There used to be a put_line limit of 255 in Oracle, now the limit is 32k or so. There is, however, a limit of 400 in the dbms_output_get function in DBD/Oracle.pm:

    sub dbms_output_get {
        my $dbh = shift;
        my $sth = $dbh->prepare_cached("begin dbms_output.get_line(:l,
+ :s); end;")
                or return;
        my ($line, $status, @lines);
        # line can be greater that 255 (e.g. 7 byte date is expanded o
+n output)
        $sth->bind_param_inout(':l', \$line,  400, { ora_type => 1 });
        $sth->bind_param_inout(':s', \$status, 20, { ora_type => 1 });
        if (!wantarray) {
            $sth->execute or return undef;
            return $line if $status eq '0';
            return undef;
        }
        push @lines, $line while($sth->execute && $status eq '0');
        return @lines;
    }
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You could rewrite this function or write a similar function yourself and give yourself a higher limit.