Master Git: Core Concepts, Data Model, and 12 Essential Commands

Author and Development Reason

Talk is cheap. Show me the code.

This quote is from Linus Torvalds, the creator of Linux and Git.

Originally Linux used BitKeeper, but after it became non‑free, Linus wrote Git in ten days, making it a free open‑source VCS.

Version Control Systems

Version control is like keeping multiple versions of a resume or thesis.

Local VCS is simple but single‑user; centralized VCS (CVCS) like CVS, Subversion, Perforce uses a single server; distributed VCS (DVCS) like Git, Mercurial, Bazaar mirrors the whole repository, allowing work even if a server fails.

What does “mirroring the whole repository” mean?

CVCS stores only deltas; Git stores snapshots of all files, referencing unchanged files.

Git Data Model

1. What is a snapshot?

Git uses two terms:

blob

(single file) and

tree

(directory). A snapshot is the top‑level tree that is tracked.

Thus a snapshot represents the tracked “public account” folder.

2. Local repository data model

Each snapshot records its parent, forming a directed acyclic graph.

Every snapshot corresponds to a

commit

object:

<code>class commit {
  array&lt;commit&gt; parents
  String author
  String message
  Tree snapshot
}
</code>

Objects (blob, tree, commit) are addressed by SHA‑1 hashes.

git cat-file -t : show object type git cat-file -p : show object content

Git also provides references like

HEAD

.

Common Commands

Commands are divided into three parts: local operations, remote interactions, and branch collaboration.

Local Operations

Git has three areas: working directory, staging area, and local repository, with states

modified

,

staged

,

committed

.

1. git add

Add changes from working directory to staging area.

2. git commit -m "msg"

Create a commit; often include a Jira link.

To amend the last commit:

<code>$ git commit --amend
</code>

3. git log

Show commit history;

git log --oneline

for concise view,

git reflog

for reference log.

4. git reset

Move the repository to a given commit. Options:

--hard

(sync all three areas),

--soft

(only repository),

--mixed

(stage area sync).

Remote Interaction

Push and pull synchronize with remote repositories.

5. git push

Upload local commits to remote.

6. git clone

Clone a remote repository to local.

7. git pull

Fetch and merge remote changes; equivalent to

git fetch

+

git merge

. Rebase is an alternative merge strategy.

8. git rebase

Reapply commits onto another base, useful for linear history.

Branching and Merging

9. List branches

git branch

shows local branches;

git branch -v

adds details.

10. Create branch

git branch <name>

11. Switch branch

git checkout <name>

12. Merge branch

git merge <name>

merges another branch; conflicts occur when the same line is edited in both.

Learning Resources

git help

Use

git help

or

git help pull

for detailed usage and examples.

Pro Git

The book covers basic to advanced Git usage and underlying principles. Available in English ( https://git-scm.com/book/en/v2 ) and Chinese.

Play a Game

Practice Git with the interactive game learnGitBranching at https://learngitbranching.js.org/.