Shell脚本循环语句——until循环

标签：until循环语法格式   until循环应用实例   

 until循环
 使用于命题为假时执行循环的环境
 命题为假时进入循环；命题为真时退出循环
 或者说是条件不满足时就进入循环的的场景
 从逻辑判断上讲，until和while刚好相反

语法格式：
 until CONDITION; do
 循环体
 done
 进入条件： CONDITION 为false
 退出条件： CONDITION 为true
 

until循环应用实例：

1，计算1-100之间所有正整数的和

#!/bin/bash

#Author:wangjun
#Contact QQ:183530300
#Version:1.0
#Create time:2016-08-17 17:08:54
#Description:1-100 all positive integer‘s sum

declare -i I=1
declare -i sum=0

until [[ $I -gt 100 ]];do
  let sum+=$I
  let I++
done
echo "1-100 all positive integer‘s sum : $sum"

2，自动扫描1-254网段的所有主机，统计在线主机数与不在线主机数

#!/bin/bash

#Author:wangjun
#Contact QQ:183530300
#Version:1.0
#Create time:2016-08-17 16:30:28
#Description:ping all host and count the number

declare -i online=0
declare -i offline=0
declare -i host=1

until [[ $host -ge 255 ]];do
  ping -c 1 -W 1 10.1.250.$host &> /dev/null && echo "10.1.250.$host is online" && let online=$online+1 || let offline=$offline+1
  let host=$host+1
done
echo "Online hosts number : $online"
echo "Offline hosts number : $offline"

3，生成10个随机数，并找出最大随机数和最小随机数

#!/bin/bash

#Author:wangjun
#Contact QQ:183530300
#Version:1.0
#Create time:2016-08-17 20:44:27
#Description:Random number comparative

minrandom=$RANDOM
maxrandom=$minrandom
declare -i R=1

echo $minrandom

until [[ $R -gt 9 ]];do
  RD=$RANDOM
  echo $RD
  if [[ $RD -gt $maxrandom ]];then
   maxrandom=$RD
  elif [[ $RD -lt $minrandom ]];then
   minrandom=$RD
  fi
  let R++
done
echo "Minrandom is : $minrandom"
echo "Maxrandom is : $maxrandom"

4，打印九九乘法表

#!/bin/bash

#Author:wangjun
#Contact QQ:183530300
#Version:1.0
#Create time:2016-08-16 21:57:22
#Description:99 multiplication tab

declare -i Row=1
declare -i Column=1

until [[ $Row -gt 9 ]];do
  until [[ $Column -gt $Row ]];do
   echo -ne "${Column}x${Row}=$[$Column*${Row}]\t"
 let Column++
  done
  Column=1
  let Row++
  echo
done

5,每隔3秒钟查询系统上已经登录的用户信息，如果发现hacker用户登录，则将登录时间和主机记录于日志/var/log/login.log中,并提示hacker用户退出系统

#!/bin/bash

#Author:wangjun
#Contact QQ:183530300
#Version:1.0
#Create time:2016-08-17 22:36:44
#Description:Monitor whether the hacker user has logged on current system

until who | grep "^hacker\>";do
  echo -e "`date +%T`\thacker user doesn‘t logged on"
  sleep 3
done
echo -e "`date +%T`\thacker user logged on" | tee /var/log/login.log
echo "Please exit current system" | write hacker

本文出自 “爱情防火墙” 博客，请务必保留此出处http://183530300.blog.51cto.com/894387/1840663

Shell脚本循环语句——until循环

标签：until循环语法格式   until循环应用实例   

原文地址：http://183530300.blog.51cto.com/894387/1840663