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Shell（3）条件控制语句
一.if判断
单分支语句: 一个条件 一个结果
第一种写法: then在表达的后面 加个分号;
if 条件表达式;then 执行的命令集合 fi- 1
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第二种写法: then在if的下面条件表达式的后面不需要加分号;
if 条件表达式 then 执行命令 fi- 1
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案例：
if [ 20 -eq 20 ] then echo ok fi- 1
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if [ -f /etc/hosts ];then echo 文件存在 fi- 1
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if [[ root =~ ^r ]] then echo ok fi- 1
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if的单分支和&& 相同
一个条件 一个结果[root@test]# [ 10 -eq 10 ] && echo ok ok [root@test ]# [ 10 -eq 11 ] && echo ok [root@test ]# cat if.sh if [ 10 -eq 10 ] then echo ok fi 单条件 if [ 你有房 ] then 我就嫁给你 fi 双分支 一个条件 两个结果 if [ 你有房 ] then 我就嫁给你 else 拜拜 fi [ 10 -eq 10 ] && echo 成立 || echo 不成立- 1
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多分支 多个条件 多个结果
if [ 你有房 ] then 我就嫁给你 elif [ 你有钱 ] then 我也嫁给你 elif [ 你活好 ] Linux学的好 then 先处对象 else 拜拜 fi- 1
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案例: 根据不同的操作系统版本安装不同的YUM源
- 获取操作系统版本号
- 通过表达判断
- 部署YUM仓库
框架：
[root@test ]# cat if.sh #!/bin/bash #获取操作系统版本号 os_vs=`awk '{print $(NF-1)}' /etc/redhat-release` if [ ${os_vs%%.*} -eq 7 ] then # 备份默认YUM仓库 mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup # 下载新的YUM仓库 wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo elif [ ${os_vs%%.*} -eq 6 ] then # 备份默认YUM仓库 mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup # 下载新的YUM仓库 wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-6.10.repo elif [ ${os_vs%%.*} -eq 8 ] then # 备份默认YUM仓库 mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup # 下载新的YUM仓库 wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-8.5.2111.repo fi- 1
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完善脚本:
[root@test ]# cat if.sh #!/bin/bash #获取操作系统版本号 # 调用系统函数库 [ -f /etc/init.d/functions ] && . /etc/init.d/functions os_vs=`awk '{print $(NF-1)}' /etc/redhat-release` backup_yum='mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup' # 判断网络 ping -c1 -W1 www.baidu.com &>/dev/null if [ $? -ne 0 ] then systemctl restart network if [ $? -eq 0 ];then action "重启网卡成功" /bin/true else action "网卡重启失败请手动检查配置" /bin/false fi ping -c1 -W1 www.baidu.com &>/dev/null [ $? -ne 0 ] && action "请管理手动检查网络" /bin/false fi # 判断wget是否存在 不存在则安装 which wget &>/dev/null if [ $? -ne 0 ] then echo "正在安装wget请稍等........" yum -y install wget &>/dev/null if [ $? -eq 0 ];then action "wget install is " /bin/true else action "wget install is" /bin/false echo "正在安装wget安装成功继续执行脚本.." fi fi if [ ${os_vs%%.*} -eq 7 ] then # 备份默认YUM仓库 $backup_yum # 下载新的YUM仓库 wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo &>/dev/null if [ $? -eq 0 ];then action "yum仓库安装" /bin/true else action "yum仓库安装" /bin/false fi elif [ ${os_vs%%.*} -eq 6 ] then # 备份默认YUM仓库 $backup_yum # 下载新的YUM仓库 wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-6.10.repo elif [ ${os_vs%%.*} -eq 8 ] then # 备份默认YUM仓库 $backup_yum # 下载新的YUM仓库 wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-8.5.2111.repo fi- 1
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案例: 输入两个整数判断比较两个数大小
[root@test ]# cat num.sh #!/bin/sh read -p "Please Input two Number: " num1 num2 if [[ ! $num1 =~ ^[0-9]+$ || ! $num2 =~ ^[0-9]+$ ]];then echo "请输入整数" exit fi if [ $num1 -gt $num2 ] then echo "$num1 > $num2" elif [ $num1 -lt $num2 ] then echo "$num1 < $num2" else echo "$num1 = $num2" fi- 1
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案例: if菜单
打印输出菜单 安装多个不同的版本
[root@test ]# cat server.sh #!/bin/sh echo -e "\t\t\t\t\t \033[40;32m 1.PHP \033[0m" echo -e "\t\t\t\t\t \033[40;32m 2.Redis \033[0m" echo -e "\t\t\t\t\t \033[40;32m 3.MySQL \033[0m" echo -e "\t\t\t\t\t \033[40;32m 4.Nginx \033[0m" cat<<EOF 1.PHP 2.Redis 3.MySQL 4.Nginx EOF- 1
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二级菜单:
[root@test ]# cat server.sh #!/bin/sh echo -e "\t\t\t\t\t \033[40;32m 1.PHP \033[0m" echo -e "\t\t\t\t\t \033[40;32m 2.Redis \033[0m" echo -e "\t\t\t\t\t \033[40;32m 3.MySQL \033[0m" echo -e "\t\t\t\t\t \033[40;32m 4.Nginx \033[0m" read -p "请输入你要安装的服务名称或者编号:[1|PHP|2|Redis|3|MySQL|4|Nginx] " num if [ $num = 1 -o $num = PHP ] then echo -e "\t\t\t\t\t \033[40;34m 1.PHP5.4 \033[0m" echo -e "\t\t\t\t\t \033[40;34m 2.PHP7.1 \033[0m" echo -e "\t\t\t\t\t \033[40;34m 3.PHP7.2 \033[0m" echo -e "\t\t\t\t\t \033[40;34m 4.PHP7.4 \033[0m" read -p "请选择你要安装的版本号:[1|2|3]" num if [ $num -eq 1 ];then echo "yum_install_php5.4............." elif [ $num -eq 2 ];then echo "yum_install_php7.1............." else echo "请按照菜单选择别瞎选!!!" exit fi elif [ $num = 2 -o $num = Redis ] then echo -e "\t\t\t\t\t \033[40;33m 1.Redis-1.6 \033[0m" echo -e "\t\t\t\t\t \033[40;33m 2.Redis-1.7 \033[0m" echo -e "\t\t\t\t\t \033[40;33m 3.Redis-1.8 \033[0m" echo -e "\t\t\t\t\t \033[40;33m 4.Redis-1.9 \033[0m" read -p "请选择你要安装的版本号:[1|2|3]" num if [ $num -eq 1 ];then echo "yum_install_redis1.6............." elif [ $num -eq 2 ];then echo "yum_install_redis1.7............." fi else echo "请按照菜单选择别瞎选!!!" exit fi- 1
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完善脚本:
[root@test ]# cat server.sh #!/bin/sh while true do echo -e "\t\t\t\t\t \033[40;32m 1.PHP \033[0m" echo -e "\t\t\t\t\t \033[40;32m 2.Redis \033[0m" echo -e "\t\t\t\t\t \033[40;32m 3.MySQL \033[0m" echo -e "\t\t\t\t\t \033[40;32m 4.Nginx \033[0m" echo -e "\t\t\t\t\t \033[40;32m 5.退出脚本 \033[0m" read -p "请输入你要安装的服务名称或者编号:[1|PHP|2|Redis|3|MySQL|4|Nginx] " num if [ $num = 1 -o $num = PHP ] then while true do echo -e "\t\t\t\t\t \033[40;34m 1.PHP5.4 \033[0m" echo -e "\t\t\t\t\t \033[40;34m 2.PHP7.1 \033[0m" echo -e "\t\t\t\t\t \033[40;34m 3.PHP7.2 \033[0m" echo -e "\t\t\t\t\t \033[40;34m 4.PHP7.4 \033[0m" echo -e "\t\t\t\t\t \033[40;34m 5.返回主菜单 \033[0m" read -p "请选择你要安装的版本号:[1|2|3]" num if [ $num -eq 1 ];then echo "yum_install_php5.4............." elif [ $num -eq 2 ];then echo "yum_install_php7.1............." elif [ $num -eq 5 ];then break else echo "请按照菜单选择别瞎选!!!" exit fi done elif [ $num = 2 -o $num = Redis ] then echo -e "\t\t\t\t\t \033[40;33m 1.Redis-1.6 \033[0m" echo -e "\t\t\t\t\t \033[40;33m 2.Redis-1.7 \033[0m" echo -e "\t\t\t\t\t \033[40;33m 3.Redis-1.8 \033[0m" echo -e "\t\t\t\t\t \033[40;33m 4.Redis-1.9 \033[0m" read -p "请选择你要安装的版本号:[1|2|3]" num if [ $num -eq 1 ];then echo "yum_install_redis1.6............." elif [ $num -eq 2 ];then echo "yum_install_redis1.7............." fi elif [ $num = 5 ] then exit else echo "请按照菜单选择别瞎选!!!" echo "请重新输入编号" fi done- 1
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案例: 猜数字游戏
1.生成一个随机数
2.让用户输入数字
3.猜大小 大了提示大了 小则提示小了 输入正确则提示恭喜猜对了$RANDOM 数字范围: 0-32767
echo $((RANDOM%100+1)) 1-100的数字
[root@test ]# cat ran.sh #!/bin/bash ran=`echo $((RANDOM%100+1))` while true do let i++ read -p "请你输入要猜的数字[1-100]: " num if [ $num -gt $ran ] then echo "你输入数字的大了" elif [ $num -lt $ran ] then echo "你输入数字的小了" else echo "恭喜你猜对了中奖号码是: $ran" echo "总共猜了$i 次" exit fi done- 1
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案例：系统自动猜 并且统计猜的数字
系统猜过的数字放入一个文本
然后过滤统计判断 如果有则重复赋值
(重复赋值)[root@test ]# cat test.sh #!/bin/bash > 1.txt num=`echo $((RANDOM%100+1))` while true do while true do ran=`echo $((RANDOM%100+1))` if [ `grep -w $ran 1.txt|wc -l` -eq 1 ];then continue else let i++ echo $ran >> 1.txt break fi done if [ $num -eq $ran ];then echo "恭喜系统猜对了$i 次" exit fi done- 1
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案例：双色球
6红+1个篮球 共7个号码
6红数字范围: 1-33
1个篮球: 1-16
当前1-33里的数字被赋值 不能在给其他变量赋值#!/bin/bash > 1.txt > red.txt while true do ran=`echo $((RANDOM%33+1))` if [ `grep -w $ran 1.txt|wc -l` -eq 1 ];then continue else let i++ if [ $i -eq 7 ];then echo "红色球号码出球完毕! 等待篮色球出球" sleep 2 num=`echo $((RANDOM%16))` echo -e "蓝色球号码为: \033[40;34m $num \033[0m"|tee blue.txt break fi echo $ran >> 1.txt sleep 2 echo -e "第 $i 个双色球红球号码为: \033[40;31m $ran \033[0m"|tee -a red.txt fi done sleep 3 echo -e "本期双色球出球结果为: 红球 \033[40;31m `cat red.txt |awk '{print $5}'|sort -n|xargs -n6` \033[0m 篮球: \033[40;34m $num \033[0m"- 1
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二.for循环
语法结构: for 变量名称 in 取值列表 do 动作 done- 1
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案例：取值列表:
数字 字符串 命令 序列 以空格为分隔符
循环数字:
[root@test ]# cat for.sh #!/bin/bash for i in 1 2 3 4 5 do echo $i done [root@test ]# sh for.sh 1 2 3 4 5- 1
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循环字符串
[root@test ]# cat for.sh #!/bin/bash for i in ahui test1 b13k do echo $i done [root@test ]# sh for.sh ahui test1 b13k- 1
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值的列表可以使用双引号引用
[root@test ]# cat for.sh #!/bin/bash for i in "ahui test1" b13k do echo $i done [root@test ]# sh for.sh ahui test1 b13k- 1
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注意: 输出的结果可以和for循环的列表没有任何关系 和循环次数有关 赋值几次则动作执行几次
[root@test ]# cat for.sh #!/bin/bash for i in a b c do echo ok done [root@test ]# sh for.sh ok ok ok- 1
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统计循环或者赋值次数
[root@test ]# cat for.sh #!/bin/bash for i in a b c do let a++ done echo $a [root@test ]# sh for.sh 3- 1
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案例：for循环读取文件
[root@test ]# cat /etc/hosts 127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6 [root@test ]# cat for.sh #!/bin/bash for i in `cat /etc/hosts` do echo $i done [root@test ]# sh for.sh 127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6- 1
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for循环支持序列
支持字符
[root@test ]# cat for.sh #!/bin/bash for i in {a..c} do echo $i done [root@test ]# sh for.sh a b c- 1
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支持数字
[root@test ]# cat for.sh #!/bin/bash for i in {1..10} do echo $i done [root@test ]# sh for.sh 1 2 3 4 5 6 7 8 9 10- 1
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支持命令
[root@test ]# cat for.sh #!/bin/bash for i in `seq 10` do echo $i done- 1
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案例1: 测试一个网段内的IP地址是否在线
ping通则为在线
[root@test ]# cat for.sh #!/bin/bash for i in {1..10} do { ip=10.0.0.$i ping -c1 -W1 $ip &>/dev/null if [ $? -eq 0 ] then echo "$ip 在线" fi } & done wait # 等待后台程序执行完毕后继续往下执行 echo done..................- 1
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案例2: 批量创建用户 每个用户8位随机密码 并且保存用户名对应密码关系表
要求用户输入前缀 用户输入个数test01…test10
[root@test ]# cat user.sh #!/bin/bash read -p "请输入用户名称的前缀: " prefix read -p "请输入要创建用户的个数: " num for i in `seq $num` do echo ${prefix}$i done read -p "删除还是创建以上用户[y|n]" re if [ $re = y ] then for a in `seq $num` do user=${prefix}$a id $user &>/dev/null if [ $? -ne 0 ];then useradd $user if [ $? -eq 0 ];then echo "$user 创建成功" fi else echo "useradd: user $user 已存在" fi done elif [ $re = n ] then for b in `seq $num` do user=${prefix}$b id $user &>/dev/null if [ $? -eq 0 ];then userdel -r $user [ $? -eq 0 ] && echo "$user 删除成功" else echo "$user 不存在" fi done fi- 1
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案例3: for循环从1加到100 笔试题
[root@test ]# cat for1.sh #!/bin/bash for i in {1..100} do count=$[$count+$i] done echo $count [root@test ]# cat for1.sh #!/bin/bash for i in {1..100} do count=$[count+i] # 此处括号中可以不加$ done echo $count [root@test ]# seq -s + 100|bc 5050- 1
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案例4:反向破解随机数的MD5值
[root@test ]# cat for2.sh num1=31d30eea8d0968d6458e0ad0027c9f80 for i in `seq 15` do ran=`echo ${i}|md5sum|awk '{print $1}'` if [ $num1 = $ran ] then echo "$i $ran" fi done [root@test ]# sh for2.sh 10 31d30eea8d0968d6458e0ad0027c9f80- 1
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- 原文地址：https://blog.csdn.net/AHui_CSDN/article/details/126142907
