Commits #

What is a commit? #

To track a codebase, Git relies on a system of commits.

You can think of a commit as a snapshot of the instance of the codebase at a given point in time. For instance, when you are fixing a bug or implementing a new feature, you may want to save the current state of the codebase (take a snapshot). Every time you take a snapshot, it gets added over the previous snapshot as a set of changes that were introduced in the new version of the codebase.

Internally, Git tracks these commits by creating an Directed Acyclic Graph (DAG), with every commit representing a node in the graph and every edge points back to the previous commit that occurred.

You may notice that each commit node may have more than one incoming edge. This is where the idea of branching stems from.

We will be discussing branching in a later lesson.

Adding files to a snapshot #

By default, Git does not know what files it should be including in a snapshot (and this is a good thing because we don’t want Git to just add every file as they may contain sensitive information).

This is where the “three areas” concept comes into play. It is often good to think of your projects with Git as three separate concepts:

Working directory: where your codebase actually resides
Staging area: set of files that you want to include in a snapshot
Repository: local/remote repository storing metadata about the project and Git

By default, all of your files reside in the working directory and are not yet added to the staging area. If you want a file included in the staging area, then you must first add it to the staging area (we will cover how this happens later on).

There are also ways to remove files from the staging area!

Hands-on: Committing to your local repository #

To better understand how commits work, we have prepared a simple exercise that can work out the local repository created in the introduction.

Adding a new file #

Create a new file in the folder and add some text to it.

echo 'Hello world' >> hello.txt

The command above essentially redirects the output of the echo (Hello world) into a new file hello.txt

If you don’t want to use bash commands, you can just create the file using your preferred method as well.

Getting the status of a repository #

Now, run the following command to view the status of your repository.

git status

You should see the following:

On branch main

No commits yet

Untracked files:
  (use "git add <file>..." to include in what will be committed)
	hello.txt

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

Recall that in Adding files to a snapshot, Git does not automatically add files to a snapshot as it does not know exactly what you want. So we want to tell Git that we want hello.txt in the snapshot.

git status is to view the state of your repository in Git’s eyes. Use it to view things like the current files in the snapshot.
You may find exercises for it here.

Tracking files #

You may notice that the git status message states that hello.txt is untracked. Untracked files are those that have never been registered with Git before. They are often new files that have been added to the repository and have not existed in any snapshots.

Files that have been added to a snapshot before are considered “tracked” and Git knows to look out for changes between snapshots.

Adding files to the staging area #

As discussed in What is a commit, a file from the working directory needs to be explicitly added to the staging area for a snapshot to include it. By default, an untracked file that is added to a snapshot becomes tracked for future snapshots.

To add hello.txt to the staging area, use the following command:

We will be covering what git add does in a later lesson.

git add hello.txt

Then, use git status to view the status of your repository again:

On branch main

No commits yet

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

Notice that now, instead of stating that your file is untracked, Git is indicating that the changes have not committed. This is a sign that the file(s) have been tracked and added to the snapshot.

You can use . to add all files in the current folder as well.

Taking the snapshot #

Now, to take the snapshot (make the commit), you can use the following:

git commit -m "First commit"

The -m flag is used to specify the commit message. Every commit has an accompanying message that you can use to indicate what the commit contains/entails.

If you do not use -m, your favorite terminal/GUI editor will be launched and you can compose the commit message in that editor, save it, and close the editor

Exercises #

You may find exercises for git commit here.