$ brew update fatal: It seems that there is already a rebase-apply directory, and I wonder if you are in the middle of another rebase. If that is the case, please try git rebase (--continue | --abort | --skip) If that is not the case, please rm -fr ".git/rebase-apply" and run me again. I am stopping in case you still have something valuable there. Already up-to-date.
$ brew update-reset