How to access docker-compose environment variables in docker container bash file

Question

I am working on database backup functionality with next cloud. My script is working perfectly with hard coded Url paths. now I want to create environment variables for the username, password, paths which I am using in my code. I tried many ways but when I run my container in docker compose the env variables are not accessible and they are empty. This is my shell script:

#!/bin/bash

#set -o allexport
#source .env
#set +o allexport

echo "`date`    Starting MongoDB backup...";

# Parse Command Line Arguments
while getopts u:d: flag
do
  case "${flag}" in
    u) uri=${OPTARG};;
    d) dest=${OPTARG};;
  esac
done

# Get the current date and time
CURRENT_DATE=`date +%y%m%d-%H%M%S`;

DESTPATH="$dest/$CURRENT_DATE";
echo  "`date`    Backup destination is $DESTPATH";
echo $uri
# Create the destination directory and backup the database
mkdir -p $DESTPATH;
mongodump --uri=$uri -o $DESTPATH --gzip


# Set your nextcloud username and password
username=${NEXT_CLOUD_USERNAME};
password=${NEXT_CLOUD_PASSWORD};

# Set your mongodb path running on your system
# mongodbPath="http://localhost:8080/";
mongodbPath=${NEXT_CLOUD_PATH};

# Nextcloud path
nextcloudPath="remote.php/dav/files/";

# Concat username with the nextcloud path
nextcloudPath=$nextcloudPath$username;
nextcloudPath=$nextcloudPath"/";

# Concat the mongodb path with the nextcloud path
uriPath=$uriPath$mongodbPath;
uriPath=$uriPath$nextcloudPath;

#mkDirPath=$uriPath${NEXT_CLOUD_FOLDER};

#echo $mkDirPath
#curl -X MKCOL -u $username:$password $uriPath

uriPath=$uriPath$CURRENT_DATE;
uriPath=$uriPath".zip"

echo $uriPath

#craete zip for the backup folder
zip -r $DESTPATH.zip $DESTPATH

# Upload backup zip file to nextcloud
curl -X PUT -u $username:$password $uriPath -T $DESTPATH.zip

echo "`date`    MongoDB backup completed.";
exit 0

Docker file:

FROM mongo:latest

RUN apt-get clean
RUN apt-get update
RUN apt-get install -y cron
RUN apt-get install -y curl
RUN apt-get install -y zip

ENV MONGODB_PATH=mongodb://mongo:27017
ENV NEXT_CLOUD_PATH=http://nextcloud
ENV NEXT_CLOUD_FOLDER=backup
ENV NEXT_CLOUD_USERNAME=admin
ENV NEXT_CLOUD_PASSWORD=example

ADD /script/container_cronjob /etc/cron.d/container_cronjob
RUN chmod 0644 /etc/cron.d/container_cronjob
RUN touch /var/log/cron.log

WORKDIR /usr/src/app

COPY ./script/backup.sh /backup.sh
COPY . .

RUN chmod +x /backup.sh
CMD env
CMD cron && tail -f /var/log/cron.log

Docker-Compose file:

version: "3"

services:

  mongo:
    container_name: "mongo"
    image: "mongo:latest"

  nextcloud:
    container_name: "nextcloud"
    image: "nextcloud:latest"
    ports:
      - "8080:80"
    volumes:
      - ./data:/var/www/html/data
      - ./config:/var/www/html/config

  backup:
    container_name: "backup"
    image: "d432f54c96df"
    environment:
      - MONGODB_PATH=mongodb://mongo:27017
      - NEXT_CLOUD_PATH=http://nextcloud
      - NEXT_CLOUD_FOLDER=backup
      - NEXT_CLOUD_USERNAME=admin
      - NEXT_CLOUD_PASSWORD=example

First I tried making env variables in docker-compose file as you can see in docker-compose file and try to access in my shell script using ${} way but it didn't work then I tried making an .env file and put my variables in it and try to access in shell script it didn't work. .env file:

MONGODB_PATH=mongodb://mongo:27017
NEXT_CLOUD_PATH=http://nextcloud/
NEXT_CLOUD_FOLDER=backup
NEXT_CLOUD_USERNAME=admin
NEXT_CLOUD_PASSWORD=example

with .env file I put these line

set -o allexport
source .env
set +o allexport

in top of my shell script but it gave me error that .env is not available in my docker container but I copied both my script and .env into container.

I also tried making variables in docker file as you can see in my docker file. It still not working. my containers are working:containers

when my script run in backup docker container it shows path is not setting because username and password is not setscript error

in image you can see remote.php/dav/files//231013-111101.zip has no username of nextcloud but I set it in my env variables.

It would be really helpful if someone guide me where I am wrong or how I can access my env variables. Thanks