Re: Problems when RANDOM without $ is used as an array index

[Stephane CHAZELAS]

2010-01-9, 06:23(-06), dennis@netstrata.com:
[...]
> This produces the correct distribution of dice values for two six-sided dice:
>
>  $ unset dice; for i in {1..10000}; do ((dice[$RANDOM%6+1 + $RANDOM%6+1]++)); 
> done; echo "${dice[@]}"
>  290 582 837 1130 1375 1635 1315 1126 845 574 291
>
> The total is correct:
>
>  $ unset t; for i in ${dice[@]}; do ((t+=i)); done; echo $t
>  10000
>  
> This creates an even distribution which is incorrect:
>  
>  $ unset dice; for i in {1..10000}; do ((dice[RANDOM%6+1 + RANDOM%6+1]++)); 
> done; echo "${dice[@]}"
>  886 884 887 882 885 879 886 887 881 879 883
>
> And the total is incorrect (may be larger or smaller):
>
>  $ unset t; for i in ${dice[@]}; do ((t+=i)); done; echo $t
>  10047
[...]

I've been scratching my head for some time, but can't figure out
what's going on. I get the exact same behavior with ksh93 and
zsh. Again there, replacing RANDOM with $RANDOM fixes the
problem. Strange that all 3 shells would have the exact same
bug. Are we missing the obvious here?

-- 
Stéphane