Bukkit

If you make a command with an itemcost, if the player doesn't have enough items at the time of executing, the command will consume those items the player has and return an error message like "you don't have that many items".

In my case: 

condenseredwool:
command: /condenseredwool
type: RUN_COMMAND
runcmd:
- '%PlayerOptions%addItem: RED_WOOL:1:0:0:&aCompacted Red Wool:&b1 Inv. of Red Wool'
itemcost: 'RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64;RED_WOOL:64'

If the player has any quantity of red wool less than the itemcost, it will be consumed with the error message.