Depending on how far you want to go with using CPAN modules, it is fairly easy to redirect STDOUT to a scalar, see open:

my $var;

close STDOUT;
open(STDOUT, '>', \$var) || die "Unable to open STDOUT: $!";

print "Hollow World\n";
print "And another\n";

close (STDOUT);

my @data = split "\n", $var;

local $" = '|';
print STDERR "<@data>\n";
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Beware that this does work for STDOUT in child processes.