Is there a POSIX pathname that can't name a file?
- by Charles Stewart
Are there any legal paths in POSIX that cannot be associated with a file, regular or irregular? That is, for which test -e "$LEGITIMATEPOSIXPATHNAME" cannot succeed?
Clarification #1: pathnames
By "legal paths in POSIX", I mean ones that POSIX says are allowed, not ones that POSIX doesn't explicitly forbid. I've looked this up, and the are POSIX specification calls them character strings that:
Use only characters from the portable filename character set [a-zA-Z0-9._-] (cf. http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap03.html#tag_03_276);
Do not begin with -; and
Have length between 1 and NAME_MAX, a number unspecified for POSIX that is not less than 14.
POSIX also allows that filesystems will probably be more relaxed than this, but it forbids the characters NUL and / from appearing in filenames. Note that such a paradigmatically UNIX filename as lost+found isn't FPF, according to this def. There's another constant PATH_MAX, whose use needs no further explanation.
The ideal answer will use FPFs, but I'm interested in any example with filenames that POSIX doesn't expressly forbid.
Clarification #2: impossibility
Obviously, pathnames normally could be bound to a file. But UNIX semantics will tell you that there are special places that couldn't normally have arbitrary files created, like in the /dev directory. Are any such special places stipulated in POSIX? That is what the question is getting after.
