
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?
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.
Setting up aremote repository
Setting up aremote 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
Setting up aremote 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
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
Creative CommonsImage Attributions
● GIT picture: http://flickr.com/photos/29862082@N06/2908889599/
● Snowflake: http://commons.wikimedia.org/wiki/Image:SnowflakesWilsonBentley.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/
Creative CommonsImage 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/
Thank you!
● Sarah Sharp● @sarahsharp● http://sarah.thesharps.us
