Why does this not work:
curl -X HEAD http://www.google.com
But these both work just fine:
curl -I http://www.google.com curl -
You need to add the -i flag to the first command, to include the HTTP header in the output. This is required to print headers.
curl -X HEAD -i http://www.google.com
More here: https://serverfault.com/questions/140149/difference-between-curl-i-and-curl-x-head