osx - brew update: Error in terminal mac -

error: local changes following files overwritten merge:     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/formula/dmtx-utils.rb     library/formula/docbook-xsl.rb     library/formula/dromeaudio.rb     library/formula/dub.rb     library/formula/dvorak7min.rb     library/formula/dyld-headers.rb     library/formula/dylibbundler.rb     library/for aborting error: failure while executing: git pull -q origin refs/heads/master:refs/remotes/origin/master 

i've seen few times , don't know causes it; if you're sure haven't made modifications files want save, can go /usr/local (or wherever keep homebrew installation) , type git reset --hard head. try updating again.