[Git]-005 撤销修改

1.撤销工作区的修改

操作步骤：
1.新建demo4.txt，添加任意内容到文件中后，git add到缓存区

192:learn qingjiao$ cat demo4.txt
good good study
day day up

192:learn qingjiao$ git add demo4.txt

192:learn qingjiao$ git status demo4.txt
On branch master
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

    new file:   demo4.txt

1.1 文件修改后还未再次提交到暂存区，git checkout -- filename对工作区的修改进行撤销

2.对demo4.txt文件进行修改，误删除了一行内容

192:learn qingjiao$ cat demo4.txt  #删除后文件内容
good good study

192:learn qingjiao$ git status demo4.txt #查看此时工作区状态
On branch master
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

    new file:   demo4.txt

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:   demo4.txt

3.使用git checkout -- filename将工作区修改撤销

192:learn qingjiao$ git checkout -- demo4.txt  #将删除操作撤销

192:learn qingjiao$ git status demo4.txt #查看此时工作区状态，只有增加这个change了
On branch master
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

    new file:   demo4.txt

2.撤销暂存区的修改

操作步骤：
1.对demo4.txt中新增一行'not happy today'
2.并将修改添加到暂存区
3.查看工作区状态

192:learn qingjiao$ 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:   demo4.txt

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

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

    modified:   demo4.txt

2.1 git reset HEAD filename撤销暂存区的修改

1.执行 git reset HEAD demo4.txt
2.查看工作区和暂存区文件内容差异

192:learn qingjiao$ git reset HEAD demo4.txt
Unstaged changes after reset:
M   demo4.txt

192:learn qingjiao$ git diff demo4.txt
diff --git a/demo4.txt b/demo4.txt
index 14bfb6c..6e8d0cb 100644
--- a/demo4.txt
+++ b/demo4.txt
@@ -1,2 +1,3 @@
 good good study
 day day up
+not happy today  #工作区比暂存区多出一行，我们已经将暂存区的修改撤销了

说明：如果想要此时想要将工作区的修改进一步撤销，使用git checkout -- filename即可撤销工作区修改

192:learn qingjiao$ git checkout -- demo4.txt
192:learn qingjiao$ git diff demo4.txt
192:learn qingjiao$ cat demo4.txt
good good study
day day up    #此时工作区和暂存区的文件内容无差异