Write a simple computer using the shell

This is a computer written by the shell, support add, subtract, multiply, divide, take the mold, and provide user input content detection, share to everyone.

#!/bin/bash     #这是一个计算器!     read -p  "Please enter the first number:"  -t 30 num1    read  -p  "Please enter the second number:"  -t 30 num2    read -p  "Please enter the operation symbol (support   + - * / %): " -t 30 op    if [ -n " $num 1 "  -a -n  "$num 2"  -a -n  "$op"  ]    then     n1=$ (echo  $num 1 | sed  ' s/[0-9]//g ')     n2=$ (echo  $num 2  | sed  ' s/[0-9]//g ')     if [ -z  "$n 1"  -a -z  " $n 2 " ]    then    case  $op  in       "+")     r=$ (($num 1 +  $num 2)     ;;      "-")     r=$ (($num 1 -  $num 2)     ;;     "*")     r=$ (($num 1 *  $num 2))     ;;      "/")     r=$ (($num 1 /  $num 2)     ;;      "%")     r=$ (($num 1 %  $num 2))     ;;     *)     echo  "Please enter the correct operator!" "    exit 10    ;;     esac    else    echo  "Please enter the correct number!" "    exit 11    fi    else     echo  "Please enter the correct content!" "    exit 12    fi    echo " $num 1$op$ Num2= $R "

Write a simple computer using the shell