Amount
Changes the number of items in the target stack
/goop nbt amount <player> <slot> [±]<value>[%] [objective]
Also stores the final damage value as the score of <player> in the [objective] objective.
Args Breakdown (What everything does)
<Player>
Player whose inventory items' NBT will be edited.
Supports a few vanilla selectors.
[1.6.5] May be an Entity (dropped item) UUID
<Slot>
The slot in the player's inventory in which items will be duped or consumed. To read on slots see Inventory Slots.
Examples: mainhand, offhand, chest, feet, any, 0-8, ec*
[±]<value>[%]
The operation to apply to the damage of the item. See Plus Minus Percent page for full explanation.
[Objective]
The name of the scoreboard objective that will store (ten times) the final amount.
Tips
Max stack size using this command seems to be 127
You can read the amount of items in that slot by using +0
This will set the score of the player to 10 times this amount
Unlike testinventory with amount keyword, which will not multiply by 10.
Simple Examples:
/goop nbt amount gunging mainhand +1
Gives gunging one more of the item they are holding
/goop nbt amount atuosto * +100%
Dupes the inventory of player atuosto.