mtail.rb

class Mtail
  def initialize(dirname)
    @dirname = dirname
    @filename = nil
    @input = nil
  end

  def tail
    Encoding.default_external = "ASCII-8BIT"
    Encoding.default_internal = "ASCII-8BIT"
    Dir.chdir(@dirname) do
      while true
        latest = find_latest_file
        if latest != @filename
          @input && @input.close
          @filename = latest
          @input = File.open(@filename)
        end
        while (ch = @input.getc)
          $stdout.putc(ch)
        end
        sleep(1)
      end
    end
    @input && @input.close
    @input = nil
  end

  def find_latest_file
    latest = nil
    Dir.foreach(".") do |filename|
      next if !File.file?(filename)
      if !latest
        latest = filename
        next
      end
      if File.mtime(latest) < File.mtime(filename)
        latest = filename
      end
    end
    return latest
  end
end

if $0 == __FILE__
  Mtail.new(ARGV[0]).tail
end