Basic Bash Examples

This section contains fundamental Bash scripting examples to help you practice and understand core concepts.

Hello World Variations

Simple Hello World

#!/bin/bash
echo "Hello, World!"

Hello World with Variables

#!/bin/bash
name="World"
echo "Hello, $name!"

Interactive Hello World

#!/bin/bash
echo "What's your name?"
read name
echo "Hello, $name! Nice to meet you."

Hello World with Date

#!/bin/bash
echo "Hello, World!"
echo "Today is: $(date)"
echo "Current user: $(whoami)"

Variable Examples

Basic Variable Operations

#!/bin/bash
# Variable assignment
first_name="John"
last_name="Doe"
age=25

# Variable usage
echo "Name: $first_name $last_name"
echo "Age: $age"

# Variable concatenation
full_name="$first_name $last_name"
echo "Full name: $full_name"

Environment Variables

#!/bin/bash
echo "Your home directory: $HOME"
echo "Your username: $USER"
echo "Your shell: $SHELL"
echo "Current path: $PATH"

Variable Default Values

#!/bin/bash
# Set default values
database_host=${DB_HOST:-"localhost"}
database_port=${DB_PORT:-"5432"}
database_name=${DB_NAME:-"myapp"}

echo "Database configuration:"
echo "Host: $database_host"
echo "Port: $database_port"
echo "Database: $database_name"

Variable Length and Manipulation

#!/bin/bash
text="Hello World"

echo "Original text: $text"
echo "Length: ${#text}"
echo "Uppercase: ${text^^}"
echo "Lowercase: ${text,,}"
echo "First 5 characters: ${text:0:5}"
echo "Last 5 characters: ${text: -5}"

Command Line Arguments

Basic Argument Handling

#!/bin/bash
echo "Script name: $0"
echo "First argument: $1"
echo "Second argument: $2"
echo "All arguments: $@"
echo "Number of arguments: $#"

Argument Validation

#!/bin/bash
if [ $# -eq 0 ]; then
    echo "Usage: $0 <name> [age]"
    exit 1
fi

name="$1"
age="${2:-unknown}"

echo "Name: $name"
echo "Age: $age"

Processing Multiple Arguments

#!/bin/bash
echo "Processing all arguments:"
for arg in "$@"; do
    echo "Argument: $arg"
done

Simple Calculations

Basic Arithmetic

#!/bin/bash
a=10
b=5

echo "a = $a, b = $b"
echo "Addition: $((a + b))"
echo "Subtraction: $((a - b))"
echo "Multiplication: $((a * b))"
echo "Division: $((a / b))"
echo "Modulo: $((a % b))"

Calculator Script

#!/bin/bash
echo "Simple Calculator"
read -p "Enter first number: " num1
read -p "Enter operator (+, -, *, /): " op
read -p "Enter second number: " num2

case $op in
    +) result=$((num1 + num2)) ;;
    -) result=$((num1 - num2)) ;;
    \*) result=$((num1 * num2)) ;;
    /)
        if [ $num2 -eq 0 ]; then
            echo "Error: Division by zero"
            exit 1
        fi
        result=$((num1 / num2))
        ;;
    *) echo "Invalid operator"; exit 1 ;;
esac

echo "Result: $num1 $op $num2 = $result"

Temperature Converter

#!/bin/bash
echo "Temperature Converter"
echo "1. Celsius to Fahrenheit"
echo "2. Fahrenheit to Celsius"
read -p "Choose option (1 or 2): " choice

case $choice in
    1)
        read -p "Enter temperature in Celsius: " celsius
        fahrenheit=$(echo "scale=2; $celsius * 9/5 + 32" | bc)
        echo "$celsius°C = $fahrenheit°F"
        ;;
    2)
        read -p "Enter temperature in Fahrenheit: " fahrenheit
        celsius=$(echo "scale=2; ($fahrenheit - 32) * 5/9" | bc)
        echo "$fahrenheit°F = $celsius°C"
        ;;
    *)
        echo "Invalid choice"
        exit 1
        ;;
esac

File Operations

File Information

#!/bin/bash
filename="$1"

if [ -z "$filename" ]; then
    echo "Usage: $0 <filename>"
    exit 1
fi

if [ -f "$filename" ]; then
    echo "File: $filename"
    echo "Size: $(stat -c%s "$filename") bytes"
    echo "Last modified: $(stat -c%y "$filename")"
    echo "Permissions: $(stat -c%A "$filename")"
    echo "Owner: $(stat -c%U "$filename")"
    echo "Group: $(stat -c%G "$filename")"
else
    echo "File '$filename' does not exist"
fi

File Backup

#!/bin/bash
source_file="$1"

if [ -z "$source_file" ]; then
    echo "Usage: $0 <source_file>"
    exit 1
fi

if [ ! -f "$source_file" ]; then
    echo "Error: File '$source_file' does not exist"
    exit 1
fi

backup_file="${source_file}.backup.$(date +%Y%m%d_%H%M%S)"

if cp "$source_file" "$backup_file"; then
    echo "Backup created: $backup_file"
else
    echo "Error: Failed to create backup"
    exit 1
fi

Directory Listing

#!/bin/bash
directory="${1:-.}"

echo "Contents of directory: $directory"
echo "=================================="

if [ -d "$directory" ]; then
    for item in "$directory"/*; do
        if [ -f "$item" ]; then
            echo "FILE: $(basename "$item")"
        elif [ -d "$item" ]; then
            echo "DIR:  $(basename "$item")"
        fi
    done
else
    echo "Error: '$directory' is not a directory"
fi

Text Processing

Word Count

#!/bin/bash
filename="$1"

if [ -z "$filename" ]; then
    echo "Usage: $0 <filename>"
    exit 1
fi

if [ -f "$filename" ]; then
    lines=$(wc -l < "$filename")
    words=$(wc -w < "$filename")
    chars=$(wc -c < "$filename")

    echo "File: $filename"
    echo "Lines: $lines"
    echo "Words: $words"
    echo "Characters: $chars"
else
    echo "File '$filename' does not exist"
fi

Text Search

#!/bin/bash
if [ $# -ne 2 ]; then
    echo "Usage: $0 <search_term> <filename>"
    exit 1
fi

search_term="$1"
filename="$2"

if [ ! -f "$filename" ]; then
    echo "File '$filename' does not exist"
    exit 1
fi

echo "Searching for '$search_term' in '$filename':"
grep -n "$search_term" "$filename"

count=$(grep -c "$search_term" "$filename")
echo "Found $count occurrences"

Line Numbering

#!/bin/bash
filename="$1"

if [ -z "$filename" ]; then
    echo "Usage: $0 <filename>"
    exit 1
fi

if [ -f "$filename" ]; then
    line_number=1
    while IFS= read -r line; do
        printf "%3d: %s\n" $line_number "$line"
        ((line_number++))
    done < "$filename"
else
    echo "File '$filename' does not exist"
fi

System Information

System Status

#!/bin/bash
echo "=== System Information ==="
echo "Hostname: $(hostname)"
echo "Uptime: $(uptime -p)"
echo "Current user: $(whoami)"
echo "Current directory: $(pwd)"
echo "Date: $(date)"
echo

echo "=== Memory Usage ==="
free -h

echo
echo "=== Disk Usage ==="
df -h

echo
echo "=== CPU Information ==="
lscpu | grep "Model name"

Process Monitor

#!/bin/bash
echo "Top 10 processes by CPU usage:"
ps aux --sort=-%cpu | head -11

echo
echo "Top 10 processes by memory usage:"
ps aux --sort=-%mem | head -11

Network Information

#!/bin/bash
echo "=== Network Information ==="
echo "Hostname: $(hostname)"
echo "Domain: $(hostname -d 2>/dev/null || echo "Not set")"

echo
echo "=== Network Interfaces ==="
ip addr show | grep -E "^[0-9]+:|inet "

echo
echo "=== Routing Table ==="
ip route show

User Input Examples

Menu System

#!/bin/bash
while true; do
    echo
    echo "=== Main Menu ==="
    echo "1. Show date and time"
    echo "2. Show current directory"
    echo "3. List files"
    echo "4. Show disk usage"
    echo "5. Exit"
    echo
    read -p "Choose an option (1-5): " choice

    case $choice in
        1) date ;;
        2) pwd ;;
        3) ls -la ;;
        4) df -h ;;
        5) echo "Goodbye!"; exit 0 ;;
        *) echo "Invalid choice. Please try again." ;;
    esac

    read -p "Press Enter to continue..."
done

User Registration

#!/bin/bash
echo "User Registration Form"
echo "====================="

read -p "First Name: " first_name
read -p "Last Name: " last_name
read -p "Email: " email
read -p "Age: " age
read -s -p "Password: " password
echo

echo
echo "Registration Summary:"
echo "Name: $first_name $last_name"
echo "Email: $email"
echo "Age: $age"
echo "Password: [hidden]"

read -p "Is this information correct? (y/n): " confirm
if [ "$confirm" = "y" ] || [ "$confirm" = "Y" ]; then
    echo "Registration completed!"
else
    echo "Registration cancelled."
fi

Quiz Game

#!/bin/bash
score=0
total_questions=3

echo "Welcome to the Bash Quiz!"
echo "========================"

# Question 1
echo "Question 1: What command shows the current directory?"
echo "a) pwd"
echo "b) cd"
echo "c) ls"
read -p "Your answer: " answer1

if [ "$answer1" = "a" ] || [ "$answer1" = "A" ]; then
    echo "Correct!"
    ((score++))
else
    echo "Wrong! The correct answer is 'a) pwd'"
fi

# Question 2
echo
echo "Question 2: What symbol is used for comments in bash?"
echo "a) //"
echo "b) #"
echo "c) /*"
read -p "Your answer: " answer2

if [ "$answer2" = "b" ] || [ "$answer2" = "B" ]; then
    echo "Correct!"
    ((score++))
else
    echo "Wrong! The correct answer is 'b) #'"
fi

# Question 3
echo
echo "Question 3: What command lists files and directories?"
echo "a) list"
echo "b) dir"
echo "c) ls"
read -p "Your answer: " answer3

if [ "$answer3" = "c" ] || [ "$answer3" = "C" ]; then
    echo "Correct!"
    ((score++))
else
    echo "Wrong! The correct answer is 'c) ls'"
fi

echo
echo "Quiz completed!"
echo "Your score: $score out of $total_questions"

percentage=$((score * 100 / total_questions))
if [ $percentage -ge 80 ]; then
    echo "Excellent work!"
elif [ $percentage -ge 60 ]; then
    echo "Good job!"
else
    echo "Keep practicing!"
fi

String Manipulation

String Operations

#!/bin/bash
text="Hello World Programming"

echo "Original: $text"
echo "Length: ${#text}"
echo "Uppercase: ${text^^}"
echo "Lowercase: ${text,,}"
echo "First word: ${text%% *}"
echo "Last word: ${text##* }"
echo "Remove 'Hello': ${text/Hello/}"
echo "Replace 'World' with 'Bash': ${text/World/Bash}"
echo "First 10 chars: ${text:0:10}"
echo "From position 6: ${text:6}"

Palindrome Checker

#!/bin/bash
read -p "Enter a word to check if it's a palindrome: " word

# Convert to lowercase and remove spaces
clean_word=$(echo "$word" | tr '[:upper:]' '[:lower:]' | tr -d ' ')

# Reverse the string
reversed=$(echo "$clean_word" | rev)

if [ "$clean_word" = "$reversed" ]; then
    echo "'$word' is a palindrome!"
else
    echo "'$word' is not a palindrome."
fi

Password Generator

#!/bin/bash
read -p "Enter password length (default 12): " length
length=${length:-12}

# Generate password using /dev/urandom
password=$(tr -dc 'A-Za-z0-9!@#$%^&*' < /dev/urandom | head -c "$length")

echo "Generated password: $password"
echo "Password strength:"
echo "Length: $length characters"

# Check password strength
if [[ $password =~ [A-Z] ]]; then
    echo "✓ Contains uppercase letters"
fi

if [[ $password =~ [a-z] ]]; then
    echo "✓ Contains lowercase letters"
fi

if [[ $password =~ [0-9] ]]; then
    echo "✓ Contains numbers"
fi

if [[ $password =~ [!@#\$%\^&\*] ]]; then
    echo "✓ Contains special characters"
fi

Array Examples

Basic Array Operations

#!/bin/bash
# Create array
fruits=("apple" "banana" "orange" "grape")

echo "All fruits: ${fruits[@]}"
echo "Number of fruits: ${#fruits[@]}"
echo "First fruit: ${fruits[0]}"
echo "Last fruit: ${fruits[-1]}"

# Add element
fruits+=("mango")
echo "After adding mango: ${fruits[@]}"

# Loop through array
echo "Fruits list:"
for i in "${!fruits[@]}"; do
    echo "$((i+1)). ${fruits[i]}"
done

Shopping List

#!/bin/bash
declare -a shopping_list

echo "Shopping List Manager"
echo "===================="

while true; do
    echo
    echo "1. Add item"
    echo "2. Remove item"
    echo "3. Show list"
    echo "4. Clear list"
    echo "5. Exit"
    read -p "Choose option: " choice

    case $choice in
        1)
            read -p "Enter item to add: " item
            shopping_list+=("$item")
            echo "Added '$item' to the list"
            ;;
        2)
            if [ ${#shopping_list[@]} -eq 0 ]; then
                echo "List is empty"
            else
                echo "Current items:"
                for i in "${!shopping_list[@]}"; do
                    echo "$((i+1)). ${shopping_list[i]}"
                done
                read -p "Enter item number to remove: " num
                if [ "$num" -ge 1 ] && [ "$num" -le ${#shopping_list[@]} ]; then
                    removed_item="${shopping_list[$((num-1))]}"
                    unset shopping_list[$((num-1))]
                    shopping_list=("${shopping_list[@]}")  # Re-index array
                    echo "Removed '$removed_item'"
                else
                    echo "Invalid item number"
                fi
            fi
            ;;
        3)
            if [ ${#shopping_list[@]} -eq 0 ]; then
                echo "Shopping list is empty"
            else
                echo "Shopping List:"
                for i in "${!shopping_list[@]}"; do
                    echo "$((i+1)). ${shopping_list[i]}"
                done
            fi
            ;;
        4)
            shopping_list=()
            echo "List cleared"
            ;;
        5)
            echo "Goodbye!"
            exit 0
            ;;
        *)
            echo "Invalid choice"
            ;;
    esac
done

Grade Calculator

#!/bin/bash
declare -a grades
declare -a subjects

echo "Grade Calculator"
echo "==============="

read -p "How many subjects? " num_subjects

for ((i=1; i<=num_subjects; i++)); do
    read -p "Enter subject $i name: " subject
    read -p "Enter grade for $subject: " grade

    subjects+=("$subject")
    grades+=("$grade")
done

# Calculate average
total=0
for grade in "${grades[@]}"; do
    total=$((total + grade))
done

average=$((total / num_subjects))

echo
echo "Grade Report:"
echo "============"
for i in "${!subjects[@]}"; do
    echo "${subjects[i]}: ${grades[i]}"
done

echo
echo "Average: $average"

if [ $average -ge 90 ]; then
    echo "Grade: A (Excellent)"
elif [ $average -ge 80 ]; then
    echo "Grade: B (Good)"
elif [ $average -ge 70 ]; then
    echo "Grade: C (Average)"
elif [ $average -ge 60 ]; then
    echo "Grade: D (Below Average)"
else
    echo "Grade: F (Fail)"
fi