Use alpine linux 3.12 as default, ubuntu1804 alternative added.

Dockerfile

@@ -1,38 +1,86 @@
-FROM ubuntu:18.04 as builder
+ARG IMAGE="alpine:3.12"
+# Note that some commands such as 'apk add' won't work in arbitrary images.  For instance,
+# 'apk add' works fine under alpine, but not under Ubuntu (at least not by default.)
+# In other words, the following 'apk add' sections assume an alpine based image or a derivitive
 
-ARG DEBIAN_FRONTEND=noninteractive
+FROM $IMAGE as base
 
-RUN apt-get -y update && \
-    apt-get install -y \
+RUN apk add --no-cache \
+        bzip2 \
+        libbz2 \
+        libgcc \
+        libhistory \
+        libstdc++ \
+        make \
+        readline \
+        zlib
+
+FROM base as builder
+
+RUN apk add --no-cache \
         autoconf \
-        automake \
+        build-base \
         bison \
-        build-essential \
+        bzip2-dev \
         flex \
         git \
-        gperf && \
-    rm -rf /var/lib/apt/lists/*
+	gperf \
+        readline-dev \
+        zlib-dev
 
 COPY . .
 
-RUN bash ./autoconf.sh && \
+RUN sh autoconf.sh && \
     ./configure && \
     make && \
     make install
 
-FROM ubuntu:18.04
+FROM builder as test-builder
 
-ARG DEBIAN_FRONTEND=noninteractive
+# WORKDIR /iverilog
+RUN make check
 
-RUN apt-get -y update && \
-    apt-get install -y \
-        make && \
-    rm -rf /var/lib/apt/lists/*
+FROM base as release-candidate
 
 COPY --from=builder /usr/local /usr/local/
 
+RUN adduser --disabled-password ic
+USER ic
 WORKDIR /home/ic
+
+FROM release-candidate as release-candidate-entrypoint-make
+
 ENTRYPOINT [ "make" ]
 
+# This commented section or something similar may be used to test the release candidate
+# image before it is finally released.  A failure here would stop the process so that
+# a faulty image is not released.
+#
+# The make and make clean lines below fail if iverilog/dockerfiles/test isn't available
+# and older release branches like v10_3 do not have this directory, so we need a
+# layer that does have it to copy from.  We create that layer as test-branch here:
+# FROM builder as test-branch
+# WORKDIR /iverilog
+# ARG TEST_BRANCH=master
+# RUN git checkout ${TEST_BRANCH}
+#
+# FROM release-candidate-entrypoint-make as test-release-candidate-entrypoint-make
+# COPY --from=test-branch /iverilog/dockerfiles/test /home/ic/
+# 
+# RUN make
+# RUN make clean
 
+FROM release-candidate-entrypoint-make as iverilog-make
 
+FROM release-candidate as iverilog
+
+# Below are some sample commands to build docker images.
+# 
+# The following builds iverilog from the source in the current directory
+# docker build  . -t iverilog
+#
+# The following builds the latest code from the Thirsty2/iverilog fork master branch
+# docker build --build-arg IVERILOG_REPO_URL=https://github.com/Thirsty2/iverilog.git --build-arg TEST_BRANCH=add-dockerfile . -t iverilog
+#
+# The following won't work until the pull request is accepted, but should work afterwards to build the master branch of steveicarus/iverilog
+# docker build . -t iverilog

Dockerfile.ubuntu1804

@@ -0,0 +1,84 @@
+ARG IMAGE="ubuntu:18.04"
+# Note that some commands such as 'apk add' won't work in arbitrary images.  For instance,
+# 'apt-get' works fine under ubuntu, but not under alpine (at least not by default.)
+# In other words, the following 'apt-get' sections assume a debian based image or a derivitive
+
+FROM $IMAGE as base
+
+ARG DEBIAN_FRONTEND=noninteractive
+
+RUN apt-get -y update && \
+    apt-get install -y \
+        make && \
+    rm -rf /var/lib/apt/lists/*
+
+FROM base as builder
+
+ARG DEBIAN_FRONTEND=noninteractive
+
+RUN apt-get -y update && \
+    apt-get install -y \
+        autoconf \
+        automake \
+        bison \
+        build-essential \
+        flex \
+        git \
+        gperf 
+
+COPY . .
+
+RUN bash autoconf.sh && \
+    ./configure && \
+    make && \
+    make install
+
+FROM builder as test-builder
+
+# WORKDIR /iverilog
+RUN make check
+
+FROM base as release-candidate
+
+COPY --from=builder /usr/local /usr/local/
+
+RUN adduser --disabled-password ic
+USER ic
+WORKDIR /home/ic
+
+FROM release-candidate as release-candidate-entrypoint-make
+
+ENTRYPOINT [ "make" ]
+
+# This commented section or something similar may be used to test the release candidate
+# image before it is finally released.  A failure here would stop the process so that
+# a faulty image is not released.
+#
+# The make and make clean lines below fail if iverilog/dockerfiles/test isn't available
+# and older release branches like v10_3 do not have this directory, so we need a
+# layer that does have it to copy from.  We create that layer as test-branch here:
+# FROM builder as test-branch
+# WORKDIR /iverilog
+# ARG TEST_BRANCH=master
+# RUN git checkout ${TEST_BRANCH}
+#
+# FROM release-candidate-entrypoint-make as test-release-candidate-entrypoint-make
+# COPY --from=test-branch /iverilog/dockerfiles/test /home/ic/
+# 
+# RUN make
+# RUN make clean
+
+FROM release-candidate-entrypoint-make as iverilog-make
+
+FROM release-candidate as iverilog
+
+# Below are some sample commands to build docker images.
+# 
+# The following builds iverilog from the source in the current directory
+# docker build  . -t iverilog
+#
+# The following builds the latest code from the Thirsty2/iverilog fork master branch
+# docker build --build-arg IVERILOG_REPO_URL=https://github.com/Thirsty2/iverilog.git --build-arg TEST_BRANCH=add-dockerfile . -t iverilog
+#
+# The following won't work until the pull request is accepted, but should work afterwards to build the master branch of steveicarus/iverilog
+# docker build . -t iverilog