rubyでその場しのぎ用スクリプトのテンプレ

#!/usr/bin/env ruby
# yyyy-mm-dd

require 'rubygems'
require "pp"

#--------------------------------

def usage
  puts "Usage: ruby test.rb [param ...]"
  puts "  supported: xxxx"
end

def exe(param)
  test(param)
end

def test(param)
  puts param
end

#------------ Main -------------
if ARGV.empty?
  usage
  exit
end
param = ARGV.shift
puts "start [#{param}]"
begin
  exe(param)
rescue => ex
  pp ex
  pp param
ensure
end

ensureってなんだっけか?