brutely - crawl bit.ly and similar URL shortening services using brute force methodology

brutely.pl

#!/usr/bin/perl -w
# Usage: brutely.pl URL <LENGTH> (length defaults to 6) 
# Ex: ./brutely.pl https://bit.ly/1 6
# 4/16/16 -- chris_commat_misentropic_commercial
use strict;
use warnings;
use HTTP::Tiny;

my $ua = HTTP::Tiny->new( { agent => "ayy/1.0", keep_alive => 1 } );
my $ln = $ARGV[1]; $ln ||= 6;

sub bfg {
    my @chars = ("A".."Z","a".."z",0..9) ;
    my $out =
      $ARGV[0] . join( "", @chars[ map { rand @chars } ( 1 .. $ln ) ] );
    return $out;
}

sub heed {
    my $url = shift;
    my $res = $ua->head($url);
    return $res;
}

until ( my $death ) {
    my $url = &bfg;
    my $ret = heed($url);
    next if ( $ret->{status} eq 404 or $ret->{url} eq $url );
    print "$url == $ret->{url}\n";
}

Hey, i'm new to perl. How do I use your script?