do something like this: (Assume you have a hash that has two pairs: "a" => 1, and "b" => 2. You can have a much much more complex structure than this sample)
use Fcntl; #so perl understand what is O_RDONLY
use MLDBM;
tie %hash, 'MLDBM', 'file', O_RDONLY, 0666;
print $hash{"a"};
print $hash{"b"};