What steps can be taken to troubleshoot and debug PHP scripts that rely on server variables like HTTP_REFERER?

When troubleshooting PHP scripts that rely on server variables like HTTP_REFERER, it is important to first check if the variable is set and if it contains the expected value. If the variable is not set or does not contain the expected value, you can try to simulate the variable by passing it as a query parameter in the URL. This can help identify if the issue is with the server configuration or the script itself.

if(isset($_SERVER['HTTP_REFERER'])){
    $referer = $_SERVER['HTTP_REFERER'];
    // Use $referer variable in your script
} else {
    // Simulate HTTP_REFERER by passing it as a query parameter
    $referer = isset($_GET['referer']) ? $_GET['referer'] : '';
    // Use $referer variable in your script
}