#!/bin/sh
# stdin: default config
# stdout: modified config

# 1) and 2) remember last selected entry; 3) disable submenu
sed '
  s|^GRUB_DEFAULT=0$|GRUB_DEFAULT=saved|;
  s|^#GRUB_SAVEDEFAULT="true"$|#GRUB_SAVEDEFAULT="true"|;
  s|^#GRUB_DISABLE_SUBMENU=y$|GRUB_DISABLE_SUBMENU=y|;
'