how to upload file using curl with PHP

I want to know how to upload file using cURL or anything else in PHP. I have searched in google many times but no results.

In other words, the user sees a file upload button on a form, the form gets posted to my php script, then my php script needs to re-post it to another script (eg on another server).

I have this code to receive the file and upload it

code :

echo"".$_FILES['userfile']."";
$uploaddir = './';
$uploadfile = $uploaddir . basename($_FILES['userfile']['name']);
if ( isset($_FILES["userfile"]) ) {
    echo '<p><font color="#00FF00" size="7">Uploaded</font></p>';
    if (move_uploaded_file
($_FILES["userfile"]["tmp_name"], $uploadfile))
echo $uploadfile;
    else echo '<p><font color="#FF0000" size="7">Failed</font></p>';
}

I want the code to send the file to receiver file.

Use:

if (function_exists('curl_file_create')) { // php 5.5+
  $cFile = curl_file_create($file_name_with_full_path);
} else { // 
  $cFile = '@' . realpath($file_name_with_full_path);
}
$post = array('extra_info' => '123456','file_contents'=> $cFile);
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,$target_url);
curl_setopt($ch, CURLOPT_POST,1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $post);
$result=curl_exec ($ch);
curl_close ($ch);

You can also refer:

http://blog.derakkilgo.com/2009/06/07/send-a-file-via-post-with-curl-and-php/

Important hint for PHP 5.5+:

Now we should use https://wiki.php.net/rfc/curl-file-upload but if you still want to use this deprecated approach then you need to set curl_setopt($ch, CURLOPT_SAFE_UPLOAD, false);