Shell Getting Started-variables

Shell variables are divided into system variables and user-defined variables

commands to view variables

#env System Variables

Or #set include env and custom variables and extra variables

The command to use the variable is

#echo $ "Variable"

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1. Custom variables

It is recommended to use lowercase to differentiate system variables.

[Email protected] 111]# a=1
[Email protected] 111]# echo $a
1

[Email protected] 111]# a=1;b=2;c=3
[Email protected] 111]# echo $a $b $c
1 2 3
[Email protected] 111]# echo $a $b$c
123

2. Single quotes for variables of special characters

[Email protected] 111]# a= ' ... +++--**//'
[Email protected] 111]# echo $a
...+++--**//

3. Using the command to run the result with the inverted quotation mark

[Email protected] 111]# a= ' ll 1.txt '
[Email protected] 111]# echo $a
-rw-r--r--1 root root 4 November 22:03 1.txt

=

4. Let the variable overlay with double quotation marks

[Email protected] 111]# a=1
[Email protected] 111]# b= "$a" 2
[Email protected] 111]# echo $b
12

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Global Declaration

Command: Export

Description: Global declaration

[Email protected] 111]# d=5
[Email protected] 111]# echo $d
5
[[email protected] 111]# bash////enters child shell variable a fails

[Email protected] 111]# echo $d

[[Email protected] 111]# exit//exit child shell
Exit
[[email protected] 111]# export d=6//Global declaration
[Email protected] 111]# echo $d
6
[[email protected] 111]# Bash//Enter child shell
[Email protected] 111]# echo $d
6

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Summary: A=1, echo $a//a=1;b=2;c=3 echo $a $b$c//a= ' + +. --'//a= ' cat 1.txt '//a= "$b" 1//Export a=1, bash, echo $a//

Shell Getting Started-variables