Recently I got an undefined error "0", using brew 0.9.5: /usr/local/bin/brew: /usr/local/Library/brew.rb: /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby: bad interpreter: No such file or directory /usr/local/bin/brew: line 23: /usr/local/Library/brew.rb: Undefined error: 0 I really do not know, why it is Ruby 1.8 (it is very old) being used here, but typing "ruby -version" leads to the fact, that we currently run Ruby of Version 2.0. So fixing this is pretty simple: 1. Open this file: "/usr/local/Library/brew.rb" (may depend, where exactly you have installed brew to -> see the error message!) 2. Edit the 1st line (replace 1.8 with your current version -> mine = 2.0)…