how to push parameters to DO statement from command line

PostgreSQL DO statement doesn't support parametrization. But with psql variables we are able to "inject" do statement safely and we can do it:

bash-4.1$ cat test.sh 
#!/bin/bash

echo "
set myvars.msgcount TO :'msgcount'; 
DO \$\$ 
BEGIN 
  FOR i IN 1..current_setting('myvars.msgcount')::int LOOP 
    RAISE NOTICE 'Hello';
  END LOOP; 
END \$\$" | psql postgres -v msgcount=$1

Usage:

bash-4.1$ ./test.sh 3
SET
Time: 0.386 ms
NOTICE:  Hello
NOTICE:  Hello
NOTICE:  Hello
DO
Time: 1.849 ms

most simply implementation of history table with hstore extension

Postgres has this nice extension (hstore) lot of years. It can be used for simulation some features of doc databases - or can be used for implementation of generic triggers for history table:

I have a table test and table history:

CREATE TABLE test(a int, b int, c int);

CREATE TABLE history(
  event_time timestamp(2),
  executed_by text, 
  origin_value hstore, 
  new_value hstore
);

CREATE OR REPLACE FUNCTION history_insert()
RETURNS TRIGGER AS $$
BEGIN
  INSERT INTO history(event_time, executed_by, new_value)
     VALUES(CURRENT_TIMESTAMP, SESSION_USER, hstore(NEW));
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION history_delete()
RETURNS TRIGGER AS $$
BEGIN
  INSERT INTO history(event_time, executed_by, origin_value)
     VALUES(CURRENT_TIMESTAMP, SESSION_USER, hstore(OLD));
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION history_update()
RETURNS TRIGGER AS $$
DECLARE
  hs_new hstore := hstore(NEW);
  hs_old hstore := hstore(OLD);
BEGIN
  INSERT INTO history(event_time, executed_by, origin_value, new_value)
     VALUES(CURRENT_TIMESTAMP, SESSION_USER, hs_old - hs_new, hs_new - hs_old);
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER test_history_insert AFTER INSERT ON test
  FOR EACH ROW EXECUTE PROCEDURE history_insert();

CREATE TRIGGER test_history_delete AFTER DELETE ON test
  FOR EACH ROW EXECUTE PROCEDURE history_delete();

CREATE TRIGGER test_history_update AFTER UPDATE ON test
  FOR EACH ROW EXECUTE PROCEDURE history_update();

Result:

INSERT INTO test VALUES(1000, 1001, 1002);
UPDATE test SET a = 10, c = 20;
DELETE FROM test;

postgres=# SELECT * FROM history ;
       event_time       | executed_by |           origin_value            |               new_value               
------------------------+-------------+-----------------------------------+---------------------------------------
 2015-01-15 20:59:05.52 | pavel       |                                   | "a"=>"1000", "b"=>"1001", "c"=>"1002"
 2015-01-15 20:59:05.6  | pavel       | "a"=>"1000", "c"=>"1002"          | "a"=>"10", "c"=>"20"
 2015-01-15 20:59:06.51 | pavel       | "a"=>"10", "b"=>"1001", "c"=>"20" | 
(3 rows)

Tested on PostgreSQL 9.2