Exercises

Chapter 46: Practical Exercises

Overview

This chapter provides hands-on exercises to practice bash scripting skills for real-world DevOps, SRE, and SysAdmin scenarios.

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Exercise 1: System Health Check Script

Problem

Create a script that checks system health:

• CPU usage
• Memory usage
• Disk usage
• Top 5 processes by memory

Solution

#!/usr/bin/env bash

check_cpu() {
    top -bn1 | grep "Cpu(s)" | awk '{print "CPU: " $2}'
}

check_memory() {
    free -h | awk '/^Mem:/ {print "Memory: " $3 "/" $2}'
}

check_disk() {
    df -h | awk '/\/$/ {print "Disk: " $3 " used of " $2}'
}

check_top_processes() {
    echo "Top 5 processes:"
    ps aux --sort=-%mem | awk 'NR<=6 {print $11, $6"MB"}'
}

echo "=== System Health Check ==="
check_cpu
check_memory
check_disk
check_top_processes

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Exercise 2: Log File Analyzer

Problem

Create a script to analyze Apache/Nginx logs:

• Count requests by IP
• Find most visited pages
• Show error count

Solution

#!/usr/bin/env bash

LOG_FILE="${1:-/var/log/nginx/access.log}"

echo "=== Log Analysis ==="
echo "Requests by IP:"
awk '{print $1}' "$LOG_FILE" | sort | uniq -c | sort -rn | head -5

echo -e "\nMost visited pages:"
awk '{print $7}' "$LOG_FILE" | sort | uniq -c | sort -rn | head -5

echo -e "\nError count:"
grep -c " 5[0-9][0-9] " "$LOG_FILE"

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Exercise 3: Automated Backup Script

Problem

Create a backup script that:

• Backs up specified directories
• Creates timestamped archives
• Cleans up old backups

Solution

#!/usr/bin/env bash

set -euo pipefail

BACKUP_DIR="/backup"
SOURCE_DIRS=("/home" "/etc" "/var/www")
DAYS_TO_KEEP=7

timestamp=$(date +%Y%m%d_%H%M%S)
backup_file="$BACKUP_DIR/backup_$timestamp.tar.gz"

mkdir -p "$BACKUP_DIR"

tar -czf "$backup_file" "${SOURCE_DIRS[@]}"

echo "Backup created: $backup_file"

# Cleanup old backups
find "$BACKUP_DIR" -name "backup_*.tar.gz" -mtime +$DAYS_TO_KEEP -delete

echo "Old backups cleaned up"

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Exercise 4: User Management Script

Problem

Create a script for user management:

• Add new users with home directory
• List all users
• Lock/unlock accounts

Solution

#!/usr/bin/env bash

add_user() {
    local username="$1"
    sudo useradd -m "$username"
    echo "User $username created"
}

list_users() {
    awk -F: '{print $1, $6}' /etc/passwd
}

lock_user() {
    sudo usermod -L "$1"
    echo "User $1 locked"
}

unlock_user() {
    sudo usermod -U "$1"
    echo "User $1 unlocked"
}

case "$1" in
    add) add_user "$2" ;;
    list) list_users ;;
    lock) lock_user "$2" ;;
    unlock) unlock_user "$2" ;;
esac

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Exercise 5: Network Diagnostics Script

Problem

Create a network diagnostics script:

• Check connectivity to hosts
• Show listening ports
• Display network interface info

Solution

#!/usr/bin/env bash

check_hosts() {
    local hosts=("google.com" "8.8.8.8" "cloudflare.com")
    for host in "${hosts[@]}"; do
        if ping -c 1 "$host" &>/dev/null; then
            echo "✓ $host is reachable"
        else
            echo "✗ $host is unreachable"
        fi
    done
}

list_ports() {
    echo "Listening ports:"
    ss -tuln | awk 'NR>1 {print $1, $5}' | column -t
}

network_info() {
    ip addr show | awk '/inet / {print "IP:", $2}'
    ip route | awk '/default / {print "Gateway:", $3}'
}

echo "=== Network Diagnostics ==="
check_hosts
echo
list_ports
echo
network_info

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Exercise 6: Docker Container Manager

Problem

Create a script to manage Docker containers:

• Start/Stop/Restart containers
• Show container status
• View logs

Solution

#!/usr/bin/env bash

container_status() {
    docker ps -a --format "table {{.Names}}\t{{.Status}}\t{{.Ports}}"
}

start_container() {
    docker start "$1" && echo "Started: $1"
}

stop_container() {
    docker stop "$1" && echo "Stopped: $1"
}

restart_container() {
    docker restart "$1" && echo "Restarted: $1"
}

view_logs() {
    docker logs --tail 50 "$1"
}

case "$1" in
    status) container_status ;;
    start) start_container "$2" ;;
    stop) stop_container "$2" ;;
    restart) restart_container "$2" ;;
    logs) view_logs "$2" ;;
esac

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Exercise 7: SSL Certificate Checker

Problem

Create a script to check SSL certificates:

• Check certificate expiry
• Show days remaining
• Alert if expiring soon

Solution

<function_code> #!/usr/bin/env bash

check_ssl() { local domain=“$1” local port=”${2:-443}”

local expiry=$(echo | openssl s_client -servername "$domain" -connect "$domain:$port" 2>/dev/null | openssl x509 -noout -enddate)

if [ -z "$expiry" ]; then
    echo "Error: Could not get certificate for $domain"
    return 1
fi

local expiry_date=$(echo "$expiry" | cut -d= -f2)
local expiry_epoch=$(date -d "$expiry_date" +%s)
local now_epoch=$(date +%s)
local days_left=$(( (expiry_epoch - now_epoch) / 86400 ))

echo "Domain: $domain"
echo "Expires: $expiry_date"
echo "Days remaining: $days_left"

if [ "$days_left" -lt 30 ]; then
    echo "⚠ WARNING: Certificate expires in less than 30 days!"
    return 1
fi

echo "✓ Certificate is valid"

}

for domain in ”$@”; do check_ssl “$domain” echo ”---” done </function_code>

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Exercise 8: Database Backup Script

Problem

Create a script to backup databases:

• Backup MySQL/PostgreSQL
• Compress and encrypt
• Upload to remote storage

solution

#!/usr/bin/env bash

set -euo pipefail

DB_TYPE="${DB_TYPE:-mysql}"
DB_NAME="${DB_NAME:-mydb}"
DB_USER="${DB_USER:-root}"
BACKUP_DIR="/backup/db"
REMOTE_HOST="backup-server"

timestamp=$(date +%Y%m%d_%H%M%S)
backup_file="$BACKUP_DIR/${DB_NAME}_${timestamp}.sql.gz"

mkdir -p "$BACKUP_DIR"

backup_mysql() {
    mysqldump -u "$DB_USER" -p"$DB_PASSWORD" "$DB_NAME" | gzip > "$backup_file"
}

backup_postgres() {
    pg_dump -U "$DB_USER" "$DB_NAME" | gzip > "$backup_file"
}

if [ "$DB_TYPE" = "mysql" ]; then
    backup_mysql
elif [ "$DB_TYPE" = "postgres" ]; then
    backup_postgres
fi

echo "Database backup created: $backup_file"

# Upload to remote
scp "$backup_file" "$REMOTE_HOST:/backups/"

echo "Backup uploaded to remote"

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Summary

In this chapter, you completed:

• ✅ System health check script
• ✅ Log file analyzer
• ✅ Automated backup script
• ✅ User management script
• ✅ Network diagnostics
• ✅ Docker container manager
• ✅ SSL certificate checker
• ✅ Database backup script

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Next Steps

Practice these exercises and modify them for your specific use cases. Refer back to earlier chapters for detailed explanations of specific commands and techniques.

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