[originally brought up on the bash list as a NetBSD bug, but dash is
also affected]

On 05/05/2011 08:11 AM, Eric Blake wrote:
>> I'd call that a pretty serious incompatibility on the part of ash and its
>> descendants (BSD sh, dash, etc.).  There's no good reason that
>>
>> set -- a b c d e f g h i j
>> echo $10
>>
>> should echo `j'.
> 
> Also a POSIX violation:
> 
> http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02
> 
> "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."

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)"

"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."

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

-- 
Eric Blake   eblake@redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org