`CARLA_ROOT` environment variable is not available in `run_evaluation.sh`

[c60evaporator]

Hi,
I found that the CARLA_ROOT environment variable set by users is not respected in
run_evaluation.sh.

In the setup documentation, users are instructed to set:

export CARLA_ROOT=YOUR_CARLA_PATH

However, in run_evaluation.sh, CARLA_ROOT` is unconditionally overwritten:

export CARLA_ROOT=YOUR_CARLA_PATH

This overwrites any previously defined CARLA_ROOT and prevents the script from using a user-configured CARLA installation (e.g., when multiple CARLA versions are used, or when running in Docker).

Proposed fix

Change the line in run_evaluation.sh to:

export CARLA_ROOT=${CARLA_ROOT:-YOUR_CARLA_PATH}

This allows the script to reuse an existing CARLA_ROOT if it is already set, while preserving the current default behavior when it is not.
This change is backward compatible and improves usability.

Thanks!