#!/bin/bash

if [ $# -ne 2 ] 
then
  echo "$0: need 2 arguments: directory subdirectory"
  exit 1
fi
if [[ ! -d $1 ]] 
then
  echo "${0}: $1 is not a directory"
  exit 1
fi
if [[ ! -d $1/$2 ]]
then
  echo "${0}: $2 is not a subdirectory of $1"
  exit 1
fi
ls $1/$2

# exit code is taken from last command(s) executed if not given explicitly