撤销 git reset --hard HEAD~1
方法一：
1.先通过git reflog找到上一次的历史提交记录id，git如果没有特意设置，是会保存记录一段时间的(a few days or a month)
2.git reset –hard [id]
方法二：
git reset –hard HEAD@{1}
直接回到刚才的那个结点，{}中表示的是结点的序号
方法一的例子如下：
$ git init
Initialized empty Git repository in .git/
$ echo “testing reset” > file1
$ git add file1
$ git commit -m \’added file1\’
Created initial commit 1a75c1d: added file1
1 files changed, 1 insertions(+), 0 deletions(-)
create mode 100644 file1
$ echo “added new file” > file2
$ git add file2
$ git commit -m \’added file2\’
Created commit f6e5064: added file2
1 files changed, 1 insertions(+), 0 deletions(-)
create mode 100644 file2
$ git reset –hard HEAD^
HEAD is now at 1a75c1d… added file1
$ cat file2
cat: file2: No such file or directory
$ git reflog
1a75c1d… HEAD@{0}: reset –hard HEAD^: updating HEAD
f6e5064… HEAD@{1}: commit: added file2
$ git reset –hard f6e5064
HEAD is now at f6e5064… added file2
$ cat file2
added new file