#!/usr/bin/perl
# common_subscriber given a set of Debian mailing lists, show the common subscribers
# and is released under the terms of the GNU GPL version 3, or any
# later version, at your option. See the file README and COPYING for
# more information.
# Copyright 2014 by Don Armstrong <don@donarmstrong.com>.


use warnings;
use strict;

use Getopt::Long;
use Pod::Usage;

=head1 NAME

common_subscriber -  given a set of Debian mailing lists, show the common subscribers

=head1 SYNOPSIS

common_subscriber [options]

 Options:
   --debug, -d debugging level (Default 0)
   --help, -h display this help
   --man, -m display manual

=head1 OPTIONS

=over

=item B<--debug, -d>

Debug verbosity. (Default 0)

=item B<--help, -h>

Display brief usage information.

=item B<--man, -m>

Display this manual.

=back

=head1 EXAMPLES

common_subscriber

=cut


use vars qw($DEBUG);
use IO::File;


my %options = (debug           => 0,
               help            => 0,
               man             => 0,
              );

GetOptions(\%options,
           'debug|d+','help|h|?','man|m');

pod2usage() if $options{help};
pod2usage({verbose=>2}) if $options{man};

$DEBUG = $options{debug};

my @USAGE_ERRORS;
if (not @ARGV) {
    push @USAGE_ERRORS,"You must give some mailing lists";
}

pod2usage(join("\n",@USAGE_ERRORS)) if @USAGE_ERRORS;


my %subscribers;


for my $list (@ARGV) {
    my $fh = IO::File->new('/var/list/'.$list.'/dist','r') or
        die "Unable to open /var/list/$list/dist for reading: $!";
    while (<$fh>) {
        chomp;
        next unless /\@/;
        $subscribers{$_}++;
    }
}

for my $subscriber (sort keys %subscribers) {
    print $subscriber."\n" if $subscribers{$subscriber} eq scalar @ARGV;
}



__END__