base64-encoded sha256 (the new standard):

awk '{print $2}' ssh_host_rsa_key.pub | base64 -d | sha256sum | awk '{print $1}' | xxd -r -p | base64


md5 hex digits (old standard):

awk '{print $2}' ssh_host_rsa_key.pub | base64 -d | md5sum