SSL certificate expiry checker - warns when a cert is expiring in less than 7 days.

ssl-expiry-check.sh

#!/bin/bash

# Number of days from expiry to throw warning.
warnPeriod=7

domainsFile="$( cd "$(dirname "$0")" ; pwd -P )/domains.txt"

if [ ! -f "$domainsFile" ]; then
    >&2 echo "Missing domains.txt file."
    exit 1
fi

exitCode=0
while read domain; do
    expiry=$(echo | openssl s_client -connect $domain:443 2>/dev/null | openssl x509 -noout -enddate 2>/dev/null | cut -d= -f2)
    expiryDate=$(echo $expiry | date +"%-d %b %Y" -f - )
    expiryTimestamp=$(echo $expiry | date +%s -f -)
    nowTimestamp=$(date +%s -u)
    diffTimestamp=$(expr $expiryTimestamp - $nowTimestamp)
    diffDays=$(echo "$diffTimestamp / 86400" | bc)
    echo "$domain: $expiryDate ($diffDays days)"

    if [ $diffDays -le $warnPeriod -a $diffDays -gt 0 ]; then
        >&2 echo "WARNING: $domain expires in $diffDays days!"
        ((exitCode++))
    fi
done < $domainsFile

exit $exitCode

Chuck this in your cron to check every morning at 8am and send you a slack if anything is amiss:

0 8 * * * /home/<username>/bin/ssl-expiry-check.sh 2>&1 >/dev/null | /home/<username>/bin/slack-me

See my slack-me gist for that script.

Script makes output like:

caseyfulton.com: 12 Sep 2018 (57 days)
www.caseyfulton.com: 12 Sep 2018 (57 days)