bash 计算器

输入两个数实现加减乘除运算

1，read

#!/bin/bash
print_usage () {                                    #定义一个函数，名字为print_usageprintf "please enter an integer\n"             #打印符合脚本要求的提示信息exit 1 
}
read -p "please input first number: " firstnumif [ -n "`echo $firstnum|sed 's/[0-9]//g'`" ]; then
#判断是否为整数，删除读入内容的数字部分看是否为空(-n功能),进而判断读入的内容是否为数字print_usage  #如果上诉条件变量不为空，说明不是整数，则调用用户帮助函数
fi
read -p "please input the operators: " operators
if [ "${operators}" != "+" ] && [ "${operators}" != "-" ] && [ "${operators}" != "*" ] && [ "${operators}" != "/" ]; thenecho "please use{+|-|*|/}"exit 2
fi
read -p  "please input second number: " secondnum
if [ -n "`echo $secondnum|sed 's/[0-9]//g'`" ]; thenprint_usage
fi
echo "${firstnum}${operators}${secondnum}=$((${firstnum}${operators}${secondnum}))"

2. printf

#!/bin/bash
print_usage () {printf $"USAGE:$0 NUM1 {+|-|*|/} NUM2\n"exit 1}if [ $# -ne 3 ] #如果脚本传入的参数不等于3个(两个数字一个运算符号)thenprint_usagefifirstnum=$1
secondnum=$3
op=$2if [ -n "`echo $firstnum|sed 's/[0-9]//g'`"]thenprint_usagefiif [ "$op" != "+" ]&&[ "$op" != "-" ]&&[ "$op" != "*" ]&&[ "$op" != "/" ]thenprint_usagefiif [ -n "`echo $secondnum|sed 's/[0-9]//g'`"]thenprint_usagefiecho "${firstnum}${op}${secondnum}=$((${firstnum}${op}${secondnum}))"

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