based on Unused Scanner tool by Insolita found at: https://github.com/Insolita/unused-scanner
docker run -v `pwd`:/app juanmrad/unused-scanner ./unused.php
For power users with different configs:
#add project dir reference.
PROJECT_DIR=$(pwd)
#add location of config file relative to docker container
CONFIG=/workdir/config/unused-scanner/prod.php
docker run \
--rm \
-v $PROJECT_DIR:/workdir \
-w /workdir \
$IMAGE \
$CONFIG