起风网1. 脚本判断命令输出是否为空
（1）判断字符串为空
if [ “$str” = “” ]
if [ x”$str” = x ]
if [ -z “$str” ] （-n 为非空）
注意：都要代双引号，否则有些命令会报错，养成好习惯吧！
2.输入y/n
可以使用判断符号进行数据的判断，如检查某变量是否为空 [ -z $SHELL ]，需要注意的是中括号（“[]”）内的组件必须以空格隔开。有以下脚本：
#!/bin/bashread -p "input you choice（y/n）:" choice[ "$choice" == "y" ] || [ "$choice" == "Y" ] && echo "OK,continue" && exit 0[ "$choice" == "n" ] || [ "$choice" == "N" ] && echo "Oh,interrupt!" && exit 0echo "I don't know what is your choice" && exit 0
#! /bin/shecho "Is it morning? Please answer yes or no."read YES_OR_NOif [ "$YES_OR_NO" = "yes" ]; then echo "Good morning!"elif [ "$YES_OR_NO" = "no" ]; then echo "Good afternoon!"else echo "Sorry, $YES_OR_NO not recognized. Enter yes or no." exit 1fiexit 0
(3)while条件循环
和C语言类似。比如一个验证密码的脚本：#! /bin/shecho "Enter password:"read TRYwhile [ "$TRY" != "secret" ]; do echo "Sorry, try again" read TRYdone下面的例子通过算术运算控制循环的次数：#! /bin/shCOUNTER=1while [ "$COUNTER" -lt 10 ]; do echo "Here we go again" COUNTER=$(($COUNTER+1))done
(3)case 和 while 结合
#!/bin/bashwhile : ：表示真，一直循环do 要循环执行的命令 echo -n "enter any number [1-5]:" 输入序号1-5 read nu 设置read的变量 case $nu in 进行选择，输入的要是1-5的数字 1|2|3|4|5) echo "enter anumber 1 and 5" 就循环这一行，让你不停的输入1-5 ;; *) 如果输入的不是1-5的数字 echo -n "wrong number, continue (y/n?:)" 询问你是否继续 read con 设置read的变量 case $con in 进行选择，看是不是y|yes|Y|YES这几个 y|yes|Y|YES) continue 如果是，那么就跳过，让你重新输入，如果不是 ;; *) 那么就执行这个break退出循环 break ;; esac esacdone
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