From mboxrd@z Thu Jan  1 00:00:00 1970
From: Harald van Dijk <harald@gigawatt.nl>
Subject: Re: dash: read does not ignore trailing spaces
Date: Thu, 3 Dec 2015 22:02:14 +0100
Message-ID: <5660ADD6.4020308@gigawatt.nl>
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To: Gioele Barabucci <gioele@svario.it>
Cc: dash@vger.kernel.org

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On 02/12/2015 23:37, Gioele Barabucci wrote:
> Hello,
>
> I am forwarding a bug [1] reported by a Debian user: `read` does not
> ignore trailing spaces. The current version of dash is affected by
> this bug.
>
> A simple test from the original reporter:
>
>      $ dash -c 'echo "  a b  " | { read v ; echo "<$v>" ; }'
>      <a b  >
>
>      $ bash -c 'echo "  a b  " | { read v ; echo "<$v>" ; }'
>      <a b>
>
> Other shells like posh and mksh behave like bash.

This is indeed a bug based on the current specification. In the past, 
the specification was unclear and the dash interpretation was a 
legitimate one, but currently it explicitly spells out that trailing IFS 
whitespace gets ignored.

However, unless I'm misreading the spec, mksh and bash don't seem to 
implement it properly either: only trailing IFS whitespace is supposed 
to be dropped. IFS non-whitespace is supposed to remain, even at the end 
of the input. mksh and bash remove it, posh and zsh leave it in:

   $ for shell in bash mksh posh zsh; do printf %s: "$shell"; $shell -c 
'IFS=,; echo a, | { read v; echo "<$v>"; }'; done
   bash:<a>
   mksh:<a>
   posh:<a,>
   zsh:<a,>

As far as I can tell, the posh/zsh behaviour is the correct behaviour, 
but I'm not convinced yet my interpretation is correct.

Attached is a not fully tested proof of concept to implement the 
posh/zsh behaviour in dash by extending ifsbreakup() to allow specifying 
a maximum number of arguments instead of fixing it up in 
readcmd_handle_line(). It returns <a b> in your test, and <a,> in mine. 
Feedback welcome.

Cheers,
Harald van Dijk

> This error is reproducible with dash 0.5.7 and with the current master
> git master branch, commit 2e5842258bd5b252ffdaa630db09c9a19a9717ca.
>
> [1] https://bugs.debian.org/794965
>
> --
> Gioele Barabucci <gioele@svario.it>

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