(if|unless) block
Compares the block at a given position to a given block ID
Syntax
(if|unless) block   -> [execute]
Arguments
: block_pos
Position of a target block to test
: block_predicate
A valid block ID (or predicate) to test for
Block ID optionally followed by block states (bounded by brackets – []) and/or data tags (bounded by braces – {})