Introduction to Git

• working directory
  the files currently visible on your file system, 파일이 있는 장소

• the staging area. Index
  the index of changes to be written to the repository after the next commit ,바로 다음에 커밋할 것

• the repository ,HEAD
  stores files, records the changes made to the files over time ,현재 branch 가 가리키는 포인터, 가장 마지막 커밋

File lifecycle in your working directory

• Tracked
  unmodified, modified, staged
  tracked and unmodified after first cloning
• Untracked
  not in your last snapshot and are not in your staging area
• Unmodified
  you haven’t changed this file since your last commit
• Modified
  you’ve modified this file in some fashion since your last commit
• Git really only knows about files, and nothing about directories
  touch .keep under directory for detecting directory
• git log
  shows you the basic commit history of your repository
• git log -p
  shows the commit history of your repository with the corresponding diffs.

• git diff
  to see the changes in working dir. and the changes in staging area

• git diff --staged(cached)
  compares your staged changes to your last commit