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set escape [SQL*Plus]

set escape c
Sets the escape characters (used for defined variables to c. c must be one single character. The default is the ampersand (&).
set escape *
set verify off

define somevar="bla bla bla"

select '&somevar' a, 
       '*somevar' b
from dual;
A           B
----------- -------
bla bla bla somevar