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shell学习笔记-II

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流程控制：if/case

单分支结构

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if 条件测试
then 命令序列
fi

双分支结构

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if 条件测试
then 命令序列
else 命令序列
fi

多分支结构

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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]...

case语法结构

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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

脚本实例

给用户一个提示模板

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#!/bin/bash

red_col="\e[1;31m"
reset_col="\e[0m"

read -p "请确认安装kvm[y]: " kvm_install

if [ ! ${kvm_install} = "y" ];then
        echo -e "$red_col 输入不正确! $reset_col"
        exit
fi

判断一个用户是否存在

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#!/bin/bash
read -p "please input username: " username
id $username &>/dev/null
if [ $? -eq 0 ];then
        echo "$username already exists"
else
        useradd $username
        if [ $? -eq 0 ];then
                echo "$username is created."
        fi
fi

判断当前系统版本，下载对应yum配置文件

if…else方式

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#!/bin/bash
os_version=`cat /etc/redhat-release |awk '{print $4}'|awk -F "." '{print $1}'`
repo_bk=/etc/yum.repos.d/bk/
[ -d $repo_bk ] || mkdir -p $repo_bk
mv /etc/yum.repos.d/*.repo $repo_bk

if [ "$os_version" = "7" ];then
	curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo &> /dev/null
	echo "CentOS$os_version yum configure is already."
elif [ "$os_version" = "6" ];then
	curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-6.10.repo &> /dev/null
	echo "CentOS$os_version yum configure is already."
elif [ "$os_version" = "8" ];then
	curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-8.5.2111.repo &> /dev/null
	echo "CentOS$os_version yum configure is already."
else 
	echo "The system version is not supported."
fi

case 方式

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#!/bin/bash
os_version=`cat /etc/redhat-release |awk '{print $4}'|awk -F "." '{print $1}'`
repo_bk=/etc/yum.repos.d/bk/
[ -d $repo_bk ] || mkdir -p $repo_bk
mv /etc/yum.repos.d/*.repo $repo_bk

case $os_version in 
7)
	curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo &> /dev/null
	echo "CentOS$os_version yum configure is already."
	;;
6)
	curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-6.10.repo &> /dev/null
	echo "CentOS$os_version yum configure is already."
	;;
8)
	curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-8.5.2111.repo &> /dev/null
	echo "CentOS$os_version yum configure is already."
	;;
*) 
	echo "The system version is not supported."
esac

yum安装apache

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#!/bin/bash
#install apache
#v1.0 by arlo 2022/7/20
gateway=192.168.6.254

ping -c1 t.cn &>/dev/null
if [ $? -eq 0 ];then
        yum -y install httpd
        systemctl start httpd
        systemctl enable httpd
        firewall-cmd --permanent --add-port=80/tcp --zone=public
        firewall-cmd --reload
        sed -ri s/SELINUX=enforcing/SELINUX=disabled/g /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;then
        echo "check dns..."
else
        echo "check ip address"
fi