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From: Chet Ramey <chet.ramey@case.edu>
Newsgroups: gnu.bash.bug
Subject: Re: Undocumented for-loop construct
Date: Fri, 7 Aug 2020 09:29:33 -0400
Organization: ITS, Case Western Reserve University
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On 8/6/20 5:50 PM, Klaas Vantournhout wrote:
> Dear Bash-developers,
> 
> Recently I came across a surprising undocumented bash-feature
> 
>    $ for i in 1 2 3; { echo $i; };
> 
> The usage of curly-braces instead of the well-documented do ... done
> construct was a complete surprise to me and even lead me to open the
> following question on stack overflow:
> 
> 
> https://stackoverflow.com/questions/63247449/alternate-for-loop-construct
> 
> The community is unable to find any reference to this feature, except
> 
> * a brief slide in some youtube presentation by Stephen Bourne:
> 
>     https://www.youtube.com/watch?v=2kEJoWfobpA&t=2095
>     Relevant part starts at 34:55
> 
> * and the actual source code of bash and the Bourne Shell V7

It's never been documented. The reason bash supports it (undocumented) is
because it was an undocumented Bourne shell feature that we implemented
for compatibility. At the time, 30+ years ago, there were scripts that used
it. I hope those scripts have gone into the dustbin of history, but who
knows how many are using this construct now.

I'm going to leave it undocumented; people should not be using it anyway.

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
		 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/