Valor padrão para parâmetros não passados ​​no script SQLPlus

set termout on
set serveroutput on
set feedback off
set verify off

-- start
column 1 new_value 1 noprint
select '' "1" from dual where rownum = 0;
define param = &1 "default"
-- end

begin
    dbms_output.put_line ( 'Param 1 value is &param' );
end;
/

exit 0
/