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Full Discussion: Generating a POSIX random number?
Top Forums Shell Programming and Scripting Generating a POSIX random number? Post 302977390 by wisecracker on Sunday 17th of July 2016 08:40:24 AM
Old 07-17-2016
Addendum to Rudis' post:-
MacBook Pro 13 inch, circa August 2012, OSX 10.7.5, default terminal calling OSX's 'sh'.
Test code, not conforming entirely to POSIX!
Code:
#!/bin/sh
for n in {1..4}
do
	TMP=$(awk ' BEGIN {printf( "%d %d\n", 16 * rand(), 16 * rand() )}')
	byteone=${TMP% *}; bytetwo=${TMP#* }
	echo "$byteone $bytetwo"
done

Results:-
Code:
Last login: Sun Jul 17 13:31:28 on ttys000
AMIGA:barrywalker~> cd Desktop/Code/Shell
AMIGA:barrywalker~/Desktop/Code/Shell> ./RAND2.sh
13 6
13 6
13 6
13 6
AMIGA:barrywalker~/Desktop/Code/Shell> ./RAND2.sh
13 6
13 6
13 6
13 6
AMIGA:barrywalker~/Desktop/Code/Shell> ./RAND2.sh
13 6
13 6
13 6
13 6
AMIGA:barrywalker~/Desktop/Code/Shell> _

So I assume 'srand()' is needed if only to change the seed per call...
EDIT:
Using 'srand()' and without 'sleep 1' then with 'sleep 1'...
I do test on various *nix style platforms including CygWin.
Code:
#!/bin/sh
for n in {1..4}
do
	TMP=$(awk ' BEGIN { srand(); printf( "%d %d\n", 16 * rand(), 16 * rand() ); }')
	byteone=${TMP% *}; bytetwo=${TMP#* }
	echo "$byteone $bytetwo"
	#sleep 1
done

Results:-
Code:
AMIGA:barrywalker~/Desktop/Code/Shell> ./RAND2.sh
12 13
12 13
12 13
12 13
AMIGA:barrywalker~/Desktop/Code/Shell> ./RAND2.sh
3 9
1 15
7 6
13 12
AMIGA:barrywalker~/Desktop/Code/Shell> ./RAND2.sh
11 14
11 14
11 14
11 14
AMIGA:barrywalker~/Desktop/Code/Shell> ./RAND2.sh
3 2
1 9
14 7
12 6
AMIGA:barrywalker~/Desktop/Code/Shell> _

So to conclude the 'srand()' function is only accurate to the _timer's_ second value and not 'milli' or 'micro' second values. Hence the 'sleep 1' to advance the _timer_ by 1 second.
Don's code works with or without 'sleep', hence I can now understand why 'while(1)' is being used.
Last edited by wisecracker; 07-17-2016 at 10:01 AM.. Reason: See EDIT:
 

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cpanplus::shell

CPANPLUS::Shell(3pm)					 Perl Programmers Reference Guide				      CPANPLUS::Shell(3pm)

NAME

       CPANPLUS::Shell

SYNOPSIS

	   use CPANPLUS::Shell; 	    # load the shell indicated by your
					    # config -- defaults to
					    # CPANPLUS::Shell::Default

	   use CPANPLUS::Shell qw[Classic]  # load CPANPLUS::Shell::Classic;

	   my $ui      = CPANPLUS::Shell->new();
	   my $name    = $ui->which;	    # Find out what shell you loaded

	   $ui->shell;			    # run the ui shell

DESCRIPTION

       This module is the generic loading (and base class) for all "CPANPLUS" shells. Through this module you can load any installed "CPANPLUS"
       shell.

       Just about all the functionality is provided by the shell that you have loaded, and not by this class (which merely functions as a generic
       loading class), so please consult the documentation of your shell of choice.

BUG REPORTS

       Please report bugs or other issues to <bug-cpanplus@rt.cpan.org<gt>.

AUTHOR

       This module by Jos Boumans <kane@cpan.org>.

COPYRIGHT

       The CPAN++ interface (of which this module is a part of) is copyright (c) 2001 - 2007, Jos Boumans <kane@cpan.org>. All rights reserved.

       This library is free software; you may redistribute and/or modify it under the same terms as Perl itself.

SEE ALSO

       CPANPLUS::Shell::Default, CPANPLUS::Shell::Classic, cpanp

perl v5.12.1							    2010-04-26						      CPANPLUS::Shell(3pm)
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