Re: dots in Dir.entries

At 9:10 AM -0700 3/19/02, Matt Armstrong wrote:
>Garance A Drosihn <[e-mail]> writes:
>  > If ruby always filters out the '.' and '..', then there is
>  > no way for a script to perform this trick, because there
>  > will be no way for the script to know when the '.' and '..'
>  > are processed.
>
>I think this is incorrect.  Such a script could just initialize
>its "directory seen count" to 2 instead of zero to account for
>the missing '.' and '..'.

>So this is an example where filtering '.' and '..' would cause
>some minor extra work for a script doing this optimization.
>But the filtering doesn't make it impossible or difficult.

No.  It is impossible.  You can't just add 2 for '.' and '..',
because the current directory may not have those (it depends
on what kind of filesystem you are using).  The reason I know
about this trick is because the trick doesn't always work on
AFS, due to the link-count being handled differently on AFS
in some cases...  :-)  If I recall correctly, some CD-rom file
systems also handle this differently.

My main point being that the handling of '.' and '..' is not
simply a matter of which OS you are on, but a matter of which
type of filesystem you are looking at.  Any script which does
need '.' and '..' can not blindly put them there, while any
script which does NOT need them can trivially remove them.
(although technically I suppose the script should check to
make sure they are a directory before ignoring them...)

>  > [I think there is at least one more example where it is
>  > useful to explicitly get the '.' and '..', but I do not
>  > remember it at the moment]
>
>If you think of it, please post it!

Yeah, it bugs me that I can't remember it.  When this topic
originally came up I was going to reply with a different
example, but I didn't have the time to write it out.  This
time I just happened to remember the above example due to
something else I'm working on at the moment.

I will admit that in 99.8% of the scripts that I've written,
I have to filter out those two directories.  But for the
other 0.2%, I can't just blindly add them.  The 'ls' command
has both 'ls -a' and 'ls -A', where the only difference is
whether those two are included in the listing.  It might
make sense for ruby to have both Dir.entries and some other
method -- except that I can't decide on a good name for that
other method...   :-)  Dir.entries_all ?

-- 
Garance Alistair Drosehn            =   [e-mail]
Senior Systems Programmer           or  [e-mail]
Rensselaer Polytechnic Institute    or  [e-mail]