anchor.diff:  
   MAINTAINER Andrew Heald <andrew@heald.uk>
   
  +ENTRYPOINT tarsnap
  +
   ARG hash
   ARG tarball
  +ARG dependencies=curl gcc libc6-dev make libssl-dev zlib1g-dev e2fslibs-dev gnupg2
   
   RUN apt-get -qq update && \
  -    apt-get -qq -y install curl gcc libc6-dev make libssl-dev zlib1g-dev e2fslibs-dev gnupg2
  +    apt-get -qq -y install $dependencies
   
   ADD tarsnap-signing-key-2016.asc /opt/
   
  
positive.code:     curl --fail --silent --location --retry 3 $tarball > /opt/tarsnap.tgz && \
      expected=`gpg --decrypt /opt/tarsnap.asc | awk '{print $4}'` && \
      actual=`shasum -a 256 /opt/tarsnap.tgz | awk '{print $1}'` && \
      if [ $actual != $expected ]; then echo 'Hash mismatch!'; exit 1; fi && \
      mkdir /opt/tarsnap && \
      cat /opt/tarsnap.tgz | tar -xz -C /opt/tarsnap --strip-components=1 && \
  
negative.code:     make all && \
      make install && \
      rm -fr /opt/* && \
      apt-get -qq -y --auto-remove remove $dependencies && \
      apt-get clean
  