Mastering Shell Scripting for DevOps Automation

✨ Building the foundations for reliable automation workflows

Shell scripting is one of the most essential skills in DevOps & DevSecOps.
Today, I explored how shells work, why automation matters, and how scripting makes deployments, server setups, and CI/CD processes more efficient and reliable.

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🐚 What is a Shell?

A shell is a command-line interface (CLI) that allows users to interact with the operating system and execute commands.

👉 Common Shell Types

• 🟦 bash

• 🟨 sh

• 🟪 zsh

• 🐍 python shell

Shells allow us to run commands, automate workflows, and build scripts that execute consistently across environments.

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⚙️ Why Shell Scripting Matters in DevOps

In real-world DevOps environments:

• Installing Docker

• Configuring Jenkins

• Deploying applications

• Running validations

…often require multiple manual commands.

With Shell Scripting, we can:
✔️ Combine all commands into one file
✔️ Run them in a single execution
✔️ Share scripts across teams
✔️ Automate builds, deployments & server provisioning
✔️ Reduce human error

Shell scripting = faster, safer, predictable automation.

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🧭 Understanding the Shebang (#!)

The first line of most shell scripts is:

#!/bin/bash

• #! → Shebang

• /bin/bash → tells OS to execute this script using bash

If you skip the shebang, the script can still run with:

bash filename.sh

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🧩 Variables & Basic Operations

✔️ Declaring Variables

name="Jayesh"
echo "Hello $name"

age="24"
echo "Your age is $age"

✔️ Arithmetic

x=4
y=7
sum=$((x+y))
echo "$sum is "

✔️ String Concatenation

greetings="Hello"
name="Jayesh"
message="$greetings, $name"
echo "$message"

✔️ String Length

string="Vishal Patil"
length=${#string}
echo "Length : $length"

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📝 Echo Behavior & Special Characters

variable="Hello World"
echo "$variable"
echo '$variable'
echo $variable
echo "both '$variable'"

special_char="\$"
echo "special char - $special_char"

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🔐 User Input Handling

✔️ Hidden Password Input

read -s -p "Your password is " password
echo "Password has been set $password"

✔️ Timeout-Based Input

read -t 6 -p "Enter something in 6 second " timed_out
echo "$timed_out"

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🧠 Conditional Statements

num=10

if [ $num -gt 10 ]; then
    echo "Number is greater than 10"
elif [ $num -eq 10 ]; then
    echo "Number is equal to 10"
else
    echo "Number is less than 10"
fi

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🔀 Switch / Case Statements

fruit="apple"

case $fruit in
    "apple")
        echo "it is an apple"
        ;;
    "banana")
        echo "it is banana"
        ;;
    "mango")
        echo "it is mango"
        ;;
    *)
        echo "Unknown fruit"
        ;;
esac

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🔁 Loops in Shell Scripting

✔️ For Loop — Numeric

for i in {1..21}; do
    echo "numbers $i"
done

✔️ For Loop — Array

fruits=("shimpi" "patil" "deshmukh")
for fruit in "${fruits[@]}"; do
    echo "fruits name $fruit"
done

✔️ While Loop

counter=1
while [ $counter -le 5 ]; do
    echo "count : $counter"
    counter=$((counter+1))
done
echo "loop finished"

✔️ Until Loop

counter=1
until [ $counter -ge 5 ]; do
    echo "count : $counter"
    counter=$((counter+1))
done
echo "loop finished"

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🧮 Functions — Local & Global Variables

✔️ Local Variable Example

calculate_sum() {
    local num1="$1"
    local num2="$2"
    local sum=$((num1+num2))
    echo "$sum"
    return "$sum"
}

result=$(calculate_sum 10 20)
echo "sum is $result"

✔️ Global vs Local

global_var="Im global variable"

local_variable() {
    local local_var="Hello I am local"
    echo "Inside function $local_var"
    echo "outside function $global_var"
}

local_variable

echo "1111 $local_var"   # Not accessible
echo "2222 $global_var"  # Accessible

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✂️ String Manipulation

✔️ Extract Substring

string="Hello,world"
substring=${string:6:5}
echo "$substring"

✔️ Replace Text

string1="ms dhoni, def"

search="def"
replace="faf du plessis"

result=${string1//$search/$replace}

echo "org $string1"
echo "org $result"

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🎯 Why Shell Scripting Matters in DevOps/DevSecOps

Shell scripting powers automation for:

• ⚙️ CI/CD pipelines

• 🚀 Automated deployments

• 📦 Server provisioning

• 📊 Log analysis

• 🔐 Security checks

• ☁️ Cloud operations

• 🔍 System monitoring

Mastering shell scripting = mastering DevOps automation.

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✅ Day 8 Summary

Today, I learned and practiced:

• Variables, arithmetic & strings

• User input, password, timeout

• Conditionals & switch-case

• Loops (for, while, until)

• Functions + local/global variables

• String manipulation (extract, replace)

These scripting fundamentals are essential for writing automation scripts used in deployments, CI/CD workflows, cloud platforms, and secure engineering systems.