use strict;
use warnings;

require v5.8;

my $hello1 = dupe_and_back();
my $hello2 = dupe_and_back();

print $hello1, $hello2;

sub dupe_and_back {
    print "call to dupe_and_back\n";

    my $output;

    open my $old_stdout, '>&=', \*STDOUT;
    close STDOUT;
    # Use of uninitialized value in open at the following line
    open STDOUT, '>', \$output;

    print "Hello world\n";

    open STDOUT, '>&=', $old_stdout;

    return $output;
}
__END__
call to dupe_and_back
call to dupe_and_back
Use of uninitialized value in open at perlmonks.pl line 21.
Hello world
Hello world