Yup -- that's the way to do it, I think. I wrote "source filter" in the original partly as it was the thing that occurred to me when the joke first came to me and partly to hint that I wasn't being serious. As people started saying "I wish that existed," I realized that to actually do it would need B (or, as diotalevi said, B::Lint) or PPI. And it should really be an external check -- or something easily turned off or commented out for production. You don't really want your CGI script to take 10 seconds to fire up because it's busy checking to see if you wrote q{} instead of ''.