1  Intro to Git

1.1 Background info

  • Git was written to allow developers work on the source code of the Linux kernel (text files)

    • One kernel release they got in a terrible mess

    • This provoked Linus Torvalds into action

    • For an excellent insight into his thinking watch this talk he gave at Google here

    • (Especially if used at the command line) Git can be intimidating to use and we can get Git errors (which like LaTeX and R errors can be quite cryptic)

      Image: xkcd.com/1597
  • A Git repository is a folder/directory on your computer which has been Git initialised

    • Using either the command line

      git init mynewfolder

    • Or GitHub Desktop

  • Repos on GitHub are already Git initialised
  • When you clone them down to your computer they work in GitHub Desktop
  • Git is commonly referred to as version control software
  • Git is better described as a content addressable filesystem
  • This means that Git tracks the contents of the files in your repo
  • Git creates a little database of the contents of your files
  • Snapshots (commits) are taken when you tell it to
  • Git looks for changes in your files when you save them, so when you have unsaved changes in a file/s Git shows no changes until you save

  • Git takes snapshots of your files when you tell it to, these are called commits
  • I saved my file from above, enter a commit message and click “Commit to master”

  • Commits are identified by the 40-character checksum SHA-1 hash of the contents of your files at that time

  • Git knows the state of your files at every commit
    • You can easily restore your files to a previous state
  • For Git the state of your files only changes when their contents change
    • If you reopen a file, make no changes, then close it, Git will show no changes in your repo
    • If you add an empty folder/directory to your repo Git will show no changes in your repo
    • This differs to OneDrive/SharePoint/Google Drive which are file synchronisation systems
  • I recommend not to place your Git repos in a location that is sync’d by either OneDrive or Google Drive

1.2 The .git folder

  • When you initialise a directory the .git folder is created

  • This contains all of the files Git uses to track the contents of your files

  • Here is the .git folder of a repo on my computer (I have selected to View hidden files in Windows Explorer)

  • GitHub (and Git servers in general) store repositories as bare repositories. This means that they only contain the .git directory which is on your local machine. Hence perhaps a little confusingly when you view your repository on GitHub you cannot see the .git directory listed in the repo contents (as you see in a File Explorer on your local machine).

  • Here are its contents - don’t edit these manually

  • Explanation of these is (from here)

1.3 Common Git commands

  • I recommend you use GitHub Desktop instead of these commands

  • These commands are what GitHub Desktop is using behind the scenes

  • Git is the name of the program, git is the name of the executable available at your command line

    git init 
git add <filename>
git status
git commit -m "Your commit message"
git commit --amend -m "Your amended commit message"
git push 
git pull 
git clone
git branch
git checkout
git merge
git fetch

  • If you use one of these commands and receive an error message including the text below, it can mean that you have made a typo in the filename you included in your Git command

    fatal: not under version control