Pretty strong words, partner ;-) I think what you mean is that to pull this off you must be able to represent the data in a sorted manner.

First off, sauoq was right on about IxHash.

Second, diotalevi says to use $DB_BTREE. An excellent suggestion, as long as you use a sensible key - maybe date/time stamp - and be aware of the possibility of duplicates. It will always be sorted - it's stored in a balanced tree. The key your script uses is $cnt, but I don't see it being initialized anywhere (probably not a sensible key ;). Every message is stuffed into the same slot, overwriting the previous message.

The most straightforward short-term solution for you IMO would be to use $DB_RECNO like so:

# tie your array to the file
tie @chat, 'DB_File', 'chat', O_CREAT | O_RDWR, 0644, $DB_RECNO;
# push the message info onto the array
push @chat, "Message number $_" for (1 ..20);
# print the last five messages
print join "\n", @chat[-5 .. -1];
__END__
output:
Message number 16
Message number 17
Message number 18
Message number 19
Message number 20
[download]

You'll be able to treat @chat like an ordinary array. As a bonus, you'll be able to view or modify the chat db file with any text editor.