http://www.shellhacks.com/en/HowTo-Check-SSL-Certificate-Expiration-Date-from-the-Linux-Shell
echo | openssl s_client -connect <hostname>:443 2>/dev/null | openssl x509 -noout -issuer -subject -dates
echo | openssl s_client -connect <hostname>:443 2>/dev/null | openssl x509 -noout -issuer -subject -dates