A simple Linux shell script to get the SHA256 hash of the public key of SSL certificate of an online server (most commonly to implement SSL pinning)

get-server-ssl-public-key-hash.sh

#!/bin/sh

if [ -z $(which openssl) ]; then
        echo "Error: OpenSSL is not installed" >&2
        exit 1
fi

if [ "$#" -lt 1 ] || [ -n "${1##*:*}" ]; then
        echo "Usage: $0 URL:PORT" >&2
        exit 1
fi

HOSTPORT=$1
echo | openssl s_client -connect $HOSTPORT 2> /dev/null | openssl x509 -pubkey -noout | openssl pkey -pubin -outform der | openssl dgst -sha256 -binary | openssl enc -base64