On Mon, Feb 21, 2011 at 13:59, Martin Bähr <
mba...@email.archlab.tuwien.ac.at> wrote:
> On Mon, Feb 21, 2011 at 11:35:09AM +0100, Jan Kanis wrote:
> > > set foo first
> > > echo $foo-(set foo second; echo)-$foo-(set foo third; echo)-$foo
> > third--third--third
> > Without the echo's inside the command substitutions the command gives an
> > empty line as output. Don't know if that's a bug or a feature. Does
> anyone
> > know if that's supposed to happen?
> >
> > > set foo first
> > > echo $foo-(set foo second; echo)-$foo-(set foo third)-$foo
>
> one of the interesting things about command substitution is that it can
> return a list and will be expanded accordingly, consider returning two
> lines:
>
> > echo start-(echo foo; echo bar)-stop
> start-foo-stop start-bar-stop
>
> so naturally, if the command returns 0 lines, the surounding string
> will be expanded 0 times.
>
> greetings, martin.
>
But fish variables are also lists - e.g. after ``set foo``, $foo is the
empty list and by similar logic the command wouldn't have to be expanded...
I dimly recall Axel explaining that commands are expanded in a separate pass
so they won't have to be run many times (because commands can be expensive
and/or have side effects).
--
Beni Cherniavsky-Paskin <c...@users.sf.net>
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