fqdn-benchmark.rb

#!/usr/bin/env ruby                                                                                     
                                                                                                        
require 'benchmark'                                                                                     
require 'socket'                                                                                        
                                                                                                        
i = 10_000                                                                                              
                                                                                                        
Benchmark.bm(9) do |x|                                                                                  
  x.report("shell out") do                                                                              
    i.times { `hostname -f`.strip }                                                                     
  end                                                                                                   
  x.report("socket") do                                                                                 
    i.times { Socket.gethostbyname(Socket.gethostname).first }                                          
  end                                                                                                   
end  

gistfile1.txt

 ~  ➔ ruby fqdn-benchmark.rb
                user     system      total        real
shell out   1.280000  11.500000  38.610000 ( 49.029772)
socket      1.330000   2.220000   3.550000 ( 22.050667)