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List:       coreutils
Subject:    Re: sort/shuf/shred: support fixed random-seed
From:       Bernhard Voelker <mail () bernhard-voelker ! de>
Date:       2015-02-10 7:44:37
Message-ID: 54D9B6E5.9000703 () bernhard-voelker ! de
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On 02/09/2015 10:06 PM, Pádraig Brady wrote:
> --- a/doc/coreutils.texi
> +++ b/doc/coreutils.texi
> @@ -1240,6 +1240,21 @@ operating system.
>  To reproduce the results of an earlier invocation of a command, you
>  can save some random data into a file and then use that file as the
>  random source in earlier and later invocations of the command.
> +@cindex random seed
> +Rather than depending on a file, one can generate a reproducible
> +arbitrary amount of pseudo-random data given a seed value, using
> +for example:
> +

The whole point of reproducibility here is that the --random-source file
is constant, i.e., that the openssl command always produces the same
output.  This is not that clear to me in the above sentence.
Maybe clarify this in a comment?

> +@example
> +get_random()
> +@{
> +  seed="$1"

+  # Given the same $seed, the following produces reproducible
+  # output of arbitrary length.

> +  openssl enc -aes-256-ctr -pass pass:"$seed" -nosalt \
> +    </dev/zero 2>/dev/null
> +@}
> +
> +shuf -i1-100 --random-source=<(get_random 42)
> +@end example
>  
>  @node Target directory
>  @section Target directory
> -- 2.1.0

Thanks & have a nice day,
Berny


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