Introduction to Version Control with Git
Originally by Andreas Skielboe
Dark Cosmology Centre Niels Bohr Institute
License
Most images adapted from Pro Git by Scott Chacon and released under license Creative Commons BY-NC-SA 3.0.
Why Use Version Control?
A Version Control System (VCS) is an integrated fool-proof framework for
Backup and Restore Short and long-term undo Tracking changes
Synchronization Collaborating Sandboxing
... with minimal overhead.
Local Version Control Systems
Conventional version control systems provides some of these features by making a local database with all changes made to files.
Centralized Version Control Systems
To enable synchronization and collaborative features the database is stored on a central VCS server, where everyone works in the same database.
Introduces problems: single point of failure, inability to work offline.
Distributed Version Control Systems
To overcome problems related to centralization, distributed VCSs (DVCSs) were invented. Keeping a complete copy of database in every working directory.
Git Basics
Git Basics
Git Basics - The Git Workflow
The simplest use of Git:
Modify files in your working directory.
Stage the files, adding snapshots of them to your staging area. Commit, takes files in the staging area and stores that snapshot permanently to your Git directory.
Git Basics - The Three States
The three basic states of files in your Git repository:
Git Basics - Commits
Each commit in the git directory holds a snapshot of the files that were staged and thus went into that commit, along with author information.
Git Basics - File Status Lifecycle
Files in your working directory can be in four different states in relation to the current commit.
Git Basics - Working with remotes
In Git all remotes are equal.
Git Basics - Working with remotes
The easiest commands to get started working with a remote are clone: Cloning a remote will make a complete local copy. pull: Getting changes from a remote.
push: Sending changes to a remote.
Note that Git will only let you push to bare repositories.
Fear not! We are starting to get into more advanced topics. So lets look at some examples.
Git Basics - Advantages
Basic advantages of using Git: Nearly every operation is local. Committed snapshots are always kept. Strong support for non-linear development.
Hands-on
Hands-on with Git (here be examples)
Hands-on - First-Time Git Setup
Before using Git for the first time:
Pick your identity
$ git config --global user.name "John Doe"
$ git config --global user.email [email protected]
Check your settings
$ git config --list
Get help
Hands-on - Initializing a working repository
If you want to do all of your development on cs1520.cs.pitt.edu, you can simply make a new web directory and initialize a repository for your site.
Initializing a working repository
$ ssh <id>@cs1520.cs.pitt.edu $ cd public/csweb/
$ mkdir git_example $ cd git_example $ git init
Hands-on - Adding files
With your local working copy you can make any changes to the files in your working directory as you like. When satisfied with your changes you add any modified or new files to the staging area using add:
Adding files to the staging area
Hands-on - Commit
Finally to commit the files in the staging area you run commit supplying a commit message.
Committing staging area to the repository
$ git commit -m <msg>
Note that so far everything is happening locally in your working directory.
Hands-on - Example working repository workload
Create an HTML file, add it, change it, and commit the change
$ ssh <id>@cs1520.cs.pitt.edu $ cd public/csweb/git_example/
$ nano example.html #create a simple "Hello World" page
$ git add example.html #start tracking example.html
$ git commit -m "adding the first file to the repo"
$ nano example.html #change the page a bit
$ git add example.html #stage the file for commit
$ git commit -m "small update to example.html" Now you can view example.html from your browser at: http://cs1520.cs.pitt.edu/ <id>/git example/example.html
Hands-on - Clone to submit
In this class, you will have to submit your assignments using Git. The submission directory for each student is:
/afs/pitt.edu/home/n/l/nlf4/submissions/cs1520/<id>/<assignment>/
or, more simply:
˜nlf4/submissions/cs1520/<id>/<assignment>/
For this exercise, I’ve made an ”example” assignment, so you can submit your git example repository (containing example.html) by cloning the repository in the submission directory a follows (from cs1520.cs.pitt.edu):
Change to the appropriate submission directory and clone your repository there
$ cd ~nlf4/submissions/cs1520/<id>/example $ git clone ~/public/csweb/git_example/
Hands-on - Installing Git on your home machine
You may want to work on your code and projects from your own laptop or desktop. Instructions for installing Git on various platforms (Linux, OSX, Windows) can be found in the Book Pro Git:
http://git-scm.com/book/en/Getting-Started-Installing-Git
On Linux and OSX, you can simply open up a terminal and start using Git.
On Windows, you’ll have to navigate to an appropriate directory, right click, and then open up a Bash shell to use msysGit.
There are also a number of GUI interfaces to Git available: http://git-scm.com/downloads/guis
Hands-on - Initializing a bare repository
As mentioned before, you can only push to bare repositories, so we’ll need to set up a bare repository on the server so that you can push changes from your home machine to cs1520.cs.pitt.edu.
Initializing a bare repository
$ ssh <id>@cs1520.cs.pitt.edu $ mkdir -p repos/git_example.git $ cd repos/git_example.git $ git --bare init
Hands-on - Cloning repositories
Clone a version of your code for Apache to display.
Cloning a repository on the same machine
$ ssh <id>@cs1520.cs.pitt.edu $ cd public/csweb/
$ git clone ~/repos/git_example.git $ cd git_example
Clone a version to work on on your home machine.
Cloning a remote repository
$ git clone <id>@cs1520.cs.pitt.edu:repos/git_example.git $ cd git_example
Hands-on - Bare repository architecture
You’ve now cloned two working repositories from the bare repository.
Hands-on - Push/Pull
To share your commits with the remote you invoke the push command:
Pushing local commits to the remote
$ git push
To recieve changes that other people have pushed to the remote server you can use the pull command:
Pulling remote commits to the local working directory
$ git pull
Hands-on - Example bare repository workload
From the git example directory cloned on a local machine:
Creating and modifying an HTML file, but now commits are pushed to a bare repository
$ nano example.html #create a simple "Hello World" page
$ git add example.html #start tracking example.html
$ git commit -m "adding the first file to the repo" $ git push origin master #push the first file to the repo
$ nano example.html #change the page a bit
$ git add example.html #stage the file for commit
$ git commit -m "small update to example.html"
$ git push #push the update commit
Hands-on - Example bare repository workload
Pull changes from the bare repository in to web directory
$ ssh <id>@cs1520.cs.pitt.edu $ cd public/csweb/git_example/ $ git pull
Now you can view example.html from your browser at: http://cs1520.cs.pitt.edu/ <id>/git example/example.html
More advanced topics
Git is a powerful and flexible DVCS. Some very useful, but a bit more advanced features include:
Branching Merging Tagging Rebasing
Checkout these slides
The LATEX-source of the original slides is freely available on GitHub.
GitHub
$ git clone git://github.com/askielboe/into-to-git-slides.git
I’m hosting the LATEX-source for these slides within the CS dept.
Source for these slides
References
Some good Git sources for information:
Git Community Book (Pro Git)- http://book.git-scm.com/ Git Reference - http://gitref.org/
GitHub - http://github.com/ Git from the bottom up
-http://ftp.newartisans.com/pub/git.from.bottom.up.pdf Understanding Git Conceptually
-http://www.eecs.harvard.edu/~cduan/technical/git/ Git Immersion - http://gitimmersion.com/
