Command Block

The Command Block is a block made with the intent to support Adventure mode and will allow mapmakers to expand the interaction with the player through server commands. The block can run specified server commands when activated by redstone current. Considering its functionality, they will not be able to be crafted and only administrators will be able to place them.

Usage
The Command Block will execute server commands like giving items or experience to a player.

To change the command executed by the block, simply right-click it, and a GUI will open.

In place of player names, it is possible to use multiple different shorthands:

When using commands, treat them as if entered from the console - you always need to specify the target, so it is not possible to use commands such as "kill" which do not take a player argument.

So for example, to change the mode to survival for the nearest player: /gamemode survival @p

Disabled commands
As of 12w32a, these commands have been disabled for the Command Block.