I mistakenly added files using the command "git add dir". I have not yet run "git commit". Is there a way to remove this dir and everything contained within it from the commit?
I have tried git reset dir, but it didn't work. Apparently git reset file is the way to undo it. But I have so many files and so little time.

git reset <path>updates the index for that path so that it matchesHEAD(the current commit). It doesn't touch the working tree.