Installation
see guide

Create and Add
Give git authority to control dir rep

mkdir rep
cd rep
git init

put f1.txt,f2.txt into rep

git add f1.txt f2.txt
git commit -m "add 2 files"

to check the current status & see the differences & check version log (commit history)

git status
git diff f1.txt
git log

use git log --pretty=oneline to compress each log to one line

Rolling back & delete
to last, second last, 100 last version, exact version with vid

git reset --hard HEAD^, HEAD^^, HEAD~100, vid

use git reflog to see the vid of previous changes (command history)

to revoke the change (did not add to the stage)

git checkout -- f1.txt

for already adding to the stage

git reset HEAD f1.txt

to delete the file

git rm f1.txt
git commit

Connect to remote repository
set the name of remote rep as origin and push from local to remote, add para -u for the first time in order to link the local and remote

git remote add origin git@github.com:GITHUBNAME/learngit.git
git push -u origin master

clone from remote to local

git clone git@github.com:GITHUBNAME/learngit.git

create a branch nb and point to it

git checkout -b nb

to create & point separately

git branch nb
git checkout nb

use git branch to see current branch, git merge nb to merge nb to master and abandon the branch, git merge --no-ff to merge and keep the branch simultaneously

Fixing Bug
to fix a bug on master branch, store the current work status in stash

git stash
git checkout master
git checkout -b tmp_branch

after fixing

git branch -d tmp_branch
git stash pop

Tagging
tag current version, previous version, delete tag

git tag v1.0, git tag v0.9 vid, git tag -d v0.9

delete remote tag, first git tag -d v0.9, then git push origin :refs/tags/v0.9