Is it possible to use relative coordinates (~) in target selectors?

Question

I'm trying to test for a player in a certain area relative to the command block executing the command, so if I need to move the location of what I'm making, the command block isn't sensing for something 3000 blocks away. What I have is this:

/testfor @a[x=~1,dx=0,z=~-3,dz=0,y=~4,dy=102]

And this (these are 2 separate command blocks sensing 2 different areas):

/testfor @a[x=~1,dx=0,z=~3,dz=0,y=~4,dy=102]

But when I test them, they say "The entity UUID provided is in an invalid format." What am I doing wrong?

Answer 1

You cannot use the ~ character in target selectors, meaning you'd need to rely on command syntax and not selector syntax. You cannot use relative coordinates with /testfor as its command syntax does not support it.

You would instead need to place an entity at the desired position and execute from it relatively using /execute:

/execute <target> X Y Z <command>

<target> is the target entity to change the coordinate origin to, while XYZ is going to further modify the origin. Using relative coordinates would cause "command" to be executed relative from the target's position.

Sample armor stand to create:

/summon ArmorStand X Y Z {Tags:["anchor"]}

For example, assuming there is an armor stand tagged anchor at the intended location, the following tests for players relative to the armor stand:

/execute @e[type=ArmorStand,tag=anchor] ~1 ~4 ~-3 /testfor @a[dx=0,dz=0,dy=102]
/execute @e[type=ArmorStand,tag=anchor] ~1 ~4 ~3 /testfor @a[dx=0,dz=0,dy=102]

Answer 2

1.13+ update

As of 1.13+, command syntax has received an overhaul. It is now possible to execute a command at an arbitrary position using /execute positioned.

This means that a utility entity, such as an armour stand, is no longer required.

execute positioned ~1 ~4 ~-3 if entity @a[dx=0,dz=0,dy=102] run …
execute positioned ~1 ~4 ~3 if entity @a[dx=0,dz=0,dy=102] run …