update.rb

#!/usr/bin/env ruby

def update_git
  puts `git fetch` if Dir['.git'].any?
end

def update_svn
  puts `svn up` if Dir['.svn'].any?
end

def do_update
  update_git
  update_svn
  # update_hg
end

Dir['*'].select {|f| File.directory? f }.each do |dir|
  Dir.chdir(dir)
  puts "Updating #{dir}..."
  do_update
  Dir.chdir('..')
end