catalog_yaml.rb

require 'puppet/application/face_base'
require 'puppet/face'

class Puppet::Application::CatalogYaml < Puppet::Application::FaceBase
end

catalog_yaml.rb

require 'puppet/face'

Puppet::Face.define(:catalog_yaml, '0.0.1') do
  action :compare do
    when_invoked do |*args|
      # actions (e.g. filepath = args[0])
      node_list = args[0]
      Puppet.info "Using node list file: #{node_list}"
    end
  end
end

Output

% puppet catalog_yaml
Unable to find application 'catalog_yaml'.

% puppet faces
status:
	Terminuses: local, rest
	Actions: destroy, find, info, save, search
facts:
	Terminuses: active_record, couch, facter, inventory_active_record, memory, rest, yaml
	Actions: destroy, find, info, save, search, upload
resource:
	Terminuses: ral, rest
	Actions: destroy, find, info, save, search
file:
	Terminuses: 
	Actions: destroy, find, info, save, search
catalog_yaml:
	Terminuses: 
	Actions: compare
parser:
	Terminuses: 
	Actions: validate
certificate_revocation_list:
	Terminuses: ca, file, rest
	Actions: destroy, find, info, save, search
certificate:
	Terminuses: ca, file, rest
	Actions: destroy, destroy, find, find, generate, info, info, list, save, save, search, search, sign
report:
	Terminuses: processor, rest, yaml
	Actions: destroy, find, info, save, search, submit
node:
	Terminuses: active_record, exec, ldap, memory, plain, rest, yaml
	Actions: destroy, find, info, save, search
help:
	Terminuses: 
	Actions: help
certificate_request:
	Terminuses: ca, file, rest
	Actions: destroy, find, info, save, search
catalog:
	Terminuses: active_record, compiler, queue, rest, yaml
	Actions: apply, destroy, download, find, info, save, search, select
resource_type:
	Terminuses: parser, rest
	Actions: destroy, find, info, save, search
key:
	Terminuses: ca, file
	Actions: destroy, find, info, save, search
configurer:
	Terminuses: 
	Actions: synchronize
config:
	Terminuses: 
	Actions: print