Using PHP header() Function: Redirects, HTTP Headers, Status Codes, and Cache Control

In PHP, the header() function is a crucial tool for performing page redirects and setting HTTP response header information.

The basic syntax of header() 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 with the same name; default is true.

$http_response_code (optional): the HTTP status code to set; must be a valid code.

1. Page Redirection

The header() function can redirect users 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 for JSON output:

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

3. Setting HTTP Status Codes

Use header() to define the response status, for example a 404 Not Found:

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

4. Preventing Page Caching

To stop browsers from caching a page, send cache‑control headers:

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

5. Enabling File Downloads

By setting Content-Disposition to attachment , you can force 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 versatile for redirects, header manipulation, status codes, cache control, and file downloads. It must be called before any output is sent; otherwise, PHP will raise an error. After sending headers, it is advisable to terminate the script with exit to avoid unintended output.

Understanding and correctly using header() enables developers to manage HTTP responses effectively in PHP web applications.