Fix brew update && brew upgrade error

fatal: It seems that there is already a rebase-merge directory, and
I wonder if you are in the middle of another rebase. If that is the
case, please try

❯ brew update && brew upgrade && brew cleanup
==> Updating Homebrew…
fatal: It seems that there is already a rebase-merge 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-merge"
and run me again. I am stopping in case you still have something
valuable there.

How to Fix It

1. Check for and remove the stray rebase directory:
   • • For Intel Macs: bash find /usr/local/Homebrew -name "rebase-merge"
   • • For Apple Silicon (M1/M2/M3): bash find /opt/Homebrew -name "rebase-merge"
2. If a directory like /opt/Homebrew/Library/Taps/homebrew/homebrew-core/.git/rebase-merge appears, remove it: bash rm -rf /opt/Homebrew/Library/Taps/homebrew/homebrew-core/.git/rebase-merge After that, retry:bash brew update && brew upgrade This resolves the issue for most users.