To be a 100% solution, I'd have to go one step further and intercept the C library calls. A 90% solution would be to intercept the Perl 'open' and 'opendir' and 'glob' opcodes. (once you have a file handle, you can tie it to intercept all the rest) But really, I'd be ok starting with a 60% solution of letting people opt-in by using a VFS module instead of calling 'open'. This is the point I was making about "have a Path::Class / Path::Tiny themed module" and "If "VFS::Path" happened to have your favorite API for traversing trees"