Scripting Classroomnotes 28/Apr/2023

Scripting Types

• We create scripts for two major usecases
  • a person executing it (should inform user about the activites)
  • automated execution (should not ask for user interaction)
• For DevOps/Cloud related activities we need automated execution

More on Scripting

• According to last classes, we have a script to install jenkins

#!/bin/bash
apt update 
apt install openjdk-17-jdk -y
curl -fsSL https://pkg.jenkins.io/debian-stable/jenkins.io-2023.key | sudo tee \
  /usr/share/keyrings/jenkins-keyring.asc > /dev/null
echo deb [signed-by=/usr/share/keyrings/jenkins-keyring.asc] \
  https://pkg.jenkins.io/debian-stable binary/ | sudo tee \
  /etc/apt/sources.list.d/jenkins.list > /dev/null
apt-get update
apt-get install jenkins -y

• Lets try to look at this script in a different way by drawing a flowchart
  
• Lets try to draw a flowchart which will install jenkins on ubuntu and redhat systems
  
• Below is the script to install jenkins on redhat as well as ubuntu systems

#!/bin/bash
distribution=$(. /etc/os-release && echo $ID)
echo $distribution
# for ubuntu 
if  [[ $distribution == "ubuntu" ]]
then
    apt update 
    apt install openjdk-17-jdk -y
    curl -fsSL https://pkg.jenkins.io/debian-stable/jenkins.io-2023.key | sudo tee \
    /usr/share/keyrings/jenkins-keyring.asc > /dev/null
    echo deb [signed-by=/usr/share/keyrings/jenkins-keyring.asc] \
    https://pkg.jenkins.io/debian-stable binary/ | sudo tee \
    /etc/apt/sources.list.d/jenkins.list > /dev/null
    apt-get update
    apt-get install jenkins -y
elif [[ $distribution == "rhel" ]]
then
    sudo yum install wget -y
    sudo wget -O /etc/yum.repos.d/jenkins.repo \
        https://pkg.jenkins.io/redhat-stable/jenkins.repo
    sudo rpm --import https://pkg.jenkins.io/redhat-stable/jenkins.io-2023.key
    sudo yum upgrade
    # Add required dependencies for the jenkins package
    sudo yum install java-11-openjdk
    sudo yum install jenkins
    sudo systemctl daemon-reload
else
    echo "This script runs only on ubuntu and redhat"
fi

Expression

• An expression is combination of operands and operators which return some value

Operators in bash

• Refer Here or operators in bash

Conditional statements

• We have 4 conditional statements in shell
  • if
  • if else
  • if elif else
  • switch
• Conditional statements require boolean operators

References

• Cheatsheet Refer Here
• Style Guide:
  • Shell: Refer Here
  • Python: Refer Here

Installations

• Install draw.io from diagrams.net Refer Here

Exercise

• Write a shell script to do the following
  • if the os is redhat
    • install jenkins with jdk 11
    • install awscli
    • install azure cli
  • if the os is ubuntu
    • install jenkins with jdk 17
    • install awscli
    • install azurecli