Serhiy Storchaka writes:
> The readlink utility from GNU coreutils has three mode for resolving
> file path:
>
> -f, --canonicalize
> canonicalize by following every symlink in every
> component of the given name recursively; all but the last component must
> exist
>
> -e, --canonicalize-existing
> canonicalize by following every symlink in every
> component of the given name recursively, all components must exist
>
> -m, --canonicalize-missing
> canonicalize by following every symlink in every
> component of the given name recursively, without requirements on
> components existence
In Mac OS X (and I suppose other BSDs), realpath(3) implements -e.
glibc does none of these, instead:
GNU extensions
If the call fails with either EACCES or ENOENT and
resolved_path is not NULL, then the prefix of path that is not
readable or does not exist is returned in resolved_path.
I suppose this nonstandard behavior is controlled by a #define, but
the Linux manpage doesn't specify it.
> Current behavior of posixpath.realpath() is matches (besides one minor
> detail) to `readlink -m`. The behavior of Path.resolve() matches
> `readlink -e`.
This looks like a bug in posixpath, while Path.resolve follows POSIX.
http://pubs.opengroup.org/onlinepubs/009695399/functions/realpath.html
sez:
RETURN VALUE
Upon successful completion, realpath() shall return a pointer to
the resolved name. Otherwise, realpath() shall return a null
pointer and set errno to indicate the error, and the contents of
the buffer pointed to by resolved_name are undefined.
ERRORS
The realpath() function shall fail if:
[...]
[ENOENT] A component of file_name does not name an existing file or
file_name points to an empty string.
[ENOTDIR] A component of the path prefix is not a directory.
which corresponds to -e.
> I have proposed a patch that adds three-state optional parameter to
> posixpath.realpath() and I'm going to provide similar patch for
> Path.resolve(). But I'm not sure this is good API. Are there better
> variants?
Said parameter will almost always be a constant. Usually in those
cases Python prefers to use different functions. Eg,
posixpath.realpath -e
posixpath.realpath_require_prefix -f
posixpath.realpath_allow_missing -m
posixpath.realpath_gnuext GNU extension
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