curl, the seminal swiss army knife of HTTP requests, is quite good at many things. Practically everybody knows that you can show headers using the -I flag:

$curl -I

However, this is plain wrong in a subtle way. See, I sends a HEAD request, which is sometimes used to probe the server for the last modification date and such. However, most of the time you want to check a real GET as opposed to a HEAD. Also, not all web frameworks will automatically implement a HEAD responder for you in addition to a GET responder. It’s also downright misleading because with quite a few proxies the headers you are going to be getting from the server will be different for a GET as opposed to a HEAD.

To perform a “real” GET, hit curl with a lowercase i as opposed to upprecase.

$curl -i

However, this will pollute your terminal with horrible binary-encoded strings (which is normal for a PNG after all)… There are ways to do a full GET and only show a header, the easiest being doing this:

$curl -s -D - -o /dev/null

Works a treat but is long and not memorizable. I put it in my .profile as headercheck:

alias headercheck='curl -s -D - $1 -o /dev/null'

So anytime you want to check headers with a real GET request, hit:

$headercheck http://url.that/you-want-to-check

and you are off to the races.