package MyDBM;

require SDBM_File;
require Tie::Hash;
@ISA = qw( Tie::Hash );

sub TIEHASH {
    my $type = shift;
    my $ref  = SDBM_File->new(@_);
    return bless {dbm => $ref}, $type;
}
sub FETCH {
    my $self = shift;
    my $ref  = $self->{dbm};
    $ref->FETCH(@_);
}
sub STORE {
    my $self = shift;
    if (defined $_[0]){
        my $ref = $self->{dbm};
        $ref->STORE(@_);
    } else {
        die "Cannot STORE an undefined key in MyDBM\n";
    }
}

package main;
use Fcntl qw( O_RDWR O_CREAT );

tie %foo, "MyDBM", "sdbmfile1", O_RDWR|O_CREAT, 0640;
$foo{Fred} = 123;
print "foo-Fred = $foo{Fred}\n";

tie %bar, "MyDBM", "sdbmfile2", O_RDWR|O_CREAT, 0640;
$bar{Barney} = 456;
print "bar-Barney = $bar{Barney}\n";