SHELL下常用的语句 for,while

for,while

for循环

for NUM in 1 2 3
for NUM in {1..3}
for NUM in `seq 1 3`  
for NUM in {a..f}

for NUM in {1..$a}

for ((A=1;A<=10;A++))

for NUM in `seq 1 2 10`

查看网段里面连通的主机

#!/bin/bash
for NUM in {0..254}
do
        ping -c1 -w1 172.25.254.$NUM &> /dev/null &&{
        echo -e "172.25.254.$NUM"       
} || {
        echo ""
}
done
~                                                                              
~                       

备份数据库linux,mysql,test,,westos，并且放在/mnt/maysql_backup里面

    #!/bin/bash
    DATABASE_MESSAGE=`mysql -uroot -EN -e "show databases;" | grep -E "^\*|schema$" -v`     
    mkdir -p /mnt/mysql_dump
    for DATABASE_NAME in $DATABASE_MESSAGE
    do
        mysqldump -uroot $DATABASE_NAME > /mnt/mysql_dump/${DATABASE_NAME}.sql
        [ "$?" -eq "0" ] && {
                echo -e "\033[47m$DATABASE_NAME is backuped \033[0m"
        }
    done

while循环

格式
while 条件
do

done

实验1

使用whiel时实刷新uptime

[root@desktop ~]# vim mysql.sh
[root@desktop ~]# vim uptime.sh
[root@desktop ~]# sh uptime.sh 
^C:37:53 up 2:40, 2 users, load average: 0.01, 0.04, 0.0505
[root@desktop ~]# cat uptime.sh 
#!/bin/bash
while true
do	
	echo -n `uptime`
	echo -ne "\r \r"
	sleep 1
done

如何用非交互的方式传送邮件

[root@localhost ~]# echo hello world | mail -s "test" root  非交互式 -s表示主题是test
You have mail in /var/spool/mail/root
[root@localhost ~]# mail                 直接查看
Heirloom Mail version 12.5 7/5/10.  Type ? for help.
"/var/spool/mail/root": 2 messages 1 new
    1 root                  Thu Jun 21 13:31  21/768   "test"
>N  2 root                  Thu Jun 21 13:31  20/757   "test"
& 
Message  2:
From [email protected]  Thu Jun 21 13:31:52 2018
Return-Path: <[email protected]>
From: root <[email protected]>
Date: Thu, 21 Jun 2018 13:31:52 -0400
To: [email protected]
Subject: test
User-Agent: Heirloom mailx 12.5 7/5/10
Content-Type: text/plain; charset=us-ascii
Status: R
 
hello world 邮件内容

根分区的使用量达到了80%就给root用户法邮件报警

[root@desktop ~]# vim warn.sh
[root@desktop ~]# cat warn.sh 
#!/bin/bash
DISK_NUM=`df | awk '/\/$/{print $5}' | awk -F "%" '{print $1}'`   
while true
do
        [ "$DISK_NUM" -ge "80" ] && {     
                echo "Your / will full !!! " | mail -s "warning" root
        }
        sleep 1     
done