How can memory usage in PHP scripts be measured and compared when using references versus values?

When measuring memory usage in PHP scripts, it's important to consider the difference between using references and values. References allow multiple variables to refer to the same underlying data, which can reduce memory usage compared to passing values. To measure and compare memory usage, you can use the `memory_get_usage()` function before and after executing your script and compare the results when using references versus values.

// Using references
$data = "Lorem ipsum dolor sit amet, consectetur adipiscing elit.";
$reference = &$data;

echo "Memory usage before: " . memory_get_usage() . " bytes\n";

// Using values
$data = "Lorem ipsum dolor sit amet, consectetur adipiscing elit.";
$value = $data;

echo "Memory usage after: " . memory_get_usage() . " bytes\n";