Sample zsh script with both interactive user menu and direct input

eat-food.zsh

#!/usr/bin/env zsh

# Call this script with:
# ./eat-food.zsh [opt]
# 
# If a food is given, and is in the valid foods (opts array), it will eat the given food
# e.g. ./eat-food.zsh bananas
#
# If a food is given, but it's not valid, it will prompt for a food to eat
# e.g. ./eat-food.zsh pineapples
#
# If no food is given, it will show the food menu
# e.g. ./eat-food.zsh

declare -A opts
opts=( [1]=apples [2]=potatoes [3]=bananas [q]=quit )

function eat_food() {
  food_name="$1"
  echo "I am eating $food_name!"
}

function opts_has_value() {
  for value in ${(v)opts}; do
    if [ "$value" = "$1" ]; then
      return 0
    fi
  done
  return 1
}

function opts_has_key() {
  for key in ${(k)opts}; do
    if [ "$key" = "$1" ]; then
      return 0
    fi
  done
  return 1
}

function print_menu() {
  echo "== Make your selection:"
  for key in ${(kon)opts}; do
    echo "$key -> $opts[$key]"
  done
}

function read_from_menu() {
  while true; do
    print_menu
    while true; do
      echo -n "> "
      read selection
      echo
      if ! opts_has_key $selection
      then
        echo "[ERROR] Invalid option: $selection"
        echo
        break
      elif [ $selection = "q" ]
      then
        echo "Ok, bye!"
        exit 0
      else
        food_name=$opts[$selection]
        eat_food "$food_name"
        exit 0
      fi
    done
  done
}

if [ $1 ] && opts_has_value $1
then
  eat_food "$1"
else
  read_from_menu
fi