Re: [PATCH 0/5] more aggressive on ${a:-b}

[Eric Blake]

On 08/26/2010 11:27 AM, Ralf Wildenhues wrote:
> Hi Eric,
>
> * Eric Blake wrote on Thu, Aug 26, 2010 at 01:18:16AM CEST:
> > On cygwin, attempts to do a glob() with a filename that contains
> > a backslash can issue a warning; but I have been unable to reliably
> > reproduce that in my environment (otherwise, I would have used it
> > as an example in the second patch).  But see these links for an
> > example of where unintended globbing matters:
> > http://cygwin.com/ml/cygwin/2009-04/msg00531.html
>
> I'm sure somebody thought that it would be a good idea to print that
> warning, I can't imagine any reason that wouldn't outweigh its downsides
> now though.  Do you have a link to the corresponding implementation
> discussion?  Thanks.

The best I could find was the release announcement where it first appeared:
http://sourceware.org/ml/cygwin/2008-12/msg00225.html

The idea was that cygwin is intended to be a Posix-style platform, 
except for the fact that it uses \ as an alternate spelling of / as a 
directory separator; additionally, when using \, you lose cygwin's 
emulation of Posix permissions (basically, using \ means that you are 
going straight to Windows APIs and giving up some of the very reason 
that you were using cygwin in the first place).  Since the use of \ can 
cause rather surprising behaviors because it shortcuts so much of 
cygwin's emulation, it is worth encouraging people to use Posix-style 
pathnames.  Any open() or stat() (and thus any higher-layer function 
like glob()) that encounters \ in the context of a file name is treated 
as probable evidence of a user that does not understand why cygwin 
favors / in file names, so it triggers a one-time warning per session 
(maybe that's why I'm having a hard time reliably reproducing a setup to 
spit out a warning; if my current session has already issued the 
warning, then nothing else I do with \ will re-trigger it).  And it is 
an option controllable by the $CYGWIN variable (if you want to use \ 
without even the one-time warning, set CYGWIN=nodosfilewarning prior to 
starting a cygwin session).

Since the one-time warning goes to the terminal rather than stderr, it 
is unlikely to impact script behavior (that is, you can't capture it via 
redirections, only to stumble later because you captured more text than 
planned); conversely, since it goes straight to the terminal, it is 
highly visible to the user if a package accidentally does anything that 
accessed a string containing \ in a context of a file name.

> If you (still) need somebody to test IRIX, OSF, Solaris 2.6, AIX, please
> ping me.  I definitely would feel a bit less worried if these changes
> were thoroughly tested before the next release.

Agreed that more testing would be nice.

--
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org