generational backup using rsync

timemachine.rb

#! /usr/bin/ruby

if ARGV.empty?
  puts "Usage: #{$0} [rsync-options] <src-host:src-dir>"
  exit 0
end

generations = Dir.glob("*").grep(/^[0-9]{8}-[0-9]{6}$/).sort

argv = ARGV
argv.push Time.new.strftime('%Y%m%d-%H%M%S') # destination directory
argv.prepend '--chmod=a-w' #  prohibit write, as one file may represent multiple generations of backups
argv.prepend '--link-dest', "../#{generations.last}" unless generations.empty?

exec 'rsync', *argv