init.lua

minetest.register_chatcommand("who_exists", {
    description = "find people that exist",
    func = function(name, param)
        local ptable = {}
        for _, player in ipairs(minetest.get_connected_players()) do
            table.insert(ptable, player:get_player_name())
        end
        minetest.chat_send_player(name, "Connected players: " .. table.concat(ptable, ", "))
    end,
})