Get the list of all the files by using DBMS_BACKUP_RESTORE

DECLARE
   pattern VARCHAR2(1024) := '/u01/oracle/admin/SID/udump';
   ns VARCHAR2(1024);
BEGIN
   SYS.DBMS_BACKUP_RESTORE.searchFiles(pattern, ns);
   FOR each_file IN (SELECT FNAME_KRBMSFT AS name FROM X$KRBMSFT WHERE FNAME_KRBMSFT LIKE '%.trc') 
   LOOP
 DBMS_OUTPUT.PUT_LINE(each_file.name);
   END LOOP;
END;
/

Note: it only available in 10g
Reference: http://www.chrispoole.co.uk/tips/plsqltip2.htm