gistfile1.rb

libarch = case node[:kernel][:machine]
  when 'x86_64' then 'lib64'
  else 'lib'
end

template "/etc/nagios/nrpe.cfg" do
  source "nrpe.erb"
  mode "0644"
  owner "root"
  group "root"
  notifies :restart, resources(:service => "nrpe")
end

--- And the ERB
command[check_users]=/usr/<%= @libarch %>/nagios/plugins/check_users -w 5 -c 10
...