Irregularities when using -v, -z, -n

[eduardo-chibas]

> Sent: Friday, July 30, 2021 at 2:21 AM
> From: "Leonid Isaev (ifax)" <leonid.isaev@ifax.com>
> To: help-bash@gnu.org
> Subject: Re: Irregularities when using -v, -z, -n
>
> On Thu, Jul 29, 2021 at 03:38:06PM +0200, eduardo-chibas@caramail.com wrote:
> > Have begun to understand a little bit from your comments.
>
> First, could you please ditch that crap of a mail client you are using and 
> stop
> top-posting? Please use this my reply as an EXACT model of how yours should
> look like.

Then suggest a mail client to use rather than bitching.

> > This means that -z and -n never test existence or if the variable
>
> They test strings, as the manual says.
>
> > If variable does not exist, it still says that the size is zero
>
> Yes, unless "nounset" is enabled:
> -----8<-----
> help set:
> ...
> nounset      same as -u
> -u  Treat unset variables as an error when substituting.
> ...
> ----->8-----
>
> For example:
> -----8<-----
> I-akula-++-10:16-~-> [[ ! -v x ]] && echo -E "x unset"
> x unset
> I-akula-++-10:16-~-> [[ -z "$x" ]] && echo -E "x empty"
> x empty
> I-akula-++-10:16-~-> set -u
> I-akula-++-10:16-~-> [[ ! -v x ]] && echo -E "x unset"
> x unset
> I-akula-++-10:16-~-> [[ -z "$x" ]] && echo -E "x empty"
> bash: x: unbound variable
> ----->8-----
>
> > Thusly, to determine if a variable value is set and not zero size, one has 
> > to
> > do
> >
> > if [[ -v var && -n "$var" ]]; then
> >   echo "Variable is set with finite length."
> > fi
>
> There is a logic flaw here: how can a variable be unset but contain a 
> non-empty
> string? You don't need [[ -v var ]] -- [[ -n "$var" ]] is sufficient.
>
> --
> Leonid Isaev
>
>