Declare variable from other variable

Hi

PostgreSQL 12.1

How can I declare another variable from another variable.
Basically from oracle, I can just:

> var1 := 'asda'||var2;

In postgres, I have the following example, I would like to use variable j
to add number of months there.

" interval 'j month')::date; "

DO $$
> DECLARE
> v_var integer := 1;
> v_from_date date;
> BEGIN
> for j in 0..v_var LOOP
> v_from_date := (date_trunc('month',current_date) + interval 'j
> month')::date;
> RAISE NOTICE '%', v_from_date;
> END LOOP;
> END;
> $$ LANGUAGE plpgsql;

> ERROR: invalid input syntax for type interval: "j month"
> LINE 1: ...LECT (date_trunc('month',current_date) + interval 'j month')...

Raul