Apple - How do I force homebrew to update installed software?
I don't know why this happens with Homebrew when you don't do anything to mess with it, but here's how I fixed it:
- Change to your Homebrew cellar directory
cd `brew --cellar` - Reset git repository
git reset --hard HEAD - Upgrade pianobar, at last!
brew upgrade pianobar
FYI, brew update will update Homebrew to the latest version, so you may want to do that before step 3.
As @Felix said, use upgrade not update.
If the problem comes from your dirty git tree and you just want to forget about your modifications, type git reset --hard HEAD before upgrading.