/clear

Syntax

/clear [<targets> [<item> [<maxCount>]]]

Argument	Kind of value	What to type
<targets>	Target selector	The players whose inventories are cleared. Defaults to yourself. One or more players.
<item>	Item test	Which items to remove: an item id such as minecraft:diamond, an item tag such as #minecraft:logs, or * for any item, optionally followed by component tests in square brackets. Defaults to every item.
<maxCount>	Whole number	The largest number of items to remove from each player. A whole number of 0 or more. 0 only counts. Without it, all matching items are removed. At least 0.

Permission level	2: operators, worlds with cheats on, command blocks and functions
Works in	Singleplayer with cheats enabled and multiplayer servers. Needs permission level 2 (gamemasters): server operators, players with cheats, command blocks, and functions can all run it.
Result	Reports how many items were removed and from whom, or how many matching items were found when only counting. The number /execute store saves is that number of items, added up over all targeted players.
No arguments	Removes everything from your own inventory. This form only works when a player runs it.
Only targets	Removes every item from the targeted players.
What is searched	The whole inventory including armor and off hand, the 2x2 crafting grid, and the item held on the mouse cursor.
Counting only	A maxCount of 0 removes nothing and just reports how many matching items the players have. This is a way to test whether a player carries an item.
Failure	Fails with "No items were found" if no targeted player had a matching item.

/clear

Empties your own inventory.

/clear @a minecraft:diamond

Removes all Diamonds from every player.

/clear @s minecraft:dirt 32

Removes up to 32 Dirt from you.

/clear @p #minecraft:logs

Removes every kind of log from the nearest player.

/clear @s minecraft:diamond 0

Counts your Diamonds without removing any.