Re: Quoted closing brace in variable default expansion

[Jonathan Nieder <jrnieder@gmail.com>]

Hi Herald,

Harald van Dijk wrote:

>   $ ksh -c 'echo "${x:-"}"}"'
>   }
>   $ dash -c 'echo "${x:-"}"}"'
>   dash: 1: Syntax error: Unterminated quoted string
>   $ busybox sh -c 'echo "${x:-"}"}"'
>   sh: syntax error: unterminated quoted string
> 
> It looks like dash and other ash derivatives stop the expansion with
> the first }, instead of the first unquoted }. I'm getting confused
> trying to figure out whether this is a bug in dash or in the script
> relying on it.

The answer depends on how portable the script is meant to be.  If
the goal is to be portable to shells implementing future versions of
the POSIX standard, there seems to be have been an interpretation[1]
approved for the next major revision:

 http://austingroupbugs.net/view.php?id=221
 note #399

which would make the example nonconformant because there are an odd
number of unescaped double-quotes before the first unescaped closing
brace.

See http://thread.gmane.org/gmane.comp.shells.dash/262/focus=263 for
a nice summary (thanks, Jilles!).

Hope that helps,
Jonathan