Session 3 · Basic terminology#

The big idea#

Git has a small vocabulary and every command uses it: repository, commit, branch, merge, remote, clone. Learn these words once and the rest of Git reads like plain English.

Everyday example: a recipe notebook. The notebook is the repository. Each time you finish a version of a recipe you take a dated snapshot (a commit). Trying a spicier variation on a separate page is a branch; adding the good variation back to the main recipe is a merge. Photocopying the whole notebook for a friend is a clone, and the friend’s shared copy on a shelf in the library is a remote.

Your computer has a repository with commits and branches. A remote repository is a copy on a server; clone, push and pull move commits between them.

The words, in action#

03-terminology.sh uses every term on a tiny recipe project and prints what Git says.

git config --global user.name "Dev User"
git config --global user.email "dev@example.com"
git config --global init.defaultBranch main

echo '--- repository: a folder plus a hidden .git folder'
git init -q recipes
cd recipes
ls -a
ls .git | head -8

echo '--- commit: a snapshot with a message'
echo "tea, water, milk" > chai.txt
git add chai.txt
git commit -q -m "Add chai recipe"
git log --oneline

echo '--- branch: a parallel line of work'
git switch -q -c add-coffee
echo "coffee, milk, sugar" > coffee.txt
git add coffee.txt
git commit -q -m "Add coffee recipe"
git branch

echo '--- merge: bring the branch back to main'
git switch -q main
ls
git merge -q add-coffee
ls
git log --oneline

echo '--- clone: a full copy, with its history, and a remote called origin'
cd ..
git clone -q recipes recipes-copy
cd recipes-copy
git remote -v
git log --oneline | wc -l

--- repository: a folder plus a hidden .git folder
.
..
.git
branches
config
description
HEAD
hooks
info
objects
refs
--- commit: a snapshot with a message
544bf04 Add chai recipe
--- branch: a parallel line of work
* add-coffee
  main
--- merge: bring the branch back to main
chai.txt
chai.txt
coffee.txt
a9fd494 Add coffee recipe
544bf04 Add chai recipe
--- clone: a full copy, with its history, and a remote called origin
origin	~/work/recipes (fetch)
origin	~/work/recipes (push)
2

The glossary#

Term	Meaning	Seen above
Repository	Your project plus its full history, stored in a hidden `.git` folder	`ls -a` shows `.git`
Commit	A snapshot of the project with a message and an id	`544bf04 Add chai recipe`
Branch	A movable label for a line of work; the default is `main`	`add-coffee` and `main`
HEAD	“Where you are now”: the commit or branch you have checked out	the `*` in `git branch`
Merge	Combine the work of one branch into another	`coffee.txt` appeared on `main`
Clone	Copy a repository, with all its history	`recipes-copy`
Remote	A repository on another computer or server; the first is called `origin`	`git remote -v`
Push / Pull	Send your commits to a remote / bring new ones down	next courses
Fork	Your own server-side copy of someone else’s repository (GitHub)
Pull request	A request to merge your branch into someone’s project, with review
Merge conflict	Two branches changed the same lines, so a human must decide

What the output proves#

A repository is just a folder with a .git inside; delete .git and it is an ordinary folder again.
After the merge, main has both recipes and the log lists both commits.
The clone has the full history (2 commits) and remembers where it came from as origin.
A commit’s id is a hash of its contents, author, date and parent, so the same content with a different date or author gets a different id. That is why Git can detect any tampering.

Common mistakes#

Calling the working folder “the repository”. The repository is the history in .git; the folder is your working copy.
Mixing up clone and fork. Clone is a Git command that copies to your computer. A fork is a copy on GitHub’s server.
Thinking a branch is a copy of the files. It is only a pointer to a commit, which is why branches are cheap.
Deleting .git “to clean up”. That erases the entire history.
Treating master and main as different things. They are only names; main is the modern default.

Hands-on exercises#

Exercise 1. Match each: (a) “copy of a repo on my laptop with history”, (b) “a line of work”, (c) “a snapshot with a message”.

Solution

(a) clone, (b) branch, (c) commit.

Exercise 2. Repeat the demo in a scratch folder with your own two files, and list what git log --oneline prints after the merge.

Solution

git init notes && cd notes
echo one > a.txt && git add a.txt && git commit -m "Add a"
git switch -c feature
echo two > b.txt && git add b.txt && git commit -m "Add b"
git switch main && git merge feature
git log --oneline

You see two commits, newest first. (If your default branch is master, use that name.)

Exercise 3. Run git remote -v in a repository you made with git init. Why is the output empty?

Solution

A repository made with git init has no remote, because it was not cloned from anywhere. Only git clone (or git remote add) creates one.

Practice#

Take the Session 3 quiz on the glossary. The original Basic Terminologies page is in the reference section.