How to create a stand alone plpgsql proc

Dear Sir:
In Oracle, I can create a stand-alone procedure like that:
DECLARE
A NUMBER;
B NUMBER;
BEGIN
A := 1;
B := 2;
INSERT INTO TABLE1 VALUES (A, B);
END;
/
Then I run it(a.sql) with the command in shell:
sqlplus username/passwd @a.sql
In postgresql, how do I write similar plpgsql procedure without
using "CREATE FUNCTION" or "CREATE PROCEDURE" ..., and how to
execute it?
Thank you
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