pre-commit_rubocop.rb

#!/usr/bin/env ruby

# Adapted from https://gist.github.com/hanloong/9849098

require 'english'
require 'rubocop'

ADDED_OR_MODIFIED = /A|AM|^M/.freeze

changed_files = `git status --porcelain`.split(/\n/)
  .select { |file_name_with_status|
    file_name_with_status =~ ADDED_OR_MODIFIED
  }
  .map { |file_name_with_status|
    file_name_with_status.split(' ')[1]
  }
  .select { |file_name|
    File.extname(file_name) == '.rb'
  }.join(' ')

system("rubocop --force-exclusion #{changed_files}") unless changed_files.empty?

exit $CHILD_STATUS.to_s[-1].to_i