Re: $RANDOM initial state doesn't change

[Jan Larres <jan@xxxxxxxxxxxxxx>]

On 24/02/15 09:22, Timo Sirainen wrote:
> I was trying to use $RANDOM for a simple 1/0 check, but it kept failing.
> After a while I realized a new subshell always gives the same $RANDOM
> result:
>
> % for i in {1..10}; do echo `echo $RANDOM`; sleep 1; done
> 13490
> 13490
> 13490
> 13490
> 13490
> 13490
> 13490
> 13490
> 13490
> 13490
>
> Surely it should be more random than that?

From the manual:

RANDOM <S>
       A  pseudo-random  integer  from 0 to 32767, newly generated each
       time this parameter is referenced.  The random number  generator
       can be seeded by assigning a numeric value to RANDOM.

       The   values   of   RANDOM   form   an  intentionally-repeatable
       pseudo-random sequence; subshells  that  reference  RANDOM  will
       result  in  identical  pseudo-random  values unless the value of
       RANDOM is referenced or seeded in the parent  shell  in  between
       subshell invocations.


$ for i in {1..10}; do echo $(echo $RANDOM) $RANDOM; done
30686 30686
8933 8933
4452 4452
6983 6983
21425 21425
27288 27288
18721 18721
22501 22501
1008 1008
29465 29465

-Jan