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From: Oliver Kiddle <opk@zsh.org>
References: <CAH+w=7Zag5MG5D=cRS2UMSsqJ0t=iw5MH9j8=HBO1Q77nbs03w@mail.gmail.com> <20201125131921.vay7h3xk5qn4odgg@chazelas.org> <CAMP44s0-ki=TBzTwnqx10FcTLX4mbphwN88UCx0+h97JTecBWA@mail.gmail.com> <20201126061029.in5tpnrg5bplam5k@chazelas.org> <CAMP44s1XgxdDAAL+7nL3_GK=dZUasPmSWZaKqWg0T-v5iq1eYg@mail.gmail.com>
To: Felipe Contreras <felipe.contreras@gmail.com>
Subject: Re: More rabbit-holes with unset variables
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The original Bourne shell did I believe have both export and the
${...-...} form. Using /bin/sh from Solaris (available for Linux as
heirloom sh):
  export FOO
  echo ${FOO-replacement}
Will output the replacement.

It appears that export VAR will not export an empty VAR even in zsh
(unless you do VAR=""). So zsh's not exactly consistent.
typeset [-x] is arguably just a variant of export.

This does change how I regard zsh's behaviour. It isn't zsh taking a
different but equally valid approach on an extension but an sh
incompatibility. It once was a bug even if now too entrenched.

Zsh's behaviour is long-standing - I've even checked 2.5.03. And it is
well-defined behaviour so declaring it a feature is an option.

It does make the KSH_TYPESET option somewhat less appropriate because
this effect also applies to sh emulation.

But if we decide to "fix" it for zsh, I don't think it'll break too much.
Given that empty values are rarely especially useful, I've always used
the :- form. If the change sits in git for a reasonable time, we might
find out how much it might break.

I did reply on the initial thread but the References: header hit
a mail server limit for line length and it failed.
So I've covered my main point but just to pick out something from this
thread:

Felipe Contreras wrote:
> The discussion is about what "typeset var" (with no type) should do.

That is not "with no type", it has the default type which effectively is
a string. Other shells also treat such variables as an empty string for
the purposes of other features. Try += for example.

Oliver