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Git Essential Training
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The history of Git


From:

Git Essential Training

with Kevin Skoglund

Video: The history of Git

There are five important version control systems that predate Git that I want us to look at. There have been many others over the years, but these are some of the most popular and the most influential. The first of these is SCCS, it wasn't the first, but it was the first to become popular. It was released in 1972 and was developed by AT&T and bundled free with Unix. Now Unix was also free, and as a consequence it spread quickly to places like universities, so therefore universities also taught their students how to do version control using SCCS. So if you were writing Unix programs that's what you learned to use.
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  1. 2m 46s
    1. Introduction
      1m 7s
    2. How to use the exercise files
      1m 39s
  2. 20m 24s
    1. Understanding version control
      4m 48s
    2. The history of Git
      7m 58s
    3. About distributed version control
      5m 4s
    4. Who should use Git?
      2m 34s
  3. 26m 12s
    1. Installing Git on a Mac
      3m 44s
    2. Installing Git on Windows
      5m 37s
    3. Installing Git on Linux
      1m 30s
    4. Configuring Git
      7m 29s
    5. Exploring Git auto-completion
      5m 35s
    6. Using Git help
      2m 17s
  4. 15m 49s
    1. Initializing a repository
      1m 58s
    2. Understanding where Git files are stored
      2m 34s
    3. Performing your first commit
      2m 4s
    4. Writing commit messages
      5m 22s
    5. Viewing the commit log
      3m 51s
  5. 17m 44s
    1. Exploring the three-trees architecture
      3m 57s
    2. The Git workflow
      3m 15s
    3. Using hash values (SHA-1)
      4m 7s
    4. Working with the HEAD pointer
      6m 25s
  6. 25m 52s
    1. Adding files
      5m 59s
    2. Editing files
      3m 56s
    3. Viewing changes with diff
      3m 35s
    4. Viewing only staged changes
      2m 28s
    5. Deleting files
      5m 29s
    6. Moving and renaming files
      4m 25s
  7. 19m 18s
    1. Introducing the Explore California web site
      2m 2s
    2. Initializing Git
      3m 48s
    3. Editing the support phone number
      6m 20s
    4. Editing the backpack file name and links
      7m 8s
  8. 38m 45s
    1. Undoing working directory changes
      3m 49s
    2. Unstaging files
      2m 37s
    3. Amending commits
      4m 50s
    4. Retrieving old versions
      4m 7s
    5. Reverting a commit
      3m 12s
    6. Using reset to undo commits
      3m 44s
    7. Demonstrating a soft reset
      4m 8s
    8. Demonstrating a mixed reset
      4m 7s
    9. Demonstrating a hard reset
      5m 8s
    10. Removing untracked files
      3m 3s
  9. 27m 22s
    1. Using .gitignore files
      8m 23s
    2. Understanding what to ignore
      4m 47s
    3. Ignoring files globally
      4m 49s
    4. Ignoring tracked files
      5m 26s
    5. Tracking empty directories
      3m 57s
  10. 26m 51s
    1. Referencing commits
      4m 52s
    2. Exploring tree listings
      3m 46s
    3. Getting more from the commit log
      7m 38s
    4. Viewing commits
      4m 4s
    5. Comparing commits
      6m 31s
  11. 39m 35s
    1. Branching overview
      4m 56s
    2. Viewing and creating branches
      2m 57s
    3. Switching branches
      2m 58s
    4. Creating and switching branches
      4m 53s
    5. Switching branches with uncommitted changes
      3m 26s
    6. Comparing branches
      4m 28s
    7. Renaming branches
      2m 28s
    8. Deleting branches
      4m 18s
    9. Configuring the command prompt to show the branch
      9m 11s
  12. 28m 32s
    1. Merging code
      3m 11s
    2. Using fast-forward merge vs. true merge
      6m 49s
    3. Merging conflicts
      7m 26s
    4. Resolving merge conflicts
      7m 5s
    5. Exploring strategies to reduce merge conflicts
      4m 1s
  13. 14m 34s
    1. Saving changes in the stash
      4m 5s
    2. Viewing stashed changes
      2m 39s
    3. Retrieving stashed changes
      4m 24s
    4. Deleting stashed changes
      3m 26s
  14. 1h 5m
    1. Using local and remote repositories
      6m 38s
    2. Setting up a GitHub account
      5m 39s
    3. Adding a remote repository
      4m 0s
    4. Creating a remote branch
      4m 3s
    5. Cloning a remote repository
      4m 26s
    6. Tracking remote branches
      4m 5s
    7. Pushing changes to a remote repository
      5m 8s
    8. Fetching changes from a remote repository
      5m 47s
    9. Merging in fetched changes
      4m 50s
    10. Checking out remote branches
      3m 22s
    11. Pushing to an updated remote branch
      2m 6s
    12. Deleting a remote branch
      3m 8s
    13. Enabling collaboration
      3m 40s
    14. A collaboration workflow
      8m 43s
  15. 16m 23s
    1. Setting up aliases for common commands
      5m 14s
    2. Using SSH keys for remote login
      2m 56s
    3. Exploring integrated development environments
      1m 4s
    4. Exploring graphical user interfaces
      4m 32s
    5. Understanding Git hosting
      2m 37s
  16. 55s
    1. Goodbye
      55s

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Git Essential Training
6h 26m Beginner Aug 24, 2012

Viewers: in countries Watching now:

The course shows how to use Git, the popular open-source version control software, to manage changes to source code and text files. Using a step-by-step approach, author Kevin Skoglund presents the commands that enable efficient code management and reveals the fundamental concepts behind version control systems and the Git architecture. Discover how to track changes to files in a repository, review previous edits, and compare versions of a file; create branches to test new ideas without altering the main project; and merge those changes into the project if they work out. The course begins by demonstrating version control in a single-user, standalone context, before exploring how remote repositories allow users to collaborate on projects effectively.

Topics include:
  • Exploring the history of version control
  • Installing Git on Mac, Windows, and Linux
  • Initializing a repository
  • Writing useful commit messages
  • Understanding the Git three-tree architecture
  • Tracking when files are added, edited, deleted, or moved
  • Viewing change sets and comparing versions
  • Undoing changes and rolling back to previous versions
  • Ignoring changes to select files
  • Creating and working with code branches
  • Merging branches and resolving merge conflicts
  • Stashing changes for later
  • Working with hosted repositories and remote branches
  • Developing an effective collaboration workflow
Subject:
Developer
Software:
Git GitHub
Author:
Kevin Skoglund

The history of Git

There are five important version control systems that predate Git that I want us to look at. There have been many others over the years, but these are some of the most popular and the most influential. The first of these is SCCS, it wasn't the first, but it was the first to become popular. It was released in 1972 and was developed by AT&T and bundled free with Unix. Now Unix was also free, and as a consequence it spread quickly to places like universities, so therefore universities also taught their students how to do version control using SCCS. So if you were writing Unix programs that's what you learned to use.

And then when these students left the universities to go work in jobs, the Version Control System that they were familiar with, and they took with them, was SCCS, so you can see why it became very popular. We talked about very primitive version control earlier, that you might have something like a budget, and you might save version 1 of the budget and version 2 and version 3 just giving a different file name each time. When you do that you are actually saving the full document three different times. That's not the most efficient way to do it. What SCCS does is it keeps the original document, but then instead of saving the whole document a second time, it just saves a snapshot of what the changes were.

So if you want version 5 of the document, you just take version 1 and apply four sets of changes to it, to get to version 5, that's a much more efficient way to store the changes over time. So SCCS stayed dominant until the early '80s when RCS was developed, Revision Control System, and it just made lots of improvements over SCCS. For one thing it was cross-platform, whereas SCCS was Unix only. With the rise of the Personal Computer it was important to have a Version Control System that could work on PCs. It was also more intuitive, had a cleaner syntax with fewer commands, but more features.

And most importantly it was faster and a lot of its speed increase came from the fact that it used a smarter storage format whereas SCCS stored the original file and then kept track of all the changes that went after it, RCS flipped that around so that it kept the most recent file in its whole form, and if you wanted previous versions, then you applied the change snapshots to go backwards in time. If you think about it, that's a lot faster because most of the time what we want to work with is the current document. With SCCS if we wanted the current document, and there were 20 sets of changes, we had to pull up the original and then apply 20 sets of changes to get there, with RCS we can just bring up the original file, and it is already stored in its full state.

Now one of the problems with both SCCS and RCS was they only allowed you to work with an individual file one at a time. So you could track changes in a single file, but not in sets of files, or in a whole project. CVS allowed you to do that, that's for Concurrent Versions System. Now the real innovation now to CVS is not just the fact that you can work with multiple files, it's the concurrent part, the fact that we can have a place where we store our code, called a Code Repository, you can put that on a remote server, and more than one user can work on the same file at the same time, they can work concurrently.

With previous versions only one person could work with a file at a single time. So CVS adds a lot of features for users to be able to share their work and be able to update their file with changes that other people have made and placed in the remote repository. This idea of working with remote repositories was further improved upon with Apache Subversion or SVN for short. SVN was faster than CVS, and it allowed saving of non-text files, like images, whereas CVS couldn't do that. Most importantly, the big innovation for SVN was that it was tracking not just changes to files, or to groups of files, but actually watching what happened in a directory as a whole, watching the files in the directory and actually taking a snapshot of the directory not just the files.

Now it may seem like a small difference, but it's important. In CVS you would talk about having revision 7 of some file. In SVN, you talk about some file as it appears in revision 7. SVN could track the history of directories. For examples, CVS had a hard time if you renamed a file. SVM though would track that change with no problem. If you add a file directory, remove a file, rename it, it's watching the directory as a whole to see what happens and taking a snapshot of that, whereas CVS was just looking at a collection of individually named files.

CVS would also update files one at a time as it went to either apply or read back changes. SVN would instead do a transactional commit and apply all of the changes that happen to the directory or none of them at all. The snapshot was bigger than just the individual files, it was the entire directory, the entire set of changes that were happening to that directory at one time. It's a subtle but important difference. Now SVN stayed the most popular Version Control System for a very long time until Git came out, but there is one other Version Control System that I want us to look at before that, and that is BitKeeper SCM.

It was a closed source proprietary source code management tool. That means that a company owned it and sold it, the same way that Adobe sells Photoshop or Microsoft sells Word. One of the important features the BitKeeper had, and it wasn't the first to have it, but is Distributed Version Control. But before we get to that, let's talk a little bit more about this idea of being closed source, whereas all the other ones that we have been looking at for a while had been open source. The community version of BitKeeper was free, it had a few less features and some usage restrictions, but there was a version that they gave away for free, and that version was used for source code management of the Linux kernel from 2002 to 2005.

Now it was controversial to use a proprietary SCM for the Linux kernel because the Linux kernel is an open source project, no one owns it, whereas the SCM is owned and controlled by a company. So a lot of people objected saying, well what if they change the rules in the future, suddenly we're going to be screwed because we are stuck using this company's software? Well, guess what, in April 2005, the community version stopped being free and all those predictions came true. Now BitKeeper was never as popular CVS or SVN, but it is super important with the creation of Git because of its connection to Linux, because in April 2005, when the community version stopped being free, that's the same point at which Git was born, Git was created by Linus Torvalds, and you may recognize that name as the person who created Linux and still drives the development of the Linux kernel.

When BitKeeper stop being free they needed an alternative for managing their source code. Linus looked around, and it didn't like the other VCSs that were out there, like CVS and SVM, he did like some of the concepts of BitKeeper, but he thought he could do even better, so he wrote a new VCS from scratch. Now Git is Distributed Version Control, like BitKeeper, and we'll talk more about Distributed Version Control in the next movie. It's also open source and free, which is great for us, because it means that people like you and me can download it for free and use it for free with no license fees or anything like that.

It also means that because it's open source the community can see the source code and contribute to it as well. So they can submit bug fixes, add new features, all of those things we get to be the beneficiaries of because it's an open source project. It's also compatible with most platforms, Unix-like systems and Windows, and it's faster than most other Source Code Management tools. 100 times faster in some cases for some operations, and has better safeguards built into it to guard against data corruption, and we will talk about that a bit later. Now these improvements worked.

Git became a hit, as people discovered the power of Distributed Version Control as they got used to all of Git's nice features, Git has experienced an explosion in popularity. Now there is no official statistics on this but to give you an example, GitHub launched in 2008 to host Git source code repositories. In 2009, there were over 50,000 repositories with a 100,000 users. In 2011 just two years later, there were 2 million repositories with over a million users. So you can see this rapid growth in just two years.

So Git has definitely taken off. In the next movie, let's talk about Distributed Version Control and see why that's such an important feature.

Find answers to the most frequently asked questions about Git Essential Training.


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Q: In the Chapter 10 movie "Configuring the command prompt to show the branch," when I type the function "__git_ps1," I do not get the expected result.
A: The function "__git_ps1" was recently moved to a new file, .git-prompt.sh, as described here: https://github.com/git/git/commit/af31a456b4cd38f2630ed8e556e23954f806a3cc.

We will update the video. In the meantime, you may do the same steps you do for .git-completion.bash, but a second time using ".git-prompt.sh" as shown here: https://github.com/git/git/blob/master/contrib/completion/git-prompt.sh.
Q: When I use the code the instructor advises in the above video ("git config
--global user.name "Nelda Street"), I still get an "Illegal Instruction"
error. I have OS 10.6.8. Am I doing something wrong?
A: The current installer version of git isn't compatible with older Mac OS versions.
 
https://code.google.com/p/git-osx-installer/issues/detail?id=96
 
The workaround solutions people offer are:
 
1. To add "-mmacosx-version-min=10.6" as described here:
https://stackoverflow.com/questions/14268887/what-is-the-illegal-instruction-4-error-and-why-does-mmacosx-version-min-10
 
https://stackoverflow.com/questions/10177038/illegal-instruction-4-shows-up-in-os-x-lion
 
2. Or to use the version of git that comes with Xcode, or to use homebrew to install git instead.
http://superuser.com/questions/697144/installed-git-not-sure-how-to-get-it-working
 
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