No real need for the shell script

debian/jessie/Dockerfile

 FROM debian:jessie
-COPY setup.sh /opt/
-RUN /bin/bash /opt/setup.sh
+
+LABEL maintainer="ethitter"
+LABEL version="1.0"
+
+RUN echo "deb http://security.debian.org/ jessie/updates main" >> /etc/apt/sources.list
+
+RUN apt-get update \
+    && apt-get -yqqf install \
+        apt-transport-https \
+        lsb-release \
+        ca-certificates \
+        curl
+
+RUN curl -ssL -o /etc/apt/trusted.gpg.d/php.gpg https://packages.sury.org/php/apt.gpg
+RUN echo "deb https://packages.sury.org/php/ $(lsb_release -sc) main" > /etc/apt/sources.list.d/php.list
+
+RUN apt-get update \
+    && apt-get -y install \
+        git \
+        dh-make \
+        build-essential \
+        autoconf \
+        autotools-dev \
+        libpcre3 \
+        libpcre3-dev \
+        libz-dev \
+        shellcheck \
+        gnupg \
+        libssl-dev \
+    && apt-get clean \
+    && rm -rf /var/lib/apt/lists/*

debian/jessie/setup.sh

-#!/bin/sh
-
-echo "deb http://security.debian.org/ jessie/updates main" >> /etc/apt/sources.list
-
-apt-get update
-apt-get -y install \
-    apt-transport-https \
-    lsb-release \
-    ca-certificates \
-    curl
-curl -ssL -o /etc/apt/trusted.gpg.d/php.gpg https://packages.sury.org/php/apt.gpg
-sh -c 'echo "deb https://packages.sury.org/php/ $(lsb_release -sc) main" > /etc/apt/sources.list.d/php.list'
-
-apt-get update
-apt-get -y install \
-    git \
-    dh-make \
-    build-essential \
-    autoconf \
-    autotools-dev \
-    libpcre3 \
-    libpcre3-dev \
-    libz-dev \
-    shellcheck \
-    gnupg \
-    libssl-dev
-
-apt-get clean
-rm -rf /var/lib/apt/lists/*