We were lazy and wrote a simple PostgreSQL monitoring check in shell instead of using some proper language. The code looked about this:

out=$(psql -tAc "SELECT some_stuff, t > now() - '1 day'::interval FROM some_table" some_db 2>&1)
case $out in
    *t) echo "OK: $out" ;;
    *) echo "NOT OK: $out" ;;

If the string ends with 't', all is well, if it ends with 'f' or someting else, something is wrong.

Unfortunately, this didn't go that well:

OK: psql: FATAL: database "some_db" does not exist