cert_hash.sh

#!/bin/bash
certs=`openssl s_client -servername $1 -host $1 -port 443 -showcerts </dev/null 2>/dev/null | sed -n '/Certificate chain/,/Server certificate/p'`
rest=$certs

cert="${rest%%-----END CERTIFICATE-----*}-----END CERTIFICATE-----"
rest=${rest#*-----END CERTIFICATE-----}
echo "$cert" | openssl x509 -pubkey -noout |
   openssl rsa -pubin -outform der 2>/dev/null |
   openssl dgst -sha256 -binary | openssl enc -base64