My open source images-to-PDF utility, pdfmaker, makes use of Apple’s PDFKit. While this partnership works as it should, just one aspect bothered me: PDFKit warnings and errors don’t bubble up to the calling code, but are piped via STDERR. The upshot: anyone running pdfmaker may see messages that it hasn’t issued. pdfmaker is a CLI tool, but I can’t just redirect the output to /dev/null — you’d lose everything, not just PDFKit’s grumbles. Instead I had to figure out how to sink PDFKit’s output even though it wasn’t coming via pdfmaker. Here’s how I did the pipework.