Master PHP’s header() Function: Redirects, HTTP Headers, and Caching Tricks

In PHP, the header() function is essential for page redirection and setting HTTP response headers. This article explains its usage with syntax and parameters.

Basic syntax:

header(string $header, bool $replace = true, int $http_response_code = 0): bool

$header

(required): The HTTP header string, e.g., "Content-Type: text/html;charset=utf-8". $replace (optional): Whether to replace a previous header of the same name. Default true. $http_response_code (optional): HTTP status code to send.

Common use cases with examples:

1. Page redirection

The function can redirect users to a specified URL.

header("Location: http://www.example.com");
exit;

2. Setting HTTP response headers

Set headers such as Content-Type.

header("Content-Type: application/json");

3. Setting HTTP status codes

Send status codes like 404.

header("HTTP/1.1 404 Not Found");

4. Preventing page caching

Use Cache-Control, Pragma, and Expires headers.

header("Cache-Control: no-cache, no-store, must-revalidate");
header("Pragma: no-cache");
header("Expires: 0");

5. File download

Set Content-Disposition and related headers to force download.

header("Content-Disposition: attachment; filename=example.pdf");
header("Content-Type: application/pdf");
header("Content-Length: " . filesize("example.pdf"));
readfile("example.pdf");

Summary

The header() function is versatile for redirects, header manipulation, caching control, and file downloads. It must be called before any output, and it is advisable to follow it with exit to stop script execution.