Ruby style guide git pre-commit hook using Rubocop as the style guide checker. Only runs on staged ruby files that have been added and/or modified.

rubocop_pre_commit_hook

#!/usr/bin/env ruby

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 #{changed_files}") unless changed_files.empty?

exit $CHILD_STATUS.to_s[-1].to_i

I'm using this to run against staged files only: https://gist.github.com/drmartell/a45a0d277921943aab91c6b593956de4