http://burgestrand.se/ruby/2011/03/10/parallell-remote-execution-with-net-ssh-in-ruby.html

instructions.txt

superman 127.0.0.1 Kim whoami
database 127.0.0.1 Kim sleep 1 && echo "Database says Hello!"
localhost 127.0.0.1 Kim date

output.txt

[superman]
  Kim
[database]
  Database says Hello!
[localhost]
  Thu Mar 10 23:56:15 CET 2011

script.rb

require 'net/ssh'

ips = $stdin.readlines.map do |line|
  label, host, user, command = line.split(' ', 4)
  [label, Thread.new do
    output = nil
    Net::SSH.start(host, user) { |ssh| output = ssh.exec!(command) }
    output.to_s
  end, line]
end

ips.each do |(label, thread, _)|
  puts "[#{label}]"
  thread.value.each_line.map do |line|
    puts "  " + line
  end
end