checkout

checkout命令经常被用来切换分支，但是git checkout -- fileName 还可以将没有提交到暂存区中的修改删除，恢复未修改的状态（但是对于新建的文件无法恢复到新建之前）

现在有两个文件，README.md 和 README2.md,进行修改，并新建文件README3.md，执行git status之后

```
git$ git status

On branch master
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

    modified:   README.md
    modified:   README2.md

Untracked files:
  (use "git add <file>..." to include in what will be committed)

    README3.md

no changes added to commit (use "git add" and/or "git commit -a")
```

然后执行git add README.md将第一个文件加入到暂存区，执行git status命令如下

```
git$ git add README.md
git$ git status

On branch master
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

    modified:   README.md

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

    modified:   README2.md

Untracked files:
  (use "git add <file>..." to include in what will be committed)

    README3.md
```

现在执行git checkout -- .(.符号表示全部文件)全部恢复工作区修改之前的内容，再执行git status命令如下

```
git$ git checkout -- .
git$ git status

On branch master
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

    modified:   README.md

Untracked files:
  (use "git add <file>..." to include in what will be committed)

    README3.md
```

可见 git checkout -- file 可以恢复未被暂存的内容，但是不能恢复被暂存的内容和新建的文件，那么如果想要恢复已经暂存的内容怎么办，那么就需要用到git reset了