Linux Classroom notes 31/July/2026

Variables:

• its store infromation in memory
• key and value ==> name_varaible and value will be value of the key

rules for Variables:

• name must be start with letter or “_”
• contain only letters , “_” and numbers
• no space bettween key and value
  • name=ram
• case-sentive
  • Name , name
• Enviromnent variable use captial & scprit or automation use small letters
  • $JAVA_HOME
  • $java_path

Types of variables:

• local variable (shell)
• enviroment variables
• special variables
• Array variables
• read-only variables

local Variables

• Ex:1

name=ram
age=30
bloodgroup=A-positive

echo "my name is $name and age $age , Blood group is $bloodgroup "

• Ex:2

image=ubunt

docker pull $image

enviroment variables

• sudo vi /etc/enviroment This is default enviroment variable
• export data_value=9090 # this override default values work only when terminal activity

HOME - user directory
USER - current loggined user $(whoami)
PWD - current working dir 

BASIC shell:

• file extension “.sh“`
• #!/bin/bash

create file sample.sh and add below cmds

#!/bin/bash

sudo apt-get update 
sudo apt-get install git -y 

• chmod 755 sample.sh # provide execute permissions
• sh sample.sh or ./sample.sh

special variables:

• It is used in scrpits and automation

$0 – name of the scrpit

$1, $2 … positional args pass in script

#!/bin/bash

# file demo.sh 
echo "arg one value $1"
echo "arg one value $3"

• sh demo.sh 99 567 44

• $# – number of args passed