Very similar to Marc, only difference I would make would be to spool to a parameter like so:
WHENEVER SQLERROR EXIT 1
SET LINES 32000
SET TERMOUT OFF ECHO OFF NEWP 0 SPA 0 PAGES 0 FEED OFF HEAD OFF TRIMS ON TAB OFF
SET SERVEROUTPUT ON
spool &1
-- Code
spool off
exit
And then to call the SQLPLUS as
sqlplus -s username/password@sid @tmp.sql /tmp/output.txt