引用自https://docs.gitlab.com/ee/topics/git/numerous_undo_possibilities_in_git/

At this point there are 3 options to undo the local changes you have:

Discard all local changes, but save them for possible re-use later:

git stash

Discarding local changes (permanently) to a file:

git checkout -- <file>

Discard all local changes to all files permanently:

git reset --hard

上面这些方法都会保留unstaged files

https://stackoverflow.com/questions/52704/how-do-i-discard-unstaged-changes-in-git

如果要discard unstaged files, using

git clean -df

usage: git clean [-d] [-f] [-i] [-n] [-q] [-e <pattern>] [-x | -X] [--] <paths>...

    -q, --quiet           do not print names of files removed
    -n, --dry-run         dry run
    -f, --force           force
    -i, --interactive     interactive cleaning
    -d                    remove entire directories
    -e, --exclude <pattern>
                          add <pattern> to ignore rules
    -x                    remove ignored files, too
    -X                    remove only ignored files

Another quicker way is:

usage: git stash list [<options>]
   or: git stash show [<stash>]
   or: git stash drop [-q|--quiet] [<stash>]
   or: git stash ( pop | apply ) [--index] [-q|--quiet] [<stash>]
   or: git stash branch <branchname> [<stash>]
   or: git stash save [--patch] [-k|--[no-]keep-index] [-q|--quiet]
		      [-u|--include-untracked] [-a|--all] [<message>]
   or: git stash [push [--patch] [-k|--[no-]keep-index] [-q|--quiet]
		       [-u|--include-untracked] [-a|--all] [-m <message>]
		       [-- <pathspec>...]]
   or: git stash clear

git stash save --keep-index --include-untracked
You don’t need to include --include-untracked if you don’t want to be thorough about it.

After that, you can drop that stash with a git stash drop command if you like.

more details could be seen in https://git-scm.com/docs/git-stash