ruby refactoring multiple unlesses

unless.rb

# before:

if command == 'move'
  unless options.destination
    puts "Error - 'move' requires a --destination"
    puts "\n#{optparse}"
  end
  unless File.exist?(options.destination)
    puts "Error - destination does not exist"
    puts "\n#{optparse}"
  end
  unless File.directory?(options.destination)
    puts "Error - destination is not a directory"
    puts "\n#{optparse}"
  end
  unless File.writeable?(options.destination)
    puts "Error - destination directory is not writeable"
    puts "\n#{optparse}"
  end
end

# after

if command == 'move'
  error = case
  when !options.destination
    "Error - 'move' requires a --destination"
  when !File.exist?(options.destination)
    "Error - destination does not exist"
  when !File.directory?(options.destination)
    "Error - destination is not a directory"
  when !File.writeable?(options.destination)
    "Error - destination directory is not writeable"
  end
  if error
    puts "#{error}\n#{optparse}"
    exit 1
  end
end