How to post data with <form method="POST">

I use clearsilver 0.10.5 with mini_httpd.
I made a C CGI script to Get and Set parameters.
I want to setup my params on my webpage and send it to my CGI script.
For the moment I made a form with method="GET" but I don't like this
because all params are in web address.
For example :
# test.html
<form name="form" action="index.cgi"> <!-- method="post"> -->
  <input type="hidden" name="to" value="test">
  <input type="text" size="15" maxlength="15" name="command_line"
value="ls"
  <div>
    <input type="button" value="Apply" onclick="form.submit()"></input>
  </div>
</form>

In my cgi C script :
# cgi.c
if ((err = hdf_get_copy(cgi->hdf, "Query.command_line", &command_line,
"\0")))	NEOERR_HANDLER;
syslog(LOG_LOCAL7|LOG_DEBUG, "%s - command_line='%s'", __FUNCTION__,
command_line);

This works fine with GET method but when I use POST method I don't
have anything in my Query.
I looked with Wireshark and I send to=test&command_line=ls
So where are my params ? if there are not in Query.to Query.command_line ?

Thanks
Sebastien