Bash SSL Certificate Expiration Check

check-certs.sh

#!/bin/bash
help_text(){
    echo "Usage:"
    echo " $0 HOSTNAME:PORT"
    echo "    HOSTNAME - target hostname to check"
    echo "    ECHO     - target port. Default 443"
    echo ""
    echo "Env variables:"
    echo "    CERT_CHECK_SLACK_URL       - Slack Webhook"
    echo "    CERT_CHECK_SLACK_USERNAME  - Slack username"
    echo "    CERT_CHECK_SLACK_CHANNEL   - Slack channel"
}

TARGET="$1"
if [[ "${TARGET}" == "" ]]; then
    help_text
    exit 1
fi

HOSTNAME=${TARGET%%:*}
PORT=${TARGET##*:}

if [[ "${HOSTNAME}" == "${PORT}" ]] ; then
    PORT=443 .  # ':' not found
fi

SLACK_URL=${CERT_CHECK_SLACK_URL:-'Your incoming webhook'} # 'https://hooks.slack.com/services/SOMETHING/SOMETHING ELSE'
SLACK_USERNAME=${CERT_CHECK_SLACK_USERNAME:-'CERT CHECK'}
SLACK_CHANNEL=${CERT_CHECK_SLACK_CHANNEL:'#alerts'}

emoji=":terminator:"
DAYS=7;


expirationdate=$(date -d "$(: | openssl s_client -connect $HOSTNAME:$PORT -servername $HOSTNAME 2>/dev/null \
                              | openssl x509 -text \
                              | grep 'Not After' \
                              | awk '{print $4,$5,$7}')" '+%s'); 
in7days=$(($(date +%s) + (86400*$DAYS)));
if [ $in7days -gt $expirationdate ]; then
    message="Certificate for $HOSTNAME:$PORT expires in less than $DAYS days"
    payload="payload={\"channel\": \"$SLACK_CHANNEL\", \"username\": \"$SLACK_USERNAME\", \"icon_emoji\": \"$emoji\", \"text\": \"${message}\"}"
    curl -m 5 --data-urlencode "${payload}" $SLACK_URL
fi