use Fcntl;
use SDBM_File;
tie(%h,'SDBM_File','foodbm',O_RDWR|O_CREAT,0640) || die $!;
$h{'a'}=1;
%h{'b'}=[2,3];
if (ref $h{'b'})
{
   print "it's a ref,ok\n";
   # perl will not print this!
}
else 
{
   print "it's not a ref,just $h{'b'}\n"; 
   # this is what perl printed! 
}
if (!defined $h{'b'}->[0])
{
  print "\$h{'b'}->[0] not defined!\n";
  # perl also print this!
}
untie(%h);