#!/usr/bin/perl -w
use strict;

sub hanoi {
   warn "invoked @_";
   my ($n, $start, $end, $extra) = @_;
   if ($n == 1) {
       warn "Move disk #1 from $start to $end.";
   } else {
        hanoi($n-1, $start, $extra, $end);
        warn "Move disk #$n from $start to $end.";
        hanoi($n-1, $extra, $end, $start);
   }
}

hanoi(3, 'A', 'C', 'B');
__END__
invoked 3 A C B at hanoisub.pl line 5.
invoked 2 A B C at hanoisub.pl line 5.
invoked 1 A C B at hanoisub.pl line 5.
Move disk #1 from A to C. at hanoisub.pl line 8.
Move disk #2 from A to B. at hanoisub.pl line 11.
invoked 1 C B A at hanoisub.pl line 5.
Move disk #1 from C to B. at hanoisub.pl line 8.
Move disk #3 from A to C. at hanoisub.pl line 11.
invoked 2 B C A at hanoisub.pl line 5.
invoked 1 B A C at hanoisub.pl line 5.
Move disk #1 from B to A. at hanoisub.pl line 8.
Move disk #2 from B to C. at hanoisub.pl line 11.
invoked 1 A C B at hanoisub.pl line 5.
Move disk #1 from A to C. at hanoisub.pl line 8.