Spooling output in SQL

Generally we spool output like this

spool filename
select * from emp;
spool off;

But the following one also giving the same output

SELECT ' ALTER TABLE ' || TABLE_NAME || ' DROP CONSTRAINT ' || CONSTRAINT_NAME || ' ; '
FROM USER_CONSTRAINTS
WHERE R_CONSTRAINT_NAME IS NOT NULL
/
SPOOL CONS.SQL
/
SPOOL OFF
@CONS.SQL

Is it not compulsory to write semicolon at the end of the statement?
Could any one please explain the spooling process in second one?

SELECT ' ALTER TABLE ' || TABLE_NAME || ' DROP CONSTRAINT ' || CONSTRAINT_NAME || ' ; '
FROM USER_CONSTRAINTS
WHERE R_CONSTRAINT_NAME IS NOT NULL

sql>set heading off;
sql>spool cons.sql
sql>/
sql>spool off

ur select query outputs other querys and are stored in cons.sql then
u calling that cons.sql to drop the contraints
u must specify ; with out this u will get an error (ORA-00933)