Run Rubocop against all files that are different from upstream's master

rubocop.rb

#!/usr/bin/env ruby

changed = `git diff --numstat origin/master | awk '{ print $3 }' | grep -E '(\\.rb|\\.rake)$'`

changed = changed.split("\n").select { |c| File.exist?(c) }

if changed.length > 0
  system "rubocop #{ARGV.join(' ')} #{changed.join(' ')}"
else
  puts "No changes."
end

(ps: could be 100% bash, but I don't know how to filter a list of files to only include the ones that still exist)