Core Concepts

• Working Directory: The directory you see on your file system.
• Staging Area (Index): Stored in the .git/index file within the working directory.
• Repository (Local Repo): Stored in the .git directory.
• HEAD:
  • A pointer to the current local branch.
  • Can point to a branch or a specific commit.
  • Defines which branch is associated with the working directory and staging area for comands like add, checkout, and commit.
  • Example commands:
    • git checkout branch_name redirects HEAD to the specified branch.
    • git checkout commit_hash moves HEAD to a specific commit.
• master and origin:
  • master is the default name of the main branch in the local repository.
  • origin is the default alias for the remote repository, typically assigned during git clone.
• Local Repository: A copy of the remote repository (simplified).
• Remote Repository: Used for collaborative development and backup.
• Branch:
  • Represents an independent line of development.
  • Branches exist only in repositories, not in the working directory or staging area.
  • Common commands:
    • git checkout -b feature-branch origin/feature-branch – Creates a local branch from a remote branch.
    • git checkout -b local_branch – Creates and switches to a new local branch.
    • git push --set-upstream origin local_branch – Pushes a local branch to the remote.
    • git branch – Lists local branches.
    • git branch -a – Lists all branches (local and remote).
    • git branch -v – Shows the last commit on each local branch.
    • git branch --merged – Shows branches merged into the current branch.
    • git branch --no-merged – Shows branches not merged into the current branch.
    • git merge <branch> – Merges a branch into the current branch.
    • git branch -d [branchname] – Deletes a local branch.
    • git push origin --delete [branchname] – Deletes a remote branch.

Basic Commands

Working Directory, Staging Area, and Local Repository

Remote and Local Repository Operations

Logging

Fork Synchronization Without Overwriting Local Changes

To sync an upstream repository (ArduPilot/ardupilot:master) to your fork (huangyangl/ardupilot) without losing your own changes (e.g., on a custom branch adrc-1.0-copy):

1. Use the Sync fork button on GitHub to update your master branch from the upstream.
2. Clone your fork locally:

   git clone https://github.com/huangyangl/ardupilot.git
   git checkout -b adrc-1.0 origin/adrc-1.0
   git checkout -b adrc-1.0-copy origin/adrc-1.0-copy
   

3. Merge the updated master into your custom branch:

   git checkout adrc-1.0-copy
   git config pull.rebase false
   git pull origin master:adrc-v1.0-copy
   

4. Resolve conflicts manually, then stage and commit.
5. Update submodules if needed:

   git submodule init
   git submodule update --recursive
   # Or for ArduPilot:
   ./waf submodule_force_clean
   

6. Push the merged branch to your remote:

   git push origin adrc-1.0-copy
   

Configuring a Custom Editor

• View current editor: git config --global core.editor
• Set editor: git config --global core.editor <editor_name>

Detailed Command Examples

Local Operations

• git init: Initialize a local directory.
• git remote:
  • git remote -v – View remote URLs.
• git --help:
  • git --help – Show general help.
  • git help -a – List all subcommands.
  • git help -g – List concepts.
• git status:
  • git status – Full status.
  • git status -s – Short format.
  • git status --ignored – Include ignored files.
• .gitignore:
  • Syntax examples:

    # Ignore directory
    .idea
    # Ignore file type
    *.iml
    # Ignore all .o and .a files
    *.[oa]
    # But keep my.b
    *.[bB]
    !my.b
    # Ignore dbg directory
    dbg/
    

  • To apply .gitignore to already tracked files:

    git rm -r --cached .
    git add .
    git commit -m 'update .gitignore'
    

• git diff:
  • Working directory vs staging area: git diff
  • Working directory vs repository: git diff HEAD
  • Staging area vs repository: git diff --cached
  • Between commits: git diff <commit1> <commit2>
  • Use --stat for summary.
• git add:
  • git add * – Add all changes.
  • git add . – Add all (tracked and untracked).
  • git add -u . – Add only tracked changes.
  • git add <file> – Add a specific file.
• git reset:
  • git reset – Unstage all files.
  • git reset -- <file> – Unstage a specific file.
• git commit:
  • `git commit -m