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Re: strange expansion of <(cat p.main.{optional,extra})


From: Andreas Schwab
Subject: Re: strange expansion of <(cat p.main.{optional,extra})
Date: Wed, 18 Apr 2007 11:11:03 +0200
User-agent: Gnus/5.110006 (No Gnus v0.6) Emacs/22.0.97 (gnu/linux)

Chet Ramey <address@hidden> writes:

> address@hidden wrote:
>
>> Bash Version: 3.1
>> Patch Level: 17
>> Release Status: release
>> 
>> Description:
>> Hi,
>> 
>> The expansion of echo <(cat /etc/{passwd,motd}) is rather surprising:
>> $  echo <(cat p.main.{optional,extra})
>> ++ cat p.main.optional
>> cat: p.main.optional: No such file or directory
>> ++ cat p.main.extra
>> cat: p.main.extra: No such file or directory
>> + echo /dev/fd/63 /dev/fd/62
>> /dev/fd/63 /dev/fd/62
>> 
>> I would have expected to be expanded to <(cat /etc/passwd /etc/motd) first.
>
> That's not how it works.  Brace expansion is the first expansion performed.
> The manual page says:
>
> "Brace expansion is performed before any other expansions, and any char-
> acters special to other expansions are preserved in the result.  It  is
> strictly  textual.  Bash does not apply any syntactic interpretation to
> the context of the expansion or the text between the braces."

If it would be done strictly textual, the resulting expansion would
actually be this:

$ echo <(cat p.main.optional) p.main.extra)

which would be a syntax error.

Andreas.

-- 
Andreas Schwab, SuSE Labs, address@hidden
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."




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