PostgreSQL - is it possible to use a plpgsql function in a bash script?

Target : What i'm trying to achieve is to restore a partial backup of a database (only certain rows that satisfied certain conditions have been backed up).

Problem : Since between the partial-backup and the restore may pass some time, and certain records could be deleted, I need to perform an Upsert(Update if record exist, Insert if record doesn't exists). This operation in Mysql would have be done with REPLACE, but in PostgreSQL it doesn't exist. After some research I've found a good substitute of it(correct me if i'm wrong) in this function :

CREATE FUNCTION merge_db(key INT, data TEXT) RETURNS VOID AS
$$
BEGIN
    LOOP
        -- first try to update the key
        UPDATE db SET b = data WHERE a = key;
        IF found THEN
        RETURN;
        END IF;
        -- not there, so try to insert the key
        -- if someone else inserts the same key concurrently,
        -- we could get a unique-key failure
        BEGIN
            INSERT INTO db(a,b) VALUES (key, data);
            RETURN;
        EXCEPTION WHEN unique_violation THEN
            -- Do nothing, and loop to try the UPDATE again.
        END;
    END LOOP;
END;
$$
LANGUAGE plpgsql;

The problem with this is that I need to make dynamic the input parameters of the function, and also the UPDATE and the INSERT statements, in order to adapt it for every record and every table i'm going to upsert.

Question :

• is it possible to integrate plpgsql functions in bash scripts in order to makes them more dynamic?