> On Wed, Apr 19, 2023 at 09:16:26PM +0200, lejeczek via CentOS wrote:
>>On 19/04/2023 08:46, wwp wrote:
>>> Hello lejeczek,
> ...
>>>>> Surround ${_Val} with double quotes (as you should) and things will
>>>>> be different:
>>>>>
>>>>> $ unset _Val; test -n "${_Val}"; echo $?
>>>>> 1
>>>>>
>>>>> Now you get it? :-)
>>>>>
>>>> I don't know, am not sure, I remembered it differently, did not think
>>>> enclosing quotes were necessary(always?) for that were {}
>>> {} does not prevent this (at least not in bash):
>>>
>>> $ FOO="a b"
>>>
>>> $ test -z $FOO
>>> bash: test: a: binary operator expected
>>>
>>> $ test -z ${FOO}
>>> bash: test: a: binary operator expected
>>>
>>> Because after $FOO or ${FOO} variable expansion, bash parsed:
>>> test -z a b
>>> 'b' is unexpected, from a grammar point of view.
>>>
>>> Quoting is expected, here:
>>> $ test -z "$FOO"
>>> <no error>
>>>
>>> When FOO is unset, apparently it's a different matter, where you end up
>>> with $?=0 in all unquoted -n/-z cases, interestingly. I could not find
>>> this specific case in the bash documentation. That may not be portable
>>> to other shells, BTW. I only use {} when necessary (because of what
>>> bash allows to do between {}, plenty!, or when inserting $FOO into a
>>> literal string that may lead the parser to take the whole string for a
>>> variable name: echo $FOObar != echo ${FOO}bar).
>>>
>>>
>>> Regards,
>>There is a several ways to run tests in shell, but 'test'
>>which is own binary as I understand, defeats me..
>
> Yes, there is a binary for test (and its alternate '[').
>
> But most shells, including bash have incorporated code for test
> (and other commands) into the shell code itself for efficiency.
>
> $ type test
> test is a shell builtin
>
>>
>>I'd expect a consistency, like with what I usually do to
>>test for empty var:
>>-> $ export _Val=some; [[ -v _Val ]]; echo $?
>>0
>>-> $ unset _Val; [[ -v _Val ]]; echo $?
>>1
>>
>
> I do hope you don't use -v to test for empty variables as
> it tests for "set" variables and valid name syntax.
>
> Set variables can be "empty" ( name= ).
>
> But in your last example _Val is "un"set, it does not
> exist. Thus it can neither be empty nor occupied.
And to know if a variable is declared or not, this can be used:
if (( ${VAR+1} )); then
echo "variable \$VAR is set"
else
echo "variable \$VAR is NOT set"
fi
Regards,
Simon
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