use strict;
use warnings;

my ($d, $k1, $k2, $k3);

while (<DATA>) {
    chomp; @_ = split /\:/;
    push @{$d->{$_[0]}{$_[1]}{$_[2]}}, $_[3];
}

for $k1 (keys %$d) {
    for $k2 (keys %{$d->{$k1}}) {
        for $k3 (keys %{$d->{$k1}{$k2}}) {
            for (@{$d->{$k1}{$k2}{$k3}}) {
                print "$k1:$k2:$k3:$_\n";
            }
        }
    }
}

__DATA__
category1:category2:category3:options
categorya:categoryb:categoryc:more options
categoryd:categorye:categoryf:even more options