Getting HTTP code in PHP using curl

First make sure if the URL is actually valid (a string, not empty, good syntax), this is quick to check server side. For example, doing this first could save a lot of time:

if(!$url || !is_string($url) || ! preg_match('/^http(s)?://[a-z0-9-]+(.[a-z0-9-]+)*(:[0-9]+)?(/.*)?$/i', $url)){
    return false;
}

Make sure you only fetch the headers, not the body content:

@curl_setopt($ch, CURLOPT_HEADER  , true);  // we want headers
@curl_setopt($ch, CURLOPT_NOBODY  , true);  // we don't need body

For more details on getting the URL status http code I refer to another post I made (it also helps with following redirects):

• How can I check if a URL exists via PHP?

As a whole:

$url = 'http://www.example.com';
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_HEADER, true);    // we want headers
curl_setopt($ch, CURLOPT_NOBODY, true);    // we don't need body
curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch, CURLOPT_TIMEOUT,10);
$output = curl_exec($ch);
$httpcode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
curl_close($ch);

echo 'HTTP code: ' . $httpcode;

See also: How to post data in PHP using file_get_contents?

Basically you can use file_get_contents() and stream_context_create() for issuing a POST request. In your case:

$post = http_build_query(array(
    "username" => "user",
    "password" => "pw",
    "example" => "...",
));

$context = stream_context_create(array("http"=>array(
     "method" => "POST",
     "header" => "Content-Type: application/x-www-form-urlencodedrn" .
                 "Content-Length: ". strlen($post) . "rn",  
     "content" => $post,
))); 

$page = file_get_contents("http://example.com/login", false, $context);

Just set CURLOPT_HEADER to false.