linux12shell编程 --＞流程if判断
文章目录
流程控制之if判断
一、单分支if
1、语法
if 条件;then
要执行的命令1
要执行的命令2
要执行的命令3
...
fi
# 上述语法可以用一行代码代替
[ 条件信息 ] && xxx
# 案例
[root@openvpn shell]# cat if1.sh
# !/bin/bash
if [ $# -ne 2 ] || [[ ! $1 =~ ^[0-9]+$ ]] || [[ ! $2 =~ ^[0-9]+$ ]];then
echo "Usage: $0 arg1 arg2"
echo "arg1 必须是整型数字"
echo "arg2 必须是整型数字"
exit
fi
2、示例
# 案例一
[root@openvpn shell]# cat check_disk.sh
#! /bin/bash
use=`df -h | grep "/$" |awk '{print $5}'|cut -d% -f1`
if [ $use -gt 1 ];then
echo "df: ${use}% warning:Not enough hard disk space"
fi
# 案例二
[root@openvpn shell]# cat ps-aux.sh
#! /bin/bash
if ps -aux |grep [s]sh &>/dev/null;then
echo "sshd is up"
fi
# 案例三
[root@openvpn day1]# cat check_disk1.sh
#! /bin/bash
NUM=0
for i in `df -h | egrep '[0-9]+%' |awk '{print $5}' |cut -d% -f1`
do
if [ $i -ge 10 ];then
let NUM++
fi
done
echo "当磁盘使用率超过10%的个数：$NUM"
注意：if 测试中还可以执行命令 根据命令的返回值做判断
[root@lb4 yum.repos.d]# if ls ;then echo ok;fi
backup mm.repo
ok
[root@openvpn /]# if grep -q root /etc/passwd ;then echo Y ;fi
Y
二：双分支if
1、语法
if 条件;then
要执行的命令1
要执行的命令2
要执行的命令3
...
else
要执行的命令1
要执行的命令2
要执行的命令3
...
fi
# 上述语法可以用一行代码代替
[ 条件信息 ] && xxx || xxxx
2、示例
#!/bin/bash
username='openvpn'
password='123'
read -p 'user: ' name
read -p 'passwd: ' passwd
if [[ $name == $username ]] && [[ $password == $passwd ]];then
echo 'login successful'
else
echo 'username or password err'
fi
三：多分支if
1、语法：
if 条件;then
要执行的命令1
要执行的命令2
要执行的命令3
...
elif 条件;then
要执行的命令1
要执行的命令2
要执行的命令3
...
...
else
要执行的命令1
要执行的命令2
要执行的命令3
...
fi
示例1:猜年龄
======================版本1======================
#!/bin/bash
age=18
read -p 'num: ' n
if [ $n -eq $age ];then
echo 'you get it'
elif [ $n -gt $age ];then
echo 'too big'
elif [ $n -lt $age ];then
echo 'too small'
fi
# 方式二
[root@openvpn day1]# cat age.sh
#! /bin/bash
age=18
read -p "请输入年龄:" ager
if [ $ager -eq $age ];then
echo "ok"
elif [ $ager -ge $age ];then
echo "big"
else
echo "small"
fi
======================版本2======================
#!/bin/bash
read -p ">>> " num
[[ ! $num =~ ^[0-9]+$ ]] && echo "请输入数字" && exit
if [ $num -gt 18 ];then
echo "too big"
elif [ $num -lt 18 ];then
echo "too small"
else
echo "you got it"
fi
示例2：查询成绩
======================版本1======================
#!/bin/bash
read -p 'your score: ' score
if [ $score -ge 90 ];then
echo '优秀'
elif [ $score -ge 70 -a $score -lt 90 ];then
echo '良好'
elif [ $score -ge 60 -a $score -lt 70 ];then
echo '一般'
elif [ $score -lt 60 ];then
echo '较差'
fi
======================版本2======================
#!/bin/bash
read -p "your score>>> " score
[[ ! $score =~ ^[0-9]+$ ]] && echo "请输入数字" && exit
if [ $score -ge 90 ];then
echo "优秀"
elif [ $score -ge 70 ];then
echo "良好"
elif [ $score -ge 60 ];then
echo "一般"
else
echo "较差"
fi
示例3：判断是否是数字
read -p "请输入一个数值: " num
while :
do
if [[ $num =~ ^[0-9]+$ ]];then
break
else
read -p "不是数字，请重新输入数值: " num
fi
done
echo "你输入的数字是: $num"
# 方式二
[root@openvpn day1]# cat num1.sh
while true;
do
read -p "请输入一个数值>> " num1
if [[ $num1 =~ ^[0-9]+ ]];then
break
else
echo "不是数字重新输入"
fi
done
四 、练习
1、编写脚本，命令行传入一个文件路径，判断文件的类型
[root@localhost ~]# cat test_file.sh
#!/bin/bash
if [ -d $1 ]
then
echo "$1 is directory"
elif [ -b $1 ]
then
echo "$1 is block"
elif [ -f $1 ]
then
echo "$1 is regular file"
else
echo 'unknown'
fi
[root@localhost ~]# ./test_file.sh /etc/passwd
/etc/passwd is regular file
2、检测指定的主机是否可以ping通，必须使用$1变量
[root@openvpn test]# cat ping.sh
#!/bin/bash
ping -c2 $1 &>/dev/null
if [ $? -eq 0 ];then
echo "ok"
else
echo "down"
fi
# 方式二
[root@openvpn day1]# cat ping.sh
#!/bin/bash
read -p "请输入ip :" IP
ping -c1 -t1 $IP &>/dev/null
if [ $? -eq 0 ];then
echo "ok"
else
echo "down"
fi
[root@openvpn test]# chmod +x ping.sh
[root@openvpn test]# ./ping.sh 10.10.0.1
down
[root@openvpn test]#
3、判断一个用户是否存在
[root@openvpn test]# cat check_user.sh
#!/bin/bash
id $1 &> /dev/null
if [ $? -eq 0 ];then
echo "user $1 exists"
else
echo "user $1 not exists"
fi
[root@openvpn test]# chmod +x check_user.sh
[root@openvpn test]# ./check_user.sh openvpn
user openvpn exists
[root@openvpn test]# ./check_user.sh xx
user xx not exists
4、检测nginx软件是否安装，没有的话则安装
[root@openvpn test]# cat check_nginx.sh
#!/bin/bash
rpm -q nginx &>/dev/null
if [ $? -eq 0 ];then
echo "已经安装"
else
echo "正在安装..."
yum install nginx -y &>/dev/null
fi
5、判断80端口的状态,未开启则重启
[root@openvpn test]# cat check_port.sh
#!/bin/bash
netstat -an |grep LISTEN |grep '\b80\b' &>/dev/null
if [ $? -eq 0 ];then
echo "80端口ok"
else
echo "80端口down"
echo "正在重启..."
systemctl restart httpd &> /dev/null
if [ $? -eq 0 ];then
echo "重启成功"
else
echo "重启失败"
fi
fi
# 检测端口
[root@openvpn day2]# cat port.sh
# !/bin/bash
[ $# -ne 1 ] && echo "Usage: $0 port" && exit
netstat -an |grep -iw "listen" |grep $1 &> /dev/null
if [ $? -eq 0 ];then
echo "nginx $1 is ok"
else
echo "nginx $2 is down"
fi
6、编写监控脚本、配置邮箱
1）编写监控脚本
要求如果：
根分区剩余空间小于10%
内存的可用空间小于30%
向用户openvpn发送告警邮件，邮件的内容包含使用率相关信息
[root@openvpn day2]# cat disk.sh
#!/bin/bash
# 提取根分区剩余空间
use_disk=`df / | grep / | awk '{print $5}'`
use_percent=`echo $use_disk|cut -d% -f1`
# 提取内存剩余空间
avail_mem=`free | awk 'NR==2{print $NF}'`
total_mem=`free | awk 'NR==2{print $2}'`
avail_percent=`echo "scale=2;$avail_mem/$total_mem"|bc | cut -d. -f2`
# 注意 磁盘提取的数值单位为 kb、 内存提取的单位为 Mb
if [ $use_percent -gt 90 ];then
echo "邮件内容:根分区已经使用为${user_disk}低于10%，请及时处理！！!" | mail -s "硬盘报警邮件" 1715554782@qq.com
fi
if [ $avail_percent -lt 30 ];then
echo "邮件内容:内存剩余${free_percent}%,低于30%" | mail -s "内存报警邮件" 1715554782@qq.com
fi
2）测试：
# 查看qq邮箱
# [root@openvpn test]# cat /var/spool/mail/root
3）mailx配置
[root@openvpn ~]# yum install mailx -y
[root@openvpn ~]# cat /etc/mail.rc
set from=378533872@qq.com
set smtp=smtps://smtp.qq.com:465
set smtp-auth-user=378533872@qq.com
set smtp-auth-password="xxxxxxxxxx"
set smtp-auth=login
set ssl-verify=ignore
set nss-config-dir=/etc/pki/nssdb/
[root@openvpn day2]# cat /etc/mail.rc #正确的
set from=1715554782@qq.com
set smtp=smtp.qq.com
set smtp-auth-user=1715554782
set smtp-auth-password=tfdxmfopkacdbhae
set smtp-auth=login
解释
set from：设置发件人
set smtp：设置外部STMP服务器
set smtp-auth-user：设置STMP用户名（一般为完整邮箱地址）
set smtp-auth-password：设置SMTP密码,需要登录378533872@qq.com在设置->账户->开启POP3/SMTP服务->获取密码
测试
[root@openvpn ~]# echo "卧槽" | mail -s "报警邮件" 1715554782@qq.com
[root@openvpn ~]# Error in certificate: Peer's certificate issuer has been marked as not trusted by the.
5）上述报错的解决方式为，依次执行下述命令
mkdir -p /root/.certs/
echo -n | openssl s_client -connect smtp.qq.com:465 | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > ~/.certs/qq.crt
certutil -A -n "GeoTrust SSL CA" -t "C,," -d ~/.certs -i ~/.certs/qq.crt
certutil -A -n "GeoTrust Global CA" -t "C,," -d ~/.certs -i ~/.certs/qq.crt
certutil -L -d /root/.certs
cd /root/.certs
certutil -A -n "GeoTrust SSL CA - G3" -t "Pu,Pu,Pu" -d ./ -i qq.crt
# 最后出现这句就可以了
Notice: Trust flag u is set automatically if the private key is present.
# 重新修改配置文件的最后一行
[root@openvpn ~]# cat /etc/mail.rc
set from=378533872@qq.com
set smtp=smtps://smtp.qq.com:465
set smtp-auth-user=378533872@qq.com
set smtp-auth-password="xxxxxxxxxx"
set smtp-auth=login
set ssl-verify=ignore
# set nss-config-dir=/etc/pki/nssdb/ # 改为下面一行
set nss-config-dir=/root/.certs
# 然后重新测试邮件发送即可
6）根据操作系统不同进行yum源优化 centos6 centos7 centos8
[root@openvpn shell]# cat check_yum.sh
#!/bin/bash
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup &>/dev/null
var=$(awk '{print $(NF-1)}' /etc/redhat-release)
os_version=`echo ${var%%.*}`
if [ $os_version -eq 7 ];then
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo &>/dev/null
elif [ $os_version -eq 6 ];then
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo &>/dev/null
elif [ $os_version -eq 5 ];then
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-5.repo &>/dev/null
else
echo "请检查确认系统版本信息"
fi
