regexp_matches where clause - PG 9.1

Hi guys,

i've got this column:

path_name character varying(255)
>

I store full S3 bucket path for the attachments of my application on it;
example:

/{s3bucket}/filesuser/client/27801123/attachment/4510/main
>
/{s3bucket}/filesuser/client/27801123/attachment/4510/file
>

I wanna do a select, where path_name has only 'main' and not anything else.

Maybe using regexp_matches but then how to put it into a where clause?

Thanks!
Patrick.