Re: nullglob option breaks complex parameter expansion/deletion

[Chet Ramey]

michael@mail.endbracket.net wrote:

> Bash Version: 3.0
> Patch Level: 16
> Release Status: release
> 
> Description:
>         I had been using ${HOSTNAME%%.*} in my prompt to show the local
>         host name portion of my full host name (e.g. localhost instead
>         of localhost.localdomain).  After enabling the nullglob shell
>         option, this pattern is being replaced by a null string.  I
>         don't think this behavior is desireable.

Perhaps not desirable, but, in the example you supplied, functioning as
designed.

> 
>         I don't fully understand the wording of the relevant portion of
>         the POSIX standard on this topic, but I would expect this
>         pattern to always function as it does without nullglob set:

That part of the POSIX standard isn't relevant for two reasons.  First,
POSIX doesn't standardize `nullglob'.  Second, the expansion described
is not happening.

What happens in the example you show is that a word that looks like a
parameter expansion is part of the expanded value of $connectioninfo,
but that word is not being expanded as a parameter.  It's subject to
the normal glob expansion that the unquoted results of any parameter
expansion would be, and, since it doesn't match any filenames, is
removed when `nullglob' is enabled.

Chet
-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
( ``Discere est Dolere'' -- chet )
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Chet Ramey, ITS, CWRU    chet@case.edu    http://cnswww.cns.cwru.edu/~chet/