快速清空日志文件

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cloud_domo 2023-04-21 11:47:11 博主文章分类：shell编程学习 ©著作权

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在做日志服务时，经过遇到百个1G以上的文件需要及时删除，暂不考虑lograte滚动日志服务来解决。

先回顾常用命令：

三种数字循环--带次数控制的for循环

##从0开始，步长为2，到10终止------三种格式。
for (( c=0; c<=10; c+=2 )); do echo "Welcome $c times"; done
for i in $(seq 0 2 10);     do echo "Welcome $i times"; done
for i in {0..10..2};        do echo "Welcome $i times"; done

快速清空日志文件_if结构

#下面是默认步长，为1.
for (( c=0; c<=10; c++ )); do echo "Welcome $c times"; done
for i in $(seq 0 10);      do echo "Welcome $i times"; done
for i in {0..10};          do echo "Welcome $i times"; done

for应用的实际例子

1、查看网卡和对应的ip地址信息：
for dev in $(awk -F : '{if(NR>2)print $1}' /proc/net/dev);do printf '%+10s: ' $dev;echo $(ip addr show $dev | awk -F "[ /]+" '/inet /{print $3}'); done
2、查看网卡和对应的MAC地址：
for dev in $(awk -F : '{if(NR>2)print $1}' /proc/net/dev);do printf '%+10s: ' $dev;echo $(ip addr show $dev | awk -F "[ /]+" '/inet /{print $3}')    $(ip addr show $dev | awk -F "[ /]+" '/ether /{print $4}'); done
3、关闭3模式下所有服务：
 for server in `chkconfig --list | grep 3:on | awk ‘{print $1}’ `; do chkconfig --level 3 $server off ; done
4、10次把日志放到文件中：
for num in `seq 1 10`;do  echo $num;cat messages >> test01; done 
5、把message日志文件清空：
for VF in `ls /var/log/ | grep message`; do echo 0> /var/log/$VF  ; done
6、磁盘热加载--虚机
for i in $(ls /sys/class/scsi_host/); do echo '- - -' > /sys/class/scsi_host/$i/scan; done
7、磁盘热加载--物理主机
for i in $(ls /sys/class/scsi_host/); do echo '- - -' > /sys/class/scsi_host/$i/scan; done

快速清空日志文件_if结构_02

常见简单的判断--不一定是if结构哦

1、与或结构：

$(ip add show dev ens160) && echo "have ens160" || echo "no ens160" ##测试有无ens160网卡，如果有输出have ，如果没有输出no

aa=" ";[[ -z "$aa" ]] && echo "Empty" || echo "Not empty" #判断是否为空

又例如：

[ -o /etc/passwd ] && echo "/etc/passwd is executable" || echo "/etc/passwd NOT is executable" ##返回/etc/passwd NOT is executable

[ -r /etc/passwd ] && echo "/etc/passwd is readable" || echo "/etc/passwd NOT is readable" ##返回/etc/passwd is readable

命令由来：

##以下通过系统中的实例要验证
[localhost@root~]# ll /etc/passwd
-rw-r--r-- 1 root root 1354 Mar 20 11:20 /etc/passwd
[localhost@root~]# [ -o /etc/passwd ]
[localhost@root~]# echo $?
1
[localhost@root~]# [ -o /etc/passwd ] && echo "/etc/passwd is executable"
[localhost@root~]# echo $?
1
[localhost@root~]# [ -o /etc/passwd ] || echo "/etc/passwd NOT is executable"
/etc/passwd NOT is executable
[localhost@root~]# echo $?
0
[localhost@root~]# [ -o /etc/passwd ] && echo "/etc/passwd is executable" || echo "/etc/passwd NOT is executable"
/etc/passwd NOT is executable
[localhost@root~]# echo $?
0


[localhost@root~]# ll /etc/passwd
-rw-r--r-- 1 root root 1354 Mar 20 11:20 /etc/passwd
[localhost@root~]# [ -r /etc/passwd ]
[localhost@root~]# echo $?
0
[localhost@root~]# [ -r /etc/passwd ] && echo "/etc/passwd is readable"
/etc/passwd is readable
[localhost@root~]# echo $?
0
[localhost@root~]# [ -r /etc/passwd ] || echo "/etc/passwd NOT is readable"
[localhost@root~]# echo $?
0
[localhost@root~]# [ -r /etc/passwd ] && echo "/etc/passwd is readable" || echo "/etc/passwd NOT is readable"
/etc/passwd is readable
[localhost@root~]# echo $?
0

快速清空日志文件_if结构_03

快速清空日志文件_if结构_04

总结：

1、&& 表示,&&前后均为真，整体才为真；若任意一边为假,整体则为假；

换句话说：&&前为真才执行&&后；否则，&&前为假直接异常退出。

2、|| 表示, || 前后均为假，整体才为假；若任意一边为真,整体则为真；

换句话说：只要||前为真就不执行||后；否则，||前为假才执行||后。

3、通过以上规律，结合if [条件]；then 真，执行真；else 假，执行假；fi，得出上述结构的简单命令；

&& 如果是“前面”，则“后面”

|| 如果不是“前面”，则后面

2、if结构

格式：if [条件];then 真，执行真;else 假，执行假;fi

[root@pyramid0 ~]# [ -r /etc/passwd ] && echo "/etc/passwd is readable" || echo "/etc/passwd NOT is readable" 
/etc/passwd is readable
[root@pyramid0 ~]# echo $?
0
[root@pyramid0 ~]# if [ -r /etc/passwd ];then echo "/etc/passwd is readable";else echo "/etc/passwd NOT is readable";fi   
/etc/passwd is readable
[root@pyramid0 ~]# echo $?
0
[root@pyramid0 ~]# [ -o /etc/passwd ] && echo "/etc/passwd is executable" || echo "/etc/passwd NOT is executable" 
/etc/passwd NOT is executable
[root@pyramid0 ~]# echo $?
0
[root@pyramid0 ~]# if [ -o /etc/passwd ];then echo "/etc/passwd is executable";else echo "/etc/passwd NOT is executable";fi 
/etc/passwd NOT is executable
[root@pyramid0 ~]# echo $?
0

快速清空日志文件_if结构_05

后续：函数应用

#!/bin/bash

os_multipath_check (){
    proc_num=$(ps -ef | grep  multipathd | grep -v grep | wc -l)
    #proc_num=`ps -ef | grep  multipathd | grep -v grep | wc -l`
    if [ "${proc_num}" -gt 0 ];then
        echo  "service_status=on" 
    else
        echo  "service_status=off" 
        exit 0
    fi
}

os_multipath_check

快速清空日志文件_if结构_06

3、结合look

[ttmonitor007@~]$aa=" ";[[ -z "$aa" ]]     && echo "Empty"   || echo "Not empty"
Not empty
[ttmonitor007@~]$echo $?
0
[ttmonitor007@~]$aa=" ";if [ -z "$aa" ] ;then echo "Empty";else echo "Not empty";fi
Not empty
[ttmonitor007@~]$echo $?
0
[ttmonitor007@~]$aa=" ";if test -z "$aa";then echo "Empty";else echo "Not empty";fi
Not empty
[ttmonitor007@~]$echo $?
0

快速清空日志文件_if结构_07