dumb perl download accelerator

pget.pl

#!/usr/bin/env perl
# dumb perl download accelerator
# 10/13/21 - morb_commat_misentropic_dot_commercial
use warnings;
use strict;
use Getopt::Long;
use File::Basename;
use LWP::UserAgent;
use Parallel::ForkManager;

my $fs = 8;
my $ch = 4;
GetOptions(
    "c|C|chunks=i"   => \$fs,
    "p|P|parallel=i" => \$ch
);
my $pm = Parallel::ForkManager->new($ch);
my $ua = LWP::UserAgent->new( agent => 'Mozilla/5.0' );

my $u  = shift;
my $h  = $ua->head($u)                      or die;
my $cl = $h->{'_headers'}{'content-length'} or die;
my $fn = basename($u);
my @ls = buildlist( $cl, $fs );
my $l  = $#ls - 1;

WORK:
for ( my $i=0;$i<$#ls;$i++) {
    $pm->start and next WORK;
    $i ? ( $a = ( $ls[$i] + 1 ) ) : ( $a = ( $ls[$i] ) );
    my $ua = LWP::UserAgent->new( agent => 'Mozilla/5.0', show_progress => 1 );
    $ua->add_handler(
        request_prepare => sub {
            my ( $rq, $ua, $h ) = @_;
            $rq->header( "Range" => "bytes=$a-$ls[($i+1)]" );
        }
    );
    $ua->get( $u, ':content_file' => $fn . $i );
    $pm->finish;
}
$pm->wait_all_children;
`cat $fn\{0..$l\} > $fn && rm $fn\{0..$l\}`;

sub buildlist {
    my @ls;
    my ( $cl, $fs ) = @_;
    for ( my $i=0;$i<=$cl;$i=$i+int($cl/$fs) ) {
        push @ls, $i;
    }
    push @ls, $cl if ( $ls[ ($#ls) ] != $cl );
    return @ls;
}