checkcert -- shell script to quickly check whether a TLS cert is expiring "soon"

checkcert

#!/bin/sh

OPTSTRING="d:"
DAYS=90

while getopts ${OPTSTRING} opt; do
    case ${opt} in
        d)

            DAYS=${OPTARG}
            ;;
        *)
            ;;
    esac
done

shift $(($OPTIND -1 ))

HOSTNAME=${1}
echo "Host: $HOSTNAME, Days: ${DAYS}"
openssl x509 -noout -checkend $((86400 * $DAYS)) -in <(openssl s_client -showcerts -servername $HOSTNAME -connect $HOSTNAME:443 < /dev/null 2> /dev/null)