Re: Behaviour of an empty conditional expression is undefined?

[alex xmb ratchev]

i [[ daily , never had such..
sounds like u dont type in C in utf8

On Thu, Feb 23, 2023, 9:58 AM Qingsheng Huang <huangqqss@126.com> wrote:

> Here shows the behavious of empty conditional expressions:
>
> ------------------------------------------------------------------------
> infinite:~# [[ ]]
> -bash: syntax error near unexpected token `]]'
> infinite:~# [[ ]]
> infinite:~# [[ "$A" ]]
> -bash: syntax error near unexpected token `"$A"'
> infinite:~# [[ "$A" ]]
> infinite:~# [[ "$A" ]]
> infinite:~# [[ ]]
> infinite:~# [[ "$A" ]]
> -bash: syntax error near unexpected token `"$A"'
> infinite:~# echo $?
> 2
> infinite:~# [[ "$A" ]]
> infinite:~# echo $?
> 1
> infinite:~#
> infinite:~# bash --version
> bash --version
> GNU bash, version 5.2.15(1)-release (x86_64-pc-linux-gnu)
> ------------------------------------------------------------------------
>
> The variable $A has never been defined.
> Double brackets surrounding 1) a few spaces or 2) an empty variable even
> quoted behave illogically.  I've also try different lengths of spaces, and
> also an empty variable without quotes, the same illogical.
>
> I am curious if I am the first guy encounter such a situation.
> My observation:
> 1) An empty conditional expression will first triger an syntax error,
> return
>    with code 2;
> 2) Immediate another empty conditional expression won't triger such an
> error,
>    return with code 1;
> 3) Subsequent a conditional expression with empty variables will triger the
>    error again;
> 4) The same conditional expression won't triger the error until different
>    commands are input;
>
> I guess it has something to do with the cache of command evaluation.
> It seems there is a counter recording some state.  I hope my guess may help
> in debugging.
>
> According to the manual, I think an empty condition like ``[[   ]]'' and
> ``[[ $EMPTY ]]'' should always triger syntax error, but a condition with
> an empty string like ``[[ "" ]]'' and ``[[ "$EMPTY" ]]'' should evaluate
> to false or return 1.
>