Shell Getting Started exercise

* * Define local variables, local variables will expire when exiting the shell client * *

* * Single quote: Output AS-is * *

* * Double quotes: If there are variables, the variables will be output * *

* * No quotation marks: Output variable * *

You can pass parameters to the script when the script is called, using the $ $ ... in the script. Accept parameters that are passed and need to be enclosed in curly braces when the argument exceeds 9 ${10}

Special Invocation Parameters:

    $0：返回Shell文件名称    $$：当前脚本的PID    $#：传递的所有参数 [email protected]：程序中的所有参数，这是将参数传递给其他程序的最佳方式。 $! ：执行的上一个命令的PID $?：上一次指令的返回值 $_：此命令前面的最后一个参数 $* ：获取所有的参数

* * sh scripts that start with a command will disappear when the script ends, and other scripts cannot access their internal properties.

When source you start a script with a command, its properties are not invalidated when the script ends, and other scripts can access it.

Validated, used ./ can also execute scripts

Use unset to cancel a variable, which includes environment variables and local variables * *

Defining arrays array=(value1 value2 value3) array_name[0]=value0

Reading an array${array_name[index]}

Get all the elements in an array${my_array[@]}

Gets the length of the array${#my_array[*]}

Process Control

If

If no statement is executed in the Else statement, it cannot be written

If conditionthen command1 command2 ... CommandN fi------------------if conditionthen command1 command2 ... commandnElse commandfi------------if Condition1then command1elif condition2 Then  command2else commandnfi           

For

for var in item1 item2 ... itemNdo    command1    command2 ... commandNdone

While

while conditiondo    commanddone

Until

Similar to the Do-while cycle, at the Last Judgment condition, at least once

until conditiondo    commanddone

Case

Case Value in

Mode 1) Command1 Command2 ... CommandN;;

Mode 2) Command1 Command2 ... CommandN;; Esac

Function

demoFun(){   // 定义      echo "这是我的第一个 shell 函数!"}echo "-----函数开始执行-----"demoFun // 调用，如果需要传递参数直接在后面跟就好 demoFun 1 2 3echo "-----函数执行完毕-----"

Operator

• Expr is an expression evaluation tool that uses it to perform evaluation operations on expressions.

• expr 2 + 2To use the method, you need to be aware of 1. There is a space between the expression and the operator 2. Need to use ' ' cause

Relational operators

How to use

 if [ $a  -lt -a  $b -GT 15] then echo  "  $a less than 100 and  $b greater than 15: Returns True "else" Span class= "hljs-built_in" >echo  " $a less than 100 and  $b greater than 15: returns false" fi                   
 
  logical Operators  

Shell Getting Started exercise