Introduction to Version Control with Git

Introduction to Version Control with Git

Originally by Andreas Skielboe

Dark Cosmology CentreNiels Bohr Institute

Originally by Andreas Skielboe Git - Version Control System

License

Most images adapted from Pro Git by Scott Chacon and released underlicense Creative Commons BY-NC-SA 3.0.

See http://progit.org/


http://progit.org/

Why Use Version Control?

A Version Control System (VCS) is an integrated fool-proof frameworkfor

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 bymaking a local database with all changes made to files.

Any file can be recreated by getting changes from the database andpatch them up.


Centralized Version Control Systems

To enable synchronization and collaborative features the database isstored on a central VCS server, where everyone works in the samedatabase.

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 everyworking directory.

Actually the most simple and most powerful implementation of anyVCS.


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 snapshotpermanently 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 werestaged and thus went into that commit, along with author information.

Each and every commit can always be looked at and retrieved.


Git Basics - File Status Lifecycle

Files in your working directory can be in four different states in relationto the current commit.


Git Basics - Working with remotes

In Git all remotes are equal.

A remote in Git is nothing more than a link to another git directory.


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 lookat 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

$ git help <verb>


Hands-on - Initializing a working repository

If you want to do all of your development on cs1520.cs.pitt.edu, you cansimply 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 inyour working directory as you like. When satisfied with your changes youadd any modified or new files to the staging area using add:

Adding files to the staging area

$ git add <filepattern>


Hands-on - Commit

Finally to commit the files in the staging area you run commit supplyinga commit message.

Committing staging area to the repository

$ git commit -m <msg>

Note that so far everything is happening locally in your workingdirectory.


Hands-on - Example working repository workload

Create an HTML file, add it, change it, and commit the change


$ 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 submityour git example repository (containing example.html) by cloning therepository in the submission directory a follows (from cs1520.cs.pitt.edu):

Change to the appropriate submission directory and clone your repositorythere

$ 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 laptopor 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 usingGit.On Windows, you’ll have to navigate to an appropriate directory, rightclick, 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’llneed to set up a bare repository on the server so that you can pushchanges from your home machine to cs1520.cs.pitt.edu.

Initializing a bare repository


$ 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


$ 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 serveryou can use the pull command:

Pulling remote commits to the local working directory

$ git pull

And thats it.


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 abare 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


$ 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 moreadvanced 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

$ git clone <id>@cs1520.cs.pitt.edu:~nlf4/repos/git_slides.git


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/


http://book.git-scm.com/

http://gitref.org/

http://github.com/

http://ftp.newartisans.com/pub/git.from.bottom.up.pdf

http://www.eecs.harvard.edu/~cduan/technical/git/

http://gitimmersion.com/

Introduction to Version Control with Git

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