Smalltalk on Git

Git in a Nutshell Sort of... Mathias Meyer www.paperplanes.de Ruby User Group Berlin

What the git? • Git is not the next Subversion • Git is a content tracker • Git is almost a versioned ﬁle system • Git is distributed

What the git? • Git is a huge collection of commands • Git is f***ing fast

Ancient History • Developed to replace BitKeeper for the Linux kernel development • Started out as a couple of scripts built by Linus Torvalds • Used by Rails, Merb, Ubuntu, X.org, Wine, Rubinius and Linux (whoa!) • Started out focused on development with a central maintainer

Basics • Every working copy is a full-ﬂedged repository • Git only tracks content • Content is identiﬁed by a hash • Though that content has a name • The same content is only stored once

Basics • Everything is stored in one .git directory in the top level of your working copy • Git uses an index to ﬁnd changes in the working directory • The index is a snapshot of a speciﬁc tree in the repository

Git Objects • Git knows four types of objects • Have SHA1 IDs • Can be addressed with the six ﬁrst bytes of the hash • Are compressed with gzip

Commits • Refers to a tree and usually a parent commit (usually the commit before the current one) • Can have two or more parents, then they represent a merge • Or no parent at all • Stored with a log message

Tree • A simple structure containing names of blobs and other trees • Represents a snapshot of the source tree

Blob • Contains data, e.g. ﬁle content • Blobs don’t have names • Their names are derived from the tree • Will be found through associations from trees and commits

Tag • Glued to a speciﬁc object • Marks a speciﬁc point in the Git timeline with a name

HEAD branch commit tree tree blob tree blob blob

Git Branches • master - default development branch • origin - default upstream branch • HEAD - current branch

Git Branches • HEAD~2, master^1, wtf? • ~N references the Nth generation grandparent of a commit • ^N references the Nth parent of a commit, only useful for merges of two or more commits • So....

Git Branches • HEAD~2 is the second generation grandparent of the last commit on the current branch • master^2 is the second parent of the last commit on master • master~2^2 is the second parent of the second generation grand-parent of the last commit on the current branch

Git Branches Rrright.

Git Branches • Branches are cheap and easy • A branch is an ID pointing to a tree and a parent commit • Merging is cheap, fast and almost painless • Ergo: Branching in Git rocks

How Do I Get Git? • MacPorts (port install git-core +svn) • Git Installer for Leopard • On every Linux distribution (apt-get|rpm install git-core) • On Windows? I think so

How Do I Get Started? • mkdir project.git • cd project.git • git init • Start hacking

How Do I Get Started? • Or go to GitHub • Best GUI for Git evah

Everyday Git • Some of the commonly used Git commands • Called the Porcelain

Set up camp • git conﬁg --global user.name “Mathias Meyer” • git conﬁg --global user.email “meyer@paperplanes.de”

git clone • Creates a local working copy of a remote project • git clone git://github.com/mattmatt/ macistrano.git

git checkout • Checks out code from a branch • Will overwrite your local changes • git checkout -b will create a branch and check it out

git branch • Shows, creates and deletes branches • git branch master * show_me_the_money • git branch new_branch • git branch -d new_branch

git fetch • Fetches all objects from a remote repository which are not in the local repository

git add • Schedule changes in one or more ﬁles for the next commit

git rm • Removes ﬁles

git mv • Moves ﬁles and directories around

git commit • Isn’t it obvious? • It will check in your changes • But only the ones you added • Use git commit -a to check in all the changes without adding them • git commit <ﬁle> will commit the ﬁle without the need to add it

git status • Shows staged and unstaged changes • staged = added • unstaged = new, conﬂicts, changed

git push • Pushes your changes to a remote repository • git push origin pushes the current branch • git push origin master pushes the master branch

git pull • Different way to do a merge • git pull = git fetch + git merge

git log • Shows the commit history • Can be verbose if you want it to

git merge • Merges the changes from a branch into your current branch • git merge rails_2_1 • And that’s that • In case of conﬂicts, these need to be resolved and then committed

git tag • Duh! • Associates a tag with the

git stash • It’s like a clipboard in your repository • Need to work on something else but don’t want to commit your local changes yet? • git stash save will save all your changes • git stash apply will reapply them after you’re done • git stash list shows all the stashes • git stash show shows the changes of a stash

git show • Shows the details of a speciﬁed, or the last commit

git archive • Creates an export of your repository • Default is tar • Convenient, no? • git archive release_2_1 > release_2_1.tar

git .... • There’s lots more • Which you probably won’t need most of the time • You use 20 or so for everyday work • Some of them only on special occasions • git-<tab> and start digging

Git-Svn • The gateway drug for Subversion users • Warning:You don’t want to use the svn command ever again • Ever!

Git-Svn • Basically a couple of Perl scripts • Using the Subversion bindings • Translates Subversion commits to Git commits and vice versa

Show me how! • mkdir webistrano • git svn init -s http://labs.peritor.com/svn/ webistrano • git svn fetch • Get a coffee...

Everyday Git-Svn • git checkout -b make_me_rich • ...endless hours of coding... • ...and writing tests... • git add lib/monetize.rb spec/monetize_spec.rb • git commit

Everyday Git-Svn - Merging • git commit -a • git checkout master • git svn rebase • git merge make_me_rich • ...run tests... • git svn dcommit • git branch -d make_me_rich

Everyday Git-Svn - Merging • The potentiel downside of using git merge: • git svn dcommit will check in all the commits from the branch in one single svn commit

Everyday Git-Svn - Merging • The alternative • dcommit from the branch • rebase the changes on master

Everyday Git-Svn - Merging • git commit -a • git svn rebase # on branch make_me_rich • git svn dcommit # on branch make_me_rich • git checkout master • git svn rebase • git branch -d make_me_rich

Some Git Awesomeness • Find out what commits will be ci’d to svn • git svn dcommit -n (rather sparse) • git cherry -v trunk (full glory) • Commit partial changes of a ﬁle • git add --patch

But I don’t like the CLI • Use git gui for a “nicer” interface • Use Gitk to visualize commits and branches • For both: brace yourself to be blinded • Much nicer, less powerful: GitNub • TextMate bundle!

In the end... • Git will blow your brains out • In several ways • It takes a while to get used to it • But it’s totally worth it • Even if you’re still using Subversion as a central repository

The Bad Stuff • Poor documentation, be prepared to spend some time on Google • Complex beast, lots of small commands • No API

Resources • Git Home (http://www.git.or.cz) • Git User’s Manual (http://www.kernel.org/pub/ software/scm/git/docs/user-manual.html) • Git PeepCode (http://peepcode.com/products/ git) • Must-read: Git Internals (http://peepcode.com/ products/git-internals-pdf) • GitCasts (http://www.gitcasts.com/)

Smalltalk on Git

by mattmatt on Jun 06, 2008

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Smalltalk on Git — Presentation Transcript