SELECT nspname
  FROM pg_namespace;

psql -f multigrant.sql

DO $do$
DECLARE
    sch text;
BEGIN
    FOR sch IN SELECT nspname FROM pg_namespace
    LOOP
        EXECUTE format($$ GRANT USAGE ON SCHEMA %I TO your_role $$, sch);
    END LOOP;
END;
$do$;

DO $do$
DECLARE
    sch text;
BEGIN
    FOR sch IN SELECT nspname FROM pg_namespace where nspname != 'pg_toast'
    and nspname != 'pg_temp_1' and nspname != 'pg_toast_temp_1'
    and nspname != 'pg_statistic' and nspname != 'pg_catalog'
    and nspname != 'information_schema'
    LOOP
        EXECUTE format($$ GRANT USAGE ON SCHEMA %I TO your_role $$, sch);
    EXECUTE format($$ GRANT USAGE ON SCHEMA %I to your_role $$, sch);
    EXECUTE format($$ GRANT SELECT ON ALL SEQUENCES IN SCHEMA %I TO your_role $$, sch);
    EXECUTE format($$ GRANT SELECT ON ALL TABLES IN SCHEMA %I TO backup_user $$, sch);

    EXECUTE format($$ ALTER DEFAULT PRIVILEGES IN SCHEMA %I GRANT SELECT ON TABLES TO your_role $$, sch);
    EXECUTE format($$ ALTER DEFAULT PRIVILEGES IN SCHEMA %I GRANT SELECT ON SEQUENCES TO your_role $$, sch);
    END LOOP;
END;
$do$;