set define [SQL*Plus]

set define [SQL*Plus]
set define on
set define off
set define x
set define x
set define x specifies the prefix-character for substitution variables. The default is the ampersand (&).
set define +

select * from dba_objects
where object_name like '%+object_name%';

set define on

Turns on substitution variables.
set define on

select '&hello' from dual;
If define is set to on and SQL*Plus finds the current substituion prefix, it asks for a string to be entered. In the following example, I entered: this string was entered
Enter value for hello: this string was entered
old 1: select '&hello' from dual
new 1: select 'this string was entered' from dual

'THISSTRINGWASENTERED'
-----------------------
this string was entered
It might be annoying to see the following lines printed by SQL*Plus:
old 1: select '&hello' from dual
new 1: select 'this string was entered' from dual
This behavior can be turned off by setting verify off.
set define off
Turns off substitution variables.
set define off

select '&hello' from dual;
'&HELL
------
&hello