#!/usr/bin/perl

open F, "bzip2 -dc @ARGV 2>/dev/null | hdlist2groups - |";
foreach (<F>) {
    chop;
    /(.*):(.*)/;
    $l{$2}{$1} = undef;
}
close F or die;
foreach (sort keys %l) {
    print "$_\n";
    print "\t$_\n" foreach sort keys %{$l{$_}};
    print "\n";
}