Irregularities when using -v, -z, -n

[eduardo-chibas]

How does manual never give examples of how to use things !

6.4 Bash Conditional Expressions

Everyone is expected to figure things out by themselves.



> Sent: Friday, July 30, 2021 at 12:34 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 10:27:08AM +0200, eduardo-chibas@caramail.com wrote:
> > I am getting confused with the following code
>
> Well, perhaps you could read "help test"? If you did, you'd see:
> -----8<-----
> ...
>    String operators:
>       -z STRING      True if string is empty.
>       -n STRING      True if string is not empty.
> ...
>       -v VAR         True if the shell variable VAR is set.
>       -R VAR         True if the shell variable VAR is set and is a name
>                      reference.
> ...
> ----->8-----
>
> Therefore,
>
> >   [[ -v aa ]] && echo "[[ -v aa ]]: Variable exists."
>
> tests if a variable is set, but
>
> >   [[ -z aa ]] && echo "[[ -z aa ]]: Variable exists, size is zero."
>
> tests that a string "aa" is zero length. You need to replace aa -> "$aa" here.
> Also, [[ -z ... ]] returns 0 also for unset variables.
>
> --
> Leonid Isaev
>
>