Noah Slater of semtard vapourware fame recently demonstrated to me how to write and extremely simple IRC bot in shell scripting.
The bot below is extremely simple, it simply identifies itself, joins a channel then sends a message to a channel.

If you are interested in using IRC bots, you may enjoy Phenny, which has a Debian package.

To use the code below to create your own bot, first you should copy the bot into a file called bot.sh
then run:

chmod a+x bot.sh

then run the bot with

./bot.sh

If you wanted to run the bot in the background for an extended period of time, you might want to do something like:

nohup /bot.sh 2> ~/mybotlog.txt &

For more information about learning shell scripting have a look on google