Automated SSL Certificate Expiration Check and Notification

#!/bin/bash

# Configuration
DOMAIN="example.com"
PORT="443"
WARNING_DAYS=30 # Notify if certificate expires within this many days
RECIPIENT_EMAIL="[email protected]"

# Get certificate expiry date
EXPIRY_DATE_STR=$(echo | openssl s_client -servername "$DOMAIN" -connect "$DOMAIN":"$PORT" 2>/dev/null | openssl x509 -noout -enddate | cut -d= -f2)

# Check if expiry date was retrieved successfully
if [ -z "$EXPIRY_DATE_STR" ]; then
  echo "Error: Could not retrieve SSL certificate expiry date for $DOMAIN." >&2
  exit 1
fi

# Convert expiry date to Unix timestamp
EXPIRY_TIMESTAMP=$(date -d "$EXPIRY_DATE_STR" +%s)
CURRENT_TIMESTAMP=$(date +%s)

# Calculate days remaining until expiry
DAYS_REMAINING=$(( (EXPIRY_TIMESTAMP - CURRENT_TIMESTAMP) / (60*60*24) ))

echo "Certificate for $DOMAIN expires on: $EXPIRY_DATE_STR (Days remaining: $DAYS_REMAINING)"

# Send notification if certificate is nearing expiry
if [ "$DAYS_REMAINING" -le "$WARNING_DAYS" ]; then
  SUBJECT="SSL Certificate for $DOMAIN Expiring Soon!"
  MESSAGE="The SSL certificate for $DOMAIN expires in $DAYS_REMAINING days on $EXPIRY_DATE_STR. Please renew it."
  
  echo "Sending email notification to $RECIPIENT_EMAIL:"
  echo "Subject: $SUBJECT"
  echo "Message: $MESSAGE"

  # Use mail command to send email (ensure 'mailutils' or similar is installed)
  # echo "$MESSAGE" | mail -s "$SUBJECT" "$RECIPIENT_EMAIL"
  echo "Notification sent (mail command commented out for safety)."

else
  echo "Certificate for $DOMAIN is valid for more than $WARNING_DAYS days. No action needed."
fi

echo "Script finished."