Стандартные переменные окружения

5.b. Defining Variables Globally
Occasionally you might be asked to set a certain environment variable system-wide. As an example we take the http_proxy variable. Instead of messing about with /etc/profile, you can now just create a file (/etc/env.d/99local) and enter your definition(s) in it
5.c. Defining Variables Locally
If you want to define an environment variable locally, you should use ~/.bashrc or ~/.bash_profile

# cat /etc/profile
...
# Load environment settings from profile.env, which is created by
# env-update from the files in /etc/env.d
if [ -e /etc/profile.env ] ; then
        . /etc/profile.env
fi

# You should override these in your ~/.bashrc (or equivalent) for per-user
# settings.  For system defaults, you can add a new file in /etc/profile.d/.
export EDITOR=${EDITOR:-/bin/nano}
...

# cat /etc/profile.env
export VAR='string'

обратите внимание, что в /etc/profile есть строка
export EDITOR=${EDITOR:-/bin/nano}
но если вы в /etc/env.d/99local напишете
export EDITOR=${EDITOR:-/bin/nano}
и сделаете env-update, то в /etc/profile.env попадёт
export EDITOR='${EDITOR:-/bin/nano}'
а это не одно и то же.

Если кратко - /etc/env.d/ вы не сможете вставлять переменные в переменные.
Ваш случай - "5.c. Defining Variables Locally"

См также http://bugs.gentoo.org/show_bug.cgi?id=4854