and here is the dns resolution library w/ examples + license

MIT-LICENSE

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+Copyright (c) 2008 Ryan Allen, FlashDen Pty Ltd
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

dns.rb

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+#
+# automate using dig to check our DNS migration, coz liek, i am so seriously
+# sick of doing this manually :)
+#
+# author: ryan allen (ryan@eden.cc)
+#
+# you can use this syntax to check against your local dns resolution:
+# 
+# DNS.verify('flashden.net').resolves_to('72.32.2.225')
+# DNS.verify('www.flashden.net').is_aliased_to('flashden.net')
+# DNS.verify('blog.flashden.net').resolves_to('64.13.250.227')
+#
+# see example.rb for some real world usage.
+#
+module DNS
+
+  def self.delay=(seconds)
+    Verifier.delay = seconds
+  end
+
+  def self.verify(domain)
+    Verifier.new(domain)
+  end
+
+  class Verifier
+
+    @@delay = nil
+
+    def self.delay=(seconds)
+      @@delay = seconds
+    end
+
+    def initialize(domain)
+      @server = nil
+      @domain = domain
+      yield self if block_given?
+      self
+    end
+
+    def with_server(server)
+      @server = server
+      yield self if block_given?
+      self
+    end
+
+    def resolves_to(ip)
+      check! 'A', ip
+    end
+
+    def is_aliased_to(domain)
+      check! 'CNAME', domain
+    end
+
+    def maps_mail_to(domain, args = {})
+      check! 'MX', domain, args
+    end
+
+    # or it.answers_to ??
+    def has_authorative_nameserver_of(domain)
+      check! 'NS', domain
+    end
+
+  private
+
+    def check!(query, against, args = {})
+      if ['A', 'CNAME', 'NS'].include?(query)
+        pattern = /#{@domain}\.\s+\d+\s+IN\s+#{query}\s+#{against}/
+      elsif query == 'MX'
+        pattern = /#{@domain}\.\s+\d+\s+IN\s+MX\s+#{args[:priority]}\s+#{against}/
+      else
+        raise "Unsupported query (#{query.inspect}): only A, CNAME and MX."
+      end      
+      send(result!(query) =~ pattern ? :pass! : :fail!, query, against, args)
+    end
+
+    def result!(query)
+      @last_dig_command = if @server
+        "dig @#{@server} #{@domain} #{query}"
+      else
+        "dig #{@domain} #{query}"
+      end
+      sleep(@@delay) if @@delay
+      @last_dig_output = `#{@last_dig_command}`
+    end
+
+    def pass!(*args)      
+      report! 'PASS', *args
+    end
+
+    def fail!(*args)
+      report! 'FAIL', *args
+      puts @last_dig_command
+      puts @last_dig_output
+    end
+
+    def report!(result, query, against, args = {})
+      puts "#{result}: #{@domain} #{query} #{against} #{"@#{@server}" if @server} #{args.inspect if args.any?}"
+    end
+
+  end
+
+end

example.rb

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+#
+# this will print results to $stdout, so to see it working, run this file.
+#
+require 'dns'
+
+# the nameservers we want to check against
+@local_dns = [nil]
+@slicehost_dns = %w(ns1.slicehost.net ns2.slicehost.net)
+
+# 1 second between dig requests so nameservers don't block us (this default to 
+# no delay, and it's super fast, good for local queries)
+DNS.delay = 1
+
+(@local_dns + @slicehost_dns).each do |server|
+
+  DNS.verify('yeahnah.org').with_server(server) do |it|
+    # checks A records
+    it.resolves_to('208.78.102.114')
+    # checks MX records
+    it.maps_mail_to('ASPMX.L.GOOGLE.COM', :priority => 10)
+    it.maps_mail_to('ALT1.ASPMX.L.GOOGLE.COM', :priority => 20)
+    it.maps_mail_to('ALT2.ASPMX.L.GOOGLE.COM', :priority => 30)
+  end
+
+  DNS.verify('www.yeahnah.org').with_server(server) do |it|
+    # checks CNAME records
+    it.is_aliased_to('yeahnah.org')
+  end
+
+  DNS.verify('tumble.yeahnah.org').with_server(server) do |it|
+    it.resolves_to('72.32.231.8') # tumblr :)
+  end
+
+end
+
+# shorthand that checks against your local dns
+DNS.verify('yeahnah.org').resolves_to('208.78.102.114')
+DNS.verify('tumble.yeahnah.org').resolves_to('72.32.231.8')
+
+# oh, and check authorative ns :)
+DNS.verify('yeahnah.org').has_authorative_nameserver_of('ns1.slicehost.net')
+DNS.verify('yeahnah.org').has_authorative_nameserver_of('ns2.slicehost.net')
+
+# and FYI this is the output of the script, will display dig output on failures
+# PASS: yeahnah.org A 208.78.102.114  
+# PASS: yeahnah.org MX ASPMX.L.GOOGLE.COM  {:priority=>10}
+# PASS: yeahnah.org MX ALT1.ASPMX.L.GOOGLE.COM  {:priority=>20}
+# PASS: yeahnah.org MX ALT2.ASPMX.L.GOOGLE.COM  {:priority=>30}
+# PASS: www.yeahnah.org CNAME yeahnah.org  
+# PASS: tumble.yeahnah.org A 72.32.231.8  
+# PASS: yeahnah.org A 208.78.102.114 @ns1.slicehost.net 
+# PASS: yeahnah.org MX ASPMX.L.GOOGLE.COM @ns1.slicehost.net {:priority=>10}
+# PASS: yeahnah.org MX ALT1.ASPMX.L.GOOGLE.COM @ns1.slicehost.net {:priority=>20}
+# PASS: yeahnah.org MX ALT2.ASPMX.L.GOOGLE.COM @ns1.slicehost.net {:priority=>30}
+# PASS: www.yeahnah.org CNAME yeahnah.org @ns1.slicehost.net 
+# PASS: tumble.yeahnah.org A 72.32.231.8 @ns1.slicehost.net 
+# PASS: yeahnah.org A 208.78.102.114 @ns2.slicehost.net 
+# PASS: yeahnah.org MX ASPMX.L.GOOGLE.COM @ns2.slicehost.net {:priority=>10}
+# PASS: yeahnah.org MX ALT1.ASPMX.L.GOOGLE.COM @ns2.slicehost.net {:priority=>20}
+# PASS: yeahnah.org MX ALT2.ASPMX.L.GOOGLE.COM @ns2.slicehost.net {:priority=>30}
+# PASS: www.yeahnah.org CNAME yeahnah.org @ns2.slicehost.net 
+# PASS: tumble.yeahnah.org A 72.32.231.8 @ns2.slicehost.net 
+# PASS: yeahnah.org A 208.78.102.114  
+# PASS: tumble.yeahnah.org A 72.32.231.8  
+# PASS: yeahnah.org NS ns1.slicehost.net
+# PASS: yeahnah.org NS ns2.slicehost.net