Re: [Help-bash] How random is $RANDOM?

[Peng Yu]

No. I don’t want to call any external program. I want to stay with the
shell.

On Thu, May 9, 2019 at 7:47 AM Andreas Kusalananda Kähäri <
address@hidden> wrote:

> Re-sent since I managed to send it from the wrong address the first time
> around.
>
> On Thu, May 09, 2019 at 07:29:51AM -0500, Peng Yu wrote:
> > Why only 16 bits $RANDOM is supported? Is there a problem to set 32
> > bits as the default?
>
> If you are writing an application that has very specific requirements
> with regards to random number generation, it strikes me that writing it
> as a shell script may not be optimal.  You may want to use a generator
> ased on e.g. arc4random() [1], or to use that function directly from a
> C program.
>
>
> [1] https://man.openbsd.org/arc4random
>
> Regards,
> Kusalananda
>
> >
> > On 5/9/19, Andreas Kusalananda Kähäri <address@hidden> wrote:
> > > On Thu, May 09, 2019 at 06:33:07AM -0500, Peng Yu wrote:
> > >> Let's say two bash processes call $RANDOM at the exact same time. Will
> > >> the results be the same? Or the results will be different.
> > >
> > > The random number generator used in bash is seeded using a number that
> > > contains the PID of the current shell (as well as the current time).
> > >
> > > https://git.savannah.gnu.org/cgit/bash.git/tree/variables.c#n1369
> > >
> > >
> > >>
> > >> Also, is the low bits of $RANDOM more random or the high bits of
> > >> $RANDOM more random. I see examples using $RANDOM%n to map the random
> > >> number to a smaller range. But my understanding in other random
> > >> numbers is that the high bits are more random and using the modulus is
> > >> discouraged. I am not sure what is the recommended usage of $RANDOM to
> > >> map it to a smaller range. Does anybody know the best use of $RANDOM
> > >> in this case? Thanks.
> > >
> > > The random number generator itself is short and has a reference to the
> > > relevant paper describing it.
> > >
> > > https://git.savannah.gnu.org/cgit/bash.git/tree/variables.c#n1329
>
> --
> Kusalananda
> Sweden
>
-- 
Regards,
Peng