Re: test -n "${var+set}"?

[Derek Robert Price]

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Paul Eggert wrote:

>Derek Robert Price <address@hidden> writes:
>
>>Just wondering what the logic behind all the constructs like, `test
>>"${var+set} = set', was in recently generated configure scripts.
>
>
>I suspect it's the shortest portable test for whether a shell variable
>is set.  Can you think of a shorter?


Ah:

$ var=
$ unset var2
$ echo ${var+set}
set
$ echo ${var2+set}

$

Got it now.  I read the bash man page as stating that this construct
wouldn't echo "set" for a variable set to the empty string.

Thanks,

Derek

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