How to Retrieve the Referrer URL in PHP: Why is $_SERVER[\'HTTP_REFERER\'] Sometimes Empty?

How to Retrieve the Referrer URL in PHP

When tracking user behavior on your website, it's often desirable to know where they came from. PHP provides a convenient way to access the referrer URL through the $_SERVER['HTTP_REFERER'] variable.

However, it's essential to note that this variable may not always contain the expected value. For instance, if a user comes directly to your site by typing in the URL or using a bookmark, $_SERVER['HTTP_REFERER'] will be empty.

Additional Considerations

If you're using the $_SERVER['HTTP_REFERER'] variable and finding that it's consistently empty, consider the following possibilities:

• The user may have disabled the option to send referrer information in their browser settings.
• The user may have used a script or bot to access your site, which generally does not provide referrer information.
• You may have accidentally omitted the leading underscores from $_SERVER['HTTP_REFERER'].

Here's a more comprehensive list of the variables contained in the $_SERVER array:

• DOCUMENT_ROOT: The root folder of your webserver.
• GATEWAY_INTERFACE: The version of the CGI.
• HTTP_ACCEPT: The types of content that the client can accept.
• HTTP_ACCEPT_ENCODING: The encoding that the client can accept.
• HTTP_ACCEPT_LANGUAGE: The language that the client can accept.
• HTTP_CACHE_CONTROL: Controls the caching of the page.
• HTTP_CONNECTION: The connection type used to access the page.
• HTTP_COOKIE: The cookies sent by the client.
• HTTP_HOST: The hostname of the server.
• HTTP_USER_AGENT: The user agent of the client.
• PATH: The search path for scripts.
• QUERY_STRING: The query string sent to the script.
• REDIRECT_STATUS: The status code of the redirect performed by the server.
• REMOTE_ADDR: The IP address of the client.
• REMOTE_PORT: The port number used by the client.
• REQUEST_METHOD: The method used to access the page (GET, POST, etc.).
• REQUEST_URI: The path and query string of the requested page.
• SCRIPT_FILENAME: The absolute path to the script being executed.
• SCRIPT_NAME: The path to the script being executed.
• SERVER_ADDR: The IP address of the server.
• SERVER_ADMIN: The email address of the server administrator.
• SERVER_NAME: The hostname of the server.
• SERVER_PORT: The port number used by the server.
• SERVER_PROTOCOL: The protocol used by the server (HTTP/1.1, HTTP/1.0).
• SERVER_SIGNATURE: The signature of the server (Apache, IIS, etc.).
• SERVER_SOFTWARE: The software used by the server (Apache, IIS, etc.).
• UNIQUE_ID: A unique session identifier.
• PHP_SELF: The name of the current script.
• REQUEST_TIME: The timestamp when the request was made.
• argv: An array of command-line arguments.
• argc: The number of command-line arguments.

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