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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