Ansible host reverse lookup script

ansible-lookup.rb

#!/usr/bin/env ruby

version_parts = RUBY_VERSION.split(".").map(&:to_i)
if version_parts[0] < 2 && version_parts[1] < 9
  abort "Ruby >= 1.9 required."
end

require "set"

if ARGV.size != 1
  puts <<EOF
Usage:

    $ ansible-lookup SEARCH_TERM

where SEARCH_TERM is partial string query that matches some hostname.
EOF
  exit 1
end

search_term = ARGV[0]
host_file = ENV["ANSIBLE_HOSTS"]
abort "No ANSIBLE_HOSTS set." if host_file.empty?

groups = Set.new

File.open(host_file).each do |line|
  if line =~ /^\[([^\]]+)\]/
    groups << $1.split(":")[0]
  end
end

# Dictionary of pid, output, status keyed by group.
results = {}

groups.each do |group|
  rerr, werr = IO.pipe
  rout, wout = IO.pipe
  results[group] = {
    :pid => Kernel.spawn("ansible", group, "--list-hosts", :err => werr, :out => wout),
    :rerr => rerr, :werr => werr,
    :rout => rout, :wout => wout,
  }
end

puts "Ansible groups matching '#{search_term}':"

results.each do |group, result|
  _, status = Process.wait2(result[:pid])
  result[:werr].close
  result[:wout].close
  if status != 0
    puts "Ansible error (exit status #{status}):"
    puts result[:rout].read
    puts result[:rerr].read
    exit 1
  end
  if result[:rout].readlines.any? { |line| line[search_term] }
    puts group
  end
  result[:rerr].close
  result[:rout].close
end

The groups a host is part of is available via the "group_names" host fact :

---
- name: test playbook2
  hosts: "{{cli_hosts}}"
  gather_facts: no
  tasks:
    - debug: var=group_names