How to create a stand alone plpgsql proc

Dear Sir：
　　In Oracle, I can create a procedure like following:

DECLARE
A NUMBER;
BEGIN
INSERT INTO DB1 VALUES(A);
END;
/
and I run it(a.sql) use: sqlplus user/passwd @a.sql

How I create a plpgsql that like the procedure above?
(no 'create function', 'create procedure' ..., just a procedure
that I can run?)
And how to run it?

Thank your
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