Using variable interpolation in Gunicorn inside DockerFile

Question

Looking for a way to pass PORT environment variable to gunicorn command inside DockerFile

current setup

.env

PORT=8080

DockerFile

EXPOSE ${PORT}

CMD ["gunicorn"  , "--timeout" , "120" ,"-b", "0.0.0.0:8080", "wsgi:app"]

First attempt

CMD ["gunicorn"  , "--timeout" , "120" ,"-b", "0.0.0.0:${PORT}", "wsgi:app"]

Failed

Second attempt

CMD ["gunicorn"  , "--timeout" , "120" ,"-b", "0.0.0.0:{PORT}", "wsgi:app"]

Failed

What is the correct way to pass PORT to gunicorn?

Update:

I can run the command in bash successfully

#!/bin/bash
PORT=8879
SERVER_PORT=0.0.0.0:${PORT}
echo ${SERVER_PORT}
gunicorn --bind ${SERVER_PORT} wsgi:app