Re: Future [exec] overhaul

"Alexandre Ferrieux" <alexandre.ferrieux@...> wrote:
> In a future TIP I will propose a new, extended [exec] (all options are
> still open as to the script API: [exec -extended], [exec -list],
> [exec2], you name it...), with the following main targets:

>  (1) Fix the impossibility to pass > < | etc. as isolated arguments.

Some year ago I proposed a new option to classic exec, that would
cause some special quote-char to be eaten away from each arg that
starts with it. 
The proposed syntax was really ugly, but it solved problem (1).
I didn't ever TIP it, because I found it so ugly, myself.  Anyway,
it might still be reconsidered, as a low-level building block for
a high-level  exec2 (painted whichever color), which then could be
done in pure tcl based on old exec with that quote-extra.

If you don't remember it, here's an abstract:
  exec -quoted  echo '<hello> '| ''blah' >foo
would end up writing the literal string:
<hello> | 'blah'
into file foo. There are of course a couple of different colors
available for painting the option's name.

The trick would be, that a first round parses all the usual 
exec magic arguments, skipping all those starting with that 
quote-char, since it is not magic to exec. Then, just before
really executing the command, it would strip at most one 
quote-char from each argument, thus making it possible to
also have arguments starting with that quote-char.

I once had a (technically even uglier) patch for this based
on 8.4.3, which didn't cleanly apply to 8.5 and I gave up on
it.  The old patch still exists.

The effect can roughly be experienced w/o change in tcl but 
with a helper-command, that does the quote-stripping, and
calling it like that:

  exec quotestripper  echo '<hello> '| ''blah' | \
       quotestripper  grep {'<...} >foo

Unfortunately the quotestripper cannot be a tcl-script, and
it needs to be specified for each part of a multi-command
pipeline.

The rest applies both, to a real new exec2 sibling of exec,
or to a wrapper proc exec2 that builds on exec...

>  (2) Get rid of complicated legacy rules regarding the scope and
> semantics of redirection. These include the csh-style >&, the
Good!

>     (impossible)       --> [exec2 foo 2>& $ch1 | bar 2>& $ch2]
Ah, now I see, why we must get rid of csh syntax relicts 
(Otherwise I'd have suggested to leave them in as well)

>  (3) Generalize on unix to fds above 2 as in Bourne shell and as shown
> in the TIP under section "Directions for future work":
Good!

>  (4) Give a means to get the exit status at the end of an [exec2 ... &].
Good, too, but I can't name any favourite color for that.

PS: If anyone reads this out of context later, the references to
  "color" are references to the "bikeshed" parable.
  <http://en.wikipedia.org/wiki/Color_of_the_bikeshed>

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