Check the 'getcwd' function instead of 'cwd'. This does not use an external command. It's a lot more intensive, but does a more thorough job (and may perhaps be how 'pwd' does it internally, actually). Data may still be considered tainted, though. I don't really think there's going to be a way to get at filesystem information in such a way that you can't consider it unsafe/tainted to begin with, since any part of it can be arbitrarily supplied by any user. If you trust it, un-taint it.