#!/usr/bin/perl -w
use strict;
use CGI;
my $q = new CGI;
print $q->header();

if ( $q->param('filled') eq 'this form' ) {
    # the user submitted the form so process it
    # here we get the value the user put into the username field
    my $username = $q->param('username');

    # display some sort of thank you page
    print "You submitted $username";

} else {
    # the script was not called by the form below so show the form
    print <<HTML;
<form action="http://mysite.com/cgi-bin/myscript.pl" method="post">
<input type="hidden" name="filled" value="this form">
<p>Username: <input type="text" name="username">
<p><input type="submit" name="submit" value="Submit Form">
HTML
}

exit;