🔒 Day 5 — Bash Scripting for Automation | 🔧 Programmierung

Modern infrastructure runs on automation.

Whether you're a:

DevOps Engineer

Linux Administrator

Cloud Engineer

Cybersecurity Professional

Backend Developer

You will eventually write Bash scripts.

From automating backups to deploying servers, monitoring systems, managing logs, and running CI/CD pipelines — Bash is everywhere.

If Linux is the operating system of the internet, then Bash is its automation language.

🔗 Resources

GitHub Repo:

Linux Cron Job Scheduler:

📦 Linux Package Managers

Package managers install software.

Different Linux distributions use different package managers.

Distribution	Package Manager	Example
Ubuntu	APT	`apt install nginx`
Debian	APT	`apt update`
CentOS 7	YUM	`yum install docker`
RHEL	YUM/DNF	`dnf install git`
Fedora	DNF	`dnf update`
Arch Linux	Pacman	`pacman -S nginx`
Alpine Linux	APK	`apk add curl`

🚀 What is Bash?

Bash stands for:

Bourne Again SHell

It is the default shell for most Linux distributions.

A shell is simply a program that allows users to interact with the operating system.

Example:

CODE

pwd

ls

mkdir project

These commands are executed through the shell.

🧠 What is Bash Scripting?

A Bash script is a file containing Linux commands executed sequentially.

Instead of manually typing commands repeatedly, you automate them inside a script.

Example:

    CODE      
#!/bin/bash

echo "Hello Rahul"

date

uptime

Save as:

CODE

hello.sh

Make executable:

CODE

chmod +x hello.sh

Run:

CODE

./hello.sh

⚡ Why Bash Automation Matters

Without automation:

❌ Manual server setup

❌ Repetitive deployments

❌ Manual backups

❌ Human errors

❌ Slow operations

With Bash automation:

✅ Faster workflows

✅ Repeatable processes

✅ Infrastructure consistency

✅ Reduced human mistakes

✅ Better productivity

📂 Bash Script Structure

Basic structure:

    CODE      
#!/bin/bash

# Comments start with #

echo "Starting Script"

# Commands here

🔥 Variables in Bash

Variables store data.

✅ Creating Variables

    CODE      
name="Rahul"

age=22

city="Delhi"

Access variables using $.

    CODE      
echo $name

echo $age

⚠️ Important Rule

No spaces around =.

❌ Wrong:

CODE

name = "Rahul"

✅ Correct:

    CODE      
name="Rahul"

🧾 User Input

Take input dynamically.

    CODE      
#!/bin/bash

echo "Enter your name:"

read name

echo "Welcome $name"

📌 Command Line Arguments

Arguments passed while running scripts.

    CODE      
#!/bin/bash

echo "First argument: $1"

echo "Second argument: $2"

Run:

CODE

./script.sh Rahul Linux

Output:

CODE

First argument: Rahul

Second argument: Linux

🔍 Conditional Statements

Conditions allow decision-making.

✅ If Statement

    CODE      
#!/bin/bash

age=20

if [ $age -ge 18 ]

then

    echo "Adult"

fi

✅ If-Else

    CODE      
#!/bin/bash

num=5

if [ $num -gt 10 ]

then

    echo "Greater than 10"

else

    echo "Less than or equal to 10"

fi

✅ If-Elif-Else

    CODE      
#!/bin/bash

marks=75

if [ $marks -ge 90 ]

then

    echo "Grade A"

elif [ $marks -ge 70 ]

then

    echo "Grade B"

else

    echo "Grade C"

fi

🧠 Comparison Operators

Operator	Meaning
`-eq`	Equal
`-ne`	Not equal
`-gt`	Greater than
`-lt`	Less than
`-ge`	Greater or equal
`-le`	Less or equal

🔁 Loops in Bash

Loops repeat tasks automatically.

✅ For Loop

    CODE      
#!/bin/bash

for i in 1 2 3 4 5

do

    echo "Number: $i"

done

✅ Range Loop

    CODE      
for i in {1..10}

do

    echo $i

done

✅ While Loop

    CODE      
#!/bin/bash

count=1

while [ $count -le 5 ]

do

    echo $count

    ((count++))

done

✅ Infinite Loop

    CODE      
while true

do

    echo "Running..."

    sleep 2

done

🔨 Functions in Bash

Functions help organize reusable code.

    CODE      
#!/bin/bash

greet() {

    echo "Hello $1"

}

greet Rahul

📦 Arrays in Bash

    CODE      
#!/bin/bash

fruits=("apple" "banana" "mango")

echo ${fruits[0]}

echo ${fruits[1]}

Loop through array:

    CODE      
for fruit in "${fruits[@]}"

do

    echo $fruit

done

📁 File Operations

✅ Check if File Exists

    CODE      
#!/bin/bash

if [ -f test.txt ]

then

    echo "File exists"

else

    echo "File not found"

fi

✅ Create File

CODE

touch file.txt

✅ Append to File

    CODE      
echo "New Log Entry" >> logs.txt

⚙️ Process Automation

✅ Kill Process

CODE

pkill nginx

✅ Restart Service

CODE

systemctl restart nginx

✅ Check Service Status

CODE

systemctl status docker

🕒 Cron Jobs for Scheduling

Cron automates scripts at scheduled times.

Open cron:

CODE

crontab -e

✅ Run Every Day at Midnight

    CODE      
0 0 * * * /home/ubuntu/backup.sh

✅ Run Every 5 Minutes

    CODE      
*/5 * * * * /home/ubuntu/monitor.sh

🚀 Real-World Automation Scripts

Now the fun begins.

🔥 1️⃣ Automated Backup Script

    CODE      
#!/bin/bash

SOURCE="/home/ubuntu/data"

DEST="/backup"

DATE=$(date +%Y-%m-%d)

tar -czf $DEST/backup-$DATE.tar.gz $SOURCE

echo "Backup completed"

What it does:

✅ Compresses files

✅ Creates timestamp backup

✅ Automates backup process

🔥 2️⃣ Disk Usage Monitoring Script

    CODE      
#!/bin/bash

THRESHOLD=80

USAGE=$(df / | grep / | awk '{ print $5 }' | sed 's/%//g')

if [ $USAGE -gt $THRESHOLD ]

then

    echo "Disk usage exceeded threshold!"

else

    echo "Disk usage normal"

fi

Useful for:

Servers

Cloud VMs

Production systems

🔥 3️⃣ Website Monitoring Script

    CODE      
#!/bin/bash

URL="https://example.com"

STATUS=$(curl -o /dev/null -s -w "%{http_code}" $URL)

if [ $STATUS -eq 200 ]

then

    echo "Website is UP"

else

    echo "Website is DOWN"

fi

🔥 4️⃣ Auto Deployment Script

    CODE      
#!/bin/bash

echo "Pulling latest code..."

git pull origin main

echo "Installing dependencies..."

npm install

echo "Restarting application..."

pm2 restart app

Used heavily in:

DevOps

CI/CD

Production deployments

🔥 5️⃣ Log Cleanup Script

    CODE      
#!/bin/bash

find /var/log -type f -name "*.log" -mtime +7 -delete

echo "Old logs deleted"

Deletes logs older than 7 days.

🛡️ Error Handling in Bash

Always validate failures.

    CODE      
#!/bin/bash

mkdir test

if [ $? -eq 0 ]

then

    echo "Directory created"

else

    echo "Failed"

fi

$? stores previous command status.

0 = success

Non-zero = failure

📌 Exit Codes

CODE

exit 0

Success.

CODE

exit 1

Failure.

🧪 Debugging Bash Scripts

✅ Run in Debug Mode

CODE

bash -x script.sh

Shows command execution step-by-step.

✅ Strict Mode (Highly Recommended)

    CODE      
#!/bin/bash

set -euo pipefail

This helps catch:

Undefined variables

Failed commands

Pipeline failures

⚡ Bash Automation in DevOps

Bash is heavily used in:

Area	Usage
CI/CD	Build automation
Kubernetes	Cluster scripts
Docker	Container automation
AWS	EC2 setup scripts
Monitoring	Health checks
Security	Log scanning
Linux	System administration

🔐 Security Best Practices

Never write insecure scripts.

❌ Avoid Hardcoding Passwords

Bad:

    CODE      
password="admin123"

Better:

CODE

read -s password

✅ Quote Variables

Bad:

    CODE      
rm -rf $dir

Good:

    CODE      
rm -rf "$dir"

✅ Validate Inputs

Always sanitize user input.

📚 Important Bash Commands Every Engineer Should Know

Command	Purpose
`grep`	Search text
`awk`	Text processing
`sed`	Stream editing
`cut`	Extract columns
`find`	Search files
`xargs`	Command chaining
`curl`	API requests
`tar`	Archive files
`cron`	Scheduling
`systemctl`	Manage services

🚀 Bash vs Python for Automation

Bash	Python
Best for Linux automation	Best for complex logic
Fast scripting	Better readability
Native shell access	Huge libraries
Lightweight	Cross-platform

Most DevOps engineers use both.

🎯 Best Practices for Bash Scripting

✅ Use meaningful variable names

✅ Add comments

✅ Use functions

✅ Handle errors properly

✅ Use strict mode

✅ Keep scripts modular

✅ Log important actions

✅ Test before production

🧠 Final Thoughts

Bash scripting is one of the most valuable skills in Linux, DevOps, Cloud, and Cybersecurity.

The engineers who automate repetitive tasks become exponentially more productive.

Start small:

Automate backups

Monitor servers

Deploy applications

Clean logs

Schedule tasks

Over time, Bash becomes your operational superpower.

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Day 5 — Bash Scripting for Automation

🔗 Resources

📦 Linux Package Managers

🚀 What is Bash?

🧠 What is Bash Scripting?

⚡ Why Bash Automation Matters

📂 Bash Script Structure

🔥 Variables in Bash

✅ Creating Variables

⚠️ Important Rule

🧾 User Input

📌 Command Line Arguments

🔍 Conditional Statements

✅ If Statement

✅ If-Else

✅ If-Elif-Else

🧠 Comparison Operators

🔁 Loops in Bash

✅ For Loop

✅ Range Loop

✅ While Loop

✅ Infinite Loop

🔨 Functions in Bash

📦 Arrays in Bash

📁 File Operations

✅ Check if File Exists

✅ Create File

✅ Append to File

⚙️ Process Automation

✅ Kill Process

✅ Restart Service

✅ Check Service Status

🕒 Cron Jobs for Scheduling

✅ Run Every Day at Midnight

✅ Run Every 5 Minutes

🚀 Real-World Automation Scripts

🔥 1️⃣ Automated Backup Script

🔥 2️⃣ Disk Usage Monitoring Script

🔥 3️⃣ Website Monitoring Script

🔥 4️⃣ Auto Deployment Script

🔥 5️⃣ Log Cleanup Script

🛡️ Error Handling in Bash

📌 Exit Codes

🧪 Debugging Bash Scripts

✅ Run in Debug Mode

✅ Strict Mode (Highly Recommended)

⚡ Bash Automation in DevOps

🔐 Security Best Practices

❌ Avoid Hardcoding Passwords

✅ Quote Variables

✅ Validate Inputs

📚 Important Bash Commands Every Engineer Should Know

🚀 Bash vs Python for Automation

🎯 Best Practices for Bash Scripting

🧠 Final Thoughts

Community-Analysen & Experten-Meinungen 0

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