You code doesn't allow for parameters that aren't options. Let's introduce --. And let's handle the case with no previous --option. Then you can do

command --option ... -- file1 file2
[download]

sub parse_args {
    my $last_opt = '';
    my %opts;

    while (@ARGV) {
        my $arg = shift(@ARGV);
        if ($arg eq '--') {
            last;
        } elsif ($arg =~ s/^--?//) {
            $opts{$last_opt = $arg} = [];
        } else {
            push @{ $opts{$last_opt} }, $arg;
        }
    }

    unshift @ARGV, @{ delete $opts{''} } if $opts{''};

    return \%opts;
}
[download]

Supporting val=0 as an option makes no sense. It would prevent you from having values with equal signs in them.

If -list a b c wasn't supported, we could do away with requiring --.