04Shell流程控制

流程控制

if

单分支结构

if 条件测试
then 命令序列
fi

双分支结构

if 条件测试
then 命令序列
else 命令序列
fi

多分支结构

if 条件测试 1
then 命令序列
[elif 条件测试 2
then 命令序列
elif 条件测试 3
then 命令序列]...
else 命令序列
fi  

示例说明

例1

安装httpd脚本(初始版本)：判断网络是否正常，正常就安装，异常就直接退出

[root@hadoop04 shell_if]# vim install_apache01.sh 
#!/usr/bin/bash
##########################################
# install apache                         #
# v1.0 by ElegantSmile 8/12/2019         #
##########################################

ping -c1 www.baidu.com &> /dev/nul

if [ $? -ne 0 ];then
  echo "connect: unreachable"
  exit
fi


yum -y install httpd

systemctl start httpd

systemctl enable httpd

firewall-cmd --permanent --add-service=http
firewall-cmd --permanent --add-service=https
firewall-cmd --reload

sed -ri '/^SELINUX=/cSELINUX=disabled' /etc/selinux/config

setenforce 0

例2

安装httpd脚本(改进版)：判断网络是否正常，正常就安装，异常就先判断是否可以测通网关，否则提示检查IP地址

[root@hadoop04 shell_if]# vim install_apache02.sh
#!/usr/bin/bash
##########################################
# install apache                         #
# v1.1 by ElegantSmile 8/12/2019         #
##########################################

gateway=172.22.34.1

ping -c1 www.baidu.com &> /dev/nul

if [ $? -eq 0 ];then
        yum -y install httpd
        systemctl start httpd
        systemctl enable httpd
        firewall-cmd --permanent --add-service=http
        firewall-cmd --permanent --add-service=https
        firewall-cmd --reload
        sed -ri '/^SELINUX=/cSELINUX=disabled' /etc/selinux/config
        setenforce 0

        curl http://127.0.0.1 &> /dev/null
        if [ $? -eq 0 ];then
                echo "Apache ok..."
        fi
elif ping -c1 ${gateway} &> /dev/null
        echo "check dns..."
else
        echo "check ip address!"
fi

例3

read -p "确认开始安装 KVM [y]: " kvm_install
if [ ! "${kvm_install}" = "y" ];then
echo -e "$red_col 输入不正确! $reset_col"
exit
fi  

例4

配置yum源脚本

阿里云yum配置帮助：https://developer.aliyun.com/mirror/centos?spm=a2c6h.13651102.0.0.53322f70C917rC

阿里云镜像仓库：https://developer.aliyun.com/mirror

#!/usr/bin/bash
##########################################
# yum  config                            #
# v1.0 by ElegantSmile 8/12/2019         #
##########################################

yum_server=10.18.40.100
os_version=`cat /etc/redhat-release | awk '{print $(NF-1)}' | awk -F "." '{print $1}'`

# 备份yum源文件方式1
# [ -d /etc/yum.repos.d/bak ] || mkdir /etc/yum.repos.d/bak
#mv /etc/yum.repos.d/*.repo /etc/yum.repos.d/bak/

# 备份yum源文件方式2
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup

# 7纯属测试本地yum源，建议使用6和8的方式下载阿里云的yum源文件
if [ "${os_version}" = "7" ];then
        cat > /etc/yum.repos.d/centos7u6.repo
        [centos7u6]
        name=centos7u6
        baseurl=ftp://$yum_server/centos7u6
        gpkcheck=0
        EOF
# 建议做法: curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

# 6和8下载阿里云的yum源文件
elif [ "${os_version}" = "6" ];then
        curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo
elif [ "${os_version}" = "8" ];then
        curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-8.repo
fi

例5

检查某软件包是否已经安装

#!/usr/bin/bash
##########################################
# check vsftpd install                   #
# v1.0 by ElegantSmile 9/12/2019         #
##########################################

# 可以通过$1传参
# rpm_name=$1
rpm_name=vsftpd

# 检查安装包是否已经安装
rpm -qa | grep ${rpm_name}

# 已经安装的话，提示已经安装
if [ $? -eq 0 ];then
        echo "${rpm_name} is installed."
# 未安装的话，可以提示未安装，也可以执行安装操作
else
        echo "${rpm_name} is not installed."
fi

case

语法结构

case 变量 in
模式 1)
命令序列 1
;;
模式 2)
命令序列 2
;;
模式 3)
命令序列 3
;;
*)
无匹配后命令序列
esac 

示例说明

例1

配置yum源脚本

[root@hadoop04 shell_case]# vim yum_config.sh
#!/usr/bin/bash
##########################################
# yum  config                            #
# v1.0 by ElegantSmile 9/12/2019         #
##########################################

os_version=`cat /etc/redhat-release | awk '{print $(NF-1)}' | awk -F "." '{print $1}'`

# 备份yum源文件
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup &> /dev/null && echo "CentOS-Base.repo backup done"

# 下载阿里云的yum源文件
case "${os_version}" in
"8")
        curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-8.repo
        echo "yum configure done"
        ;;
"7")
        curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
        echo "yum configure done"
        ;;
"6")
        curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo
        echo "yum configure done"
        ;;
"*")
        echo "error"
esac

# if 结构的yum配置
#if [ "${os_version}" = "7" ];then
#       curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
#elif [ "${os_version}" = "6" ];then
#       curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo
#elif [ "${os_version}" = "8" ];then
#       curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-8.repo
#fi

例2

删除用户脚本：判断用户是否存在，如果存在，询问是否确认删除

[root@hadoop04 shell_case]# cat del_user.sh
#!/usr/bin/bash
##########################################
# yum  config                            #
# v1.0 by ElegantSmile 9/12/2019         #
##########################################

red_col="e[31m"
green_col="e[32m"
reset_col="e[0m"


read -p "Please input a username: " username

id ${username} &> /dev/null

if [ $? -ne 0 ];then
	echo -e "user ${red_col}${username}${reset_col} not exists."
	exit 1
fi


read -p "Are you sure?[y/n]: " action
case "${action}" in 
y|Y|yes|YES)
	userdel -r ${username}
	echo -e "user ${green_col}${username}${reset_col} is deleted."
	;;
*)
	echo "error"
esac

例3

系统管理工具箱(初始版本)

[root@hadoop04 shell_case]# vim system_manage01.sh
#!/usr/bin/bash
##########################################
# system  manage                         #
# v1.0 by ElegantSmile 9/12/2019         #
##########################################

red_col="e[31m"
green_col="e[32m"
reset_col="e[0m"
blue_col="e[34m"

menu() {
        cat <<-EOF
        ##########系统管理工具箱#############
        #       Command action              #
        #       h 显示命令帮助              #
        #       f 显示磁盘分区              #
        #       d 显示磁盘挂载              #
        #       m 查看内存使用              #
        #       u 查看系统负载              #
        #       q 退出程序                  #   
        #####################################
        EOF
}

menu

echo -e "${blue_col}command (h for help):${reset_col} c"

read action

#echo "Your choice is ${choice}"

case "${action}" in
"h")
		clear
		menu
		;;
"f")
		fdisk -l
		;;
"d")
		df -Th
		;;
"m")
		free -m
		;;
"u")
		uptime | awk -F ",  " '{print $NF}'
		;;
"q")
		#exit
		break
		;;
*)
		echo "error input"
		;;
esac

例4

系统管理工具(优化版)：增加循环，不会输入一次选项就直接退出，输入q才会退出；输入空白跟输入错误的提示不同

[root@hadoop04 shell_case]# vim system_manage02.sh
#!/usr/bin/bash
##########################################
# system  manage                         #
# v1.1 by ElegantSmile 9/12/2019         #
##########################################

red_col="e[31m"
green_col="e[32m"
reset_col="e[0m"
blue_col="e[34m"

menu() {
	cat <<-EOF
	##########系统管理工具箱#############
	#	Command action   	    #
	#	h 显示命令帮助		    #
	#	f 显示磁盘分区		    #
	#	d 显示磁盘挂载		    #
	#	m 查看内存使用		    #
	#	u 查看系统负载              #
	#	q 退出程序                  #   
	#####################################
	EOF
}


menu

# while :循环，相当于 while true:
while :
do

        echo -e "${blue_col}command (h for help):${reset_col} c"

        read action

        #echo "Your choice is ${choice}"

        case "${action}" in
        "h")
                clear
                menu
                ;;
        "f")
                fdisk -l
                ;;
        "d")
                df -Th
                ;;
        "m")
                free -m
                ;;
        "u")
                uptime | awk -F ",  " '{print $NF}'
                ;;
        "q")
                #exit
                break
                ;;
        "")
                ;;
         *)
                echo "error input"
                ;;
        esac

done

简单的 JumpServer

虚拟机准备

jumpserver 172.22.34.20

client server1 172.22.34.16

client server2 172.22.34.15

client server配置

创建alice用户，并设置密码

[root@hadoop00 ~]# useradd alice
[root@hadoop00 ~]# passwd alice

jump server配置

编写jumpserver.sh脚本

[root@hadoop04 shell_case]# cat jump_server.sh 
#!/usr/bin/bash
##########################################
# jump server                            #
# v1.0 by ElegantSmile 9/12/2019         #
##########################################

reset_col="e[0m"
blue_col="e[34m"
red_col="e[31m"

# 捕捉到相应的键盘信号，不做任何操作
trap "" HUP INT OUIT TSTP

web1=172.22.34.16
web2=172.22.34.17
mysql1=172.22.34.18

clear

while :
do
        cat <<-EOF
        +------------------------------------------------+      
        |       Jump server                              |
        |       1.web1                                   |
        |       2.web2                                   |
        |       3.mysql1                                 |
        +------------------------------------------------+
        EOF
		# 文字显示颜色，并且不换行，有两种实现方式
		# -e c
		# -en
        # echo -e "${blue_col}请选择要连接的主机[1-3]:${reset_col} c"
        echo -en "${blue_col}请选择要连接的主机[1-3]:${reset_col}"

        read action

        case "${action}" in
        "1")
                ssh alice@${web1}
                ;;
        "2")
                ssh alice@${web2}
                ;;
        "3")
                ssh alice@${mysql1}
                ;;
        "")
                ;;
        *)
                echo -e "${red_col}error input${reset_col}"
                ;;
        esac
done

创建用户alice

[root@hadoop04 ~]# useradd alice
[root@hadoop04 ~]# passwd alice
# 将jumpserver.sh拷贝到alice的家目录

生成密钥

# 切换到alice用户
[root@hadoop04 ~]# su - alice

[alice@hadoop04 ~]$ ssh-keygen 
Generating public/private rsa key pair.

Enter file in which to save the key (/home/alice/.ssh/id_rsa): Created directory '/home/alice/.ssh'.
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/alice/.ssh/id_rsa.
Your public key has been saved in /home/alice/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:TiwMdEGhaYU3zv3N9b8aNHBglFr9Wh9i4Rj6tyT7e/U alice@hadoop04
The key's randomart image is:
+---[RSA 2048]----+
|    .o*o  .+o    |
|   ..=o   .+.o   |
|    =+ o  +.+.o  |
|   . oo..o .o+.+ |
|      o S..o.++.o|
|       +  .o++. +|
|        .   =.. +|
|           . ...E|
|            .++..|
+----[SHA256]-----+

拷贝密钥

[alice@hadoop04 ~]$ ssh-copy-id 172.22.34.16


[alice@hadoop04 ~]$ ssh-copy-id 172.22.34.17


[alice@hadoop04 ~]$ ssh-copy-id 172.22.34.18

配置执行脚本

切换到alice用户，配置.bashrc文件

[alice@hadoop04 ~]$ vim ~/.bashrc

/bin/bash /home/alice/jump_server.sh

实际效果

登录到alice用户

只能输入数字1-3，Ctrl+C之类的命令无效，无法退出，也就说只能通过这台机器跳转到其他机器，无法在该机器上进行其他操作