Sendmail
The Towers of Hanoi implemented through Sendmail's configuration (.cf) file mechanism.
# The Towers Of Hanoi (hanoi.cf)
# sendmail
# Copyright (C) 1998 Amit Singh. All Rights Reserved.
# http://hanoi.kernelthread.com
#
# Last tested with sendmail 8.12.5 (version 10 of .cf file)
#
# Acceptable input (number of disks) is a positive integer between
# 1 and 9, both inclusive. In order to solve Hanoi for N disks, try:
#
# echo 99 N | sendmail -bt -d21.3 -C hanoi.cf
#
# To suppress the debug output, and get only the list of moves, try
# the following:
#
# echo 99 N | sendmail -bt -d21.3 -C hanoi.cf | awk -F: '/move/{print $NF}'
#
V10
S99
R1 $: .
R2 $: ..
R3 $: ...
R4 $: ....
R5 $: .....
R6 $: ......
R7 $: .......
R8 $: ........
R9 $: .........
R$+ $@ $>98 1 3 2 $1
S98
R$- $- $- $* :$* $: $1 $2 $3 $4
R$- $- $- $@ $1 $2 $3
R$- $- $- . $* $: $>98 $1 $3 $2 $4
R$- $- $- $* $: $>98 $2 $3 $1 $4 :move $1 to $3
R$- $- $- $* $: $3 $2 $1 . $4
# __END__