Collapsing Folder Trees with Ruby

This is a quick script I whipped up to collapse some folder trees down to individual folders. The specific situation that arose was my formerly-itunes collection (it's currently organized Music\artist\album\songs.(mp3|m4a) and I'd really prefer it to be Music\artist\song.(mp3|m4a)).

#!/usr/bin/ruby

require 'optparse'
require 'pp'
require 'fileutils'

### parsing command line options via optparse, nothing to see here
options={}
optparse = OptionParser.new do|opts|
  opts.on('-h', '--help', 
          'Display this screen') do
    puts opts
    exit
  end
  opts.on('-t', '--type a,b,c', 
          Array, 'Specify filetypes to flatten out (defaults to mp3,m4a)') do|t|
    options[:types] = t
  end
end
optparse.parse!

### the setup (ideally, this would be in a `let` statement)
origin = Dir.pwd
if not options[:types]
  options[:types] = ["mp3", "m4a"]
end

### the actual work
ARGV.each do |target|
  FileUtils.cd("#{origin}/#{target}")
  options[:types].each{|ext| `find -iname '*.#{ext}' -exec mv {} ./ \\\;`}
  `find -depth -type d -empty -exec rmdir {} \\\;`
end
FileUtils.cd(origin)

Am I doing anything eye-stabbingly wrong? Is there a better way of handling any of the above?

Specifically, I suspect that I could replace the find calls with native Ruby methods, but I can't see how without complicating it significantly. I also suspect that there's a better way of writing FileUtils.cd("#{origin}/#{target}"), but a cursory reading of Dir doesn't reveal anything. Any tips?

#!/usr/bin/ruby

require 'optparse'
require 'pp'
require 'fileutils'

### parsing command line options via optparse
options={:types => ["mp3", "m4a"]}
optparse = OptionParser.new do|opts|
  opts.on('-h', '--help', 'Display this screen') do
    puts opts
    exit
  end
  opts.on('-t', '--type a,b,c', Array, 'Specify filetypes to flatten out (comma separated, defaults to mp3,m4a)') do|t|
    options[:types] = t
  end
end
optparse.parse!

### the actual work
ARGV.each do |target|
  FileUtils.cd(target) do
    options[:types].each{|ext| `find -iname '*.#{ext}' -exec mv {} ./ \\\;`} ##move all matched files into [target]
    `find -depth -type d -empty -exec rmdir {} \\\;` ##recursively delete all empty folders in [target]
  end
end

• options is now initialized beforehand rather than being checked after .parse!
• using the block option on FileUtils.cd
• removed useless final cd back
• tried the glob option, but it just errors without continuing if it hits a matched file in target (ie. one that needs to stay where it is). This seems to happen when I pass :force => TRUE too. The find call notes such files, but still flattens what it can. The glob route also doesn't seem to be case-insensitive.