#!/usr/bin/perl -w
  use Benchmark;
  our $nonspace = ('abc' x 100) . "\n";
  our    $space = ('a c' x 100) . "\n";
  Benchmark::cmpthese(-1, {
       space => q{ my $copy =    $space; $copy =~ s/\s+\z// },
    nonspace => q{ my $copy = $nonspace; $copy =~ s/\s+\z// },
  });

               Rate    space nonspace
  space     32880/s       --     -89%
  nonspace 300755/s     815%       --