Re: PATCH: pws-19: minor syntactic innovation

[Peter Stephenson <pws@ibmth.df.unipi.it>]

"Andrej Borsenkow" wrote:
> > What's the parse of something like ${(f)"${"$(typeset)"}"} ?  It doesn't
> > seem to be the `obvious' one -- it appears that the quoted strings are
> > actually nesting, because of the enclosing braces, which is something
> > pretty radically new.  (I may be wrong.)  Is this a good thing?
> 
> No. It breaks the basic shell grammar. The main problem is, it can have
> unexpected side effects when running in sh or ksh compatibility mode - and
> this is definitely bad thing.

This isn't due to the change I made, it simply showed up because of that.
The cause is dquote_parse(), which is doing brace-counting; in other words,
it rejects the second `"' as the end of the quoted string because it
detected the ${.  So this behaviour seems to be entirely deliberate.

I'm not so sure it's either new or wrong.  I discovered in an
initialisation file here,
      if [ -n "${BASH_VERSION:-""}" ]; then
which is obviously for bash rather than zsh (and works in bash, too).  If
the quotes don't parse in a nested fashion, this is meaningless, and
wouldn't parse in zsh because it always matches up braces, including inside
quotes.

Furthermore,
  bash$ echo "${FOO"<RET>
  > 

It's at the continuation prompt, so it's still parsing after the brace,
just like zsh (bash will report an error if it ever gets the remaining
`"}"', though).  sh reports `bad subsitution' at this point, however; but
even so, I can't think offhand of a working piece of sh code which would be
broken by this feature.  The fact that bash works happily as sh tends to
reinforce that view.

-- 
Peter Stephenson <pws@ibmth.df.unipi.it>       Tel: +39 050 844536
WWW:  http://www.ifh.de/~pws/
Dipartimento di Fisica, Via Buonarroti 2, 56127 Pisa, Italy