post_install() {
  if [ ! "`grep /usr/bin/fish etc/shells`" ]; then
    echo "updating /etc/shells... done."
    sed -i "s|/bin/bash|/bin/bash\n/usr/bin/fish|" etc/shells
  fi
}

post_upgrade() {
  post_install $1
}

pre_remove() {
  echo -ne "updating /etc/shells... \n"
  sed -i '/^\/usr\/bin\/fish/d' /etc/shells
}

op=$1
shift

$op $*