On Sat, 2005-07-02 at 12:24 -0400, Chet Ramey wrote:
> Michael Wardle wrote:
> > Hi Chet
> >
> > Thanks for your very prompt reply.
> >
> > I understand that globbing is happening, but I don't understand why
> > deleting a parameter should occur with nullglob set if the parameter
> > matches but the word to delete doesn't. The bash behavior seems to make
> > this construct useful only for file name deletion if nullglob is set,
> > when it seems to be useful for any substring deletion if nullglob is
> > unset.
>
> The word in question is *not* being parameter expanded. It is the
> result of a *different* parameter expansion: the unquoted expansion
> of $connectioninfo.
I wasn't saying that the right-hand side was being parameter expanded.
I was trying to use the wording in the POSIX standard, which states:
"The word shall be expanded to produce a pattern." I think this is
supposed to refer to file name expansion (globbing), but I confess to
being confused by this wording myself.
> Since the results of the parameter expansion of $connectioninfo are
> subject to filename expansion, the unquoted `*' in that word is run
> through *normal filename expansion*. Since that expansion looks only
> for filenames and, since nullglob is set, deletes words containing
> globbing operators that don't match filenames, the word ends up being
> removed.
I understand that normal file name expansion is occurring, but I can't
see any use for it in this construct. I would be happy to learn of such
a use, but in the absence of one, I would advocate the parameter
deletions such as ${parameter%word} be a special case not subject to
nullglob.
> You might get a clearer picture of what's happening if you ran
>
> echo "$connectioninfo"
>
> and inhibited the filename expansion that normally takes place.
I believe my followup exhibited this understanding.
> > I also noticed in the POSIX standard that quoting the word part should
> > cause it to be literal and prevent globbing. If I try this in bash, I
> > get the same result as in my original message, that is:
>
> You have misunderstood which expansion needs to be quoted. It's the
> expansion of $connectioninfo that needs quoting, as above.
POSIX says this:
${x#"*"}
The literal asterisk is quoted and not special.
Which leads me to believe that quoting the asterisk should have the
desired result, and certainly at least a different result from that
which I am seeing.
Again, I don't understand why nullglob is useful inside ${parameter%%
word}, and it's certainly not obvious why quoting the right-hand side
should be necessary.
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