php check if gravatar exists header error

Question

I'm trying to check if a gravatar exists. When I try the approach recommended in earlier questions, I get an error " Warning: get_headers() [function.get-headers]: This function may only be used against URLs" Anyone seen this or see the error in my code? PS I do not want to specify a default image for gravatar to serve as there could be more than one default possibilities if no gravatar exits.

Also, I found a reference to error possibly being related to my ini file which I don't think my host gives me access to. If so, is there an alternative to getheaders? Many thanks.

$email = $_SESSION['email'];
$email= "[email protected]"; //for testing
$gravemail = md5( strtolower( trim( $email ) ) );
$gravsrc = "http://www.gravatar.com/avatar/".$gravemail;
$gravcheck = "http://www.gravatar.com/avatar/".$gravemail."?d=404";
$response = get_headers('$gravcheck');
echo $response;
exit;
if ($response != "404 Not Found"..or whatever based on response above){
$img = $gravsrc;
}

Answer 1

Observation

A. get_headers('$gravcheck'); would not work because of use of single quote '

B. calling exit; would terminate script prematurely

C. $response would return an array you can not use echo to print the information use print_r insted

D. $response != "404 Not Found" would not work because $response is array

This is the proper way to do it :

$email= "[email protected]"; //for testing
$gravemail = md5( strtolower( trim( $email ) ) );
$gravsrc = "http://www.gravatar.com/avatar/".$gravemail;
$gravcheck = "http://www.gravatar.com/avatar/".$gravemail."?d=404";
$response = get_headers($gravcheck);
print_r($response);
if ($response[0] != "HTTP/1.0 404 Not Found"){
    $img = $gravsrc;
}