Merge environment variables to Docker container files

docker-entrypoint.sh

#!/bin/sh
if [[ -n "$CONFIG_PATH" ]]; then
  printf "Merging environment variables to '$CONFIG_PATH'.\n"
  
  if [[ -n "$BASE_URL" ]]; then
    tmp=$(mktemp)
    jq '.baseUrl = $value' $CONFIG_PATH --arg value $BASE_URL > $tmp && mv $tmp $CONFIG_PATH    
    printf "baseUrl = '$BASE_URL'\n"
  fi
  chmod 644 $CONFIG_PATH
  printf "Merge operation has been done.\n"
fi
exec "$@"

Dockerfile

FROM nginx:alpine
EXPOSE 80
RUN apk add --update --no-cache jq
ADD ./docker-entrypoint.sh /
ADD ./config.json ./index.html /usr/share/nginx/html/
ENV CONFIG_PATH=/usr/share/nginx/html/config.json
ENTRYPOINT ["/docker-entrypoint.sh"]
CMD ["nginx", "-g", "daemon off;"]