PHP header() Function

Example

Send three HTTP headers to prevent page caching:

<?php
// Date in the past
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
header("Cache-Control: no-cache");
header("Pragma: no-cache");
?>

<html>
<body>
...
...

Note: There are options that users may set to change the browser's default caching settings. By sending the headers above, you will override any of those settings and force the browser to not cache!

Definition and Usage

The header() function sends a raw HTTP header to a client.

It is important to notice that the header() function must be called before any actual output is sent!

Syntax

header(header, replace, http_response_code)

Parameter Values

Parameter	Description
header	Required. Specifies the header string to send
replace	Optional. Indicates whether the header should replace a previous similar header or add a new header of the same type. Default is TRUE (will replace). FALSE allows multiple headers of the same type
http_response_code	Optional. Forces the HTTP response code to the specified value

Technical Details

Return Value:	Nothing
PHP Version:	4.0+
PHP Changelog:	PHP 5.1.2: Now prevents that more than one header to be sent at once. This is a protection against header injection attacks

More Examples

Example

Let the user be prompted to save a generated PDF file (Content-Disposition header is used to supply a recommended filename and force the browser to display the save dialog box):

<?php
header("Content-type:application/pdf");

// It will be called downloaded.pdf
header("Content-Disposition:attachment;filename='downloaded.pdf'");

// The PDF source is in original.pdf
readfile("original.pdf");
?>

<html>
<body>

...
...

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