Creating a Repository

Estimated time: 10 minutes

Overview

Questions

• Where does Git store information?

Objectives

• Create a local Git repository.
• Describe the purpose of the .git directory.

Once Git is configured, we can start using it.

We will continue with the story of Frary and Cecil who are investigating if it is possible to send a planetary lander to Mars.

First, let’s create a new directory in the Desktop folder for our work and then change the current working directory to the newly created one:

BASH

$ cd ~/Desktop
$ mkdir planets
$ cd planets

Then we tell Git to make planets a repository: a place where Git can store versions of our files:

BASH

$ git init

It is important to note that git init will create a repository that can include subdirectories and their files—there is no need to create separate repositories nested within the planets repository, whether subdirectories are present from the beginning or added later. Also, note that the creation of the planets directory and its initialization as a repository are completely separate processes.

If we use ls to show the directory’s contents, it appears that nothing has changed:

BASH

$ ls

But if we add the -a flag to show everything, we can see that Git has created a hidden directory within planets called .git:

BASH

$ ls -a

OUTPUT

.	..	.git

Git uses this special subdirectory to store all the information about the project, including the tracked files and sub-directories located within the project’s directory.

Callout

The .git Directory is Sacred

Never manually edit files in the .git directory. It contains critical metadata that Git relies on. If you accidentally corrupt it, you can lose your entire project history. If something goes wrong, ask for help from someone familiar with Git internals rather than trying to fix it yourself.

If we ever delete the .git subdirectory, we will lose the project’s history.

Next, we will change the default branch to be called main. This might be the default branch depending on your settings and version of git. See the setup episode for more information on this change.

BASH

$ git checkout -b main

OUTPUT

Switched to a new branch 'main'

We can check that everything is set up correctly by asking Git to tell us the status of our project:

BASH

$ git status

OUTPUT

On branch main

No commits yet

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

If you are using a different version of git, the exact wording of the output might be slightly different.

Challenge

Places to Create Git Repositories

Along with tracking information about planets (the project we have already created), Cecil would also like to track information about moons. Despite Frary’s concerns, Cecil creates a moons project inside his planets project with the following sequence of commands:

BASH

$ cd ~/Desktop   # return to Desktop directory
$ cd planets     # go into planets directory, which is already a Git repository
$ ls -a          # ensure the .git subdirectory is still present in the planets directory
$ mkdir moons    # make a subdirectory planets/moons
$ cd moons       # go into moons subdirectory
$ git init       # make the moons subdirectory a Git repository
$ ls -a          # ensure the .git subdirectory is present indicating we have created a new Git repository

Is the git init command, run inside the moons subdirectory, required for tracking files stored in the moons subdirectory?

Show me the solution

No. Cecil does not need to make the moons subdirectory a Git repository because the planets repository can track any files, sub-directories, and subdirectory files under the planets directory. Thus, in order to track all information about moons, Cecil only needed to add the moons subdirectory to the planets directory.

Additionally, Git repositories can interfere with each other if they are “nested”: the outer repository will try to version-control the inner repository. Therefore, it’s best to create each new Git repository in a separate directory. To be sure that there is no conflicting repository in the directory, check the output of git status. If it looks like the following, you are good to go to create a new repository as shown above:

BASH

$ git status

OUTPUT

fatal: Not a git repository (or any of the parent directories): .git

Challenge

Correcting git init Mistakes

Frary explains to Cecil how a nested repository is redundant and may cause confusion down the road. Cecil would like to remove the nested repository. How can Cecil undo his last git init in the moons subdirectory?

Solution – USE WITH CAUTION!

Background

Removing files from a Git repository needs to be done with caution. But we have not learned yet how to tell Git to track a particular file; we will learn this in the next episode. Files that are not tracked by Git can easily be removed like any other “ordinary” files with

BASH

$ rm filename

Similarly a directory can be removed using rm -r dirname or rm -rf dirname. If the files or folder being removed in this fashion are tracked by Git, then their removal becomes another change that we will need to track, as we will see in the next episode.

Solution

Git keeps all of its files in the .git directory. To recover from this little mistake, Cecil can just remove the .git folder in the moons subdirectory by running the following command from inside the planets directory:

BASH

$ rm -rf moons/.git

But be careful! Running this command in the wrong directory will remove the entire Git history of a project you might want to keep. Therefore, always check your current directory using the command pwd.

Callout

Never Nest Git Repositories

Avoid creating Git repositories inside other Git repositories. The outer repository will try to track the inner one, causing unexpected behavior and merge conflicts. Always check with git status and pwd before running git init. If you accidentally create nested repositories, remove the inner .git directory.

Key Points

• git init initializes a repository.
• Git stores all of its repository data in the .git directory.