I have created a WildCard managed path named “departments”, and then under this managed path I have created five “Publishing site- enterprise Wiki” site collections. 
Now by default each of the enterprise site collection will have a Search functionality out of the box to search all the Pages content, attachments , etc.

But what if I want to allow users to either search specific Site collection or to search all the site collection under specific managed path.?
Any advice on this?
BR