text: FROM debian:buster-slim
  
  RUN set -eux; \
  	apt-get update; \
  	apt-get install -y --no-install-recommends \
  		bzip2 \
  		ca-certificates \
  		libffi-dev \
  		libgmp-dev \
  		libssl-dev \
  		libyaml-dev \
  		procps \
  		zlib1g-dev \
  	; \
  	rm -rf /var/lib/apt/lists/*
  
  # skip installing gem documentation
  RUN set -eux; \
  	mkdir -p /usr/local/etc; \
  	{ \
  		echo 'install: --no-document'; \
  		echo 'update: --no-document'; \
  	} >> /usr/local/etc/gemrc
  
  ENV LANG C.UTF-8
  ENV RUBY_MAJOR 2.5
  ENV RUBY_VERSION 2.5.8
  ENV RUBY_DOWNLOAD_SHA256 0391b2ffad3133e274469f9953ebfd0c9f7c186238968cbdeeb0651aa02a4d6d
  ENV RUBYGEMS_VERSION 3.0.3
  
  # some of ruby's build scripts are written in ruby
  #   we purge system ruby later to make sure our final image uses what we just built
  RUN set -eux; \
  	\
  	savedAptMark="$(apt-mark showmanual)"; \
  	apt-get update; \
  	apt-get install -y --no-install-recommends \
  		autoconf \
  		bison \
  		dpkg-dev \
  		gcc \
  		libbz2-dev \
  		libgdbm-compat-dev \
  		libgdbm-dev \
  		libglib2.0-dev \
  		libncurses-dev \
  		libreadline-dev \
  		libxml2-dev \
  		libxslt-dev \
  		make \
  		ruby \
  		wget \
  		xz-utils \
  	; \
  	rm -rf /var/lib/apt/lists/*; \
  	\
  	wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz"; \
  	echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum --check --strict; \
  	\
  	mkdir -p /usr/src/ruby; \
  	tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1; \
  	rm ruby.tar.xz; \
  	\
  	cd /usr/src/ruby; \
  	\
  # hack in "ENABLE_PATH_CHECK" disabling to suppress:
  #   warning: Insecure world writable dir
  	{ \
  		echo '#define ENABLE_PATH_CHECK 0'; \
  		echo; \
  		cat file.c; \
  	} > file.c.new; \
  	mv file.c.new file.c; \
  	\
  	autoconf; \
  	gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)"; \
  	./configure \
  		--build="$gnuArch" \
  		--disable-install-doc \
  		--enable-shared \
  	; \
  	make -j "$(nproc)"; \
  	make install; \
  	\
  	apt-mark auto '.*' > /dev/null; \
  	apt-mark manual $savedAptMark > /dev/null; \
  	find /usr/local -type f -executable -not \( -name '*tkinter*' \) -exec ldd '{}' ';' \
  		| awk '/=>/ { print $(NF-1) }' \
  		| sort -u \
  		| xargs -r dpkg-query --search \
  		| cut -d: -f1 \
  		| sort -u \
  		| xargs -r apt-mark manual \
  	; \
  	apt-get purge -y --auto-remove -o APT::AutoRemove::RecommendsImportant=false; \
  	\
  	cd /; \
  	rm -r /usr/src/ruby; \
  # make sure bundled "rubygems" is older than RUBYGEMS_VERSION (https://github.com/docker-library/ruby/issues/246)
  	ruby -e 'exit(Gem::Version.create(ENV["RUBYGEMS_VERSION"]) > Gem::Version.create(Gem::VERSION))'; \
  	gem update --system "$RUBYGEMS_VERSION" && rm -r /root/.gem/; \
  # verify we have no "ruby" packages installed
  	! dpkg -l | grep -i ruby; \
  	[ "$(command -v ruby)" = '/usr/local/bin/ruby' ]; \
  # rough smoke test
  	ruby --version; \
  	gem --version; \
  	bundle --version
  
  # don't create ".bundle" in all our apps
  ENV GEM_HOME /usr/local/bundle
  ENV BUNDLE_SILENCE_ROOT_WARNING=1 \
  	BUNDLE_APP_CONFIG="$GEM_HOME"
  ENV PATH $GEM_HOME/bin:$PATH
  # adjust permissions of a few directories for running "gem install" as an arbitrary user
  RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
  
  CMD [ "irb" ]
  