This is a really useful tip, many thanks. It has probably largely been a personal comfort zone, but I haven't dug much deeper than site: or ext: operators in recent years. A lazy habit. Also, strangely, I have always had doubt as to the real efficiency of the OR operator in web search (maybe it has yielded unsatisfactory results in some distant past, and for different engines, not only Google; hence the prejudice). I didn't even know that the "pipe" symbol should actually work for that.

Your example is a really good one, because it illustrates the power of OR remarkably well. The key is using it to combine several different operators, not just duplicating a single one, e.g. "query site:a.com | site:b.com". That has been my main way of digging deeper over the years, along with "#" to specify a date range.

Interestingly, in case of "query site:firstsite.ee|secondsite.ee" the "|" doesn't seem to work, I get zero results. Why is that? To narrow down the results based on both the domain name and top level domain, I have to add the inurl: operator. E.g. "query inurl:firstsite|secondsite site:.ee"

Strangely, "piping" is the essential thing I do on the Unix command line every day. I haven't put (that) much thought into using Google's "|" operator in a similar vein, that is, to combine several (3-4) different operators. Possibly partly because one used to get pages and pages of results even with very simple, single-operator queries.

Time to refresh my memory about Google's search operators, I guess. Thanks again for sharing this example.