Watch files, in Ruby

julio.rb

require 'docopt'

require 'pathname'
require 'set'


USAGE = <<DOCOPT
Julio.

Usage:
  julio [--interval=<seconds>] <includes>...
  julio (-h | --help)
  julio (-v | --version)

Options:
  --interval=<seconds>  Interval between loops, in seconds [default: 1].
  -h --help             Show this screen.
  -v --version          Show version.
DOCOPT


def stat f
  stat = File::Stat.new(f)
  {
    inode: [ stat.ino, stat.dev_major, stat.dev_minor ],
    size: stat.size,
    mtime: stat.mtime
  }
rescue Errno::ENOENT
  nil
end

def was_appended? old_stat, new_stat
  return false if new_stat.nil?
  return new_stat[:size] > 0 if old_stat.nil?
  return new_stat[:size] > old_stat[:size]
end

def was_truncated? old_stat, new_stat
  return false if new_stat.nil?
  return false if old_stat.nil?
  return new_stat[:size] < old_stat[:size]
end

def was_replaced? old_stat, new_stat
  return false if new_stat.nil?
  return false if old_stat.nil?
  return new_stat[:inode] != old_stat[:inode]
end


def watch includes, known
  now_known = Set.new

  includes.each do |i|
    Dir.glob(i).each do |entry|
      now_known.add Pathname.new(entry).cleanpath
    end
  end

  created = now_known - known
  deleted = known - now_known
  return created, deleted, now_known
end


def report known, created, deleted, stats
  deleted.each do |d|
    puts 'report deleted:%s stat:%s' % [
      d.inspect, stats[d].inspect
    ]
  end

  created.each do |c|
    puts 'report created:%s stat:%s' % [
      c.inspect, stats[c].inspect
    ]
  end

  new_stats = {}

  known.each do |f|
    new_stats[f] = stat(f)

    if was_appended? stats[f], new_stats[f]
      puts 'report appended:%s stat:%s' % [
        f.inspect, new_stats[f].inspect
      ]
    elsif was_replaced? stats[f], new_stats[f]
      puts 'report replaced:%s stat:%s' % [
        f.inspect, new_stats[f].inspect
      ]
    elsif was_truncated? stats[f], new_stats[f]
      puts 'report truncated:%s stat:%s' % [
        f.inspect, new_stats[f].inspect
      ]
    end
  end

  return new_stats
end


def tail interval, includes
  known   = Set.new
  created = Set.new
  deleted = Set.new
  stats   = Hash.new

  loop do
    created, deleted, known = watch includes, known
    stats = report known, created, deleted, stats
    sleep interval
  end
end



begin
  args = Docopt::docopt(USAGE)
rescue Docopt::Exit => e
  puts e.message
end

if args.nil?
  # help mode, nop
elsif args['--version']
  puts 'VERSION'
elsif includes = args['<includes>']
  interval = args['--interval'].to_i
  if interval < 1
    puts 'WARNING: Invalid <interval> provided, falling back to default...'
    interval = 1
  end

  tail interval, includes
end