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, 12:50 alex xmb ratchev <fxmbsw7@gmail.com> wrote:

>
>
> On Thu, Mar 23, 2023, 12:38 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
>>
>> $ (( 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
>>
>
> this is my one cmd there
>
> cpuc() {
> declare -gi cpuc
>  ((
> ! cpuc ? cpuc = $( 2>&- grep -c ^processor /proc/cpuinfo ) : 0 ,
> cpuc >4 ? cpuc -=2 : cpuc >1 ? cpuc-- : ( cpuc =1 )
>  ))
>   }
>

notice how first -=2 works , but last =1 i had to ( .. ) it ..

maybe chet see s a bug

also a comment on && || bitwise or whatever
while , i rather remember , many and me coded (( a && b )) , normally , ..

greets

no idea about speeds , .. if i find out its slower than the 'normal' way
> ill switch
>
> thank you mate
>>
>> --
>>> Kerin Millar
>>>
>>