CWD is a useful concept. If I run gimp in a particular directory, I'd like it to show that directory in the file dialogue when I try to load or save an image.
What is evil is a program changing its working directory. That's when it becomes an evil global variable, rather than a non-evil global constant.
I think that's probably the best way to look at it. You are given the parent node with CWD and you can attempt to modify child nodes by relatively addressing them.
I was wondering before if it would be interesting to have a filesystem with transactional locking of paths, though I'm sure the performance would take a hit. Would be kind of cool to be able to do filesystem operations without constantly opening yourself up to race conditions and requiring extremely defensive programming.
Why limit that to one directory? As I expanded on a bit in my response to ygra, I don't mean eliminating any notion of carrying a directory, just that I don't know that there is actually good reason to privilege one particular path universally.
I agree that treating cwd as a global constant solves most (at least) of the issues, I'm just poking assumptions to see what ideas arise.
You'd have to use absolute paths everywhere, but that probably doesn't hurt that much in programs or scripts. The CWD seems most useful in interactive shells, I guess. A fun thing is PowerShell on Windows where you have two CWDs, one from the process and another one from the shell which had is own VFS handling (e.g. the registry is a place that has no representation in the normal file system). Cmdlets use one of them and external commands and .NET APIs use the other. So in the latter case you always need Resolve-Path foo.bar instead of just foo.bar for things to work properly.
You wouldn't have to use absolute paths everywhere - you could use paths relative to any file descriptor that pointed at a directory. The shell itself wouldn't seem to have any problem - it could maintain a logical CWD without assistance. Utilities would probably need some other convention - maybe fd 4 points at the directory they are to operate in at start?
In a sense, this is "still a CWD" - but the differences would be 1) you can maintain multiple at the same time, and 2) you could close it.
