#! perl -slw
use strict;
use Time::HiRes qw[ time ];

my $string = 'X' x 1e6;
my $ref = \$string;
my $subRef = \substr $string, 0;

my $start;
my $x;

$start = time;
$x = substr $string, $_*50, 50 for 0 .. 2e4;
print time() - $start;

$start = time;
$x = substr $$ref, $_*50, 50 for 0 .. 2e4;
print time() - $start;

$start = time;
$x = substr $$subRef, $_*50, 50 for 0 .. 2e4;
print time() - $start;

__END__
c:\test>junk1
0.0107600688934326
0.0100328922271729
22.2601997852325

c:\test>\Perl510\bin\perl5.10.0.exe junk1.pl
0.00995421409606934
0.0109601020812988
21.9631989002228