Minecraft wiki entry for Development_versions, associated text: Added the /attribute command.
Used to get, set, or modify attributes.
Syntax:
attribute <target> <attribute> get [<scale>]: get total value of attribute
attribute <target> <attribute> base set <value>: sets base value
attribute <target> <attribute> base get [<scale>]: get base value
attribute <target> <attribute> modifier add <uuid> <name> <value> (add|multiply|multiply_base): adds modifier (fails if modifier is already present)
attribute <target> <attribute> modifier remove <uuid>: removes modifier
attribute <target> <attribute> modifier value get <uuid> [<scale>]: get value of modifier
Parameters:
<target>: single entity (note: only players, armor stands and mobs have attributes)
<attribute>: name of attribute (like minecraft:generic.max_health)
<name>: string (in optional quotes) describing human-readable name of modifier
<value>: floating point value (note: certain attributes have limits on final value, so the change might not be noticeable)