add "EXPIRE" tag in header while serving content

does adding "EXPIRE" tag in header forces the brows开发者_运维技巧er to cache the content till the time expired ?

How to do so while serving an static image/css/js in PHP ?

You can use header and gmdate functions:

// Actualy date in GTM 0
header('Date: '.gmdate('D, d M Y H:i:s \G\M\T', time())); 

// Las modify date (now, for example)
header('Last-Modified: '.gmdate('D, d M Y H:i:s \G\M\T', time())); 

// The expire time (one hour in the future) <-- sorry my english!!!
header('Expires: '.gmdate('D, d M Y H:i:s \G\M\T', time() + 3600)); 

Always make sure to send headers before sending data, ex:

// GOOD!
header('Expires: '.gmdate('D, d M Y H:i:s \G\M\T', time() + 3600));
echo "content";

// BAD!
echo "some content";
header('Expires: '.gmdate('D, d M Y H:i:s \G\M\T', time() + 3600));

If you need generate the content before send header, you can use a ob functions:

ob_start();

echo "content";
echo "more content";


header('Expires: '.gmdate('D, d M Y H:i:s \G\M\T', time() + 3600));
ob_end_flush();

For static content use web server config. For apache it's .htaccess, for iis it's web.config.