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Date: Mon, 14 Jan 2013 17:13:07 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: stat() and tilde prefix (was bad bash tab completion)
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On Jan 15 01:36, Shaddy Baddah wrote:
> Hi,
> 
> On 14/01/13 21:00, Corinna Vinschen wrote:
> >On Jan 14 01:17, Christopher Faylor wrote:
> >>On Mon, Jan 14, 2013 at 04:21:25PM +1100, Shaddy Baddah wrote:
> >>>In investigating this, I believe the issue I am having is due to how
> >>>stat() handles tilde prefixed paths. On linux we see:
> >>>
> >>>linux$ $ python -c 'import os; print os.stat("~/..")'
> >>>Traceback (most recent call last):
> >>>   File "<string>", line 1, in<module>
> >>>OSError: [Errno 2] No such file or directory: '~/..'
> >>>
> >>>and on cygwin we see:
> >>>
> >>>cygwin$ python -c 'import os; print os.stat("~/..")'
> >>>posix.stat_result(st_mode=16832, st_ino=562949953496729L,
> >>>st_dev=4174909669L, st_nlink=1, st_uid=42037, st_gid=10513, st_size=0L,
> >>>st_atime=1357616166, st_mtime=1357616166, st_ctime=1357616166)
> >>
> >>It is a bug.  It's not just "~".  Any nonexistent directory will
> >>work, like "foo/..".
> >
> >And it's a bug which isn't easily fixed.  Since about the dawn of time,
> >Cygwin's core path handling evaluates the path in a non-POSIX manner,
> >mainly for performance reasons.
> 
> Thank you both for your explanations. If my understanding is correct,
> stat() will be returning for the current working directory.

In the above case, yes.

> It seems to me then that a patch to bash may be in order? I can see how
> the bash check is the right thing to do. It doesn't want the special
> tilde expansion to mask and disallow referencing of real tilde prefixed
> paths. So the stat() check is the quick win to determine that.
> 
> From what I make of it, there needs to be a patch that, although can
> work generically, adds checks only required for Cygwin. And therefore
> is specific to the Cygwin package.
> 
> The check would be an extension of the file_exists() function, perhaps
> called tilde_file_exists(), which determines if the tilde prefix forms
> a directory component of the path (strchr('/')?). If it does not, the
> file_exists() check is sufficient. If it does, then the check of if
> that directory exists is logically and'ed to the result of
> file_exists().
> 
> Does that sound about right?

A check like this might be a good idea.  Ultimately I would be glad to
be able to come up with more correct code in Cygwin while not getting
slower, of course.  But that's wishful thinking for now.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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