Ephemeral Interactive Bash Menu with Up/Down selection or numeral selection

bash_menu.sh

# Original solution sourced from:
#       https://unix.stackexchange.com/questions/146570/arrow-key-enter-menu
#
# Updated to do the following:
#   - Display index with each option
#   - Choose options 1-9 with numeric input
#   - Clear the menu and reset the cursor when an option is selected
#
#  Arguments:
#    array of options
#
#  Return value:
#    selected index (0 for opt1, 1 for opt2 ...)

function select_option {
  local header="\nAdd A Header\nWith\nAs Many\nLines as you want"
  header+="\n\nPlease choose an option:\n\n"
  printf "$header"
	options=("$@")

	# helpers for terminal print control and key input
	ESC=$(printf "\033")
	cursor_blink_on()	{ printf "$ESC[?25h"; }
	cursor_blink_off()	{ printf "$ESC[?25l"; }
	cursor_to()			{ printf "$ESC[$1;${2:-1}H"; }
	print_option()		{ printf "\t   $1 "; }
	print_selected()	{ printf "\t${COLOR_GREEN}  $ESC[7m $1 $ESC[27m${NC}"; }
	get_cursor_row()	{ IFS=';' read -sdR -p $'\E[6n' ROW COL; echo ${ROW#*[}; }
  key_input() {
    local key
    # read 3 chars, 1 at a time
    for ((i=0; i < 3; ++i)); do
      read -s -n1 input 2>/dev/null >&2
      # concatenate chars together
      key+="$input"
      # if a number is encountered, echo it back
      if [[ $input =~ ^[1-9]$ ]]; then
        echo $input; return;
      # if enter, early return
      elif [[ $input = "" ]]; then
        echo enter; return;
      # if we encounter something other than [1-9] or "" or the escape sequence
      # then consider it an invalid input and exit without echoing back
      elif [[ ! $input = $ESC && i -eq 0 ]]; then
        return
      fi
    done

    if [[ $key = $ESC[A ]]; then echo up; fi;
    if [[ $key = $ESC[B ]]; then echo down; fi;
  }
  function cursorUp() { printf "$ESC[A"; }
  function clearRow() { printf "$ESC[2K\r"; }
  function eraseMenu() {
    cursor_to $lastrow
    clearRow
    numHeaderRows=$(printf "$header" | wc -l)
    numOptions=${#options[@]}
    numRows=$(($numHeaderRows + $numOptions))
    for ((i=0; i<$numRows; ++i)); do
      cursorUp; clearRow;
    done
  }

	# initially print empty new lines (scroll down if at bottom of screen)
	for opt in "${options[@]}"; do printf "\n"; done

	# determine current screen position for overwriting the options
	local lastrow=`get_cursor_row`
	local startrow=$(($lastrow - $#))
  local selected=0

	# ensure cursor and input echoing back on upon a ctrl+c during read -s
	trap "cursor_blink_on; stty echo; printf '\n'; exit" 2
	cursor_blink_off

	while true; do
    # print options by overwriting the last lines
		local idx=0
    for opt in "${options[@]}"; do
      cursor_to $(($startrow + $idx))
      # add an index to the option
      local label="$(($idx + 1)). $opt"
      if [ $idx -eq $selected ]; then
        print_selected "$label"
      else
        print_option "$label"
      fi
      ((idx++))
    done

		# user key control
    input=$(key_input)

		case $input in
			enter) break;;
      [1-9])
        # If a digit is encountered, consider it a selection (if within range)
        if [ $input -lt $(($# + 1)) ]; then
          selected=$(($input - 1))
          break
        fi
        ;;
			up)	((selected--));
					if [ $selected -lt 0 ]; then selected=$(($# - 1)); fi;;
			down)  ((selected++));
					if [ $selected -ge $# ]; then selected=0; fi;;
		esac
	done

  eraseMenu
	cursor_blink_on

	return $selected
}

# example usage
one="Option One"
two="Option Two"
three="Option Three"
options=("$one" "$two" "$three")

select_option "${options[@]}"
result="${options[$?]}"

echo "You chose: $result"