[Haskell-cafe] Re: File path programme
robdockins at fastmail.fm
Mon Jan 31 15:08:30 EST 2005
> Well, there is a sort-of canonic version for every path; on
> most Unix systems the function realpath(3) will find it.
Here is the BUGS listing from 'man realpath' on my system:
Never use this function. It is broken by design since it is impossible
to determine a suitable size for the output buffer. According to
POSIX a buffer of size PATH_MAX suffices, but PATH_MAX need not be a
defined constant, and may have to be obtained using pathconf(). And
asking pathconf() does not really help, since on the one hand POSIX
warns that the result of pathconf() may be huge and unsuitable for
mallocing memory. And on the other hand pathconf() may return -1 to
signify that PATH_MAX is not bounded.
> My interpretation is that two paths are equivalent iff they
> point to the same target.
You might do better (on *nix) to check if two paths terminate in the
same filesystem and then see if the inode numbers match (with some stat
variant). Even that may break down for networked filesystems or FAT
wrappers or other things that may lie about the inode number.
You could also unravel the path manually, but that seems error-prone and
This strikes me as yet another case of a simple-seeming operation that
simply cannot be implemented correctly on file names.
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