useradd_by_remote_host.rb

#!/usr/bin/env ruby
require 'tempfile'

def main
  user = ARGV[0]
  remote = ARGV[1]
  if user_existed?(user)
    STDERR.puts "already exist user #{user}. do nothing."
    exit 1
  end

  pub_key = retrieve_pub_key(user, remote)
  if pub_key.to_s.chomp.empty?
    STDERR.puts "could not retrieve #{user}'s authorized_keys on #{remote}."
    exit 1
  end

  create_user_and_set_pub_key(user, pub_key)
end

def retrieve_pub_key(user, remote)
  pub_key = %x(ssh #{remote} sudo cat ~#{user}/.ssh/authorized_keys)
  $? == 0 ? pub_key : nil
end

def user_existed?(user)
  %x(id #{user})
  $? == 0
end

def create_user_and_set_pub_key(user, pub_key)
  path = create_pub_key_temp_file(pub_key)
  %x(sudo /usr/sbin/useradd #{user})
  %x(sudo mkdir ~#{user}/.ssh)
  %x(sudo chmod 700 ~#{user}/.ssh)
  %x(sudo cp #{path} ~#{user}/.ssh/authorized_keys)
  %x(sudo chmod 600 ~#{user}/.ssh/authorized_keys)
  %x(sudo chown -R #{user}:mmj ~#{user}/.ssh)
end

def create_pub_key_temp_file(pub_key)
  tempfile = Tempfile.new('pubkey')
  tempfile.write pub_key
  tempfile.close
  tempfile.path
end

if $0 == __FILE__
  main
end