Getting started with git

Overview

Teaching: 20 min
Exercises: 0 min

Questions

• What are repositories and how are they created?

• What do add and commit mean?

Objectives

• initiate a git repository

• track changes to files in a project

• persist changes to a git repository

Using Git

One of the main barriers to getting started with git is the language. Although some of the language used in git is fairly self-explanatory, other terms are not so clear. The best way to get to learn the language - which consists of a number of verbs such as add, commit and push (precdeded by the word ‘git’) - is by using it, which is what we will be doing during this lesson. These commands will be explained as we proceed from setting up a new version-controlled project to publishing our own website.

We will try to do this session as a group, but those who prefer to go at a slower pace can follow the instructions on the GitHub page.

Creating a repository

A git repository is a data structure used to track changes to a set of project files over time. Repositories are stored within the same directory as these project files, in a hidden directory called .git. We can create a new git repository either by using GitHub’s web interface, or via the command line. Let’s use the command line to create a git repository for the experiments that we’re going to do today.

First, we will create a new directory for our project and enter that directory. <!explain commands as we go along>

$ mkdir hello-world
$ cd hello-world

We will now create an empty git repository to track changes to our project. To do this we will use the git init command, which is simply short for initialise.

$ git init

The hello-world directory is now a git repository.

If we run the ls command now, the repository might seem empty, however, ls -a will show all hidden files, which in this case includes the new hidden directory .git.

Note that whenever we use git via the command line, we need to preface each command (or verb) with git, so that the computer knows we are trying to get git to do something, rather than some other program.

Displaying the current project’s status

We can run the git status command to display the current state of a project. Let’s do that now.

$ git status

On branch master
Initial commit
nothing to commit (create/copy files and use "git add" to track)

The output tells us that we are on the master branch (more on this later) and that we have nothing to commit (no unsaved changes).

Adding and committing

We’ll now create and save our first project file. This is a two-stage process. First, we add any files for which we want to save the changes to a staging area, then we commit those changes to the repository. This two-stage process gives us fine-grained control over what should and should not be included in a particular commit.

Let’s create a new file using the touch command, which is a quick way to create an empty file.

$ touch index.md

The .md extension above signifies that we have chosen to format that we have chosen to use Markdown, a lightweight markup language with plain text formatting syntax. We will explore Markdown a bit later.

Let’s check the status of our project again.

$ git status

On branch master
Initial commit
Untracked files:
  (use "git add <file>..." to include in what will be committed)

    index.md

nothing added to commit but untracked files present (use "git add" to track)

This status is telling us that git has noticed a new file in our directory that we are not yet tracking. With colourised output, the filename will appear in red. To change this, and to tell Git we want to track any changes we make to index.md, we use git add.

$ git add index.md

This adds our Markdown file to the staging area (the area where git checks for file changes). To confirm this we might want to use git status again.

$ git status

On branch master

Initial commit

Changes to be committed:
  (use "git rm --cached <file>..." to unstage)

    new file:   index.md

If we are using colourised output, we will see that the filename has changed colour (from red to green). Git also tells us that there is a new file to be committed but, before we do that, let’s add some text to the file.

We will open the file index.md with any text editor we have at hand (e.g. Notepad on Windows or TextEdit on Mac OSX) and enter # Hello, world!. The hash character is one way of writing a header with Markdown. Now, let’s save the file within the text editor and check if Git has spotted the changes.

$ git status

On branch master

Initial commit

Changes to be committed:
  (use "git rm --cached <file>..." to unstage)

	new file:   index.md

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

	modified:   index.md

This lets us know that git has indeed spotted the changes to our file, but that it hasn’t yet staged them, so let’s add the new version of the file to the staging area.

$ git add index.md

Now we are ready to commit our first changes. Commit is similar to ‘saving’ a file to Git. However, compared to saving, a commit provides a lot more information about the changes we have made, and this information will remain visible to us later.

$ git commit -m 'Add index.md'

[master (root-commit) e9e8fd3] Add index.md
 1 file changed, 1 insertion(+)
 create mode 100644 index.md

We can see that one file has changed and that we made one insertion, which was a line with the text ‘#Hello, world!’. We can also see the commit message ‘Add index.md’, which we added by adding the -m flag to git commit. The commit message is used to record a short, descriptive, and specific summary of what we did to help us remember later on without having to look at the actual changes. If we just run git commit without the -m option, Git will launch nano (or whatever other editor we configured as core.editor) so that we can write a longer message.

Having made a commit, we now have a permanent record of what was changed, along with metadata about who made the commit and at what time.

Staging Area

If you think of Git as taking snapshots of changes over the life of a project, git add specifies what will go in a snapshot (putting things in the staging area), and git commit then actually takes the snapshot, and makes a permanent record of it (as a commit). If you don’t have anything staged when you type git commit, Git will prompt you to use git commit -a or git commit --all, which is kind of like gathering everyone for the picture! However, it’s almost always better to explicitly add things to the staging area, because you might commit changes you forgot you made. (Going back to snapshots, you might get the extra with incomplete makeup walking on the stage for the snapshot because you used -a!) Try to stage things manually, or you might find yourself searching for “git undo commit” more than you would like!

But at the moment our changes are only recorded locally, on our computer. If we wanted to work collaboratively with someone else they would have no way of seeing what we’ve done. We will fix that in the next episode by using GitHub to share our work.

Key Points

• git repositories are data-structures used to track changes to files over time

• Git uses a two-stage commit process. Changes must first be added to the staging area, then committed from there