The Search Preferences in Safari for Mac contains a list of search engines, such as Bing, DuckDuckGo, and Google, from which you can pick one as your default search engine. But what if you want to use multiple search engines in Safari? It turns out that you can! The same preference pane also contains a little known feature, Enable Quick Website Search.
According to the Safari User Guide, Enable Quick Website Search will "Record information about your searches within a website to expedite later searches on that site. You can then search within that website by entering the name of the site, followed by your search term, in the Smart Search field." When you click the "Manage Websites…" button, you see a list of sites. You can remove any sites you want from the list, but unfortunately you can't add any sites from this menu. You have to visit a site and search for something, then hopefully Safari will save that site in the list.
The mystery is, how does this feature work exactly? I haven't found any further documentation about how to use Enable Quick Website Search, but I was able to figure it out by the tried and true method of trial and error! From what I can tell, you have to type at least the first three characters of the website, followed by a space character, followed by your search query.
Then down-arrow to select google.com and press return to search.
The result is that you've searched Google from the location bar, even though your default search engine is DuckDuckGo!
In place of goo for google.com, you can use ama for amazon.com and you for youtube.com. I found that wik works for en.wikipedia.org.
Beware: If you use the "Clear History…" command in Safari, it will also clear your quick search websites list, as I discovered to my dismay.
Three characters is the minimum to specify the search engine, but you can use more. For example, you may find it easier to remember the prefixes amaz, duck, goog, and wiki.
We have now reached the end of my knowledge on the subject, and thus the end of the blog post. I would like to thank Tom Harrington for raising the question of how this all works and bringing it to my attention.
I've been informed by Nicolas Bouilleaud that Quick Website Search uses the OpenSearch description format. With that information, I was able to discover that Safari stores its website search list in the ~/Library/Safari/SearchDescriptions.plist file. I warned above that Safari clears this list when you clear Safari history. The workaround for this problem is to make a copy of the file, and then replace the new empty version of the file with the old full version of the file after you clear Safari history. (Do this only when Safari is not running.)
It's a mystery why the user interface for this feature in Search Preferences is so bad.