gistfile1.rbx

require 'csv'

codes = []

CSV.open("codes.csv", 'r') do |row|
# put the contents of the first column in each row in codes.csv,
# into the second column of each of codes
  codes[row[1].to_i] = row[0]
end

Dir.chdir 'export'
wd = Dir.getwd

Dir.glob('*') do |dirname|
  Dir.chdir(dirname)
  Dir.glob('*.png') do |filename|
    # strip out everything in the filename that isn't the number, 
    # and set the new integer value as number
    number = filename.gsub(/\D/, '').to_i
    code = codes[number]
    new_filename = "#{code}.png"
    puts "Renaming #{filename} to #{new_filename}."
    File.rename(filename, new_filename)
  end
  Dir.chdir(wd)
end