SHA256 | base64

By the way, my version of the base64 command defaults to encoding, while it looks like the one mentioned above defaults to decoding; and they don't take the same options so you can't write something portable to both (mine doesn't have the -e option).

If we're already using the openssl command, we can work around that difference with:

sha256sum () {
    openssl sha256 -binary "$@" | openssl base64
}