The first line of an HTTP request includes the method - sometimes also referred to as the verb. When doing a simple GET request as this command line would do:
curl http://example.com/file
…the initial request line looks like this:
GET /file HTTP/1.1
You can tell curl to change the method into something else by using the -X
or --request command-line options followed by the actual method name. You
can, for example, send a DELETE instead of GET like this:
curl http://example.com/file -X DELETE
This command-line option only changes the text in the outgoing request, it
does not change any behavior. This is particularly important if you, for
example, ask curl to send a HEAD with -X, as HEAD is specified to send all
the headers a GET response would get but never send a response body, even if
the headers otherwise imply that one would come. So, adding -X HEAD to a
command line that would otherwise do a GET will cause curl to hang, waiting
for a response body that will not come.
When asking curl to perform HTTP transfers, it will pick the correct method
based on the option so you should only rarely have to explicitly ask for
it with -X. It should also be noted that when curl follows redirects like
asked to with -L, the request method set with -X will be sent even on the
subsequent redirects.