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, 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

$ (( a = 2 , a > 1 && (a -= 2) || a-- )); declare -p a
> declare -- a="-1"
>
> If you must do this sort of thing, use the conditional operator instead
> e.g. (( a = 8, a = (a > 4) ? a - 2 : a - 1 )). Alternatively, just avoid
> doing assignments in arithmetic expressions except where there's a clear
> advantage (I cannot see one in this case).
>

ill do such yes , ? and : stead && and || works also
.. or similiar .. im fiddeling
did this

 ((
cpuc >4 ? cpuc -=2 : cpuc >1 ? cpuc-- : 0
 ))

>
the adv is 3 small cmds in one cmd , not 3 separate
i ve seen massive speed up ment of just chaining var=val assignments ,
instead of ( nonsensissily ) ; or \n

thank you mate

-- 
> Kerin Millar
>