whois $(dig +short yoursitehere.com) | grep -i 'Cloudflare' 1>/dev/null; if [[ $? -eq 1 ]]; then echo 'Didnt find CloudFlare'; else echo 'Found CloudFlare'; fi

Not at a terminal now, but this long one-liner should work.

Like you said, not 100% reliable though. For example, I'm pretty sure Reddit uses CloudFlare, but their whois mentions Fastly, which is a competitor.

We moved off of CloudFlare to Fastly before this vulnerability.

Confirmed, reddit.com was removed from the list. My mistake for not double checking this one.

If you find any domains with this please add them to the list:

https://github.com/pirate/sites-using-cloudflare