sqlplus

SET NEWPAGE 0
SET SPACE 0
SET LINESIZE 80
SET PAGESIZE 0
SET ECHO OFF
SET FEEDBACK OFF
SET VERIFY OFF
SET HEADING OFF
SET MARKUP HTML OFF SPOOL OFF

SELECT DISTINCT OWNER FROM DBA_OBJECTS ORDER BY OWNER;

SELECT USERNAME FROM ALL_USERS ORDER BY USERNAME;

SELECT USERNAME FROM DBA_USERS ORDER BY USERNAME;