git commit --amend的撤销方法

某同事执行git commit 时太兴奋，执行了

git commit --amend

慌了，不敢编辑上一个commit的description了，直接选择了wq退出，然而git毕竟强大，默认将改动合并提交并覆盖了上一个commit生成了一个新的commit id，这下更慌了，上一个commit id在git log里没了，没了，没了

此时只有两个字，奔溃

好在git有撤销方法，下面的代码拿来举例。

---

当前代码仓有如下文件：

$ ll
total 4
-rw-r--r-- 1 ****** 1051817 3 九月 13 15:49 1.txt
-rw-r--r-- 1 ****** 1051817 3 九月 13 16:00 2.txt
-rw-r--r-- 1 ****** 1051817 2 九月 13 14:16 3.txt
-rw-r--r-- 1 ****** 1051817 7 九月 13 13:54 README.md

修改1.txt和2.txt，并提交。

$ echo "12" >> 1.txt
$ echo "22" >> 2.txt
$ git add .
$ git commit -m "modified 1/2.txt"
[master b82585f] modified 1/2.txt
 3 files changed, 3 insertions(+)
 create mode 100644 3.txt

在未push前，继续修改3.txt，并执行git commit --amend覆盖上一个commit。

$ echo "32" >> 3.txt
$ git add 3.txt
$ git commit --amend
[master 6889e84] modified 1/2/3.txt
 Date: Thu Sep 14 14:18:40 2017 +0800
 3 files changed, 4 insertions(+)
 create mode 100644 3.txt

执行git log发现最新的commit id 已经从b82585f变为了6889e84

$ git log
commit 6889e8402d8f40b38f5e6c0aff686b6b3ca82389 (HEAD -> master)
Author: ******
Date:   Thu Sep 14 14:18:40 2017 +0800

    modified 1/2/3.txt

$ git status
On branch master
Your branch is ahead of 'origin/master' by 1 commit.
  (use "git push" to publish your local commits)
nothing to commit, working tree clean,

这就演示到文章开头同事遇到的问题了，amend覆盖了上一个commit，且提交了对文件的修改，只是他未修改description。

---

撤销开始

如果我们忘记了被覆盖的那个commit id，那就用reflog命令看一下

$ git reflog
6889e84 (HEAD -> master) HEAD@{0}: commit (amend): modified 1/2/3.txt
b82585f HEAD@{1}: commit: modified 1/2.txt

$ git reset b82585f
Unstaged changes after reset:
M       3.txt

$ git status
On branch master
Your branch is ahead of 'origin/master' by 1 commit.
  (use "git push" to publish your local commits)
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:   3.txt

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

$ git log
commit b82585f65b4c467a7e5855191b73a613fcf20892 (HEAD -> master)
Author: ares.wang <[e-mail]>
Date:   Thu Sep 14 14:18:40 2017 +0800

    modified 1/2.txt

可以看出，reset已经恢复到上一个被覆盖的commit id了，且对文件的修改回退到代码仓not staged的状态了

不使用 git reset --hard的目的就是为了保留本地修改，否则修改就会被丢弃！演示如下：

$ git reset --hard b82585f
HEAD is now at b82585f modified 1/2.txt

$ git status
On branch master
Your branch is ahead of 'origin/master' by 1 commit.
  (use "git push" to publish your local commits)
nothing to commit, working tree clean

3.txt的modified没有了，切记慎用--hard参数，除非你确定放弃当前未提交的所有修改！