来自Action的URL中的变量

<body>

<?php 
$domain = $_POST['domainname'];
?>

<form action="http://" "<?php print $domain; ?>:2083/login" method="POST">
<input type="hidden" name="login_theme" value="cpanel">
<table width="200" class="login" cellpadding="0" cellspacing="0">
    <tr>
        <td align="left"><b>Login</b></td>
        <td>&nbsp;</td>
    </tr>
    <tr>
        <td>Domain</td>
        <td>
            <input autocomplete="off" type="text" name="domainname" size="16">
        </td>
    </tr>
    <tr>
        <td>Username</td>
        <td>
            <input autocomplete="off" type="text" name="user" size="16">
        </td>
    </tr>

    <tr class="row2">
        <td>Password</td>
        <td>
            <input type="password" name="pass" size="16">
        </td>
    </tr>
    <tr>
        <td colspan="2" align="center">
            <input type="submit" value="Login" class="input-button">
        </td>
    </tr>
</table>
</form>
</body>

I have this code on a basic php file. My goal is to have a centralised hub for cpanel users to login into.

They will input their domain name, username and password into the form, the form will take them to http://theirdomain.com/cpanel and log them in by passing the credentials through.

Only problem I am having is outputting the domain variable in the form's action to make it go there. Just getting 'about:blank'

EDIT: I have moved the redirect script over to a second file, and it seems to be redirecting to the domain fine now. However, now the credentials won't pass through.

</div>

Ended up with this (probably not the cleanest, but it works)
index.php

<?php 
    $domain = $_POST['domainname'];
?>

    <form action="cplogin.php" method="post">
        Domain: <input type="text" name="domainname" size="50" /><br />
        Username: <input type="text" name="user" size="50" /><br />
        Password: <input type="password" name="pass" size="20" autocomplete="off" /><br />
        <input type="submit" class="btn btn-red" name="login" value="Login" />
    </form>


and cplogin.php

        <?php
        $domain = $_POST['domainname'];

        if(!$_POST['login']) {
            exit;
        }

    $user = $_POST['user'];
    $pass = $_POST['pass'];
    $port = "2083";

    $port == "2083" || $port == "2083" ? $pre = "https://" : $pre = "https://";
?>
<body onLoad="setTimeout('document.forms[0].submit();',10)">
    <form action="<?php echo "".$pre."".$domain.":".$port."/login/"; ?>" method="post">
        <input type="hidden" name="user" value="<?php echo $user; ?>">
        <input type="hidden" name="pass" value="<?php echo $pass; ?>">
    </form>

<form action="http://<?php echo  $domain; ?>:2083/login" method="POST">
    <!--form content-->
</form>