Introduction to version control with Git

Kyle Niemeyer

Oregon State University

2025-01-08

Introduction to version control

Where is version control needed?

Backing up changing files
Storing and accessing an annotated history of changes
Managing the merging of changes between different change sets

Why is this important?

Comic on file versions from PhD Comics https://phdcomics.com/comics/archive.php?comicid=1323 — Image credit: Jorge Cham, PhD Comics

Saving copies

important_code.py

important_code-2.py

important_code-fix.py

important_code-final.py

important_code-final-4Apr.py

Git commits

important_code.py

Types of version control

Centralized:

Concurrent Version System (cvs)
Subversion (svn)
Perforce (p4)

Distributed:

Decentralized CVS (dcvs)
mercurial (hg)
bazaar (bzr)
Git (git)

Git

giant Swiss Army knife with far too many tools

Git is a knife whose handle is also a knife. – Philip Guo

If that doesn't fix it, git.txt contains the phone number of a friend of mine who understands git. Just wait through a few minutes of 'It's really pretty simple, just think of branches as...' and eventually you'll learn the commands that will fix everything.

Image credit: xkcd

Getting started with Git

$ git --help

$ git config --global user.name "Kyle Niemeyer"
$ git config --global user.email "kyle.niemeyer@oregonstate.edu"
$ git config --global core.editor "vim"

~ $ mkdir analysis_code
~ $ cd analysis_code

~/analysis_code $ git init
Initialized empty Git repository in ~/analysis_code/.git/

~/analysis_code $ ls
~/analysis_code $ ls -A
.git

~/analysis_code $ cd .git && ls -A
HEAD    config    description    hooks    index    info    logs

Tip

Try this yourself.

Adding files

~/analysis_code $ touch README.md
~/analysis_code $ git add README.md
~/analysis_code $ git status

Tip

Try this yourself.

Committing changes

Snapshot of repository = revision

Committing a revision:

Saves current state with a unique ID (hash)
Names you as the author
Allows you to add a message

~/analysis_code $ git commit

Tip

Try this yourself.

Options to save time

~/analysis_code $ git commit -m "This is my message"

~/analysis_code $ git commit -am "This is my message 
                  committing all changes"

Commit messages

Bad commit message:

Fixed bug

Better commit message:

Fixed bug in mass calculation

Due to incorrect density value, mass was being calculated
orders of magnitude larger than it should. The correct value
of density fixed this problem.

Merge branch 'asdfasjkfdlas/alkdjf' into sdkjfls-final

Image credit: xkcd

Viewing history and differences

~/analysis_code $ git log

~/analysis_code $ git diff

Undoing work

Un-add a file that has been staged:

~/analysis_code $ git restore --staged <filename>

Reset all tracked files to previous commit:

~/analysis_code $ git reset [mode] [commit]

Remove uncommitted changes:

~/analysis_code $ git checkout -- <filename>

Branches

~/analysis_code $ git branch
* main

~/analysis_code $ git branch experimental
~/analysis_code $ git branch
  experimental
* main

~/analysis_code $ git branch new
~/analysis_code $ git branch
  experimental
* main
  new

~/analysis_code $ git branch -d new
~/analysis_code $ git branch
  experimental
* main

~/analysis_code $ git switch experimental
~/analysis_code $ git branch
* experimental
  main

Merging branches

~/analysis_code $ git switch main
~/analysis_code $ git merge experimental
~/analysis_code $ git log