Martin wrote:
>On Tue, 5 Aug 2025 at 02:17, Stan Marsh <gaze...@xmission.com> wrote:
>> (I am talking about things like ${var:-default value})
>>
>> I have long wished there was a substitution for "substitute a string if var
>> is
>> unset else substitute nothing".
>I've wondered about that myself at times.
>I like the idea, but I'm currently undecided whether I would support * as
>the indicator symbol. In any case, I think that it's important that the
>chosen symbol not be valid as the first character of a numeric expression,
>including reasonable future enhancements.
True. I just gave * as an example - it was the first unused symbol that popped
into
my head. As you say, it would have to be carefully thought out to make sure
whatever character is chosen doesn't interfere with anything else.
>> In fact, even better would be a generalized if-then-else, so you could do
>> something like:
>>
>> echo ${var*var is set to $var*var is not set}
>>
>That extra level doesn't seem compelling, since we could just write:
> ${foo+Foo is set}${foo*Foo is unset}
Yes, if we had the proposed "*" syntax, then you don't need the if-then-else
(for
this specific case/need), but the point is that we don't currently *have* that
new
syntax, and also that many of the existing "var:X" syntaxes are special cases
of a
generalized if-then-else. Not that I am suggesting that the existing syntaxes
be
removed, of course. But I've always felt when reading the man-page
descriptions of
these syntaxes that "These are all just special cases of a generalized
if-then-else,
but the specific thing that I want right now is missing, so it'd be nice to
have the
generalized version."
>I assume you would also want both colon and non-colon versions?
> ${foo*Foo is unset}
> ${foo:*Foo is empty or unset}
Yes.
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