Ruby script to determine the architecture of a PE file. A port of the Perl version from http://stackoverflow.com/questions/495244/how-can-i-test-a-windows-dll-to-determine-if-it-is-32bit-or-64bit, courtesey of Paul Dixon

command_prompt_win7_x64

D:\temp>ruby petype.rb petype.rb
Not an executable

D:\temp>ruby petype.rb C:\Windows\system32\notepad.exe
amd64

D:\temp>ruby petype.rb C:\Windows\system32\jscript9.dll
amd64

D:\temp>ruby petype.rb C:\Windows\syswow64\jscript9.dll
i386

petype.rb

#!/usr/bin/env ruby
#
# port from http://stackoverflow.com/questions/495244/how-can-i-test-a-windows-dll-to-determine-if-it-is-32bit-or-64bit,
# courtesey of Paul Dixon
#
# usage: petype.rb <exefile>

exe = ARGV.first

File.open(exe, 'rb') do |file|
  doshdr = file.read 68
  magic, skip, offset = doshdr.unpack 'a2a58l'
  unless magic == 'MZ'
    puts 'Not an executable'
    return
  end
  
  file.pos = offset
  pehdr = file.read 6
  sig, skip, arch = pehdr.unpack 'a2a2v'
  unless sig == 'PE'
    puts 'Not a PE file'
    return
  end
  archname = case arch
    when 0x014c; 'i386'
    when 0x0200; 'IA-64'
    when 0x8664; 'amd64'
    end
  puts archname
end

Did you know you can get the very same results if you reduce the DOS header maximum position from 68 to 64?
Yeah, I just stumbled upon the same issue and work on the same kind of script after checking out some perl and python scripts. XD
It's quite easy to achieve the same with Ruby even if you need to verify multiple files' architectures. Just in case anybody wants to know this, add:

filenames = Dir['.exe'].sort + Dir['.dll'].sort
filenames.each {|fn| arch_of(fn) }

I assumed you'd name your method arch_of(filename) so...