gistfile1.rb

#!/usr/bin/env ruby

if ARGV.size < 2
  $stderr.puts 'usage: monitor <path> <command> [arg1 arg2 ...]'
  exit 100
end

PATH = ARGV[0]
COMMAND = ARGV[1]
ARGS = ARGV[2..-1]

INDEX = {}
def scan(path)
  if File.exists? path
    if File.directory? path
      children = Dir.entries path
      children.delete '.'
      children.delete '..'
      results = children.map { |f| scan "#{path}/#{f}" }
      results.any? { |r| r }
    else
      if INDEX[path] != (File.mtime path)
        INDEX[path] = File.mtime path
        true
      else
        false
      end
    end
  else
    false
  end
end

puts "Monitoring path '#{PATH}' for changes..."
while true
  if scan PATH
    system COMMAND, *ARGS
    
    puts
    puts "Monitoring path '#{PATH}' for changes..."
  end
  
  sleep 3
end