一、checkout&&reset

git checkout指令是用来还原一个代码仓库中的文件的。

huangxiaolei@huangxiaolei MINGW64 /f/GitTest (master)
$ 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:   test

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

huangxiaolei@huangxiaolei MINGW64 /f/GitTest (master)
$ git checkout test

huangxiaolei@huangxiaolei MINGW64 /f/GitTest (master)
$ git status
On branch master
nothing to commit, working tree clean

在修改文件之后，执行git add指令之前，如果执行checkout指令，则会抛弃当前本地的所有修改，恢复到上次最后的提交版本。

如果修改文件并执行git add指令后继续修改文件，此时再执行checkout指令，查看代码仓库状态。

huangxiaolei@huangxiaolei MINGW64 /f/GitTest (master)
$ 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:   test

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

huangxiaolei@huangxiaolei MINGW64 /f/GitTest (master)
$ git add test

huangxiaolei@huangxiaolei MINGW64 /f/GitTest (master)
$ git checkout test

huangxiaolei@huangxiaolei MINGW64 /f/GitTest (master)
$ git status
On branch master
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

        modified:   test

git checkout <file>指令其实是用版本库里的版本替换工作区的版本，无论工作区是修改还是删除。

git reset HEAD <file>指令将一个文件移出暂存区。

二、回退版本

在Git中，用HEAD表示当前版本，那么上一个版本就是HEAD^，上上一个版本就是HEAD^^，如果往上100个版本可以写成HEAD~100。

回退到上个版本

$ git reset --hard HEAD^
HEAD is now at 4269b25 添加README

也可以写commit id来表示对应的版本。

huangxiaolei@huangxiaolei MINGW64 /f/GitTest (master)
$ touch test2

huangxiaolei@huangxiaolei MINGW64 /f/GitTest (master)
$ git add
Nothing specified, nothing added.
Maybe you wanted to say 'git add .'?

huangxiaolei@huangxiaolei MINGW64 /f/GitTest (master)
$ git add test2

huangxiaolei@huangxiaolei MINGW64 /f/GitTest (master)
$ git commit -m "add test2"
[master c896e52] add test2
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 test2

huangxiaolei@huangxiaolei MINGW64 /f/GitTest (master)
$ git lg
* c896e52 (HEAD -> master)add test2(3 seconds ago)<huangxiaolei>--abbrev-commit
* 4269b25添加README(76 minutes ago)<huangxiaolei>--abbrev-commit

huangxiaolei@huangxiaolei MINGW64 /f/GitTest (master)
$ git reset --hard 4269b25
HEAD is now at 4269b25 添加README