I followed the advice from this Stack Overflow question thread, but I keep hitting a snag.

I am receiving the following error message: Unsupported protocol: sftp

Here is my code:

$ch = curl_init();
if(!$ch)
{
    $error = curl_error($ch);
    die("cURL session could not be initiated.  ERROR: $error."");
}


$fp = fopen($docname, 'r');
if(!$fp)
{
    $error = curl_error($ch);
    die("$docname could not be read.");
}

curl_setopt($ch, CURLOPT_URL, "sftp://$user_name:$user_pass@$server:22/$docname");
curl_setopt($ch, CURLOPT_UPLOAD, 1);
curl_setopt($ch, CURLOPT_PROTOCOLS, CURLPROTO_SFTP);
curl_setopt($ch, CURLOPT_INFILE, $fp);
curl_setopt($ch, CURLOPT_INFILESIZE, filesize($docname));

//this is where I get the failure
$exec = curl_exec ($ch);
if(!$exec)
{
    $error = curl_error($ch);
    die("File $docname could not be uploaded.  ERROR: $error.");
}

curl_close ($ch);

I used the curl_version() function to see my curl information, and found that sftp doesn't seem to be in the array of supported protocols:

[version_number] => 462597
    [age] => 2
    [features] => 1597
    [ssl_version_number] => 0
    [version] => 7.15.5
    [host] => x86_64-redhat-linux-gnu
    [ssl_version] =>  OpenSSL/0.9.8b
    [libz_version] => 1.2.3
    [protocols] => Array
        (
            [0] => tftp
            [1] => ftp
            [2] => telnet
            [3] => dict
            [4] => ldap
            [5] => http
            [6] => file
            [7] => https
            [8] => ftps
        )

Is this a matter of my version of cURL being outdated, or is the SFTP protocol simply not supported at all?

Any advice is greatly appreciated.