> Ugh — lots of annoying problems, caused not because we don’t have enough flexibility, but because we have too much.

I don't think this is quite right. The problem isn't weird characters in filenames, it's that the system itself handles them poorly. The default separator should have been '\0' to begin with. Globs for files should expand names in the current directory with the "./" prefix even if you didn't explicitly prefix the glob with "./".

Then for printing/inputting unprintable characters there should be a universal standardized escaping format, which takes as input what it prints as output, used by all standard utilities and with conversion functions in the standard library that convert from escaped names to binary names and vice versa.

Actually prohibiting the characters from the filesystem creates other problems.

Suppose I have an existing filesystem, or one mounted from a foreign system without these restrictions. It has files "foo" and "foo\nbar" and " foo" and "foo " etc. in the same directory. If we restrict what the filesystem accepts, do my existing files become unreadable? Impossible to delete or rename using standard utilities? Impossible to reversibly backup to a different machine that uses the new restrictions?

Suppose I get an arbitrary name from an external source and intend to store it in a filename in a way that can be losslessly converted back to the original name later. If the only disallowed characters are '\0' and '/' then I can handle those and be done. If filenames had many other restrictions, which can change over time as they add Unicode control characters or people decide something new should be prohibited, now the programmer has to handle escaping all of those too and you're just moving the problem over there. Moreover, if the set of characters you're not allowed to use isn't fixed ahead of time then the safe thing is something like base64 encoding the name, but then that makes the common case worse because you get gibberish names in all cases even though they would otherwise have been meaningful to humans >99% of the time.

The place for prohibiting weird characters isn't at the filesystem level, it's somewhere above it. It's perfectly reasonable for a program to restrict what characters it is willing to put in a filename, because there are many contexts where it makes no sense to have newlines and such. But that's for the program to decide, because some, including the system utilities, should accept anything. If you already have a file called "-this\nfilename\nis\nlame " then it's quite important that things like rm and mv (i.e. rename) should be able to work on it.

Moreover, the problem with portability is that it goes both ways. If you want to be portable then you shouldn't create filenames that start with '-' because some systems don't support them, but if you want to be portable then you still have to be able to handle filenames that start with '-' because some systems do have them which means there may be existing files with those names.

That said, many of the proposed solutions are still good. The continued existence of encodings other than UTF-8 seems almost entirely without merit at this point, and if the filename contained binary data that isn't valid UTF-8 then it could be losslessly escaped in the same way that unprintable UTF-8 characters could be.