🚀 Bash Scripting Made Easy – Learn by Example (With Outputs!)

Bash scripting is a way to automate tasks in Linux using a series of shell commands written in a text file. Think of it as creating a to-do list for your computer to follow — automatically..

📌 1. Getting Started with Bash Scripts

Every Bash script should start with this line:

bashCopyEdit#!/bin/bash

Why? This is called a shebang. It tells the computer: “Use the Bash shell to run this file.”

🧪 Example:

bashCopyEdit#!/bin/bash
echo -e "🎉 Welcome to Bash Scripting!\nLet's start learning... 💻"

• echo prints the message

• -e enables special characters like \n (new line) and \t (tab)

✅ How to Run:

bashCopyEditchmod +x hello.sh   # Make it executable
./hello.sh          # Run the script

📤 Output:

vbnetCopyEdit🎉 Welcome to Bash Scripting!
Let's start learning... 💻

---

💡 2. Variables – Store and Use Data

📌 Static Variables

You can define your own variables to store information:

bashCopyEdit#!/bin/bash
name="Alice"
city="Paris"
company="OpenAI"
echo "Hi, I'm $name from $city, and I work at $company."

• $name pulls the value stored in the variable

• Quotes are not required but help with spacing

📤 Output:

vbnetCopyEditHi, I'm Alice from Paris, and I work at OpenAI.

---

📌 Dynamic Input

Let the user provide input at runtime:

bashCopyEdit#!/bin/bash
echo "Enter your name:"
read name
echo "Enter your city:"
read city
echo "Enter your company:"
read company
echo "Hi $name from $city! You work at $company. 👍"

• read waits for user input and stores it in the variable

📤 Output:

yamlCopyEditEnter your name:
Alice
Enter your city:
Paris
Enter your company:
OpenAI
Hi Alice from Paris! You work at OpenAI. 👍

---

🔐 3. Password Input – Hidden Typing

Sometimes we don’t want to show the password as someone types it.

bashCopyEdit#!/bin/bash
echo "Enter your username:"
read user
read -sp "Enter your password: " pass
echo -e "\nWelcome, $user! Your password is safely captured. 🔐"

• -s makes read silent (hides input)

• -p adds a prompt message inline

---

🎯 4. Script Arguments – Pass Data from Command Line

You can pass values when you run the script:

bashCopyEdit#!/bin/bash
echo "Name: $1"
echo "Country: $2"
echo "Company: $3"
echo "All arguments: $@"
echo "Script name: $0"

• $1, $2, etc. refer to each input argument

• $@ means all arguments

• $0 is the script filename

✅ Run:

bashCopyEditsh info.sh Alice France OpenAI

---

✅ 5. If Conditions – Logic in Scripts

📌 Simple If Statement

bashCopyEditnum=10
if [[ $num -eq 10 ]]; then
    echo "✔️ The number is exactly 10"
fi

• -eq means “equal to” (used for numbers)

• Double square brackets [[ ]] are safer than single [ ]

---

📌 If-Else

bashCopyEditnum=5
if [[ $num -eq 10 ]]; then
    echo "Number is 10"
else
    echo "❌ Number is not 10"
fi

• else runs only when if fails

---

📌 Nested If / Grading System

bashCopyEditecho "Enter your score:"
read score

if [[ $score -eq 100 ]]; then
    echo "🏆 First Prize!"
elif [[ $score -eq 50 ]]; then
    echo "🥈 Second Prize"
elif [[ $score -eq 25 ]]; then
    echo "🥉 Third Prize"
else
    echo "😔 Better luck next time!"
fi

• elif lets you check multiple conditions

• else is the default if none match

---

🔢 6. Comparing Strings and Numbers

📌 String Comparison

bashCopyEditperson1="Alice"
person2="Alice"

if [[ $person1 == $person2 ]]; then
    echo "✅ Both names match"
fi

• Use == for string comparison

• Use != for "not equal"

---

📌 Number Comparison

bashCopyEdita=20
b=10

if [[ $a -gt $b ]]; then
    echo "🔼 a is greater than b"
fi

• -gt: greater than

• -lt: less than

• -ge: greater or equal

• -le: less or equal

• -ne: not equal

• -eq: equal

---

🔐 7. Simple Login Script (AND / OR)

Using AND (&&)

bashCopyEditread -p "Username: " user
read -sp "Password: " pass

if [[ $user == "admin" && $pass == "admin@123" ]]; then
    echo -e "\n✅ Welcome, admin!"
else
    echo -e "\n❌ Invalid credentials"
fi

• Both username and password must match

---

Using OR (||)

bashCopyEditif [[ $user == "admin" || $pass == "admin@123" ]]; then
    echo -e "\n✔️ At least one credential is correct"
else
    echo -e "\n❌ Neither is correct"
fi

---

📁 8. File Checking

bashCopyEditfile="/home/user/data.txt"

if [[ -e $file ]]; then
    echo "📄 File exists!"
else
    echo "❌ File not found!"
fi

• -e checks if a file exists

• You can also use -f for regular files and -d for directories

---

🏁 Final Thoughts

You now know how to:

• Write basic scripts

• Use variables and input

• Pass arguments

• Add logic (if/else)

• Read passwords safely

• Check for files