Creating a Repository

Overview

Teaching: min
Exercises: min

Questions

• Where does Git store information?

Objectives

• Create a local Git repository.

• Describe the purpose of the .git directory.

Now, We can start using it.

On a command line, Git commands are written as git verb options, where verb is what we actually want to do and options is additional optional information which may be needed for the verb.

We will use the story of Wolfman and Dracula who are investigating if it is possible to send a planetary lander to Mars.

Werewolf vs dracula by b-maze / Deviant Art. Mars by European Space Agency / CC-BY-SA 3.0 IGO. Pluto / Courtesy NASA/JPL-Caltech. Mummy © Gilad Fried / The Noun Project / CC BY 3.0. Moon © Luc Viatour / https://lucnix.be / CC BY-SA 3.0.

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 subdirectory 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 subdirectory, 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

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.

Places to Create Git Repositories

Along with tracking information about planets (the project we have already created), Dracula would also like to track information about moons. Despite Wolfman’s concerns, Dracula creates a moons project inside his 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 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?

Solution

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

$ git status

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

Correcting git init Mistakes

Wolfman explains to Dracula how a nested repository is redundant and may cause confusion down the road. Dracula would like to remove the nested repository. How can Dracula 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. 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, Dracula 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.