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GitDistributed Version Control
Local Version Control
Image stolen from http://progit.org/book/ which is really good, go read it.
Old-school version control like RCS
Centralized Version Control
Image stolen from http://progit.org/book/ which is really good, go read it.
This is how Subversion works
Distributed Version Control
Image stolen from http://progit.org/book/ which is really good, go read it.
This is how Git works
Why Do I Care?
Because it has been mandated that you care about version control by Prof. Laurendeau
Because you will use version control at every single coding job you get in the real world If your company doesn’t have version control in
place, that’s a huge warning sign Because it will change the way you think about
programming, for the better Because it stops you from completely screwing
yourselves the day before an iteration is due
Installing Git
Let’s install Git and try some things out.
Linux: use your favourite package manager Ubuntu: aptitude install git
Windows: use the MSysGit installer http://code.google.com/p/msysgit/
Mac: use the OS X installer http://code.google.com/p/git-osx-installe
r/
Learning Git
Read Pro Git, it’s excellent and free http://progit.org/book/
Git is extraordinarily powerful and you’ll be a better programmer if you take the time to understand it
If in doubt, always use the built in manual Every git command has a --help flag e.g. git cherry-pick --help
Seriously go read http://progit.org/book/.
Getting Started
Let’s tell Git our name and email address It attaches these to any commits we make so
people know who to kill for breaking the build an hour before an iteration is due
git config --global user.name “Your Name” git config --global user.email
“[email protected]” --global sets the variable for your OS user▪ --system sets the variable for all users on your machine
Omit the --global and --system flags to set a git config variable for just this repository
Creating a Repository
git init Creates a local, empty git repository in
the folder where the command is run Creates a .git folder for the guts of the
repository▪ Only one .git folder, at the root of your
repository▪ This is way nicer than creating a new .svn
folder for every single subfolder in your repository
We’ll go over how to work with other people on a remote repository soon
Anatomy of a Repository
Image stolen from http://progit.org/book/ which is really good, go read it.
Anatomy of a Repository
Crazy important! Memorize this! The working directory consists of the
actual files and folders on your machine The staging area lets you build commits
out of snapshots taken of the files and folders in your working directory
The repository maintains a collection and complete hierarchical history of all commits
Oh God, What’s Happening?
git status Shows you the state of your staging area
and of your working directory git log
Shows a commit history of your repository
git diff Shows changes between commits, your
working directory, the staging area, etc. git diff --help to learn moreOr you could just go read http://progit.org/book/ and you’ll be an expert.
Adding & Removing Files
git add file Adds a snapshot of file to your staging area▪ You can change file and the snapshot will remain as it
is git rm file
Removes the file snapshot from your staging area and deletes file from your working directory
git rm --cached file Removes the file snapshot from your staging
area while keeping file in your working directory intact
.gitignore
Tells Git which files to ignore outright Uses glob syntax for pattern matching
There’s a decent summary of glob syntax at linux.about.com/library/cmd/blcmdl7_glob.htm
Git adds re-inclusion rules with !pattern “Include any files matched by pattern, even if
they’ve been ignored by a previous pattern.” There’s a sample .gitignore on the website
Stack Overflow is a good source of .gitignore files
Making Commits
git commit -m “your message” Creates a commit from the contents of your
staging area and adds it to the repository -m “your message” sets the commit message
If we keep adding commits we get a linked list that represents the history of our repository gitk --all gives a graphical history of all
branches Leaving out the --all shows just this branch
And the book at http://progit.org/book/ has a whole bunch more information. Read the damn book!
GitK Screenshot
Branching & Why It Is Awesome
Branching allows us to create a tree of commits instead of a linked list Merging will let us turn this into a DAG
Easy, painless branching is the most important and powerful feature of Git Give each new feature its own branch,
which can be merged back into the main (master) branch after it’s been completed and is stable
GitK With Branching
Creating Branches
Git maintains a pointer to the current checked out branch, called HEAD
git branch newbranch Creates a new branch starting at the current
commit, but does not move the HEAD pointer git checkout newbranch
Changes HEAD to point to newbranch Run git branch then git checkout to create
and start working from a new branch Shortcut: git checkout -b newbranch
Branching Example
Images again stolen from http://progit.org/book/ which you should read because it’s good.
$ git branch testing
$ git checkout testing
Branching Example
$ git commit
$ git checkout master
Images stolen from http://progit.org/book/
Branching Example
At this point, the branch history has diverged
We want to branch for new features and merge them back into the master branch This makes your life infinitely easier
$ git commit
Images once again stolen from http://progit.org/book/
Merge Tools
git config --global merge.tool toolname Sets the merge tool for your OS user
A merge tool allows you to fix any conflicts that arise from merging two branches
Google will give you a list of merge tools I use p4merge, it’s hard to go wrong just
choosing a random merge tool and using it git mergetool
Run this command if anything goes wrong with a merge, it’ll allow you to fix things
Merging
git merge branchname Allows you to take another branch and
merge its changes into the currently checked out branch
Git has hyper-intelligent algorithms that track your content, not your files If you move or rename a file and make
changes to it, it will still be detected as the same content
Branching & Merging in SVN It’s relevant to see how the approach taken by Git
differs from that of terrible legacy systems like SVN Subversion doesn’t have real branches
A branch is just a copy of your repository in a named folder
SVN has no concept of branch history and therefore cannot determine common ancestry to help with merging
Subversion doesn’t have real merging The svn merge command should be called svn diff-and-
apply-patch because that’s all it does “If a merge fails, run svn revert and do it by hand.” There is no way to tell whether a given set of changes
were the result of a merge or were just straight edits
Remote Repositories
git remote add reponame url Adds an external Git repository called name
git fetch reponame Fetches updated branches from reponame
including all updated data▪ A remote branch shows up as reponame/branchname
Your local information about remote repositories isn’t updated automatically You need to run git fetch periodically on your
remotes to get new branch/commit information
Pushing
git push reponame branchname Adds a local branch to a remote Git repository▪ You need to have write access to the remote repository
Alternatively, merges your local branch into a remote branch of the same name
git push reponame localbranch:remotebranch Explicit syntax for merging your changes from
localbranch into remotebranch Always fetch and merge before you push
Save yourself grief and error messages
Pulling
git pull reponame branchname Fetches from reponame then merges the
remote branchname into your local branchname
git pull reponame localbranch:remotebranch Fetches from reponame then merges
reponame/remotebranch into localbranch
Syntactic sugar for fetching and merging Your workflow should be “git pull; git
push”
Tracking Branches
git checkout -b branch remote/otherbranch Gives you a tracking branch that you can
work on, that starts where remote/otherbranch is
Tracking branches are local branches that have a direct relationship to a remote branch You can just call git push/pull with no
arguments and it know which remote branch to change
Cloning a Repository
git clone url Creates a new local git repository, creates new
tracking branches for each branch in the cloned repository, creates and checks out an initial branch that is forked from the remote’s active branch
Watch out if the remote repository doesn’t have any commits yet (really common thing) Cloning will fail, you need to do git init, git remote
add origin url, create an initial commit with some content, then run git push origin master
And We’re Done!
There’s some stuff I didn’t get to cover due to time constraints
Look up git stash, git submodule TortoiseGit is a Windows-only frontend for Git
It’s a knockoff of TortoiseSVN and is really easy to use
Go read the Pro Git book because it’s short, awesome, free, etc. Reading it will make you taller and more popular
with members of your preferred gender Thanks for your time :)
