Failure of nested substring processing inside double-quotes

[Paul Smith <paul@mad-scientist.net>]

Hi all.  I recently found a bug in dash's handling of substring
processing, when the variable is contained within quotes.

In bash, this works:

  bash$ echo $PWD
  /home/psmith

  bash$ echo ${PWD%${PWD##*/}}.
  /home/.

  bash$ echo "${PWD%${PWD##*/}}."
  /home/.

which is what I expect.  However, in dash we get:

  dash$ echo $PWD
  /home/psmith

  dash$ echo ${PWD%${PWD##*/}}.
  /home/.

  dash$ echo "${PWD%${PWD##*/}}."
  .

Whoops!  Inside double-quotes dash is mishandling the nested string
substitution.  If I break it up into two steps it works OK, regardless
of whether or not it's quoted.

This is dash 0.5.7-4ubuntu1 (from Ubuntu GNOME 14.04).