/fill: Fills a box between two corners with one block, with options to hollow it, outline it or only replace certain blocks.
Syntax
<angle brackets> are required, [square brackets] optional. /fill has 4 forms:
/fill <from: position> <to: position> <tileName: block> <blockStates: block_state_array> [oldBlockHandling: fillmode]
/fill <from: position> <to: position> <tileName: block> [oldBlockHandling: fillmode]
/fill <from: position> <to: position> <tileName: block> <blockStates: block_state_array> <oldBlockHandling: replace> [replaceTileName: block] [replaceBlockStates: block_state_array]
/fill <from: position> <to: position> <tileName: block> <oldBlockHandling: replace> [replaceTileName: block] [replaceBlockStates: block_state_array]