A simple script to interleave several files, which may be very large

interleave.rb

#!/usr/bin/env ruby

filenames = ARGV
usage = "USAGE: interleave.rb <filename> ..."

unless filenames.length > 0
  STDERR.write(usage + "\n")
  exit(1)
end

// Open streams to all files
files = filenames.map do |filename| 
  fd = IO.sysopen(filename, "r") 
  IO.new(fd, "r")
end

// Emit the files line by line, interleaved.
while(files.any? { |file| !file.eof? }) do
  files.each do |file|
    next if file.eof?

    line = file.gets
    STDOUT.write(line);
  end
end

// Close the handles.
files.each { |file| file.close }