Linux Advanced Bash Programming quad (built-in variable)

A: Basic review

1: File Empty

[Email protected] test]$ >log.txt

2: Normal and Error redirect output

Normal and error append output to same place

[Email protected] test]$ ifconfig &>>log.1

Normal output redirect
[Email protected] test]$ ifconfig >log

Error output redirection
[Email protected] test]$ ifconfig 2>log.2
3: Command execution control

Sleep for 1 seconds

[[email protected] test]$ sleep 1
4:bash Script Start

The bash script must start with this, declaring the command interpreter path

#!/bin/bash
5: User interaction, read user input information and save to variable

Syntax: Read variable 1 variable 2

[[Email protected] bash] $vi read.sh

!#/bin/bash

Echo-n "Please input your name:"

Read name

echo "Your name is: $name"

[[Email protected] bash] $bash read.sh

[[email protected] bash] $please input your name: Jackchen

Your name Is:jackchen

Two: Built-in variable use

Built-in variables: The system is already existing variables, can be used directly. When executing a script, it can be passed inside the script with parameters.

Built-in variables are: $ The script itself

$ .... Parameters

$# a total of several parameters

Exercise 1: inside.sh script as follows, carry 3 parameters 1, 2, 3, print $0,$1,$2,$ #的值

650) this.width=650; "Title=" inside. JPG "src=" http://s1.51cto.com/wyfs02/M01/7E/72/wKiom1b_wmWzf0BGAACeTiIIwsQ155.jpg "alt=" wkiom1b_ Wmwzf0bgaacetiiiwsq155.jpg "/>

Exercise 2: Write a bash script that implements two numbers of additions? Write a calculator?

Write a bash script

[[Email protected] bash] $vi add.sh

#!/bin/bash

Echo $[$1+$2]

[[Email protected] bash] $bash add.sh 3 2

5

Write a calculator

[[Email protected] bash] $vi calc.sh

#!/bin/bash

echo "$" |BC

[[Email protected] bash] $bash calc.sh 2+3*5-6/2

14

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Linux Advanced Bash Programming quad (built-in variable)