use variable "DEBIAN_FRONTEND noninteractive" to apt-get noninteractive install and set environment and use shell script in Dockerfile

env-Dockerfile

ENV QT_BASE_DIR=/opt/qt55
ENV QTDIR=$QT_BASE_DIR
ENV PATH=$QT_BASE_DIR/bin:$PATH
ENV LD_LIBRARY_PATH=$QT_BASE_DIR/lib/x86_64-linux-gnu:$QT_BASE_DIR/lib:$LD_LIBRARY_PATH
ENV PKG_CONFIG_PATH=$QT_BASE_DIR/lib/pkgconfig:$PKG_CONFIG_PATH

# Reconfigure locale
RUN locale-gen en_US.UTF-8 && dpkg-reconfigure locales

# Docker offical ENVIRONMETN REPLACEMENT
ENV foo /bar
WORKDIR ${foo}   # WORKDIR /bar
ADD . $foo       # ADD . /bar
COPY \$foo /quux # COPY $foo /quux

# ENV like shell script syntax
ENV abc=hello
ENV abc=bye def=$abc
ENV ghi=$abc

noninteractive-installer-Dockerfile

# forked from docker.io [tstumm/qt-opencv](https://hub.docker.com/r/tstumm/qt-opencv/~/dockerfile/)
ENV DEBIAN_FRONTEND noninteractive

# Install updates & requirements:
#  * git, openssh-client - for Drone
#  * curl, p7zip - to download & unpack Qt bundle
#  * build-essential, pkg-config, libgl1-mesa-dev - basic Qt build requirements
#  * libsm6, libice6, libxext6, libxrender1, libfontconfig1 - dependencies of Qt bundle run-file
RUN apt-get -qq update && apt-get -qq dist-upgrade && apt-get install -qq -y --no-install-recommends \
    git \
    openssh-client \
    ca-certificates \
    curl \
    p7zip \
    build-essential \
    pkg-config \
    libgl1-mesa-dev \
    libsm6 \
    libice6 \
    libxext6 \
    libxrender1 \
    libfontconfig1 \
    && apt-get -qq clean

setup-sshd-Dockerfile

# setup sshd login without passwd

RUN mkdir /var/run/sshd \
    && echo 'root:root' | chpasswd \
    && sed -i 's/PermitRootLogin without-password/PermitRootLogin yes/' /etc/ssh/sshd_config \
    && echo "export VISIBLE=now" >> /etc/profile

shell-script-Dockerfile

# use "&&" and "\" to write a shell script in Dockerfile
# This is a compile/build source codes example in Dockerfile
RUN cd /opt \
     && wget https://github.com/Itseez/opencv/archive/3.0.0.zip \
     && unzip 3.0.0.zip \
     && cd opencv-3.0.0 \
     && mkdir release \
     && cd release \
     && cmake -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local -D WITH_TBB=ON -D BUILD_NEW_PYTHON_SUPPORT=ON -D WITH_V4L=ON -D INSTALL_C_EXAMPLES=ON -D INSTALL_PYTHON_EXAMPLES=ON -D BUILD_EXAMPLES=ON -D WITH_QT=ON -D WITH_OPENGL=ON .. \
     && make -j4 \
     && make install \
     && bash -c 'echo "/usr/local/lib" > /etc/ld.so.conf.d/opencv.conf' \
     && ldconfig \
     && rm /opt/3.0.0.zip \
     && rm -R /opt/opencv-3.0.0

# use ";" and "&&" and "\" to write shell script in Dockerfile
RUN /bin/bash -c "while true;do env | sort && sleep ${SLEEP_SECONDS:-30};done"

RUN /bin/bash -c "source /application.sh"

# The application.sh like the following lines:
# while true; \
# do env | sort && sleep ${SLEEP_SECONDS:-30}; \
# done
#
# command2
#
# command3

Good to have examples. Appreciate it.