select.sh

select.sh

#!/usr/bin/env bash

# Renders a text based list of options that can be selected by the
# user using up, down and enter keys and returns the chosen option.
#
# Usage:
# echo "Select one option using up/down keys and enter to confirm:"
# options=("one" "two" "three")
# select_option "${options[@]}"
# choice=$?
# echo "Choosen index = $choice"
# echo "        value = ${options[$choice]}"
select_option() {
  # little 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 "   $1 "; }
  print_selected()   { printf "  $ESC[7m $1 $ESC[27m"; }
  get_cursor_row()   { IFS=';' read -sdR -p $'\E[6n' ROW COL; echo ${ROW#*[}; }
  key_input()        { read -s -n3 key 2>/dev/null >&2
    if [[ $key = $ESC[A ]]; then echo up;    fi
    if [[ $key = $ESC[B ]]; then echo down;  fi
    if [[ $key = ""     ]]; then echo enter; fi; }

  # initially print empty new lines (scroll down if at bottom of screen)
  for opt; do printf "\n"; done

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

  # 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

  local selected=0
  while true; do
    # print options by overwriting the last lines
    local idx=0
    for opt; do
      cursor_to $(($startrow + $idx))
      if [ $idx -eq $selected ]; then
        print_selected "$opt"
      else
        print_option "$opt"
      fi
      ((idx++))
    done

    # user key control
    case `key_input` in
      enter) break;;
      up) ((selected--)); if [ $selected -lt 0 ]; then selected=$(($# - 1)); fi;;
      down) ((selected++)); if [ $selected -ge $# ]; then selected=0; fi;;
    esac
  done

  # cursor position back to normal
  cursor_to $lastrow
  printf "\n"
  cursor_blink_on

  return $selected
}

echo "Select one option using up/down keys and enter to confirm:"
options=("one" "two" "three")
select_option "${options[@]}"
choice=$?
echo "Choosen index = $choice"
echo "        value = ${options[$choice]}"