grub-menu.sh

#!/usr/bin/env bash

#kernel_version="5.4.0-88"

#kernlist=$(grep -i "menuentry '" /boot/grub/grub.cfg|sed -r "s|--class .*$||g")
#menuline=$(echo "$kernlist" | grep -ne $kernel_version | grep -v recovery | cut -f1 -d":")
#menunum=$(($menuline-2))

#echo "Boot menu list:"
#echo "$(echo "$kernlist" | grep -ne "")"
#echo "kernel $kernel_version menu entry num: $menuline - 2 = $menunum"


# NAME: grub-menu.sh
# PATH: $HOME/bin
# DESC: Written for AU Q&A: https://askubuntu.com/q/1019213/307523
# DATE: Apr 5, 2018. Modified: May 7, 2018.

# $TERM variable may be missing when called via desktop shortcut
CurrentTERM=$(env | grep TERM)
if [[ $CurrentTERM == "" ]] ; then
	notify-send --urgency=critical "$0 cannot be run from GUI without TERM environment variable."
	exit 1
fi

AllMenusArr=()										# All menu options.
# Default for hide duplicate and triplicate options with (upstart) and (recovery mode)?
HideUpstartRecovery=false
if [[ $1 == short ]] ; then
	HideUpstartRecovery=true						# override default with first passed parameter "short"
elif [[ $1 == long ]] ; then
	HideUpstartRecovery=false						# override default with first passed parameter "long"
fi
SkippedMenuEntry=false								# Don't change this value, automatically maintained
InSubMenu=false										# Within a line beginning with `submenu`?
InMenuEntry=false									# Within a line beginning with `menuentry` and ending in `{`?
NextMenuEntryNo=0									# Next grub internal menu entry number to assign
# Major / Minor internal grub submenu numbers, ie `1>0`, `1>1`, `1>2`, etc.
ThisSubMenuMajorNo=0
NextSubMenuMinorNo=0
CurrTag=""											# Current grub internal menu number, zero based
CurrText=""											# Current grub menu option text, ie "Ubuntu", "Windows...", etc.
SubMenuList=""										# Only supports 10 submenus! Numbered 0 to 9. Future use.

while read -r line; do
	# Example: "           }"
	BlackLine="${line//[[:blank:]]/}" 				# Remove all whitespace
	if [[ $BlackLine == "}" ]] ; then
		# Add menu option in buffer
		if [[ $SkippedMenuEntry == true ]] ; then
			NextSubMenuMinorNo=$(( $NextSubMenuMinorNo + 1 ))
			SkippedMenuEntry=false
			continue
		fi
		if [[ $InMenuEntry == true ]] ; then
			InMenuEntry=false
			if [[ $InSubMenu == true ]] ; then
				NextSubMenuMinorNo=$(( $NextSubMenuMinorNo + 1 ))
			else
				NextMenuEntryNo=$(( $NextMenuEntryNo + 1 ))
			fi
		elif [[ $InSubMenu == true ]] ; then
			InSubMenu=false
			NextMenuEntryNo=$(( $NextMenuEntryNo + 1 ))
		else
			continue								# Future error message?
		fi
		# Set maximum CurrText size to 68 characters.
		CurrText="${CurrText:0:67}"
		AllMenusArr+=($CurrTag "$CurrText")
	fi

	# Example: "menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu" ...
	#          "submenu 'Advanced options for Ubuntu' $menuentry_id_option" ...
	if [[ $line == submenu* ]] ; then
		# line starts with `submenu`
		InSubMenu=true
		ThisSubMenuMajorNo=$NextMenuEntryNo
		NextSubMenuMinorNo=0
		SubMenuList=$SubMenuList$ThisSubMenuMajorNo
		CurrTag=$NextMenuEntryNo
		CurrText="${line#*\'}"
		CurrText="${CurrText%%\'*}"
		AllMenusArr+=($CurrTag "$CurrText")			# ie "1 Advanced options for Ubuntu"
	elif [[ $line == menuentry* ]] && [[ $line == *"{"* ]] ; then
		# line starts with `menuentry` and ends with `{`
		if [[ $HideUpstartRecovery == true ]] ; then
			if [[ $line == *"(upstart)"* ]] || [[ $line == *"(recovery mode)"* ]] ; then
				SkippedMenuEntry=true
				continue
			fi
		fi
		InMenuEntry=true
		if [[ $InSubMenu == true ]] ; then
			: # In a submenu, increment minor instead of major which is "sticky" now.
			CurrTag=$ThisSubMenuMajorNo">"$NextSubMenuMinorNo
		else
			CurrTag=$NextMenuEntryNo
		fi
		CurrText="${line#*\'}"
		CurrText="${CurrText%%\'*}"
	else
		continue									# Other stuff - Ignore it.
	fi
done < /boot/grub/grub.cfg

LongVersion=$(grub-install --version)
ShortVersion=$(echo "${LongVersion:20}")
DefaultItem=0

if [[ $HideUpstartRecovery == true ]] ; then
	MenuText="Menu No.     ----------- Menu Name -----------"
else
	MenuText="Menu No. --------------- Menu Name ---------------"
fi

while true ; do
	Choice=$(whiptail \
		--title "Use arrow, page, home & end keys. Tab toggle option" \
		--backtitle "Grub Version: $ShortVersion" \
		--ok-button "Display Grub Boot" \
		--cancel-button "Exit" \
		--default-item "$DefaultItem" \
		--menu "$MenuText" 24 76 16 \
		"${AllMenusArr[@]}" \
		2>&1 >/dev/tty)

	clear
	if [[ $Choice == "" ]]; then break ; fi
	DefaultItem=$Choice

	for (( i=0; i < ${#AllMenusArr[@]}; i=i+2 )) ; do
		if [[ "${AllMenusArr[i]}" == $Choice ]] ; then
			i=$i+1
			MenuEntry="menuentry '"${AllMenusArr[i]}"'"
			break
		fi
	done

	TheGameIsAfoot=false
	while read -r line ; do
		if [[ $line = *"$MenuEntry"* ]]; then TheGameIsAfoot=true ; fi
		if [[ $TheGameIsAfoot == true ]]; then
			echo $line
			if [[ $line = *"}"* ]]; then break ; fi
		fi
	done < /boot/grub/grub.cfg

	read -p "Press <Enter> to continue"
done

exit 0