What best practices should be followed when updating an older PHP script to be compatible with newer PHP versions like 5.4?

When updating an older PHP script to be compatible with newer PHP versions like 5.4, it's important to address deprecated features and syntax changes. This may involve updating functions that have been removed, replacing deprecated functions with newer alternatives, and adjusting syntax to adhere to the latest PHP standards. 

// Before updating:
mysql_connect("localhost", "username", "password");

// After updating:
$mysqli = new mysqli("localhost", "username", "password");
if ($mysqli->connect_error) {
    die("Connection failed: " . $mysqli->connect_error);
}

Keywords

PHP 5.4 backward compatibility deprecated functions error handling compatibility testing

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