Lecture 44

Version control with git

MCS 275 Spring 2022
Emily Dumas

Lecture 44: Version control with git

Course bulletins:

• Please complete your course evaluations. The deadline is 11:55pm Sunday.
• Project 4 due today at 6pm.

Version control

A system to:

• Track changes
• Document changes
• Archive previous versions
• Allow concurrent work

Version control systems (VCS) are also known as "source code management" (SCM).

Do you have this?

        project4.py
        project4draft.py
        project4-new.py
        project4-fixed.py
        project4-fixed-debug.py
        project4final.py
        project4final2.py
        project4final3.py
        project4final3 (1).py
        project4final_fixed-new2_revised\ (1).2022-04-27.py

A version control system (VCS) can help.

git

A VCS created by Linus Torvalds in 2005.

Key properties:

• Open source
• Distributed
• Nonlinear
• Offline-friendly

Online services

There are some popular online services that will keep a copy of your project on a server that everyone working on it can exchange updates with. E.g.

• gitlab
• github
• bitbucket

These let you voluntarily centralize a purposely decentralized system.

Repository

A set of files and directories for which git tracks changes and a database of previous changes to those files.

Think of it as a single "project".

git init

Creates a git repository in the current directory.

Initially has empty history and doesn't track any files.

Data lifecycle

git add

Put current version of the file in a staging area.

git commit

Record staged changes in the database.

(These files will be tracked from now on.)

git log

Show recent commits and descriptions.

git status

Show summary of current situation.

Another commit

git push

Contact a remote repository and send it commits that are in our database but not theirs.

Fails if remote has changed since our last push!

git pull

Contact a remote repository and get commits from its database that are not yet in ours.

May trigger a merge if there have been changes to both local and remote since we last pulled.

Looking at history

git show COMMIT:FILE

will display file contents at any commit.

git clone

Make a local copy of an existing repository (from URL, directory, ...).

Not covered

• reset – undo things / restore files or repo to an earlier state
• branch – named series of commits; related commands:
• checkout
• merge
• rebase