git reset hard,mixed,soft
首先，我们得了解git reset命令的形式之一：
git reset [<mode>] [<commit>]
此命令的作用是恢复HEAD分支到<commit>位置，并根据<mode>决定是否恢复index file和working tree。恢复是指将staging area和working tree的状态还原到commit的状态（如果不指定commit，则默认为last commit）。如果没有pick哪个mode，即omitted mode，则mode默认为–mixed。<commit>可以为commit的hash id或引用值。
此外，mode还有两个值：–soft和–hard。
–soft不会改动(touch) index file和working tree，但是会撤销head到commit之间的all history，这是三个模式所共有的作用。
$ git statusOn branch mainChanges not staged for commit:(use "git add <file>..." to update what will be committed)(use "git restore <file>..." to discard changes in working directory) modified: README.mdno changes added to commit (use "git add" and/or "git commit -a")$ git add README.md$ git statusOn branch mainChanges to be committed:(use "git restore --staged <file>..." to unstage) modified: README.md$ git log --graph --oneline\* 0a071ac (HEAD -> main) A\* 0c888f4 Initial Commit$ git reset --soft 0c888f4$ git statusOn branch mainChanges to be committed:(use "git restore --staged <file>..." to unstage) modified: README.md$ git log --graph --oneline\* 0c888f4 (HEAD -> main) Initial Commit
可以观察到commit A的committed changes都reset为staged changes to be committed。原本已经stage等待commit的changes不会被reset。HEAD指向<commit>，HEAD到<commit>的提交都会被undo。
–mixed在–soft的基础上，进一步reset，它会恢复index到<commit>时的状态。已经在index中的changes会reset回working tree，note that modify working tree≠reset working tree。
$ git reset 0c888f4Unstaged changes after reset:M README.md
git reset会报告影响到的changes。
–hard会在–mixed的基础上恢复working tree的状态。被跟踪的changes会被丢弃。
Any untracked files or directories in the way of writing any tracked files are simply deleted.
Git文档中的这句话我不是太理解，通过询问ChatGPT，翻译为：任何阻碍跟踪文件的写入的未跟踪文件或目录将被删除。
下面是一个Stack Overflow对该疑问的解释代码例子：
There is a case in which git reset --hard has effects on untracked files.$ touch a.txt$ git add .$ git commit -m'A'$ echo hello >> a.txt$ git add .$ git commit -m'B'$ git rm a.txt$ echo world > a.txt$ git status -sThe status output isD a.txt?? a.txtThe a.txt in the index is removed and the one in the work tree is untracked.$ cat a.txtworldReset in the mode of --hard,$ git reset --hard$ cat a.txthello$ git statusOn branch masternothing to commit, working tree clean
The untracked a.txt in the work tree is deleted. But we could also say it’s been overwritten with the tracked a.txt in HEAD.