subject ack utility

I don't sure if it possible but I must to ask the following question
Because I have a big problem -

I use the ack utility to find string in very very very large files

The problem is when ack find the string in the file , but ack continue to search the same string until end of the file

my question is if it possible to stop search in the file when the first string was found ?

My problem is that ack take allot of time because the biggest files

any way my target is only to find the first match string and get out immediately from the file to other files

can some on have creative idea how to use ack as I explained ?

```
  ./ack -a some_string  /var 

```