Re: "readlink -f foo" fails if the target of foo does not exist

[Paul Eggert]

Jim Meyering <address@hidden> writes:

> So here's a better spec:
> 
>   If canonicalize_file_name (FILE) succeeds, work exactly as now.
>   else if lstat (FILE) succeeds,
>     linkname = readlink (FILE)
>     if linkname starts with `/', print linkname
>     otherwise, print $(readlink -f $(dirname FILE))/linkname
>   else, work exactly as now.

Hmm, the above algorithm doesn't canonicalize linkname.  If linkname
contains "." or ".." components, shouldn't they be canonicalized out?
For example, linkname might be "../bar", and if so the above algorithm
would print /a/b/c/../bar when it should print /a/b/bar.

Another possibility is that linkname could refer to symbolic links.
For example, if linkname is "s/x" where s is a symbolic link to "/",
and "/x" does not exist, then you should print "/x", not "/a/b/c/s/x".

Canonicalizing linkname as described above would result in a different
file name FILE1 which couldn't be printed immediately, since it you
would then have to fed back into the above algorithm.  Unless the file
system was mutating under you, presumably canonicalize_file_name
(FILE1) would fail for the same reason that canonicalize_file_name
(FILE) failed.  However, lstat (FILE1) might succeed, or might fail.
If it fails, you're done: if it succeeds and if readlink (FILE1) gives
you an absolute link, you're done as well; but if readlink (FILE1)
gives you a relative link, you have to construct a new name FILE2 and
start over again.  So this whole process might loop.

Ouch!  My head is spinning.