#!/bin/bash
read -p  "input a integer:"  num
flag=true
while $flag
do
expr $num + 0 &>/dev/null
  [ $? -eq 0 ] && flag=false || read -p "please input a integer:" num
done

 [[ ${num}%7 -eq 0 && ${num}%3 -ne 0 ]] && b="first"
 [[ ${num}%7 -eq 0 && ${num}%3 -eq 0 ]] && b="second"
 [[ ${num}%7 -ne 0 && ${num}%3 -eq 0 ]] && b="third"
 [[ ${num}%7 -ne 0 && ${num}%3 -ne 0 ]] && b="fourth"
 case $b in
first)
  echo "第一类"
;;
second)
  echo "第二类"
;;
third)
  echo "第三类"
;;
fourth)
  echo "第四类"
;;
*)
  echo "输入有误"
esac