Bash SSL Certificate Expiration Check

check-certs.sh

#!/bin/bash

#
# Usage: check-certs.sh domain.name
#

TARGET="$@"; 

RECIPIENT="[email protected]";
DAYS=30;

echo "checking if $TARGET expires in less than $DAYS days";
expirationdate=$(date -d "$(: | openssl s_client -connect $TARGET:443 -servername $TARGET 2>/dev/null \
                              | openssl x509 -text \
                              | grep 'Not After' \
                              | awk '{print $4,$5,$7}')" '+%s'); 

in_days=$(($(date +%s) + (86400*$DAYS)));

if [ $in_days -gt $expirationdate ]; then
    echo "KO - Certificate for $TARGET expires in less than $DAYS days, on $(date -d @$expirationdate '+%Y-%m-%d')" \
    | mail -s "Certificate expiration warning for $TARGET" $RECIPIENT;
else
    echo "OK - Certificate expires on $(date -d @$expirationdate '+%Y-%m-%d')";
fi;