Updated:

1. The basic form

execute store result score <targets> <objective> run <command>
execute store success score <targets> <objective> run <command>

result saves the number the command returns. success saves 1 if it worked and 0 if it failed. Besides score you can store into entity, block, storage and bossbar.

2. Setup

/scoreboard objectives add count dummy
/scoreboard objectives add y dummy
/scoreboard objectives add hp dummy

3. Count players

execute store result score #players count if entity @a[gamemode=adventure]

Ending with if entity stores how many entities matched. Use it to count players still in a minigame.

4. Save position and health

execute as @a store result score @s y run data get entity @s Pos[1]
execute as @a store result score @s hp run data get entity @s Health

Decimals are dropped, so Y 64.5 becomes 64. See the data command for paths.

5. Save the day and time

execute store result score #day count run time query minecraft:day repetitions
execute store result score #time count run time query minecraft:day

This is the Java 26.1+ form; on 1.21.11 and older use time query day and time query daytime. See the day counter and clock to show them.

6. Write a score to a bossbar or mob

execute store result bossbar minecraft:timer value run scoreboard players get #time count
execute store result entity @e[type=zombie,tag=boss,limit=1] Health float 1 run scoreboard players get #hp count

The first line fills a bossbar. float 1 means store as a decimal, multiplied by 1.

7. Branch on success

execute as @a store success score @s count run clear @s minecraft:diamond 1
execute as @a[scores={count=1}] run give @s minecraft:golden_apple

A tiny shop: only players who paid one diamond get the apple.

Troubleshooting

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