Command block output - how many players in an area

Question

Is it possible to detect how many players are in an area with a testfor?

Will the command block output from a comparator equal the number found?

I'm working in 1.12.2.

I'd test myself, but am the only one currently on the server.

Answer 1

The selector constraint r=[num] checks for entities within a radius of the executor.

/testfor @a[r=10]

This will test for all players within a radius of 10 meters of the command block, and will produce the correct comparator output up to 15.

Note that you could test this by yourself with armor stands and replacing @a with @e.