Look into .git directory

$ git init foo  
$ cd foo  
$ tree  

.  
├── HEAD  
├── config  
├── description  
├── hooks  
│   ├── applypatch-msg.sample  
│   ├── commit-msg.sample  
│   ├── post-update.sample  
│   ├── pre-applypatch.sample  
│   ├── pre-commit.sample  
│   ├── pre-push.sample  
│   ├── pre-rebase.sample  
│   ├── prepare-commit-msg.sample  
│   └── update.sample  
├── info  
│   └── exclude  
├── objects  
│   ├── info  
│   └── pack  
└── refs  
    ├── heads  
    └── tags  

• refs
  • HEAD, tag, branch
• objects
  • blob, tree, commit
    • blob
      • type, bytes, content of blob
      • ex: blob 13hello,world
    • tree
      • main file directory for the project
      • tree: point to the next tree object
      • blob: ref name for blob object (one for every related object files for this tree)
    • commit
      • parent: point to the last commit
      • message: commit message
  • store files for git
  • SHA1 hash
  • Compressed
  • commit action will add a commit object and tree object into the objects
  • tree objects have filenames for blob objects
  • blob files which have exactly same content will be stored as the same hash not only in the same project but also among all users.

Branch

• branch just store the hash of the newest commit for that branch

Tag

• regular tags do not have hash value
• be stored in refs/tags
• just a text file contain the commit object hash
• annotated tag
  • git tag -a $tag_name
  • tagger, annotation
  • has a hash value

Webhook

• use http://requestb.in/ as payload url in github, so every time there's a event github will send event message to the payload url.
• Travis CI
• https://github.com/muan/emoji

Misc

• if you delete tree objects manually, git fsck will tell you what happened.
• Git does not support empty directory
• .gitkeep
• Every files in Git are treated as binary, so the blob file is not just a plaintext file
• git clone won't clone unreferenced files in default, but you can specify that.
• git push/pull won't do anything about unreferenced files

$ watch -n .1 tree  

Git commands

git ls-tree  
git ls-tree HEAD  

git fsck  

git show $tag_name --pretty=raw`  

git rebase $branch  

git reflog  
// use reflog to get the hash or alias and use git reset to undo your actions  

git gc  
// delete useless files (unreferenced files) after 90 days when someone do the action  

Reference

• Example at NCTU by johndbritton · Pull Request #132 · muan/emoji · GitHub

Thoughts

雖然內容大部份在 GitBook 都有
不過真的覺得 Mr.Britton 真的講解得蠻清楚的
比較理解 .git folder 裡面的東西是在做什麼用的
CI 的部分只有提到 Travis CI 在 GitHub 上面的 Webhook
然後 show 一下 GitHub Repo 綁 Traivs CI 後
在 PR 的時候會幫忙跑測試
原本以為會介紹一下 Travis CI 大概要怎麼用
看來得自己找時間研究一下了

然後今天又拿到 Octocat 的新貼紙啦

感謝 muan 的這則 Twitter 訊息 才有機會在交大聽到這場 Talk
原來 https://github.com/muan/emoji 是她的 Repo
GitHub 上越來越多 emoji 了XDD