Re: wget GET vs HEAD

[Darshit Shah]

On 03/02/2020 16:08, Peng Yu wrote:
> Hi,
>
> I'd like to understand the following two commands. One uses GET, the
> other uses HEAD.
>
> wget -q -O /dev/null -S -o- URL
> wget -q --spider -S -o- URL
>
> Is there first still download response body? Does wget know that its
> /dev/null so that it just download the header and ignore the response
> body?

No. Wget does not perform this optimization. As mentioned by Tim, there 
are many valid usecases where one would want to actually download the 
body, but not store it.

> If I only want the reponse header, and GET and HEAD result in the same
> header for my purpose, I should use the 2nd one to save time as it
> does not have response body?

Yes. In an ideal world, GET and HEAD should always return exactly the 
same headers (See RFC2616, sec. 9.4). However, some servers do not 
follow this (*cough* Google *cough*). If it works fine for you, yes, you 
can simply use the `--spider` option to get only the headers.

If that doesn't work, there is another possible hack, __if__ the server 
supports HTTP/1.1 Range Headers. You can explicitly send
`--header=Range: bytes=0-1`. This will cause the server to send only 1 
byte of the body. If you pass `--unlink` or `-O/dev/null` then the file 
will be automatically deleted for you as well
> Thanks.