Why doesn't path work from a variable?

Question

bash

dir="/home/$USER/temp"
wget -P $dir http://download.redis.io/releases/redis-$release.tar.gz
tar xzf $dir/redis-$release.tar.gz

tarswears on the way. Moreover, if I use it without a variable, it works.

Answer 1

Where do you set the $release variable?
$USER is a system variable, it is set by the bash itself when starting the bash process as a user. What is $release?