Send an email notification whenever a file or directory changes

To send an email notification whenever a file or directory changes in multiple watch directories while excluding certain subdirectories, 
you can use inotifywait (from inotify-tools) along with mail or sendmail.

sudo apt update
sudo apt install inotify-tools mailutils -y

Here 
inotify-tools: Monitors filesystem changes.
mailutils: Enables email sending (for mail command).

sudo nano /usr/local/bin/watch_changes.sh

#!/bin/bash

# Set email recipient
EMAIL="[email protected]"

# Log file
LOG_FILE="/var/log/inotify_changes.log"

# Directories to monitor (separated by space)
WATCH_DIRS=("/etc" "/root" "/home" "/var/www")

# Excluded directories (patterns matched within WATCH_DIRS)
EXCLUDE_PATTERNS=("node_modules" "cache" "logs")

# Convert exclude patterns into grep format
EXCLUDE_REGEX=$(printf "|%s" "${EXCLUDE_PATTERNS[@]}")
EXCLUDE_REGEX=${EXCLUDE_REGEX:1}  # Remove leading "|"

# Monitor changes
inotifywait -m -r -e modify,create,delete,move --format '%w%f %e' "${WATCH_DIRS[@]}" |
while read FILE EVENT; do
    # Skip excluded directories
    if [[ "$FILE" =~ $EXCLUDE_REGEX ]]; then
        continue
    fi
    # Log event
    echo "$EVENT" | tee -a "$LOG_FILE"
    # Send email notification
    echo "Change detected:\n$EVENT" | mail -s "File Change Alert" "$EMAIL"
done

Make the Script Executable.
sudo chmod +x /usr/local/bin/watch_changes.sh

Run the script in the background so it continuously monitors file changes.
nohup /usr/local/bin/watch_changes.sh >/dev/null 2>&1 &

To stop it, find the process
ps aux | grep watch_changes.sh

Then kill it
kill <PID>

#To start the script on system boot, add it to cron
#sudo crontab -e
#@reboot nohup /usr/local/bin/watch_changes.sh >/dev/null 2>&1 &

Create a systemd service for automatic start and restart.
Create a systemd service file

sudo nano /etc/systemd/system/filewatch.service

Add the following content

[Unit]
Description=Monitor directory changes and send email notifications
After=network.target

[Service]
ExecStart=/usr/local/bin/watch_directories.sh
Restart=always
User=root

[Install]
WantedBy=multi-user.target

Enable and start the service

sudo systemctl enable filewatch
sudo systemctl start filewatch