How to find the exact number of players on a server?

Question

As players join and leave, I need something(s) giving a redstone signal for every number of players from 1-10, then if there is more than 10. So I can have one thing happen at 1 player, something different happen at 2, 3, 4 ...

I have tried using a comparator output from "/testfor @a", but I couldn't get it to do things like having the command blocks for players=1 and players=2 to turn off if players=3. Everything else I've tried had the same problems, and everything I've found online is for testing for a min/max amount of players.

Answer 1

I'd use a scoreboard to hold the value of the amount of players, you can count how many are on with:

/execute @a ~ ~ ~ /scoreboard players add <dummy player> <objective> 1

then you can use conditional command blocks after a command like this:

/scoreboard players test <dummy player> <objective> <min> <max>

note: min and max can be set the same for an exact number

but if you want a redstone value of player count, @mookooy gave the answer for that

Answer 2

Have a Repeating, Always Active command block with the command /testfor @a and a comparator and no repeater this will produce a signal strength based on the number of players online

Answer 3

Set up some command blocks like this:

[Repeating, always active] /scoreboard players set @e[name=Counter] players 0

[Chain, always active] /execute @a ~ ~ ~ /scoreboard players add @e[name=Counter] players 1

Create a scoreboard objective named players:

/scoreboard objectives add players dummy

Then place some entity in the world and name it "Counter". I'd recommend summoning an invisible armor stand:

/summon ArmorStand ~ ~ ~ {CustomName:Counter,Invisible:1,Marker:1,NoGravity:1}

Finally, it really depends on what you need to do. If you REALLY need a redstone output out of it, add these to commands blocks:

[Chain, always active] /setblock x y z air

[Chain, always active] /execute @e[name=Counter,score_players_min=10,score_players=10,c=1] ~ ~ ~ /setblock x y z redstone_block

Replace x y z with the X Y and Z coordinates of where you want the redstone block to be placed. Press Fn-F3 to open Debug Mode, and then you can see coordinates.

If there 10 players in the world, it will place a block.

Hope this helps!