how to create duplicate role of a user in postgres

Try something like:

GRANT A TO B;

It will grant all right of role A to B.

For details read this chapter of the manual.

First understand that roles and users are the same thing. In fact there isn't a thing called a user really, it's just a ROLE with a LOGIN option.

Second roles can be granted to other roles.

Third priviledges on roles can be inherited.

So assuming you have created your user a like:

CREATE ROLE A LOGIN;
GRANT SELECT ON table1 TO a;
GRANT EXECUTE ON FUNCTION xxx TO a;

You should be able to create a second role that mirrors the first role like:

CREATE ROLE b LOGIN;
GRANT a TO b;

I had to write the pgpsql code to loop through the privileges of User A and grant it to User B. It was done without any problem.

create or replace function update_user_privileges() returns text as
$$
declare

       info record;
       str text;

begin
       /*Grant privileges to user B the same as with user A for a given table schema*/
      str:=''; 
      FOR info IN 
          select * from information_schema.table_privileges where table_schema='public' and grantee = 'A'   
      LOOP 
          /*append the tables' name, for which we are assigning privileges from user A to B*/
          str:= str  ||info.table_name || ',';

         /*this is the main statement to grant any privilege*/
         execute 'GRANT '|| info.privilege_type ||' on table public.'|| info.table_name || ' to B';

      END LOOP;

  return str;
end

$$ language 'plpgsql';

Usage: Copy/paste this code to crate this function and then do

select update_user_privileges();

**You have to adapt it for your table-schema and table-names. Hope it helps anyone

Here's a quick way to create grant statements for newuser, by copying all grants on db mydb to grantee myuser.

pg_dump mydb -s | egrep '^(GRANT|REVOKE).+TO "myuser"' | sed -E "s/\"myuser\"/\"newuser\"/g"

Note: The -s flag makes pg_dump execute quickly, because it's only dumping schema info.

Example output

GRANT SELECT,INSERT,UPDATE ON TABLE tabl1e TO "newuser";
GRANT SELECT,INSERT,DELETE,UPDATE ON TABLE table2 TO "newuser";
GRANT ALL ON PROCEDURE myprocedure(ids bigint[]) TO "newuser";

Simply run the output SQL grants or pipe them to psql and you're all set.