How To make program that scan all external link from google engine?

I want to a program on php that scan all link of website and downloadable file link related to my keyword. I type window 8 iso then it should return all links of website that have window 8 ISO or iso file link . if some file available on torrent then no problem.

I will setup a schedule in my php code then every time it will search self and return result then it will save on my database. i can use laravel framework for this. but i have no idea ,how to scan external link form search engine?

via Chebli Mohamed