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

test.sh

#!/bin/bash

minute=$(( RANDOM % 60 ))
hour=$(( RANDOM % 8 + 9 ))

web=$(ruby -e "
puts [
'http://www.amazon.es',
'http://www.amazon.de'
].sample")

line="$minute $hour * * * open $web"

(crontab -l; echo "$line" ) | crontab -