my $filename = shift @*ARGS or die "You need to pass in a filename.";

##</code><code>##

sub MAIN($filename) { 
    # rest of the mainline code here 
}

##</code><code>##

sub natural_cmp ($a, $b) {
    my ($first, $second) = ($a, $b);
    my ($one, $two) = ($first, $second).map({ .=subst(/(\d+)/, 
      -> $/{ sprintf( "%s%c%s", 0, $0.chars, $0) }, :g).lc });
    return ($one cmp $two);
}

##</code><code>##

sub natural_cmp ($a, $b) {
    my ($one, $two) = ($a, $b).map(*.subst(/(\d+)/, 
      -> $/{ sprintf( "%s%c%s", 0, $0.chars, $0) }, :g).lc);
    return $one cmp $two;
}