Git教程-撤销修改

撤销修改（丢弃工作区中的修改，没有add到暂存区）

当前的readme.txt内容：

Git is a distributed version control system.
Git is free software distributed under the GPL.
Git has a mutable index called stage.
Git tracks changes of files.

对其做修改后:

Git is a distributed version control system.
Git is free software distributed under the GPL.
Git has a mutable index called stage.
Git tracks changes of files.
My stupid boss still prefers SVN.

发现错误，想要删掉最后一行，返回到上一次的状态，可以手动删除readme.txt的最后一行，再重新提交
Git会告诉你，git checkout – file可以丢弃工作区的修改

命令git checkout – readme.txt意思就是，把readme.txt文件在工作区的修改全部撤销，这里有两种情况：

1. 一种是readme.txt自修改后还没有被放到暂存区，现在，撤销修改就回到和版本库一模一样的状态；

2. 一种是readme.txt已经添加到暂存区后，又作了修改，现在，撤销修改就回到添加到暂存区后的状态。

总之，就是让这个文件回到最近一次git commit或git add时的状态。
操作一遍理解下：

开始的readme.txt已经git commit了，第二次修改没有git add,此时的git status:

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

        modified:   readme.txt

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

Git会告诉你，git checkout – file可以丢弃工作区的修改
此时用git checkout -- readme.txt：

$ cat readme.txt
Git is a distributed version control system.
Git is free software distributed under the GPL.
Git has a mutable index called stage.
Git tracks changes.

再查看git status：

$ git status
On branch master
nothing to commit, working tree clean

撤销修改（修改已经add到暂存区了）

当前readme.txt内容：

Git is a distributed version control system.
Git is free software distributed under the GPL.
Git has a mutable index called stage.
Git tracks changes.

修改后并且已经add到暂存区的内容:

Git is a distributed version control system.
Git is free software distributed under the GPL.
Git has a mutable index called stage.
Git tracks changes of files.
My stupid boss still prefers SVN.

在commit之前，用git status查看：

$ git status
On branch master
Changes to be committed:
  (use "git reset HEAD ..." to unstage)

        modified:   readme.txt

Git同样告诉我们，用命令git reset HEAD 可以把暂存区的修改撤销掉（unstage），重新放回工作区：

$ git reset HEAD readme.txt
Unstaged changes after reset:
M       readme.txt

再用git status查看，发现当前的暂存区是干净的，工作区有修改：

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

        modified:   readme.txt

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

此时再$ git checkout -- readme.txt丢弃掉工作区中的修改：

$ git status
On branch master
nothing to commit, working tree clean