How do you use script variables in PostgreSQL?

set myvariable value

SELECT * FROM :myvariable.table1;

SELECT * FROM table1 WHERE :myvariable IS NULL;

SELECT * FROM table1 WHERE column1 = ':myvariable';

set myvariable 'value'

set quoted_myvariable ''' :myvariable '''

INSERT INTO :myvariable.table1 SELECT * FROM table2 WHERE column1 = :quoted_myvariable;