Use PHP in a component

[Ampersand]

yes echo works, so it must have to do with something different than escaping quotes. When I put a filename into a component,

component content
require_once("filename.php");
template content:
<?php get_component('componentname'); ?>

it stops page rendering.

However this way:

template content:
<?php require_once("filename.php"); ?>

it works fine, even with further call of filename functions in the template.