Источник:

if cmp a b &> /dev/null  # Suppress output.
then echo "Files a and b are identical."
else echo "Files a and b differ."
fi

Код скрипта:

if cmp ${conf} ${conf}.old &> /dev/null
    then  exit; fi
...

выходит по exit

Ручное сравнение:

# diff parked_domains.list parked_domains.list.old
2a3
> test.ru       /subinfo/demo2
\ No newline at end of file