Listing 1. skokie-lookup.rb

#!/usr/bin/ruby

require 'net/http'

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 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

  # Ask the library what it knows about our ISBN
  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(response.body)
    output << "ISBN #{isbn} is not in the Skokie collection.\n"
  elsif on_shelf_re.match(response.body)
    output << "ISBN #{isbn} is on the shelf.\n"
  elsif checked_out_re.match(response.body)
    output << "ISBN #{isbn} is currently checked out.\n"
  else
    output << "ISBN #{isbn} response: Unparseable!\n"
  end
end

# Show everyone what we've learned
puts output