untar.rb

#!/usr/bin/env ruby -wKU

# Pure Ruby minimal .tar file un-archiver

class Untar
  def initialize(file, root_directory)
    @root = root_directory
    @f = file
    loop do
      name, size = read_header
      break if name.nil? or name.length == 0
      if name =~ /.*\/$/
        create_directory(name)
      else
        save_file(name, size)
      end
    end
  end
  
private
  def read_header
    name = @f.read(100).unpack('A*')[0]
    @f.seek(8*3, IO::SEEK_CUR)
    size = @f.read(12).unpack('A*')[0].oct
    @f.seek(512-100-8*3-12, IO::SEEK_CUR)
    [name, size]
  end

  def create_directory(name)
    fn = File.join(@root, name)
    p fn
    begin
      Dir.mkdir(fn)
    rescue 
    end
  end
  
  def save_file(name, size)
    fn = File.join(@root, name)
    p fn
    File.open(fn, 'w') {|f| f.write(@f.read(size)) }
#    @f.seek(size, IO::SEEK_CUR)
    m = size % 512
    if m != 0
      @f.seek(512-m, IO::SEEK_CUR)
    end
  end
end

if $0 == __FILE__
  tar = ARGV[0]
  dir = ARGV[1] || '/tmp'
  File.open(tar) do |f|
    Untar.new(f, dir)
  end
end