You could try somethig like

    my $dbh = DBI->connect('dbi:Oracle:',
                qq{$bu_username/$bu_passwd@DESCRIPTION=
                 (ADDRESS=(PROTOCOL=TCP)
                 (HOST= $bu_host)(PORT$bu_port))
                 (CONNECT_DATA=(SID=$bu_sid)))}, "",
                 {RaiseError=>1});
[download]

RaiseError is used in conjunction with eval {...} to catch the exception that is being thrown

perldoc DBI at the command prompt and a search for RaiseError
will get a fuller explanation
Hope this helps