yesかnoを訪ねて、yesの場合は処理をする

yes_or_no_prompt.sh

#!/bin/sh

while true; do
  read -p "Do you wish to install this program? [y/n]" yn
  case $yn in
      [Yy] ) echo "Install!"; break;;
      [Nn] ) exit;;
      * ) echo "Please answer y or n.";;
  esac
done