Write PHP code in PHP

<?php echo htmlentities('<?php echo \'aoeu\'; ?>'); ?>

Try This

<<< is Heredoc

<?php

echo <<< EOF

<?php
echo <<< EOF
EOF;
?>

EOF;

?>

If you output some complex code definitely use a template engine like smarty.. otherwise your code will look a complete mess.

I once patched the propel ORM which does output PHP code without using a template engine. It generates all the model classes based on the XML configuration files. Their code was a big mess. Don't do it.