Introduction to version control with Git

Author

Affiliation

Kyle Niemeyer

Oregon State University

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?

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

important_code.py

important_code.py

important_code.py

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

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

---

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.

---

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