Re: bash tries to parse comsub in quoted PE pattern

[Chet Ramey]

On 10/18/23 1:08 PM, Emanuele Torre wrote:
> On Wed, Oct 18, 2023 at 11:24:11AM -0400, Chet Ramey wrote:
> > On 10/18/23 10:50 AM, Chet Ramey wrote:
> >
> > > > Is it really ok to break that behaviour?
> > >
> > > That's why, if you want the first problem repaired, you have to specify
> > > which word expansions are ok to parse and which are not. Should it be
> > > only command and process substitution, which can independently specify
> > > brace expansions? Should it be other parameter expansions, which can
> > > contain quoted strings and command substitutions? Neither? Both?
> >
> > It looks like the answer is probably "neither."
>
> I have examined the code, and I now understand why "${foo:-"{1..2}"}"
> etc were allowed, but were not supposed to.

We can get closer with changes to how the command substitutions are
parsed while performing brace expansion.


> While we are at it, when examining this issue now, I have also noticed
> that, regardless of whether brace expansion is enabled or not, the bash
> parser always reads single quotes in double quoted PEs as if they are
> not literal, even though they are literal if the PE is -, =, or +.
        [...]
> Could/Should this also be fixed so that  "${foo:-'}"  (and +, and =) is
> read correctly? Other shells including ksh93, mksh, dash, NetBSD ash,
> and busybox can read it correctly.

It behaves as you want in posix mode. Here's the comment explaning it:

  /* The big hammer.  Single quotes aren't special in double quotes.  The
     problem is that Posix used to say the single quotes are semi-special:
     within a double-quoted ${...} construct "an even number of
     unescaped double-quotes or single-quotes, if any, shall occur." */
  /* This was changed in Austin Group Interp 221 */

Bash in default mode uses its historical behavior, which is what POSIX
originally specified.

--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/