Renaming filenames and case-sensitivity: a race condition in the OS?

Question

There appears to be a curious set of circumstances where the OS doesn't allow you to rename a file where the only changes are case-sensitive. For example, "foo.JPG" to "foo.jpg". You can see an example using the command-shell "tcsh". Start this shell (type "tcsh" at any command prompt), and then type:
% touch foo.JPG
% mv foo.JPG foo.jpg
overwrite foo.jpg? (y/n [n])
Now, you may think it's no problem because few people use tcsh, but the problem is more systemic that should be addressed because I'm finding the problem at a programming level as well. The simplistic tcsh example illustrates the problem: the internals of tcsh call the OS-layer library function rename(2) to move or rename a file. However, something in the OS that reports back that the new filename exists (even though it doesn't) Because it sees foo.JPG, and it doesn't differentiate letter case, it thinks foo.jpg exists, so it returns an error to the calling program. In this case, it's tcsh, which is what prompts the user to overwrite. It doesn't matter what you answer, the result is the same. If you say yesthe OS doesn't see them as different, so it doesn't do anything.
If you're a programmer, you can see this happen for yourself by writing a small program that does the same thing:
#!/usr/bin/perl
if (!rename "foo.JPG", "foo.jpg") {
print "Error: $!\n";
This simple perl script just calls the rename(2) library call, which is part of the OS.
What I don't understand is why this error happens, when, and how to get around it. Obviously, other programs that rename files don't have this problem. The default shell, bash, doesn't have a problem either--even though tcsh (also a similar command-line shell) does. In fact, most programs don't have this problem. But as a programmer, I'm not sure what I should be doing. This exact same perl script (and correlating C programs) work perfectly well on all other unix platforms I've tried.
G5 Mac OS X (10.4.5)

Answer 1

It's not at the os layer, it's at the filesystem
layer. The filesystem you have is not case sensitive.
well, the filesystem is part of the operating system, although it's clearly only one component of it. In fact, one of the primary defining characteristics of unix is how the filesystem works, albeit there are variations of implementation. But this is a nit=picking point.
As to the issue of whether the filesystem truly is case-insensitive, that isn't so clear. I can rename a file from foo.JPG to foo.jpg easily in the Finder (just click and edit a file to change it's name from upper to lower, or mixed), and the new name you give it DOES change. similarly, I can do this with virtually any other app that has a file-finder style dialog box. Why I can't do it with the shell (or at an API level) is the real mystery, and there is no doc on the subject that I'm aware of. Clearly, the OS is preserving the change somewhere, somehow. the question is, who's doing it? (and if it's not part of the filesystem, why?)
It could be that some other layer is sitting on top of the filesystem that is overseeing such actions, and is preserving the case of the filenames, but this is such a huge waste of time and work, all for a "feature" whose value is still as yet unclear to me.
If it is, as you say, that "my version" of the filesystem happens to be case-insensitive, I'd love to know where that came from, and what the rationale was behind it. And, of course, how to get some version of the filesystem that doesn't have this feature. I've been working with unix systems at every layer since 1983, and have never run into such a thing before.
dan