On 19/04/2023 08:46, wwp wrote:
Hello lejeczek,
On Wed, 19 Apr 2023 08:10:16 +0200 lejeczek <peljasz@xxxxxxxxxxx> wrote:
On 19/04/2023 08:04, wwp wrote:
Hello lejeczek,
On Wed, 19 Apr 2023 07:50:29 +0200 lejeczek via CentOS <centos@xxxxxxxxxx> wrote:
Hi guys.
I cannot wrap my hear around this:
-> $ unset _Val; test -z ${_Val}; echo $?
0
-> $ unset _Val; test -n ${_Val}; echo $?
0
-> $ _Val=some; test -n ${_Val}; echo $?
0
What is this!?
How should two different, opposite tests give the same result
Is there some bash option which affects that and if so, then what would be the purpose of such nonsense?
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..
in those three examples - regardless of how one can "bend"
quoting & expanding - the same identical variable syntax is
used and yet different tests render the same result.
I thought 'test' broke and I had remembered it differently -
meaning 'test' used to give results I thought it did - or
perhaps some 'shopt' changed and affected its behavior.
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
Learning, re-learning, round & round it goes..
thanks, L.
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