json_pack.rb

#!/usr/bin/ruby

require 'json'

files = []
offset = 0
ARGV.map{|fn|
  fsz = File.size(fn)
  files << {'filename'=> fn, 'offset'=> offset, 'length'=> fsz}
  offset += fsz
}
puts files.to_json
ARGV.each{|fn|
  File.open(fn,'rb'){|f|
    STDOUT.write f.read(4096) until f.eof?
  }
}