Oracle: using substitution variables in sqlplus

Get the value:

ACCEPT my_password CHAR PROMPT 'Password: ' HIDE
ACCEPT birthday DATE FORMAT 'dd/mm/yyyy' DEFAULT '01/01/1950' PROMPT 'Enter birthday date: '

Declaring the variable

DEFINE the_answer = 42

Undefine the variable

UNDEFINE the_answer

How to remember the result of the query

COLUMN the_date new_value the_rundate noprint;
SELECT TO_CHAR(SYSDATE, 'DDMMYYYY_HH24MI') the_date FROM dual;

SELECT '&the_rundate' FROM dual ;

Save the variables to the file

store SET myvars.txt CREATE
store SET myvars.txt REPLACE
store SET myvars.txt append

Assign several values to the variable

DEFINE my_list = " 'the Life', 'the Universe', 'and Everything'"

SELECT *
FROM Book
WHERE answer IN ( &my_list );