It is correct, and + is because of the webpage syntax.

$DB_BTREE->{'flags'} = R_DUP ;
$x = tie %dictf, "DB_File", "f.db", O_RDWR|O_CREAT, 0666, $DB_BTREE or
+ die "Cannot open file f.db: $!\n";
 
my $number = keys %dictf;
print "$number\n";

my $number = keys %dictf;
print "$number\n";

$key = $value = 0 ;
for ($status = $x->seq($key, $value, R_FIRST) ;
$status == 0 ;
$status = $x->seq($key, $value, R_NEXT) )
{ print "$key -> $value\n"; }
[download]

However, I made it work with :

$DB_BTREE->{'flags'} = R_DUP ;
my $file="f.db";
my $x = tie %h, "DB_File", $file, O_RDWR|O_CREAT, 0666, $DB_BTREE or d
+ie "Cannot open file $file: $!\n";
[download]