Git

• Git is an implementation of version control (remember that it's not Git that invented the concept of version control)
• Git focuses on plain text files
• Git allows you to
  • revert selected files back to a previous state
  • revert the entire project back to a previous state
  • compare changes over time
  • see who last modified something that might be causing a problem

Version Control

• VCS (Version Control System) is any system that records changes (the history) of a file/ set of file that helps you understand how it has progressed
  • saving a file is a simplified version control system, which only allows you to move forward
• History
  • Local VCS
    • keep patch sets (differences) in a local database
  • Centralized VCS
    • keep versioned files in a single center server
  • Distributed VCS
    • All clients don't just check out the latest snapshot of the files; rather, they fully mirror the repository, including its full history
    • Every clone is really a full backup of all the data

Git vs Other VCS

• Snapshots vs Delta-Based VC
  • Delta(difference)-based:
    
  • Snapshots:
    
• Nearly Every Operation In Git In Local
  • Hence Git is super fast
• Integrity by Hash
  • Git stores everything in its database not by file name but by the hash value of its contents
  • Git uses checksum to guarantee integrity
• Git Generally Only Adds Data
  • We can experiment without the danger of severely screwing things up

Concepts

Three States

1. Modified: changed the file but have not committed it to your database yet
2. Staged: marked a modified file in its current version to go into your next commit snapshot
   *

3. Committed: the data is safely stored in your local database

Commit

Someone make some changes, then they commit to annotate the history of changes. Once committed, a "snapshot" was taken of the differences made to the system at a given point in time.

Push & Pull

When collaborating (even with yourself), you may want to host a remote repository (repository is just a folder of your project) that can accessed by anyone. Push is just submitting your commits (changes with annotations) to the remote; while pull is the opposite.

Branches

In a large collaborating project, you may have different lines of work that have different focus and progress. Then you create branches, which leave the main (used to called master 😆) branch at some point and will eventually merge to the main branch.

In essence, when a branch gets merged into master, its commits get added to the top of the master history.

Other

• clone fully copy a repository, including all the history

• add take changes into the control of git

• fetch get the changes from other repo but without automatically merging them

• merge accept the fetched changes

• pull request a GitHub tool that allows users to easily see the changes (the difference or "diff") that a feature branch is proposing as well as discuss any tweaks that said branch might require before it is merged into master

• stash temporarily commit

Usage

Update

On Linux

sudo add-apt-repository ppa:git-core/ppa
sudo apt update
sudo apt install git

Configuration

• User name and email

git config --global user.name "Your Name"
git config --global user.email "yourname@example.com"

• Set the default branch to match the default branch name of GitHub (main)

git config --global init.defaultBranch main

SSH Management

• Generate an SSH key for the first time

ssh-keygen -C "hello@gmail.com"

• Read and read the SSH key

cat ~/.ssh/id_rsa.pub | clip.exe

• clip.exe is only available on WSL, use xclip on other Linux systems, use pbcopy on macOS

• Go to GitHub to add the SSH key
• Test the key (for GitHub)

ssh -T git@github.com

• When first run, it will ask you to add a host to known hosts, type yes

Workflow

# Initialize a repo
git init
# Clone a repo
git clone <repo_url>
# Stage all changes in the **directory**
git add .
# Stage all changes in the **repository**
git add -A
# Commit
git commit -m "commit message"
# Check status
git status
# Push
git push [-u origin main]
# See history
git log

by zcysxy