core/bash/bash-shcompat.install

#!/bin/sh

post_install() {
  for i in 'sh' 'rsh'; do
    grep -qx "/bin/${i}" 'etc/shells' || echo "/bin/${i}" >> 'etc/shells'
  done
  unset i
}

post_upgrade() {
  post_install
}

post_remove() {
  for i in 'sh' 'rsh'; do
    sed -i "\|^/bin/${i}$|d" 'etc/shells'
  done
  unset i
}