Problem updating homebrew Trying to update homebrew, I get this:

$ brew update

error: Your local changes to the following files would be overwritten by merge:
    .gitignore
    Library/Contributions/brew_bash_completion.sh
    Library/Contributions/brew_fish_completion.fish
    Library/Contributions/brew_zsh_completion.zsh
    Library/Contributions/manpages/brew.1.md
    Library/ENV/4.3/cc
    Library/ENV/4.3/make
    Library/ENV/4.3/xcrun
    Library/ENV/libsuperenv.rb
Please, commit your changes or stash them before you can merge.
error: The following untracked working tree files would be overwritten by merge:
    CONTRIBUTING.md
    Library/Aliases/ag
    Library/Aliases/heroku


... etc...

Any way to just clean that up? Looks like it's using git under the hood?
That would depend on whether you care about local changes to those files. Did you change them yourself, or did you run a program that changed them, or something else?

If you didn't mean to change them at all, cd /usr/local and run git reset --hard HEAD; this will reset them all to their original state. Then try updating Homebrew.