The Testforblock Command

The /testforblock command is a pretty useful command for adventure maps.

Overview'
The /testforblock is a command that can test for a certain block in a certain coordinates. A comparator coming out from the command block will turn on once the testforblock sends a true value. Using in it the chat bar will also return a value.

Syntax
/testforblock   

Explanation
The x, y, and z values are the coordinates of the block that is trying to be tested. The block value is the block that the command is looking for in that area.

Trivia

 * Very similar to The Testfor Command.
 * Mostly used to see if someone had placed something.