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Re: eval

From: Eric Blake
Subject: Re: eval
Date: Thu, 05 May 2011 08:45:29 -0600
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On 05/05/2011 08:43 AM, Chet Ramey wrote:
>> "The parameter name or symbol can be enclosed in braces, which are
>> optional except for positional parameters with more than one digit or
>> when parameter is followed by a character that could be interpreted as
>> part of the name."
> I agree with this interpretation, but the following sentence can be
> interpreted as placing the burden on the shell programmer:
> "When a positional parameter with more than one digit is specified, the
> application shall enclose the digits in braces (see Parameter Expansion)."
> Still, sh has required the braces since time immemorial.  It makes no
> sense that ash would have done it differently

Additionally from POSIX:

"If the parameter name or symbol is not enclosed in braces, the
expansion shall use the longest valid name (see XBD Name)"

Then XBD Name:
"In the shell command language, a word consisting solely of underscores,
digits, and alphabetics from the portable character set. The first
character of a name is not a digit."

In "$10", 10 is not a name, so the longest name after $ is the empty
string, and in place of a name, we use the single-character symbol 1
instead, such that this MUST be parsed as ${1}0, not as ${10}.

Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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