[MUSIC] Let's take a look at the tool that we're going to use for version control in this class, it's called Git. Let's talk about distributed version control with Git. Git's an open source distributed version control system that's very popular. It was created in 2005 by Linus Torvalds in order to support the development of the Linux Operating System. It's also used very extensively by the rails community. Let me tell you a few of Git's properties. It's fast, it's pretty simple to use, and it supports nonlinear development. In other words, you can have thousands of parallel development branches as a part of the Git repository. Git works well with both small and large scale development projects. For example, it was used to create the Linux operating system, which was a quite big project. Nearly every Git operation that you perform is local, that is, it occurs on your local machine. Another thing is that Git has integrity, that means that every file stored in Git is checked sum before it's stored. A check sum is computed using the file. So, if a file is modified in any way a new check sum is computed and it won't match up with the old file. And this is how Git can determine if a file has been changed. Git only adds files to your repository, and it's very difficult to get the system to do anything you can't undo if you make a mistake. Git allows you to compare the differences between various versions of your project. Remember we said that in distributed version control systems, you store snapshots of your project. So you can store these and then merge them if you need to. You can think of the various versions of the project as forming a tree. There's the main development branch, and in Git this is called master. And then you can create new versions either along the master branch or you can branch off the master branch, you can creat new branches. The branches can be merged back in if you decide you want to merge some features together. Let's go over some basic concepts associated with Git. First again remember the git tracks files and these files, they can be thought of as residing in one of three locations. They can be in your Working directory, you can stage them to the Staging area or you can store them in a Git repository. Further, the files in the working directory can be in one of two states. They can be tracked and in this case these are files that were saved by the last commit to your repository or they could be the untruck. These are files that are in your working directory that have not been saved. Furthermore tracked files can be either modified, in other words you've changed that file since it was last committed to the repository, it's unmodified, it hasn't been changed since that time, or it's staged. Let's talk more about this. These are the 3 locations I've just mentioned where files can reside. So in your working directory If you type git add. then it moves those files to the staging area. Then from the staging area, if you type git commit, then these fields will be moved to your local git repository. You can do both of these in one step by just typing git commit-a, and it will do both of them. Now, if you want to check out a branch from the local git repository, you type git check out in the branch you like to check out and then remove those files in the local git repository to your working directory and then copy them over. There's also a merge command that allows you to merge Your current working directory with the branch that's stored on the local Git Repository. Here's how to use Git with the Rails application. First of all, move to the root of your blog application. So here I'm in the root of the blog application that we previously created. And I'd like you to make sure you follow along because you're going to need to be able to use git in order to submit your first programming assignment. We like to put this application under source code control. First you have to have git configured on your machine so to make sure you do, type git and you should see a list of help commands that are available to you. Let's pick this one out, git status. It shows the working tree. Now, when I do this, it says that we don't have a git repository yet, so in order to do this, you issue the Git command called git init. git init will now create a git repository, just actually stored in our file called Dot git in your local directory. Now rails automatically also creates a file called dot git ignore, that's in the root of your project directory as well. Now this file is simply a list of the files that git will not include in the repository whenever you save to the local repository. So if I take a look at that You'll see that it knows that this is a Rails application so git with Sparks smart enough to know that this is a Rails application. It's going to ignore storing bundle config, the SQLite database files, as well as all logfiles. At this point if we type git status We'll see that there's a bunch of files it recognizes that they're all untracked. So we don;t have any tracked files yet. Remember what we need to do to start tracking the files, we have to type git. add dot. And this will add all of the files except for those in the dot git ignore file to the staging area. And so now if I type in status we can see that there are a bunch of files that are now in the staging area. Finally the last step is to type git commit. Now, if I'd like to add a message when I'm doing this commit, I can type -m. And then list a message as a part of the commit, as well. And so I'm going to type that this is the initial commit. And now, all of these files have been moved from the staging area to the local git repository. Again I can do all of these in one step by typing git commit -a and then I'm going to add the message here. Otherwise it will ask you for a message, and you can just type some message. Whatever you want. Something that describes. The changes that you've made as a part of this commit and when I try and dol this, there's nothing to commit to the master branch because there are no changes. If I were to edit some of the files in this directory and then issue this command, you'd see that it would. Both stage and then store in the local get repository the changes that I've made. The last thing I'd like to tell you is that I've been doing everything from the command line. There are also some client tools. That you can download that provide a GUI interface for GIT. If you'd like to use some of them, just look online. Do a Google search, and you can find them. I tend to do everything from the command line. But feel free to use a get client, if you'd like. If you go to the site, git-scn.com, you can actually download GIT if you don't have it on your machine. So go to the downloads and you'll see the ability to download for various operating systems. Click on the view GUI client if you want to see the clients that you can download. May of them are free so for example if you look at the source tree, it provides a GUI interface and you can see here that it has. A graphical depiction of what the branches look like, as well as the descriptions of all of the that you performed. Again, not necessary to have a client, I use the command line, but feel free to try some of these out.
