How can caching affect the ability to modify headers in PHP scripts, especially when using the echo function?

Caching can affect the ability to modify headers in PHP scripts because once content is cached, headers may not be able to be modified. To solve this issue, you can use the ob_start() function in PHP to buffer the output and then send the headers before any content is echoed out. 

<?php
ob_start();
// Start output buffering

header('Cache-Control: no-cache, no-store, must-revalidate');
header('Pragma: no-cache');
header('Expires: 0');
// Set headers before any content is echoed out

echo "Hello, World!";
// Content to be echoed out

ob_end_flush();
// Flush the output buffer
?>

Keywords

caching headers PHP scripts echo function modification

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