os

虚拟化

两种类型 why? abstraction of the os from the hardware.将os与硬件紧密相连？virtual machine image.变成了可移动的文件。

• secure very easily.快照os配置和安装的程序。
• portable。在不同的机器上移动
• not dependent on physical server

windows的c盘？历史 a b 盘是插入的软盘

cli

uname -a cat /etc/os-release lscpu/lsmem

grep:globally search for regular expression and print out.search for a particular pattern of characters and displays all lines that contains that pattern

shell

the program that interprets and executes the various commands that we type in the terminal.内核理解的指令。

• bash is a shell program, a programmin language

shebang#! 告诉os使用什么shell

• #:音乐符号，sharp
• !: bang

variables

• used to store data and can be referenced later
• variable_name=value assign the value to the var

Danger

=两边不要有空格

$var值

• variable_name=$(command) store output of a command in a variable

conditionals

• allows you to alter the control flow of the program

• execute a command only when a certain condition is true

• []=test

if [ -d "config"]
then
	echo "reading"
	config_files=$(ls config)
else
	echo "config dir not found,creating one"
	mkdir config
fi

Note

if[ condition] then statement else statement fi

basic operators

文件运算符

-d -r -w -x -f

关系运算符

数字 -eq -ne -gt -lt -ge -le

String 运算符

== != -n 大小不为0 str 不为空

passing 参数

positional parameters

arguments passed to script are processed in the same order in which they’re sent. the indexing of arguments starts at 1

config_dir=$1 "$config_dir"

read -p "please input something" user_input -p:prompt

读取所有的输入 $* represent all the arguments as a single string

$# total number of arguments provided

loops

for

Note

for var in word1 word2… do statements to be executed for every word done

echo "all params:$*"
echo "number of params: $#"
 
for param in $*
	do
		echo $param
	done
 

Note

while condition do statements to be execufted if command is true done

sum=0
while true
do
	read-p "enter a score" score
	
	if ["$socre" == "q"]
	then
		break
	fi
	
	sum=$(($sum+$score))
	echo "total score: $sum"
done

• double parenthesis for arithmetic operations $(($num1+$num2))

functions

definition + invoke

function score_sum{
 
 
}
function create_file(){
	file_name=$1
	touch $file_name
}
create_file test.txt
score_sum

$?:captures value returned by last command

function sum(){
	total =$(($1+$2))
	return $total
}
sum 2 10
result=$?
echo "$result"

environment variables

• key = value pairs 键值对
• variables store information about the environment

printenv|less printenv USER

echo $USER

环境变量 整个环境都可用

先导出 export DB_USERNAME=dbuser 只会在当前会话有效。seesion

永久 .bashrc文件里添加 source ~/.bashrc load the new env vars into the current shell session 删除 unset NAME

全局设置的env var

/etc/environment

PATH

• list of directories to executable files,separated by :
• tells the shell which directories to search for the executable in response to our executed command

不用输入可执行程序的全路径了 只需输入名字