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Re: syntax error while parsing a case command within `$(...)'

From: Koichi Murase
Subject: Re: syntax error while parsing a case command within `$(...)'
Date: Wed, 17 Feb 2021 23:53:27 +0800

2021年2月17日(水) 1:52 Oğuz <oguzismailuysal@gmail.com>:
> They resemble `[ ... ]' (I know it's a simple command, but still), maybe 
> that's why. I think it'd seem more inconsistent to ordinary user if
>   if [[ x ]] then [[ x ]] fi
> worked but
>   if [ x ] then [ x ] fi
> didn't.

``Ordinary users'' may consider it being inconsistent, but what would
you think of this?

Actually, as you have written, [ ... ] is a simple command, so there
are already many differences that ``ordinary users'' would think
inconsistent. For example, the word splitting and pathname expansion
rules are different. For another example, `tempenv=1 [[ -v tempenv ]]'
is disallowed while `tempenv=1 [ -v tempenv ]' is allowed. and more...
Letting [[ ... ]] behave differently from either of [ ... ] and ( ...
) means that we create the third category of command which
grammatically behaves like neither the simple command nor the compound
command. I actually feel it is more consistent to allow `if [[ ... ]]
then' as far as we accept `if ( ... ) then'. That would be the only
neat thing under the POSIX constraints.


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