Overview
Teaching: 35 min Exercises: 0 minQuestions
How do I gets started with Git?
Objectives
Initialize a new Git repository
Begin tracking changes
Commit changes in your repository
Why are we using the command line?
There are lots of graphical user interfaces (GUIs) for using Git: both stand-alone and integrated into text editors (e.g. VSCode). We are deliberately not using a GUI for this course because:
- you will have a better understanding of how the git commands work
- you will be able to use Git on any computer (e.g. remotely accessing HPC systems, which generally only have Linux command line access)
- you will be able to use any GUI, rather than just the one you have learned
Set configuration settings for Git
When we use Git on a new computer for the first time, we need to introduce ourselves so Git not only reords changes to files, but also who made those changes.
Git commands are written as git verb options, where verb is what we want to do and options is additional information which may be needed for the verb. So to introduce ourselves to Git:
$ git config --global user.name "Vlad Dracula" # Quotation marks are necessary, do not include the $, it's simply a commandline indicator
$ git config --global user.email "vlad@tran.sylvan.ia"
Please use your own name and address instead of Dracula’s.
Select a default editor
When version tracking, we will need to provide some short but useful information about the changes made in a version. In order to enter this information, we need a text editor, and Git needs to know our default preference when it wants us to provide some information.
$ git config --global core.editor "nano -w"
To set up alternative editors, follow the same notation e.g.
git config --global core.editor notepad, git config --global core.editor 'open -W -n',
git config --global core.editor xemacs.
You can check your settings any time, so let’s check if Git received our information:
$ git config --list
Create a new repository with Git
We will be working with a simple example in this tutorial. It will be a paper that we will first start writing as a single author and then work on it further with one of our colleagues.
First, let’s create a directory within your home directory:
$ cd # Switch to your home directory.
$ pwd # Print working directory (output should be /home/jovyan)
$ mkdir git-papers
$ cd git-papers
Now, we need to set up this directory up to be a Git repository (or “initiate the repository”):
$ git init
Initialized empty Git repository in /home/user/git-papers/.git/
The directory “git-papers” is now our working directory. If we use ls to show the directory’s contents, it appears that nothing has changed:
$ ls
But if we add the -a flsg to show all contents, we will see that Git has created a hidden directory within our repository called .git:
$ ls -a .git
branches config description HEAD hooks info objects refs
The .git directory contains Git’s configuration files and will be used to store all information about our project. Be careful not to accidentally delete this directory or we will lose the project’s history!
Tracking files with a git repository
Now, we’ll create a file. Let’s say we’re going to write a journal paper, so we will start by adding the author names and a title, then save the file.
$ vim journal.md # Vim creates a new file called journal.md and opens it for editing
# Add author names and paper title
git status allows us to find out about the current status
of files in the repository. So we can run,
$ git status
On branch master
Initial commit
Untracked files:
(use "git add <file>..." to include in what will be committed)
journal.md
nothing added to commit but untracked files present (use "git add" to track)
Information about what Git knows about the directory is displayed. We are on
the master branch, which is the default branch in a Git repository
(one way to think of branches is like parallel versions of the project.
Don’t worry – we’ll talk more about branches later).
For now, the important bit of information is that our file is listed as Untracked which means it is in our working directory but Git is not tracking it - that is, any changes made to this file will not be recorded by Git.
Add files to a Git repository
To tell Git about the file, we will use the git add command:
$ git add journal.md
$ git status
On branch master
Initial commit
Changes to be committed:
(use "git rm --cached <file>..." to unstage)
new file: journal.md
Now our file is listed underneath where it says Changes to be committed.
git add is used for two purposes. Firstly, to tell Git that a given file
should be tracked. Secondly, to put the file into the Git staging area
which is also known as the index or the cache.
The staging area can be viewed as a “loading dock”, a place to hold files we have added, or changed, until we are ready to tell Git to record those changes in the repository.
Commit changes
In order to tell Git to record our change, our new file, into the repository, we need to commit it:
$ git commit
# Type a commit message: "Add title and authors"
# Save the commit message and close your text editor (vim, notepad etc.)
Our default editor will now pop up. Why? Well, Git can automatically figure out that directories and files are committed, and by whom (thanks to the information we provided before) and even, what changes were made, but it cannot figure out why. So we need to provide this in a commit message.
If we save our commit message and exit the editor, Git will now commit our file.
[master (root-commit) 21cfbde]
1 file changed, 2 insertions(+) Add title and authors
create mode 100644 journal.md
This output shows the number of files changed and the number of lines inserted or deleted across all those files. Here, we have changed (by adding) 1 file and inserted 2 lines.
Now, if we look at its status,
$ git status
On branch master
nothing to commit, working directory clean
our file is now in the repository.
The output from the git status command means that we have a clean directory
i.e. no tracked but modified files.
Now we will work a bit further on our journal.md file by writing the introduction section.
$ vim journal.md
# Write introduction section
If we now run,
$ git status
we see changes not staged for commit section and our file is marked as modified:
On branch master
Changes not staged for commit:
(use "git add <file>..." to update what will be committed)
(use "git checkout -- <file>..." to discard changes in working directory)
modified: journal.md
no changes added to commit (use "git add" and/or "git commit -a")
This means that a file Git knows about has been modified by us but has not yet been committed. So we can add it to the staging area and then commit the changes:
$ git add journal.md
$ git commit # "Write introduction"
Note that in this case we used git add to put journal.md to the staging
area. Git already knows this file should be tracked but doesn’t know if we want
to commit the changes we made to the file in the repository and hence we have
to add the file to the staging area.
It can sometimes be quicker to provide our commit messages at the command-line
by doing git commit -m "Write introduction section".
Let’s add a directory common and a file references.txt for references we may want to reuse:
$ mkdir common
$ vim common/references.txt # Add a reference
We will also add a citation in our introduction section (in journal.md).
$ vim journal.md # Use reference in introduction
Now we need to record our work in the repository so we need to make a commit. First we tell Git to track the references. We can actually tell Git to track everything in the given sub-directory:
$ git add common # Track everything currently in the 'common' directory
$ git status # Verify that common/references.txt is now tracked
All files that are in common are now tracked. We would also have to add
journal.md in the staging area. But there is a shortcut. We can use
commit -a. This option means “commit all files that are tracked and
that have been modified”.
$ git commit -am "Reference J Bloggs and add references file" # Add and commit all tracked files
and Git will add, then commit, both the directory and the file.
In order to add all tracked files to the staging area, use git commit -a
(which may be very useful if you edit e.g. 10 files and now you want to commit all of them).
Key Points
git initinitializes a new repository
git statusshows the status of a repositoryFiles can be stored in a project’s
working directory(which users see), thestaging area(where the next commit is being built up) and thelocal repository(where commits are permanently recorded)
git addputs files in the staging area
git commitsaves the staged content as a new commit in the local repositoryAlways write a log message when committing changes