print_expiring_certificates.sh

#!/bin/bash

for certificate in certs/*; do
    expiration_date=$(openssl x509 -noout -dates -in $certificate | grep -oP "(?<=notAfter=).*")
    remaining_validity_seconds=$(($(date -d "$expiration_date" +%s) - $(date +%s)))
    remaining_validity_in_days=$(($remaining_validity_seconds / 86400))
    if [ $remaining_validity_in_days -lt 30 ]; then
        echo $(basename $certificate .pem);
    fi
done