Don't know which version of DBI you are using, but here is a snippet I'm using with DBI 1.19 that enables me to read and write LOBs.

sub ora_connect {
    my $user = shift;
    my $sid = shift;
    my ($login,$pass,$sid,$hostname) = ora_vars($user,$sid);
    my $dbh = DBI->connect("DBI:Oracle:", "$login\@$sid", $pass);
    die "Couldn't connect to Oracle: $!" unless $dbh;
    $dbh->{LongReadLen} = 66000;
    $dbh->{LongTruncOk} = 1;
    return $dbh;
}
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Oh, and ora_vars is a home grown subroutine that looks up passwords and sids based on who is running the script and what machine its on.

-Blake