Run a command when a file has been changed

runonupdate

#!/usr/bin/env ruby

# Usage:
#   runonupdate "spec spec/models/cat_spec.rb -O spec/spec.opts" app/models/cat.rb app/models/dog.rb
#
# This will run cat-specs whenever cat.rb or dog.rb is updated.

class RunOnUpdate
  attr_reader :cmd
  attr_reader :files

  def initialize(cmd, files)
    raise "No command is given." if cmd.empty?
    raise "No files given." if files.empty?
    @cmd, @files = cmd, files
    @files_times = check_times
  end

  def run
    loop do
      system(cmd) if files_changed?
      sleep 1
    end
  end

  protected

  def check_times
    files.inject({}) do |hash, filename|
      hash.merge(filename => File.stat(filename).mtime)
    end
  end

  def files_changed?
    new_times = check_times
    new_times.find do |filename, time|
      if time > @files_times[filename]
        puts "#{ filename } has been updated."
        @files_times = new_times
      end
    end
  end
end

cmd, *files = ARGV
RunOnUpdate.new(cmd, files).run