Re: whats wrong with (( a = 8 , a > 4 && a -= 2 || a-- )) , bash: ((: a = 8 , a > 4 && a -= 2 || a-- : attempted assignment to non-variable (error token is "-= 2 || a-- ")

[alex xmb ratchev]

On Thu, Mar 23, 2023, 13:03 Kerin Millar <kfm@plushkava.net> wrote:

> On Thu, 23 Mar 2023 12:38:58 +0100
> alex xmb ratchev <fxmbsw7@gmail.com> wrote:
>
> > On Thu, Mar 23, 2023, 12:21 Kerin Millar <kfm@plushkava.net> wrote:
> >
> > > On Thu, 23 Mar 2023 11:32:33 +0100
> > > alex xmb ratchev <fxmbsw7@gmail.com> wrote:
> > >
> > > > i remember doing && (( code
> > > > maybe i didnt '=' in action there
> > > >
> > > > (( a = 8 , a > 4 && a -= 2 || a-- ))
> > > >
> > > > bash: ((: a = 8 , a > 4 && a -= 2 || a-- : attempted assignment to
> > > > non-variable (error token is "-= 2 || a-- ")
> > > >
> > > >
> > > > (( a = 8 , a > 4 && a-- && a-- || a-- ))
> > > >
> > > > works
> > > > a=6
> > > >
> > > > ..
> > > > i suppose this is a (( lex bug where u didnt include || && in op for
> =
> > >
> > > I agree that it looks like a possible bug in the parser. It works if
> > > parentheses are used to disambiguate one of the subtractions.
> > >
> > > $ (( a = 8 , a > 4 && (a -= 2) || a-- )); declare -p a
> > > declare -- a="6"
> > >
> > > Even when made to work, I would consider it to be poor. Consider what
> > > happens below. It is a fine example of what can happen in the course of
> > > writing unconventional code without understanding the consequences.
> > >
> >
> > i extra >4 to prevent minus
>
> Yes, but ...
>
> >
> > $ (( a = 2 , a > 1 && (a -= 2) || a-- )); declare -p a
> > > declare -- a="-1"
>
> The point was that the intent of the code doesn't match the outcome. The
> code suggests that 2 should be deducted from 2. Instead of 0, we end up
> with -1. So, && || is a fairly effective way of writing bugs (just as it
> can be outside the arithmetic context, sometimes).
>

yes , no more && ||
but , your wrong data example ( light misunderstanding )
the : ( a =1 ) at the end of the new code
i have no -1 -2 .. i think
its a logical error here , u think i other data ( with wrong result -1 )
but i dont ..

ehm.. sorry

--
> Kerin Millar
>