use warnings;
use strict;
use Benchmark qw(cmpthese);

my $target = 'This is a string used to test the time required for a greedy match compared to a non-greedy match.';
my $greedy = qr/(\ba\b.*\bstring\b)/;
my $non = qr/(\ba\b.*?\bstring\b)/;

my ($matchG) = $target =~ $greedy;
my ($matchN) = $target =~ $non;

die "Matches generate different results\n" if $matchG ne $matchN;

cmpthese
  (
  -1,
    {
    'Greedy' => sub {$target =~ $greedy;},
    'Non' => sub {$target =~ $non;}
    }
  );

Prints:

           Rate Greedy    Non
Greedy 162689/s     --   -64%
Non    456847/s   181%     --