GIT

A version control system allows you to track the history of a collection of files and includes the functionality to revert the collection of files to another version.The collection of files is usually source code for a programming language.The collection of files and their complete history are stored in a repository.

Git is a free and open source distributed version control system designed to handle everything from small to very large projects with speed and efficiency.

In a Distributed Version Control Systems clients don’t just check out the latest snapshot of the files instead they fully mirror / clone the repository. Thus if any server dies, and these systems were collaborating via it, any of the client repositories can be copied back up to the server to restore it.

Git three states:

Committed : means that the data is safely stored in your local database
Modified : means that you have changed the file but have not committed it to your database yet
Staged : means that you have marked a modified file in its current version to go into your next commit snapshot

Git project sections:

The Git directory is where Git stores the metadata and object database for your project. This is the most important part of Git, and it is what is copied when you clone a repository from another computer.

The working directory is a single checkout of one version of the project. These files are pulled out of the compressed database in the Git directory and placed on disk for you to use or modify.

The staging area is a simple file, generally contained in your Git directory, that stores information about what will go into your next commit. It’s sometimes referred to as the index, but it’s becoming standard to refer to it as the staging area.

The basic Git workflow goes something like this:
You modify files in your working directory.
You stage the files, adding snapshots of them to your staging area.
You do a commit, which takes the files as they are in the staging area and stores that snapshot permanently to your Git directory.

Installation:

On Linux: Ubuntu
$ apt-get install git

On Windows:
http://msysgit.github.com/

Simply download the installer exe file from the GitHub page, and run it. After it’s installed, you have both a command-line version (including an SSH client that will come in handy later) and the standard GUI.

Identity :
The first thing you should do when you install Git is to set your user name and e-mail address. This is important because every Git commit uses this information, and it’s immutably baked into the commits you pass around:

$ git config –global user.name “John Doe”
$ git config –global user.email johndoe@example.com

Again, you need to do this only once if you pass the –global option, because then Git will always use that information for anything you do on that system. If you want to override this with a different name or e-mail address for specific projects, you can run the command without the –global option when you’re in that project.

Command Line: The computer program we use to input Git commands.

Repository: A directory or storage space where your projects can live. It can be local to a folder on your computer, or it can be a storage space on GitHub or another online host. You can keep code files, text files, image files, you name it, inside a repository.

Version Control: Basically, the purpose Git was designed to serve. It keeps “snapshots” of every point in time in the project’s history, so you can never lose or overwrite it.

Commit: This is the command that gives Git its power. When you commit, you are taking a “snapshot” of your repository at that point in time, giving you a checkpoint to which you can reevaluate or restore your project to any previous state.

Branch: How do multiple people work on a project at the same time without Git getting them confused? Usually, they “branch off” of the main project with their own versions full of changes they themselves have made. After they’re done, it’s time to “merge” that branch back with the “master,” the main directory of the project.

Git-Specific Commands:

git init: Initializes a new Git repository. Until you run this command inside a repository or directory, it’s just a regular folder. Only after you input this does it accept further Git commands.

git config: Short for “configure,” this is most useful when you’re setting up Git for the first time.

git help: Forgot a command? Type this into the command line to bring up the 21 most common git commands. You can also be more specific and type “git help init” or another term to figure out how to use and configure a specific git command.

git status: Check the status of your repository. See which files are inside it, which changes still need to be committed, and which branch of the repository you’re currently working on.

git add: This does not add new files to your repository. Instead, it brings new files to Git’s attention. After you add files, they’re included in Git’s “snapshots” of the repository.

git commit: Git’s most important command. After you make any sort of change, you input this in order to take a “snapshot” of the repository. Usually it goes git commit -m “Message here.” The -m indicates that the following section of the command should be read as a message.

git branch: Working with multiple collaborators and want to make changes on your own? This command will let you build a new branch, or timeline of commits, of changes and file additions that are completely your own. Your title goes after the command. If you wanted a new branch called “cats,” you’d type git branch cats.

git checkout: Literally allows you to “check out” a repository that you are not currently inside. This is a navigational command that lets you move to the repository you want to check. You can use this command as git checkout master to look at the master branch, or git checkout cats to look at another branch.

git merge: When you’re done working on a branch, you can merge your changes back to the master branch, which is visible to all collaborators. git merge cats would take all the changes you made to the “cats” branch and add them to the master.

git push: If you’re working on your local computer, and want your commits to be visible online on GitHub as well, you “push” the changes up to GitHub with this command.

git pull: If you’re working on your local computer and want the most up-to-date version of your repository to work with, you “pull” the changes down from GitHub with this command.

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