Collatz Conjecture perl

collatz.pl

#!/usr/bin/env perl
# sudo yum install -y perl-Math-BigInt-GMP || sudo apt-get install -y libmath-bigint-gmp-perl
use strict;
use Math::BigInt lib => 'GMP';
my $in = $ARGV[0] || &help;
$in=~s/,//g;
$in = Math::BigInt->new($in);

sub help{print "What number?\n"; exit;}

sub col(){
    my $i = shift;
    if ($i % 2 == 0 ){
        return $i/2;
    }else{
        return ($i*3)+1;
    }   
}   
 
my $count =0;
while($in > 1){
    $count++;
    my $r = &col($in);
    print "$count:";
    print "$r";
    print "\n";
    $in=$r;
}