Simplest functional FLAC to MP3 converter script you can make

flac2mp3.rb

#!/usr/bin/env ruby
# http://gist.github.com/gists/124242
# Deps: brew install flac lame

filename = ARGV[0]
abort "Usage: flac2mp3 FLACFILE" if filename.nil?

map = {"TITLE" => "--tt", "ARTIST" => "--ta", "ALBUM" => "--tl", "TRACKNUMBER" => "--tn", "GENRE" => "--tg", "DATE" => "--ty"}
args = ""

`metaflac --export-tags-to=- "#{filename}"`.each_line do |line|
  key, value = line.strip.split('=', 2)
  key.upcase!
  args << %Q{#{map[key]} "#{value.gsub('"', '\"')}" } if map[key]
end

basename = File.basename(filename, File.extname(filename))

puts "Encoding #{basename}.mp3"
exec %Q[flac -sdc "#{filename}" | lame -V2 #{args} - "#{basename}.mp3"]