IRC experience is helpful, but I'll take things slow enough so that an absolute beginner can understand what is taking place. This will also help those with alittle knowledge fully understand the irc protocol. Although I am no irc expert, after creating this bot I did learn a few tricks.

We start off by getting a connection underway:

#!/usr/bin/perl
use IO::Socket;

$sock = IO::Socket::INET->new(
PeerAddr => 'irc.undernet.org',
PeerPort => 6667,
Proto => 'tcp' ) or die "could not make the connection";

You can use any irc server and any port (commonly used ports are 6667-7000), so long as they are valid. If you have problems try to find a different server on that network. To make things easier you can make the PeerAddr a variable which is specified by an argument from the command line. Or purhaps map out all the servers on the network and make an arry from them, connecting to random ones and using the best connection. There are many possibilities, each work best for certain situations. We'll stick to the simple hard coded address and port.

Now we have a connection to the server. We still need to get connected/logged in to the ircd. Anything we send to or recieve from the server will go through $sock. So lets see what the server is sending us after we make a connection.

while($line = <$sock>){
print "$line\n";
}

We will see that the server prints out some lines. Each line will have a number representation to it. This will really help to tell the bot when to start and end routines. The key here is the line with 'NOTICE AUTH' in it. This is when we need to login to the irc server. To do this we send

NICK bots_nick
USER bots_ident 0 0 :bots name

With a line break after the bots_nick and a line break at the end. So in the while loop we will add something like this:

while($line = <$sock>){
print $line;
if($line =~ /(NOTICE AUTH).*(checking ident)/i){
print $sock "NICK b0ilersbot\nUSER bot 0 0 :just a bot\n";
last;
}
}

Now we are done with the login process. If you are having any problems try to read up on the irc protocol and how to login to it with telnet. Raven from www.securitywriters.org has wrote a decent tutorial on the subject, look for it.

Some servers will ask for a ping to make sure the client is active. This is only done on some servers and is a common pitfall to many bots which don't support this kind of login proceedure. To handle this we will check if the server wants us to ping it. The server will ask for a ping before it asks about nickserv registration/identification, so we will stop this loop after it mentions nickserv. This is what those numbers in the last if statment are for, the 376|422. The way to identify to nickserv is like this

NICKSERV :identify nick_password

this is just a simple irc command. The command is 'NICKSERV' and the arguments are 'identify nick_password' where nick_password is the actual password for this nick. The line ends in a line break and all irc commands are in upper case. When there is a : before something it means it is a multiple word argument (has spaces in it). This is how we will handle the possible ping and the nickserv identification.

while($line = <$sock>){
print $line;
#use next line if the server asks for a ping
if($line =~ /^PING/){
print $sock "PONG :" . (split(/ :/, $line))[1];
}
if($line =~ /(376|422)/i){
print $sock "NICKSERV :identify nick_password\n";
last;
}
}

If you want to have a registration code you can find this out on your own.. or do what I do and register the nick with a normal irc client. This way we only need the bot to identify.

When you create your bot you can customize it however you want. Most of my bots have alittle bit more AI then this tutorial shows. This bot will be pretty strait forword and doesn't make many decisions. It just connects and does something.

I like to make the bot sleep for a few seconds just to get the connection cought up. I am on a 56k and things can go slow sometimes. A few times without the sleep the bot has joined channels before the nickserv identification is complete, this can be a pain in the neck if the bot needs a usermode or other circumstances which require the nick to be identified (such as other bots, +R channel mode, or trust issues with users).

After it sleeps it will join the channel. You will see that the server prints out alot of information about the channel when you join. You can save this information in variables to allow the bot to make many decisions. Again, this is a simple bot and won't be aware of it's environment or be dynamic in anyway. But you could for example turn on/off colors by what channel modes are set or who is in the channel (some people really hate colors). This is the last bit of the login proccess, after this the bot can actually do something.

sleep 3;
print $sock "JOIN #channel\n";

Notice there is no : before #channel. This is because it does not have any spaces in it. And the JOIN command is in all caps. For a full list of commands try reading a tutorial on the IRC protocol. I don't even cover the basics here, there are tons of useful to know commands.

Now we are joining the channel. There is nothing else to do besides read the messages users send to the channel and respond to them. But inorder to read the messages we need to parse them so they make sense. The format of a priv_msg is as follows:

:nick!ident@hostname.com PRIVMSG #channel :the line of text

I like to seperate them into the following variables to make things easier to keep track of.

:$nick!$hostname $type $channel :$text

in this example here is the values of the variables:

$nick = nick
$hostname = ident
$type = priv_msg
$channel = #channel
$text = the line of text

So we are going to need to parse what is send from the server into useable data. This is how we'll do it. There is only one twist here, and that is incase the server sends a ping. They do this quite often to check and see if you are still connected. If we don't reply the the pings then we will get disconnected. When the server sends a ping you must reply with a PONG and the same characters the ping had. So this is how we will send it

while ($line = <$sock>) {
($command, $text) = split(/ :/, $line); #$text is the stuff from the ping or the text from the server

if ($command eq 'PING'){
#while there is a line break - many different ways to do this
while ( (index($text,"\r") >= 0) || (index($text,"\n") >= 0) ){ chop($text); }
print $sock "PONG $text\n";
next;
}
#done with ping handling

($nick,$type,$channel) = split(/ /, $line); #split by spaces

($nick,$hostname) = split(/!/, $nick); #split by ! to get nick and hostname seperate

$nick =~ s/://; #remove :'s
$text =~ s/://;

#get rid of all line breaks. Again, many different way of doing this.
$/ = "\r\n";
while($text =~ m#$/$#){ chomp($text); }

#end of parsing, now for actions
}

ok. That was a rather large chunk of code and some parts were rather confusing. Most of it is just getting rid of what we don't want and seperating what we do want into variables. The next bit is just for looks. We print out what is said as if this is a normal irc client.

if($channel eq '#channel'){
print "<$nick> $text";
}

The $channel check is needed incase people priv_msg or notice you things. This can be a problem when dealing with bots which need to be secure or can cause large headaches when things go wrong. I'll leave dealing with multiple channels to you. But to send Notices you simply do: print $sock "NOTICE nick :the line of text here\n"; and to send a priv_msg you do: print $sock "PRIVMSG nick :the line of text here\n";

Now the bot structure is done. Everything required is done, the only thing left to do is custimize your bot to have it do what you want it to do. This can be almost any sort of task imaginable. Simply parse the $text $nick and other variables we created to have the bot make decisions on what to do.

Here is the final bot in whole. I added one bit just to prove that the bot works:
#!/usr/bin/perl
use IO::Socket;

$sock = IO::Socket::INET->new(
PeerAddr => 'irc.undernet.org',
PeerPort => 6667,
Proto => 'tcp' ) or die "could not make the connection";

while($line = <$sock>){
print $line;
if($line =~ /(NOTICE AUTH).*(checking ident)/i){
print $sock "NICK b0ilersbot\nUSER bot 0 0 :just a bot\n";
last;
}
}

while($line = <$sock>){
print $line;
#use next line if the server asks for a ping
if($line =~ /^PING/){
print $sock "PONG :" . (split(/ :/, $line))[1];
}
if($line =~ /(376|422)/i){
print $sock "NICKSERV :identify nick_password\n";
last;
}
}

sleep 3;
print $sock "JOIN #channel\n";

while ($line = <$sock>) {
($command, $text) = split(/ :/, $line); #$text is the stuff from the ping or the text from the server

if ($command eq 'PING'){
#while there is a line break - many different ways to do this
while ( (index($text,"\r") >= 0) || (index($text,"\n") >= 0) ){ chop($text); }
print $sock "PONG $text\n";
next;
}
#done with ping handling

($nick,$type,$channel) = split(/ /, $line); #split by spaces

($nick,$hostname) = split(/!/, $nick); #split by ! to get nick and hostname seperate

$nick =~ s/://; #remove :'s
$text =~ s/://;

#get rid of all line breaks. Again, many different way of doing this.
$/ = "\r\n";
while($text =~ m#$/$#){ chomp($text); }

if($channel eq '#channel'){
print "<$nick> $text";

if($text =~ /hi b0ilerbot/gi){
print $sock "PRIVMSG #channel :hi $nick\n";
}
}
}

Not very complicated once you look at each part of it. But finding out things for yourself is the real fun of creating a bot. Much trial and error is involved in perfecting the bot, adding security and function can be alot of fun. I would like to stress the security of irc bots. They are in the most hostile environment known to the net and one security mistake and your bot could be used to execute commands on your box. I have found 4 irc perl bots vulnerable to remote command execution, don't let me find yours vulnerable aswell! Read all of the perl security related tutorials at http://b0iler.eyeonsecurity.net/tutorials/ Don't let this discurage you from coding your own bot, it's a great learning experience and as long as you are careful you should be fairly safe. I would love to hear what kind of bots you come up with. The bots I have created include:

quote bot - a bot which has many features that deal with irc quotes. it reads off funny/witty things people have said while chatting in my channels. It also has some more advanced features such as listing off all the users in the channel who have a quote and an admin feature which allows me to add quotes while the bot is running.

quiz bot - A bot which quizes the channel users. I used this while studying for networking. This bot is great when the channel is dead or to start up a conversation with others. I learned alot from this bot.

poker bot - A bot which plays poker. I started to make a ucker (sp?) bot, but I lost motivation when the other people who wantted to play quit going on irc.

channel bot - A bot which enforces the channel rules. it warns, kicks, and kick bans users for breaking the rules. it voices,half ops, and ops identified users and keeps stats of channel activity. Good for preventing channel takeovers.

The reason for creating this text was because I remember the stress I had finding info on this subject when I first created the bot. I have since read a few crappy papers on irc bots, but nothing which would be very helpful.