parser: Only accept single-digit parameter expansion outside of braces

parser: Only accept single-digit parameter expansion outside of braces

On Thu, Apr 25, 2019 at 01:39:52AM +0000, Michael Orlitzky wrote:
> The POSIX spec says,
>
>   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 a name and is followed by a character that could be
>   interpreted as part of the name.
>
> However, dash seems to diverge from that behavior when we get to $10:
>
>   $ cat test.sh
>   echo $10
>
>   $ dash ./test.sh one two three four five six seven eight nine ten
>   ten
>
>   $ bash ./test.sh one two three four five six seven eight nine ten
>   one0

This patch should fix the problem.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>