Git Basics

Binjian Xin | 2023-01-12

Table of Contents

• Git short introduction
• Inside Git
• Under the hood
• More advanced

Git short introduction

• ‘Git’ not ‘Jit’
• days of diff and patch, bitkeeper
• linus torwald
• very similar to blockchain Merkle Tree (hash tree) why is git not a blockchain

Inside Git

• SHA is not a security feature, security is a by-product
• objects: blob, tree
• references: name for raw SHA-1 value; refs
• porcelan vs plumbing: git cat-file -t -p
• features: local, fast, efficient, distributed, snapshot not patches, changes
• HEAD/Detached?

Workflow

• edit -> stage(add) -> review -> commit
• git-flow
  • git flow cheetsheet

submodule

• just update, track the new changes of the submodules (no change)
• manually : git fetch
• automatically: git submodule update –remote
  • set specific branch .gitmodules submodule.submudle_name.branch stable
  • -f: tracked; no -f locally, not tracked.
  • git config status.submodulesummary 1

Cooperative submodule

• git submodule update –remote –rebase/–merge
• caveats: has to commit locally.
• publishing submodule changes: git push –recurse-submodules=check/on-demand
• caveats:
  • accidental revert: git submodule update –remote to update .gitmodule; and commit in parent projects.
  • cannot merge: no submodule merge

Under the hood

• index/stage, repository, working tree, remote;
• plumbing:
  • git hash-object -w;
  • git cat-file -p/-t;
  • git update-index –add –cacheinfo
• file modes: 100644/100755/120000
• git write-tree

objects

• Git is content-addressable filesystem
  • tree objects
  • blob
  • commit objects
  • tag

commit

• Git commit: is a snapshot
  • Commit often!
    • history of your logic units of change
    • a story of history of the repository
• metadta: contents, messages of author, timestamp,
• change history, –amend

reference

• branch, HEAD, detached
  • branch: reference to the head of a line of work–>git update-ref refs/heads/master
  • HEAD: symbolic reference (pointer to a reference); or SHA-1 value of a git object
  • detatched HEAD: cannot commit (checkout a commit/tag/remote branch)
    • to save : git checkout -b foo/ git branch foo/ git tag foo

advanced reference

• git reflog -2 HEAD/ HEAD^^
• git symbolic-ref
• master^^
• tags： branch reference; never moves

remote

• git remote add origin git@gitlab.work:ai/ref.git
• git push
• merge
• rebase
• stashing
• log

misc

• commit amend
• rename
• gitignore
• submodule,

More advanced

• git revert
• git revision specification for
  • git log
  • git reset
  • git chery-pick
• git rebase
• A beautiful magit