Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
random() function in C.)
Example 9−26. Reseeding RANDOM
#!/bin/bash
# seeding−random.sh: Seeding the RANDOM variable.
MAXCOUNT=25
# How many numbers to generate.
random_numbers ()
{
count=0
while [ "$count" −lt "$MAXCOUNT" ]
do
number=$RANDOM
echo −n "$number "
let "count += 1"
done
}
echo; echo
RANDOM=1
random_numbers
# Setting RANDOM seeds the random number generator.
echo; echo
RANDOM=1
random_numbers
# Same seed for RANDOM...
# ...reproduces the exact same number series.
#
# When is it useful to duplicate a "random" number series?
echo; echo
RANDOM=2
random_numbers
# Trying again, but with a different seed...
# gives a different number series.
echo; echo
# RANDOM=$$ seeds RANDOM from process id of script.
# It is also possible to seed RANDOM from 'time' or 'date' commands.
# Getting fancy...
SEED=$(head −1 /dev/urandom | od −N 1 | awk '{ print $2 }')
# Pseudo−random output fetched
#+ from /dev/urandom (system pseudo−random device−file),
#+ then converted to line of printable (octal) numbers by "od",
#+ finally "awk" retrieves just one number for SEED.
RANDOM=$SEED
random_numbers
echo; echo
exit 0
The /dev/urandom device−file provides a means of generating much more "random" pseudorandom
numbers than the $RANDOM variable. dd if=/dev/urandom of=targetfile bs=1
Chapter 9. Variables Revisited 100