How can we implement search a keyword in using selected webs

I want to know How to implement following tech stuff. And I want to know any existing api / plugin/ ready to use logic is available for this.

I want to design custom search engine which can search to specific websites.

and we can add/edit/delete websites from search results.

Like In a google if we want to search a keyword from 5 diff sites

"best ecommerce" site:www.A.com OR site:www.B.com OR site:www.C.com OR site:www.D.com OR site:www.E.com

So we get result from this sites only.

So Please letme know is there any plugin available in wordpress, .net, etc