n.rb

#!/usr/bin/env ruby

require 'rubygems'
require 'nokogiri'

class MyDoc < Nokogiri::XML::SAX::Document

  def start_element(name, attrs)
    @count ||= 0
    @count +=1 if name == "item"
  end

  def end_document
    puts "found #{@count} items"
  end
end

cve = "allitems.xml"
xml = Nokogiri::XML::SAX::Parser.new(MyDoc.new)
xml.parse_file(cve)