简要说明：
提示用户输入两个数字；
判断输入的内容是否都为数字；
数字做计算并反馈结果；
计算完毕后询问客户是否继续使用；
给用户提供随时退出的方法。
[root@lb02 scripts]# cat jisuan2.sh
#!/bin/bash
###thank_oldboy
###2016/3/6
###i wish you all the best.
. /etc/init.d/functions
### read number.
function read_number(){
read -p "please enter the number1:" num1
read -p "please enter the number2:" num2
panduan_number
}
### judge $number1 $number2 both are number.
function panduan_number() {
expr $num1 + $num2 &>/dev/null
[ $? -ne 0 ] && {
[[ $num1 == exit || $num2 == exit ]] && {
echo "you had choice leave,bye."
exit 0
} || {
echo "USAGE:you must enter two numbers, or enter exit to leave."
read_number
}
} || judge_number
}
### judge continue or exit.
function continue_or_exit() {
read -p "please enter go to continue or enter out to leave: " str
case "$str" in
go)
read_number
;;
out)
echo "hope to see you again,bye."
exit 0
;;
*)
echo "USAGE:enter go or out:"
continue_or_exit
;;
esac
}
### expr $number1 $number2.
function judge_number() {
[ $num1 -eq $num2 ] && {
echo "$num1 equal $num2."
continue_or_exit
}
[ $num1 -gt $num2 ] && {
echo "$num1 greater than $num2."
continue_or_exit
}
[ $num1 -lt $num2 ] && {
echo "$num1 lower than $num2."
continue_or_exit
}
}
### the gate of the script.
function main() {
read_number
}
main
原文：http://10546390.blog.51cto.com/10536390/1748133