pre_install() {
  :
}

post_install() {
  grep -x '/bin/mksh' /etc/shells 2>/dev/null || echo '/bin/mksh' >> /etc/shells
  # need to also add /usr/bin/mksh to /etc/shells to avoid https://bugs.archlinux.org/task/55053
  grep -x '/usr/bin/mksh' /etc/shells 2>/dev/null || echo '/usr/bin/mksh' >> /etc/shells
}

pre_upgrade() {
  :
}

post_upgrade() {
  post_install
}

pre_remove() {
  # This is only necessary on alternate shells. sh and bash 
  # are at the base of Arch and cannot be removed.
  # To test this you should have a spare root shell already open.
  # Otherwise, if this doesn't work, you will need to learn how to bypass
  # the default shell on login.
  # http://stackoverflow.com/questions/11059067/what-is-the-nix-command-to-view-a-users-default-login-shell
  if getent passwd root | cut -d: -f7 | grep -qle '/bin/mksh'; then
    echo '**********************************************'
    echo '*** Warning: ROOT HAS mksh as the login shell.'
    echo '*** Shell changed to sh to prevent loss of root access.'
    echo '**********************************************'
    # sh is more likely to guarantee a login than bash because sh is typically
    # unmodified. Crappy, but guaranteed.
    chsh -s '/bin/sh'
  fi
  sed -i -r '/^(\/usr)?\/bin\/mksh$/d' '/etc/shells'
}

post_remove() {
  mandb -q
  # /usr/bin/mksh is also detected
  if getent passwd | cut -d: -f7 | grep -qle '/bin/mksh'; then
    echo '*** Warning: Some users have mksh as their login shell.'
    echo '*** Fix promptly to restore access.'
  fi
}