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Hack 33 IRC with Perl and Net::IRC

The IRC protocol looks a bit weird and can be
hard to understand. Fortunately, you don't have to
know it to make a bot.

Net::IRC is a Perl module that lets you make IRC
clients. It allows you to think about what your bot actually does,
instead of having to think about all those little noninteresting
protocol details [Hack #32] . This
hack will explain how to write a simple Perl IRC bot using
Net::IRC.

5.4.1 Preparations

You can download the
Net::IRC module from CPAN at http://search.cpan.org/dist/Net-IRC. If
you're lucky, you may be able to get it straight
from your operating system's package manager. It is
worth noting that Net::IRC is known to work on
Unix systems only. It may work on
Windows; it's
just not very well supported.

To demonstrate how Net::IRC works,
we're going to write a little infobot. The bot will
do one simple task: remember facts and repeat them when asked. This
will end up covering enough detail for you to make your own bots with
Net::IRC.

5.4.2 The Code

Create a file
called infobot.pl and write the following:

#!/usr/bin/perl
use Net::IRC;
# Set up the connection to the IRC server.
$irc = new Net::IRC;
$conn = $irc->newconn( Server => 'irc.freenode.net',
Nick => 'InfoBot_pl',
Ircname => 'InfoBot.pl' );
# Open the database.
dbmopen( %info, 'infobot', 0644 );
# Connect the handlers to the events.
$conn->add_handler( 376, \&join_channel );
$conn->add_handler( 422, \&join_channel );
$conn->add_handler( 'public', \&message );
# Start the Net::IRC event loop.
$irc->start;
sub join_channel
{
my( $conn, $event ) = @_;
print( 'We\'re connected!' . "\n" );
$conn->join( '#irchacks' );
}
sub message
{
my( $conn, $event ) = @_;
my( $msg ) = $event->args;
if( $msg =~ /^(.*)\?$/ )
{
# Someone requested information. Let's see if we know it.
if( $info{lc($1)} ne '' )
{
$conn->privmsg( $event->to, $event->nick . ': ' .
$1 . ' == ' . $info{lc($1)} );
}
}
elsif( $msg =~ /^(.+?) *=+ *(.+?)$/ )
{
# Someone gave us information. Save it.
$info{lc($1)} = $2;
$conn->privmsg( $event->to, $event->nick . ': OK' );
}
}

As you may have noticed,
Net::IRC is another
event-driven IRC bot framework. So as
soon as a certain event happens, a handler is called to handle this
event. The preceding code illustrates two event handlers: one to join the
necessary channels as soon as the connection to the server is
successfully made, and one to process incoming messages.

To handle an event, one should first write the handler. A handler is
a subroutine that accepts two arguments. The first argument is a
connection object, which allows the handler to get some information
or perform some operations on the connection where the event
happened. The second argument is the event object, which describes
the event itself. For example, a channel message or someone joining a
channel might trigger an event, which will be described by the event
object. Information can be retrieved from these objects by calling
methods. You may notice a few of the available methods in the
previous source code. Others can be found in more complete example
programs (one comes with the Net::IRC module
source).

After writing the handler, you have to tell
Net::IRC to use it. And, of course,
when to use it. To get a list of all possible

events, see the documentation
(perldoc Net::IRC::Event). As you can see in the
code, you also may specify a numeric event. This number is an
IRC status reply code. A list of valid
reply codes
can be found in the IRC RFC (RFC 2813, http://www.faqs.org/rfcs/rfc2813l). The
numbers used here are the "No MOTD
here" and "End of MOTD"
codes. Most (if not all) IRC servers try to send the
MOTD (message of the day) as
soon as the user is connected, so it's a good idea
to send the JOIN commands as soon as the MOTD is sent.

In case you were wondering, dbmopen()
ties a Perl
hash to a database file. This means that
everything you store in the %info hash will be
saved in that file. And of course, if a database already exists, all
the information in there will suddenly appear in the
%info hash. This means you can restart the bot
without it forgetting the things it just learned. Regular expressions
are used in the message handler to work out whether someone is asking
a question or if they are saying a new fact that the bot can learn.
If you are interested in extending this bot, you can get more
information about
Perl regular expressions by typing
perldoc perlre on the command line.

5.4.3 Running the Hack

You can run the bot by
entering:

% perl infobot.pl

5.4.4 The Results

When

the bot connects to your server and joins
your channel, you can begin feeding it with facts. Unless you change
the preceding source code, the bot will be called InfoBot_pl:

-!- InfoBot_pl [~wilmer@jona.ipv6.gaast.net] has joined #irc_hacks
<lintux> Perl?
<InfoBot_pl> lintux: Perl == Cool
<lintux> Perl = Cool, but sometimes hard to read
<InfoBot_pl> lintux: OK
<lintux> Perl?
<InfoBot_pl> lintux: Perl == Cool, but sometimes hard to read
<lintux> IRC Hacks?
<InfoBot_pl> lintux: IRC Hacks == A very cool book from O'Reilly
<lintux> Is there anything else you can tell me?

As you see, the bot didn't answer the last question,
because it didn't have an answer. You might wonder
why it doesn't say, "Hey, I
don't know that." The reason for
this is quite simpleyou don't want your bot
to start talking every time someone asks a question. Good bots talk
only when they're asked something.
It's often a good idea to remember this when
you're writing your own bots, otherwise you may kick
off some nasty debates. As a matter of fact, the bot shown here might
also be regarded as a bit too trigger-happy. But since
it's just a proof of concept, let's
not worry about that.

This should be enough to get you started. If you want to learn more,
you can look at some other (more complete) examples.
There's a nice sample bot inside the
Net::IRC
tarball. If you want more, try to find more examples by searching for
"Net::IRC bot" on Google. I also
recommend you to take a look at Pink, at http://www.lintux.cx/~lintux/pinkl, which
is quite a versatile bot, written using the
Net::IRC module. Unfortunately, some parts of the
source may be hard to understand for people who
don't read Dutch.

Wilmer van der Gaast