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#!/usr/bin/env bash
# Esoteric random number generator
# <http://dilbert.com/strip/2001-10-25>
self=rndn
# Define usage function
usage() {
printf 'USAGE: %s [-h | -s SEED]\n' "$self"
}
# Parse options
while getopts 'hs:' opt ; do
case $opt in
# -h for help
h)
usage
exit 0
;;
# -s to set seed manually
s)
seed=$OPTARG
;;
# Unknown option, print usage and fail
\?)
usage >&2
exit 2
;;
esac
done
shift "$((OPTIND-1))"
# If no seed given, get one from Bash's $RANDOM
: "${seed:=$((RANDOM ** 2))}"
# Truncate the seed
seed=${seed:0:32}
# Check seed meets algorithm conditions
if [[ $seed == *[^0-9]* ]] || ((seed < 0)) ; then
printf >&2 '%s: error: seed must be non-negative integer\n' "$self"
exit 2
fi
# Apply algorithm
for ((seed += 10, i = 0; i < ${#seed}; i++)) ; do
((sum += ${seed:i:1}))
done
for ((red = seed - sum; ${#red} > 1; red = redn)) ; do
for ((j = 0, redn = 0; j < ${#red}; j++)) ; do
((redn += ${red:j:1}))
done
done
# Print result
printf '%u\n' "$red"
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