Introduction

What’s version control?

Version control is a tool for managing changes to a set of files.

There are many different version control systems:

  • Git

  • Mercurial (hg)

  • CVS

  • Subversion (svn)

Why use version control?

  • Better kind of backup.

  • Review history (“When did I introduce this bug?”).

  • Restore older code versions.

  • Ability to undo mistakes.

  • Maintain several versions of the code at a time.

Git is also a collaborative tool:

  • “How can I share my code?”

  • “How can I submit a change to someone else’s code?”

  • “How can I merge my work with Sue’s?”

Git != GitHub

  • Git: version control system tool to manage source code history.

  • GitHub: hosting service for Git repositories.

How do we use version control?

Do some programming, then commit our work:

my_vcs commit

Program some more.

Spot a mistake:

my_vcs rollback

Mistake is undone.

What is version control? (Team version)

Sue

James

my_vcs commit

Join the team

my_vcs checkout

Do some programming

my_vcs commit

my_vcs update

Do some programming

Do some programming

my_vcs commit

my_vcs update

my_vcs merge

my_vcs commit

Scope

This course will use the git version control system, but much of what you learn will be valid with other version control tools you may encounter, including subversion (svn) and mercurial (hg).

Practising with Git

Example Exercise

In this course, we will use, as an example, the development of a few text files containing a description of a topic of your choice.

This could be your research, a hobby, or something else. In the end, we will show you how to display the content of these files as a very simple website.

Programming and documents

The purpose of this exercise is to learn how to use Git to manage program code you write, not simple text website content, but we’ll just use these text files instead of code for now, so as not to confuse matters with trying to learn version control while thinking about programming too.

In later parts of the course, you will use the version control tools you learn today with actual Python code.

Markdown

The text files we create will use a simple “wiki” markup style called markdown to show formatting. This is the convention used in this file, too.

You can view the content of this file in the way Markdown renders it by looking on the web, and compare the raw text.

Displaying Text in this Tutorial

This tutorial is based on use of the Git command line. So you’ll be typing commands in the shell.

To make it easy for me to edit, I’ve built it using Jupyter notebook.

Commands you can type will look like this, using the %%bash “magic” for the notebook.

If you are running the notebook on windows you’ll have to use %%cmd.

%%bash
echo some output
some output

with the results you should see below.

In this document, we will show the new content of an edited document like this:

%%writefile somefile.md
Some content here
Overwriting somefile.md

But if you are following along, you should edit the file using a text editor. On windows, we recommend Notepad++. On mac, we recommend Atom

Setting up somewhere to work

%%bash
rm -rf learning_git/git_example # Just in case it's left over from a previous class; you won't need this
mkdir -p learning_git/git_example
cd learning_git/git_example

I just need to move this Jupyter notebook’s current directory as well:

import os

top_dir = os.getcwd()
top_dir
'/home/runner/work/rse-course/rse-course/module04_version_control_with_git'
git_dir = os.path.join(top_dir, "learning_git")
git_dir
'/home/runner/work/rse-course/rse-course/module04_version_control_with_git/learning_git'
working_dir = os.path.join(git_dir, "git_example")
os.chdir(working_dir)

Solo work

Configuring Git with your name and email

First, we should configure Git to know our name and email address:

git config --global user.name "YOUR NAME HERE"
git config --global user.email "yourname@example.com"

Note that by using the --global flag, we are setting these options for all projects. To set them just for this project, use --local instead.

Now check that this worked

%%bash
git config --get user.name
Turing Developer
%%bash
git config --get user.email
developer@example.com

Initialising the repository

Now, we will tell Git to track the content of this folder as a git “repository”.

%%bash
pwd # Note where we are standing-- MAKE SURE YOU INITIALISE THE RIGHT FOLDER
git init --initial-branch=main
/home/runner/work/rse-course/rse-course/module04_version_control_with_git/learning_git/git_example
Initialized empty Git repository in /home/runner/work/rse-course/rse-course/module04_version_control_with_git/learning_git/git_example/.git/

As yet, this repository contains no files:

%%bash
ls
%%bash
git status
On branch main

No commits yet

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