$ perl rabbit.pl
Use of uninitialized value in numeric lt (<) at ./rabbit.pl line 7.
{1,1,0,. . .}

$ perl -v
This is perl, v5.8.5 built for cygwin-thread-multi-64int

##</code><code>##

fib($ARGV[0])
to
fib($ARGV[0]||42)