Git Basics

Learning Goals

• Initialize a Git repository with git init
• Check the status of a repository with git status
• Track file changes with git add
• Create a commit and apply a commit message with git commit

Introduction

In the previous lesson we learned what a VCS is and how it helps us in our work. In this lesson, we'll learn how to use Git to track the changes we make to a project.

The basic process consists of the following three steps:

1. Initialize the project directory as a Git repository,
2. Tell Git to track the changes we make to individual files, and
3. When we're ready, tell Git to save the changes.

That's it! This basic workflow gives you all the main benefits of using Git to track a project.

Initialize a Git Repository with git init

Git operates on a directory level. When we have a new directory that we want to track our files in, we need to initialize the directory as a Git repository.

To get started, we'll create a new directory. In your terminal, type the following:

REMEMBER: Don't type the $. That's the universal symbol for a command prompt. It's how technical documentation says "Here's a thing for the shell to process."

$ mkdir my-git-project

This command creates new a directory. Then:

$ cd my-git-project

This command moves into the newly created directory.

Now that we're in the directory where we want Git to watch for changes (adding, removing, and editing files), we next need to initialize this directory as a Git repo. We only need to do this step once for each project we want to track.

In the terminal type git init. It should look something like this:

$ git init
Initialized empty Git repository in /Users/avi/my-git-project/.git/

The message above lets us know that our new directory is now being tracked by Git. It also shows that a new subfolder .git has been created. This hidden directory is where Git keeps important stuff, like the commit history. Don't go in there and start randomly deleting things! That said, if ever you do git init in the wrong directory, you can rm -rf .git to delete the .git folder and all its contents and return the directory to a plain-old, unprotected directory.

Be careful about making a containing directory, like our home directory or our desktop, into a Git repository accidentally. Make sure you only type git init within the directory you want git to track.

Check the Status of a Repository with git status

Now that we have Git watching this directory, let's see what it can tell us about the directory. The command we use for this is git status.

$ git status

Since we have not added any files yet, we'll see:

On branch main

No commits yet

nothing to commit (create/copy files and use "git add" to track)

Note: Older repositories may state On branch master. Branching is beyond the scope of this lesson, but to briefly explain - main and master both refer to the same thing - the core (main, get it?) branch of a repository. A single repository can have many branches, but always has only one core branch. In the past, this branch defaulted to the name master. Going forward, the branch will be named main. You'll likely see both as you work with repositories new and old.

Let's create a README.md that describes the project. Make our new file by typing touch README.md from within the my-git-project directory. We won't see any output after we run the touch command so to see that our new file has been created, we'll also run the ls command.

$ touch README.md
$ ls
README.md

With at least one new project file we can enable Git to start tracking changes. Type git status. Git will show us what our current repository looks like and what changes it sees.

$ git status
On branch main

No commits yet

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

  README.md

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

Git confirms that it's aware of the file README.md, but it's not tracking it. Git's not doing anything with the file and the file is not doing anything with Git...yet. Let's change that!

IMPORTANT: Whenever you want to check the status of your Git repository — which you will often — type git status.

Keep Track of File Changes with git add

Currently, the file in our repository is not being tracked by Git. We have to tell Git about all the files we want it to keep track of and consider as part of our project. We can do this by adding the files to our git repository with git add <filename or path>. To add our new README.md to the repository and check the status, we type:

$ git add README.md
$ git status
On branch main

No commits yet

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

  new file:   README.md

We can now see that Git is ready to keep track of README.md. All the changes in the file at the time we added it are staged. If we were to change README.md, we'd need to re-add the file. As it happens here, this staged change is "create the file, nothing inside of it" because touch created an empty file.

To have Git save a new version of our repo that includes this new file (or, later, to "capture" changes to a file) we need to commit the set of changes or diff. We "save" the changes in our repository by making commits.

Create a Commit and Apply a Commit Message with git commit

Remember: git add got our changes to the repository ready in the previous step. Those changes are the ones that will be "captured" in the commit.

To make our first commit, type:

$ git commit -m "Initial commit"

The -m flag tells Git that we are including a commit message, in this case "Initial commit". Any time you make a commit, you should include a message using this flag.

$ git commit -m "Initial commit"
[main (root-commit) e55477d] Initial commit
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 README.md

We can see that Git has created a new version of our repo, represented by the SHA (Secure Hash Algorithm) e55477d. SHAs are the identification system that git uses to keep track of versions; they're long complex numbers and letters that are unlikely to be duplicated (the value shown above is actually a shortened version of the full SHA). If you're following along, the SHA you'll see in your terminal will be different.

The commit command committed 1 file.

Now, if we type git status, we'll see that it is at a "clean state": there are no new changes which means there's nothing to commit.

$ git status
On branch main
nothing to commit, working tree clean

We won't do this just yet, but if we were to open the README.md file in our text editor and add some text to it, we could then add our file and commit this new set of changes with the following:

$ git add README.md
$ git commit -m "Updates README.md"

There are also a couple of shortcuts we can use:

$ git add .

This command adds all the files that have been changed since the last commit (in this case, just README.md).

Or we can combine the two steps of adding and committing our file into a single command:

$ git commit -am "Updates README.md"

Here we're combining the a and m flags. As with the add . shortcut, the a flag tells git to add 'all changes', i.e., all files that have been changed since the last commit. The -m flag, like before, tells git that we want to specify a commit message, in this case, "Updates README.md". This command could also be written as:

$ git commit -a -m "Updates README.md"

Remember, we haven't actually made any changes to README.md so there's nothing to add or commit. However, if we had, the commit would look something like this:

$ git commit -am "Updates README.md"
[main (root-commit) e55477d] Updates README.md
 1 file changed, 4 insertions(+), 0 deletions(2)

Good work! Commits are amazingly powerful in Git. They are the heart of many of Git's advanced features. Understanding the basic workflow of Git initialization and setup is the foundation for success.

Conclusion

In this lesson, we've learned the basics of using Git to track a directory. Specifically, we learned how to:

• make a new Git repository out of a directory using git init
• check the status of our repo using git status
• track files that have been changed using the git add <filename or path> command
• save (commit) the changes with an explanatory message using git commit -m "A message"

So far, however, we've only been using Git with our local repo. In the next two lessons, we'll learn how we can use Git in combination with GitHub to share code with other developers.

Resources

• Git Basics at git-scm.com