Listing 2. combined-lookup.rb

#!/usr/bin/ruby

require 'net/http'
require 'rexml/document'

if ARGV.length == 0
  puts "#{$0}: You must enter at least one argument."
  exit
end

output = ""

# Set up our regular expressions
not_in_collection_re = /class="yourEntryWouldBeHereData"/ix
on_shelf_re = /CHECK\s+SHELF/ix
checked_out_re = /DUE /ix

# Iterate through each of our arguments
ARGV.each do |isbn|

  # Ignore non-ISBN arguments
  if not isbn.match(/[0-9xX]{10}/)
    output << "ISBN #{isbn} is invalid.\n"
    next
  end

  output << "ISBN: #{isbn}\n"

  # ------------------------------------------------------------
  # Amazon
  # ------------------------------------------------------------

  # Put together an Amazon parameter string
  amazon_params = {'Service' => 'AWSECommerceService',
    'Operation' => 'ItemLookup',
    'AWSAccessKeyId' => 'XXX',
    'ItemId' => isbn,
    'ResponseGroup' => 'Medium,OfferFull',
    'MerchantId' => 'All'}.map {|key,value| "#{key}=#{value}"}.join("&")

  # Ask Amazon what it knows about our ISBN
  amazon_response = Net::HTTP.get_response('webservices.amazon.com',
                                           '/onca/xml?' << amazon_params)

  xml = REXML::Document.new(amazon_response.body)

  # Get the lowest new, used, and collectible prices
  new_price =
xml.root.elements["Items/Item/OfferSummary/LowestNewPrice/FormattedPrice"]
  if new_price.nil?
    output << "\tNew: None available\n"
  else
    output << "\tNew: #{new_price.text}\n"
  end

  used_price =
xml.root.elements["Items/Item/OfferSummary/LowestUsedPrice/FormattedPrice"]
  if used_price.nil?
    output << "\tUsed: None available\n"
  else
    output << "\tUsed: #{used_price.text}\n"
  end

  collectible_price =
xml.root.elements["Items/Item/OfferSummary/LowestCollectiblePrice/FormattedPrice"]
  if collectible_price.nil?
    output << "\tCollectible: None available\n"
  else
    output << "\tCollectible: #{collectible_price.text}\n"
  end

  # ------------------------------------------------------------
  # Library
  # ------------------------------------------------------------

  # Ask the library what it knows about our ISBN
  library_response = Net::HTTP.get_response('catalog.skokie.lib.il.us',
                                    "/search~S4/i?SEARCH=#{isbn}")

  # Check our regular expressions against the HTML response
  if not_in_collection_re.match(library_response.body)
    output << "\tLibrary: Not in the Skokie collection.\n"
  elsif checked_out_re.match(library_response.body)
    output << "\tLibrary: Checked out.\n"
  elsif on_shelf_re.match(library_response.body)
    output << "\tLibrary: On the shelf.\n"
  else
    output << "\tLibrary: Unparseable response\n"
  end
end

# Show everyone what we've learned
puts output