Simple solution of Linux variables

Variable

1. Custom Variables

① variable = variable value

X=5

Name= "Jie Chao" (the symbol in double quotes has meaning, the symbol in single quotation marks has no meaning)

② Call $name

③ Variable Overlay

x=123,x= "$x" 456

④ Delete variable unset variable name (without $ symbol)

⑤ View all variable set

2. Environment variables

① Setting Environment variables

Export variable = variable name

② Viewing environment Variables env

③path variable, the path of the system search command

3. Positional parameter Variables

① $n N=0..9:n is a number, and $ A represents the command itself, $1-$9 represents the first to nineth arguments, and more than 10 arguments are enclosed in curly braces, such as ${10}, to pass the input parameters to the script. Cases:

#!/bin/bash

Num1=$1

Num2=$2

sum=$ (($num 1+ $num 2))

Echo $sum

②$* returns the input parameters to the script and considers all parameters as a whole

③[email protected] Returns the input to the script parameter, treats each parameter differently

④$# returns the number of input-to-script parameters

#!/bin/bash

echo "\$* can shu Shi: $*"

echo "\[email protected] can shu Hai shi: [email protected]"

echo "\$# can shu ge shu shi: $#"

4. Pre-defined variables

①$? Determine if the previous command was executed correctly, the return value of 0 indicates correct

②$$ PID of the current process

③$! The last process number running in the background

5. Accept keyboard Input

read [options] [variable name]

-P: Prompt information

-T: Number of seconds to wait for input, over wait time program terminates

-N: Directly subject to the specified number of characters

-S: input is not displayed (password input)

Eg:read-p "Please input your name:"-T-Name

Read-p "Please input secret:"-t 30-s Age

Simple solution of Linux variables