Using an /execute command, I want to check if a certain block is, for example, either oak_fence, OR iron_bars.

However, in my specific case, I can't just use two command blocks to check for either one separately. I tried doing so, like this:

/execute as @a[tag=tagA] at @s unless block ~ ~-1 ~ oak_fence run tag @s remove tagA
/execute as @a[tag=tagA] at @s unless block ~ ~-1 ~ iron_bars run tag @s remove tagA

Note: I set both command blocks to "Repeat", "Unconditional", and "Always active".

The result is not what I expected, because:

  • if the block is oak_fence, the tag should be left on, however the second command removes it.
  • if the block is iron_bars, the tag should be left on, however the first command removes it.

What I need is to check, in a single command, for the tag to be removed only when the block is neither oak_fence OR iron_bars.

A possible solution I've thought of, but haven't tested yet, could be: setting up another 2 tags, check_oak_fence and check_iron_bars, which are given to players standing on either oak_fence or iron_bars.

/execute as @a[tag=!tagA] at @s if block ~ ~-1 ~ oak_fence run tag @s add check_oak_fence
/execute as @a[tag=!tagA] at @s if block ~ ~-1 ~ iron_bars run tag @s add check_iron_bars

And then checking for those 2 tags in the as <targets> portion of the /execute command, which apparently does permit an OR gate, like this:

/execute as @a[tag=!check_oak_fence, tag=!check_iron_bars]

I also tested this question's only answer, modifying it so it checks the same block twice:

/execute if block ~ ~-1 ~ oak_fence if block ~ ~-1 ~ iron_bars

But that obviously can't work, because that's an AND gate, meaning it checks if a block is simultaneously two types of block at once, which is impossible, thus it can never return true.

1 Answer 1


You essentially want:

not(OF or IB)

which, using De Morgan's law, is equal to:

(not OF) and (not IB)

Giving that, you should be able to chain the last command you found, but with inverted conditions:

/execute as @a[tag=tagA] at @s unless block ~ ~-1 ~ oak_fence unless block ~ ~-1 ~ iron_bars run tag @s remove tagA
  • And so Mojang is forcing people to know De Morgan's law ;)
    – kokbira
    Commented Apr 15 at 11:02
  • 1
    @kokbira and maybe, as a student, you thought it was useless :D
    – pinckerman
    Commented Apr 15 at 17:06

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