Configuration Information [Automatically generated, do not change]:
Machine: i486
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -DPROGRAM='bash' -DCONF_HOSTTYPE='i486'
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='i486-pc-linux-gnu'
-DCONF_VENDOR='pc' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL
-DHAVE_CONFIG_H -I. -I../bash -I../bash/include -I../bash/lib -g -O2 -Wall
uname output: Linux emperor 2.6.31-14-generic #48-Ubuntu SMP Fri Oct 16
14:04:26 UTC 2009 i686 GNU/Linux
Machine Type: i486-pc-linux-gnu
Bash Version: 4.0
Patch Level: 33
Release Status: release
Description:
When RANDOM is used as an array index, the behavior is different depending on
whether $RANDOM or RANDOM is used.
Also reproduced on Bash 3.2.49(23)-release under cygwin
Repeat-By:
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 + $RANDOM%6+1]++));
done; echo "${di...@]}"
290 582 837 1130 1375 1635 1315 1126 845 574 291
The total is correct:
$ unset t; for i in ${di...@]}; 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 "${di...@]}"
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 ${di...@]}; do ((t+=i)); done; echo $t
10047
The even distribution is the same as is produced by:
$ unset dice; for i in {1..10000}; do ((dice[RANDOM%11+2]++)); done; echo
"${di...@]}"
The total here, by the way, is incorrect, too, if there's no $ on RANDOM, but
correct when there is.
The indices are the same in all cases:
$ echo ${!di...@]}
2 3 4 5 6 7 8 9 10 11 12
Using a variable instead of RANDOM works correctly with or without a $:
$ unset dice t; var=0; for i in {1..10000}; do ((dice[var%11+2]++));
((var+=1)); done; echo "${di...@]}"; echo ${!di...@]}; for i in ${di...@]}; do
((t+=i)); done; echo $t
9091 9091 9091 9091 9091 9091 9091 9091 9090 9091 9091
2 3 4 5 6 7 8 9 10 11 12
100000
Fix:
