Shell Programming and Scripting

For the heck of it, using sh and /dev/random, or when shell does not have $RANDOM

Code:

#!/bin/sh

if [ -z "$1" ]; then a=0; b=65536; else b=$((1+$1)); fi
[ -z "$2" ] || { a="$1"; b=$((1+$2-a));}
echo $((a+$(od -An -dN2 /dev/random)%b))

exit 0

Usage: this_script.sh outputs a value between 0 and 65535

this_script.sh MAX outputs a value between 0 and MAX

this_script.sh MIN MAX outputs a value between MIN and MAX

Hi.

Another handy utility, jot produces, for 3 runs:

Code:

% jot -r 1 10 30
29
% jot -r 1 10 30
10
% jot -r 1 10 30
12

I first ran across jot in UNIX PowerTools, Second Edition - O'Reilly Media , but the version on Debian 5 (lenny) has been extended beyond that. There is a source tar file at http://ftp.de.debian.org/debian/pool....0.orig.tar.gz -- I unpacked, configured, and compiled the source successfully:

Code:

% ./jot -r 1 100 500
346

Like shuf, jot has more features, see Man Page for jot (FreeBSD Section 1) - The UNIX and Linux Forums

Best wishes ... cheers, drl

Hey...Thanks to all for providing such useful info.

Hi.
There is a characteristic of /dev/random that could become an issue. There may be a limit to how many bits one can pull from /dev/random because it may block. The alternate /dev/urandom is not blocked and is probably as good as /dev/random for many purposes.

For example, I can only get 200-300 numbers from the posted script before /dev/random blocks (Debian 5 -- lenny -- GNU/Linux).

See /dev/random - Wikipedia, the free encyclopedia for details on this and other aspects ... cheers, drl