#!/usr/bin/perl

use strict;
use warnings;

die "Usage: $0 <chainring> <cog> <wheelsize>\n" unless @ARGV == 3;

my ($chainring, $cog, $wheelsize) = @ARGV;
$wheelsize = $1 * .39 if $wheelsize =~ /^(\d+)m$/;

die "Chainring needs to be a positive integer\n" unless $chainring =~ /^\d+$/;
die "Cog needs to be a positive integer\n"       unless $cog =~ /^\d+$/;
die "Wheelsize needs to be a positive number\n"  unless
    $wheelsize =~ /^\d+(?:[.]\d*)?$/;

my $gearinches = sprintf "%.2f" => $wheelsize * $chainring / $cog;

print <<"--";
The gear inches for a chainring of $chainring teeth and a
cog of $cog teeth, and a wheel of $wheelsize inches is
$gearinches gear inches.
--

__END__