#变量
a=b
echo $a
#函数
function f(){
	#do something
	echo "value"
	return int
}

x=(a b c) #array
${x[0]} == a ; ${x[10]}=="" ; ${x[*]} == a b c ; ${x[@]} == "a" "b" "c"

#Math, value calculate, integer
$[a+b] ;$((a+b)); $[a*3];... # float ,pass

#if 
if condition
then
#todo
elif ....
then
#todo
fi

#for
for i in /path/
do
#for i in "间隔=空格|换行some string"
	#todo
done
#while
while condition
do
#todo
done

#异步 结尾&, 注意 &后边没有分号!!!
comand &

#命令
#路径
ls  
cd
#字符串,字符文件
cat file
grep  patten  file

#管道
echo abc | grep a
#重定向
echo abc > file ; echo abc >> file 
echo abc 2> file   #stderr
echo abc &> file   #stdout & stderr

#子进程方式
./file.sh
#当前进程执行
. ./file.sh
#暴露 变量x给父进程
export x

#ip
ip a show
ifconfig
iptables   (内核中 netfilter)

ssh 

#netstat -nltp
含义: -n 数值; -l listen; -t tcp -u udp; -p pid

network:
    # yaml version  2 = 1.2 ? 1.1  (1.0 1.1 1.2)
    version: 2
    ethernets:
        ens33:
            dhcp4: no
            addresses: [192.168.40.130/24]
            gateway4: 192.168.40.1
            nameservers: 
                addresses: [192.168.40.1]

# ssh
ssh user@host -p port      -i   id_key 

# sshd
ssh-keygen -t rsa -b 4096  # default -b 2048

~/.ssh/authorized_keys  # pub
/etc/ssh/sshd_config

​```bash
PermitRootLogin no
PasswordAuthentiction no
​```

uname -a
lsb_release -a
ps

mount
fdisk -l
mkfs
#权限
#0777 的第一个数值 作用是用来设置, 以谁来启动. #比较少用到默认写0;
chmod +x file ; chmod 0777 file  ;-R  递归目录
#user group others

#chown
...