What can I use the /testfor command In Minecraft

I found the /testfor command today in Minecraft, but when I use it in a command block it says

Usage: /testfor <player>

and when I do that it then says

/testfor must be used by command blocks with an analog output.

What does that mean and how can I use the command?

Solution 1:

As per the Minecraft Wiki Commands page, the syntax of the /testfor command is either of:

/testfor <playername>
/testfor <selector>

So, e.g., a command block that fires the command /testfor notch, with a redstone comparator attached to it, would output a signal from the comparator, assuming that Notch is playing on that server.

Using the Command Block selectors syntax lets you do things like /testfor @a[r=3], which will cause the comparator to emit a signal strength equal to the number of players within three meters. Or /testfor @a[m=2], which would cause the comparator to emit a signal strength equal to the number of Creative Mode players currently on the server.

Solution 2:

The /testfor command has many uses. For example, you might want to testfor a player with a score of at least 3 on the red team. To do this, you would use the following command:

/testfor @p[score_objname_min=3,team=red]

In this command, you testfor the nearest player with a score, on the objective "objname", of 3. This player would have to be on the red team. If you attach this command block to a clock, and put a comparator on the side of it, whenever it finds a player, it will output a redstone signal.

Click HERE for a complete list of selectors that you can use within the square brackets.

Solution 3:

You need to use it in a command block so that it can be in a clock or have a redstone input to trigger. You cannot use it from the chat.

You can use it in a lot of ways.

• To get the closest player

• To get the number of players in an area.

• To apply an effect to an area

• To apply certain commands when the testfor returns true.

• Grab the nearest player with a certain scoreboard score.

To Check the result of the command, attach an comparator out of the command block. It will become powered if the /testfor finds a player matching the selector or name.

Solution 4:

Suppose you did /testfor @p[r=3]. It would testfor a single player within 3 blocks.
Suppose you did /testfor @p[x=3,y=3,z=3]. It would testfor a player At Coordinates x=3, y=3 z=3.