tail.rb

begin
  descriptors = []
  files = []
  ARGV.each do |filename|
    io = IO.sysopen(filename, 'r')
    descriptors << io

    i = IO.open(io)
    i.seek(0, IO::SEEK_END) # TODO: go back a few lines so we have context
    files << i
  end

  loop do
    while files.map(&:eof).inject(false) {|result, it| result ||= it; result }
      sleep 0.2
    end
    files.each do |file|
      until file.eof?
        $stdout.print file.gets
      end
      $stdout.flush
    end
  end

ensure
  descriptors.each do |desc|
    begin
      IO.open(desc) { |fd| fd.close }
    rescue Errno::EBADF
      $stderr.puts "Errno::EBADF: Trying to close bad file descriptor"
    end
  end
end