Creating a Repository

Overview

Teaching: 10 min
Exercises: 0 min

Questions

• Where does Git store information?

Objectives

• Create a local Git repository.

Once Git is configured, we can start using it.

We will pretend we’re working with a team who are investigating if it is possible to send a planetary lander to Mars.

First, let’s create a directory in Desktop folder for our work and then move into that directory:

$ 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:

$ git init

It is important to note that git init will create a repository that includes 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:

$ 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:

$ ls -a

.	..	.git

Git uses this special sub-directory to store all the information about the project, including all files and sub-directories located within the project’s directory. If we ever delete the .git sub-directory, we will lose the project’s history.

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

$ git status

# On branch master
#
# Initial commit
#
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.

Places to Create Git Repositories

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

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

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

Solution

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

$ git status

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

Correcting git init Mistakes

Juan explains to Margaret how a nested repository is redundant and may cause confusion down the road. Margaret would like to remove the nested repository. How can Margaret undo her last git init in the moons sub-directory?

Solution – USE WITH CAUTION!

Background

Removing files from a git repository needs to be done with caution. To remove files from the working tree and not from your working directory, use

$ rm filename

The file being removed has to be in sync with the branch head with no updates. If there are updates, the file can be removed by force by using the -f option. Similarly a directory can be removed from git using rm -r dirname or rm -rf dirname.

Solution

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

$ 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.

Key Points

• git init initializes a repository.

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