Extraordinarily cute. ++ for creative use of splice. However, it borders on the obfuscatory, and I'd personally take a straightforward approach with the entire thing.

Note that if you want to throw out the current and parent directory entries you should generally use \A and \z instead of ^ and $ though (the latter will match in front of a terminating newline in the filename) or simply use good oldfashioned eq.

#!/usr/bin/perl -w
use strict;
use CGI qw/:standard/;

my $columns = param('cols') || 4;
my $offset = 0;

# untested

my (@dir, @file);

push @{ -d ? \@dir : \@file }, a({-href=>$_},$_) for do {
    opendir my($dh), "." or die "cannot opendir: $!";
    sort grep $_ ne '.' && $_ ne '..' && !/~\z/, readdir $dh;
};

$_ = "[ $_ ]" for @dir;

for (\@file, \@dir) {
    my @result;
    push @result, td([map b($_), splice(@$_,0,$columns)]) while @$_;
    @$_ = @result;
}

print
    header(-expires=>'now'),
    start_html('Directory Listing'),
    h1('Directory Listing'),
    table(
        {-border=>0,-cellpadding=>5,-cellspacing=>5},
        map Tr($_), @dir, @file;
    ),
    end_html;

__END__
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