This is taken directly from the CURL manual at:
http://curl.haxx.se/docs/manual.html
POST (HTTP)
It's easy to post data using curl. This is done using the -d <data>
option. [B]The post data must be urlencoded[/B].
Post a simple "name" and "phone" guestbook.
curl -d "name=Rafael%20Sagula&phone=3320780" \
http://www.where.com/guest.cgi
How to post a form with curl, lesson #1:
Dig out all the <input> tags in the form that you want to fill in. (There's
a perl program called formfind.pl on the curl site that helps with this).
If there's a "normal" post, you use -d to post. -d takes a full "post
string", which is in the format
<variable1>=<data1>&<variable2>=<data2>&...
The 'variable' names are the names set with "name=" in the <input> tags, and
the data is the contents you want to fill in for the inputs. The data *must*
be properly URL encoded. That means you replace space with + and that you
write weird letters with %XX where XX is the hexadecimal representation of
the letter's ASCII code.