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Re: parameter expansion null check fails for arrays when [*] or [@] is u

From: Greg Wooledge
Subject: Re: parameter expansion null check fails for arrays when [*] or [@] is used
Date: Wed, 23 Mar 2022 07:38:39 -0400

On Wed, Mar 23, 2022 at 01:48:48AM -0700, L A Walsh wrote:
> On 2022/03/23 00:25, Ilkka Virta wrote:
> > The POSIX phraseology is that "null" means the empty string.
> ----
>    POSIX phraseology applies to the POSIX language.
> In 'C'
> char *s = NULL
> is not the same as
> char *s="";

Yes, we know this.  But this is bug-bash, so we're discussing the shell
known as bash.  Bash doesn't have pointers, so it cannot have NULL pointers

Would I have chosen to use the word "null" to mean "empty string" in
the shell's documentation, if I were writing it?  No.  I wouldn't have,
because it's an overloaded word with very different meanings in different
contexts (cf. SQL's NULL, and the ASCII NUL character).

But as it happens, the writers of the POSIX standards *did* use that
word in some places, and so we have to live with it.

unicorn:~$ man 1p sh | grep -i null
                 argument. If FCEDIT is null or unset, ed shall be used as the
                 ables  that are unset or null. (See the Base Definitions vol‐

Back to the original topic, I have absolutely no idea what "${a[@]:+word}"
is supposed to do.  It doesn't make any sense to me, and I would never
write that in a script.  So, I have no comments about it in terms of
this bug report.

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