Using PHP's header() Function: Redirects, HTTP Headers, Status Codes, Caching, and File Downloads

In PHP, the header() function is a fundamental tool that can perform page redirects and set HTTP response header information. This article details how to use header() and provides concrete code examples.

The basic syntax of the function is:

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

$header

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

Below are five common use cases for header() with specific code snippets.

1. Implementing a Web Redirect

The function can redirect a user to a specified URL:

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

2. Setting HTTP Response Headers

It can also set various response headers such as Content-Type:

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

3. Setting HTTP Response Status Codes

Use it to send a specific status code, for example a 404 Not Found:

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

4. Preventing Page Caching

By sending cache‑control headers you can tell browsers not to cache the page:

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

5. Enabling File Downloads

Set Content-Disposition to "attachment" and provide appropriate headers to trigger a file download:

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

Conclusion

The header() function is essential for controlling HTTP behavior in PHP applications, allowing redirects, custom headers, status codes, cache control, and file downloads. It must be called before any output is sent, and it is advisable to follow it with exit to prevent unintended script execution.

By mastering header(), developers can flexibly manage HTTP responses to meet a wide range of requirements.