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.
--
Jon H. LaBadie jcu at labadie.us