IDE ignores the value of "$HOME"

Arduino ignores "$HOME", accepting the "user.home" Java property, apparently kept as "/home/$USER", instead.

Seems to be a common problem with Java applications.
https://stackoverflow.com/questions/32788763/jdk-and-idea-ignores-home-on-ubuntu

For some users, the added complexity may cause problems. For some compiler scripts calling the Arduino IDE, this undocumented behavior might be important.
https://github.com/mirage335/arduinoUbiquitous/blob/master/_prog/core.sh

Start by reproducing the Arduino IDE behavior on Ubuntu with different HOME values, then inspect how the Java user.home property is established during IDE startup. Compare the IDE's effective home directory with the environment variable and define done as consistently honoring the intended HOME behavior without breaking existing compiler-script use.

Written by the indexing model from the issue text.