I'm learning DBI as well. This might be of some help to you.

I have a hunch it might be something with your $dsn variable and the connect() call.

From the article (by monk Dominus):

use DBI;

 my $dbh = DBI->connect('DBI:Oracle:payroll', 'username', 'password')
                or die "Couldn't connect to database: " . DBI->errstr;
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John J Reiser
newrisedesigns.com