A little digging in Benchmark.pm shows that the values are returned as an array so you can:

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

my $str = 'The quick brown fox ' x 100;
my $t = timethis (1000, sub {testSub ($str)});

print "\n@$t\n";

sub testSub {
    my $str = shift;
    my @matches = $str =~ /(\b.(?!ox))/g;
}
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Prints:

timethis 1000:  3 wallclock secs ( 2.38 usr +  0.00 sys =  2.38 CPU) @
+ 421.05/s (n=1000)

3 2.375 0 0 0 1000
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