mvps-update.rb

#!/usr/bin/env ruby
#
# Downloads a new version of the MVPS hosts file and merges it into the local
# hosts file.
#
# Only lines starting with `0.0.0.0` are merged; all other lines are skipped.
#
# All entries from the MVPS hosts file are put between markers. If the markers
# are already present in the hosts file, everything between them is replaced
# with the contents of the MVPS hosts file.

require 'net/http'

MVPS_BEGIN = '# [[ MVPS BEGIN ]]'
MVPS_END = '# [[ MVPS END ]]'

def load_local
  puts 'Loading /etc/hosts'
  IO.read("/etc/hosts")
end

def load_mvps
  puts 'Downloading MVPS hosts file'
  Net::HTTP.get(URI('http://winhelp2002.mvps.org/hosts.txt'))
end

def merge_hosts(local, mvps)
  puts 'Merging /etc/hosts with MVPS hosts file'
  result = []

  # Copy from local from start to `MVPS_BEGIN` (or EOF)
  result << local.lines.take_while { | line | !line.start_with? MVPS_BEGIN }
  result << "#{MVPS_BEGIN}\n"

  # Copy from MVPS if it starts with `0.0.0.0`
  mvps.lines.each { | line | result << line if line.start_with? '0.0.0.0' }

  # Copy from local from `MVPS_END` to EOF (if present)
  size = result.size
  result << local.lines.drop_while { | line | !line.start_with? MVPS_END }
  result << "#{MVPS_END}\n" if result.size == size

  result
end

def write_hosts(hosts)
  puts 'Writing new hosts file in /etc/hosts'
  IO.write('/etc/hosts', hosts.join)
end

def reload_dns
  puts 'Flushing DNS cache'
  system('killall -HUP mDNSResponder')
end

write_hosts(merge_hosts(load_local, load_mvps))
reload_dns