You've got to find what you love.

DECLARE
 BDumpDir  VARCHAR2(200);
 SID       VARCHAR2(16);
 ObjectExists EXCEPTION;
 PRAGMA EXCEPTION_INIT(ObjectExists,-955);
BEGIN
 -- get the bdump dir
 SELECT value
 INTO BDumpDir
 FROM v$parameter
 WHERE name='background_dump_dest';

 -- create the directory for the bdump dir
 EXECUTE IMMEDIATE 'CREATE OR REPLACE DIRECTORY bdump_dir AS '''||
   BDumpDir||'''';

 -- grant the necessary privileges
 EXECUTE IMMEDIATE 'GRANT READ ON DIRECTORY bdump_dir TO system';

 -- get the SID
 SELECT instance_name INTO SID FROM v$instance;

 -- create the external table
 EXECUTE IMMEDIATE 'CREATE TABLE system.ALERT_LOG_EXTERNAL
   (TEXT VARCHAR2(255)
   ) ORGANIZATION EXTERNAL
   (TYPE ORACLE_LOADER
    DEFAULT DIRECTORY BDUMP_DIR
    ACCESS PARAMETERS
    (records delimited by newline
     nobadfile
     nologfile
    )
    LOCATION (''alert_'||SID||'.log'')
   )
   REJECT LIMIT UNLIMITED'
 ;
-- ignore ORA-955 errors (object already exists)
EXCEPTION WHEN ObjectExists THEN NULL;
END;
/

/** 사용 **/
SELECT * FROM system.alert_log_external ;