I don't do much PHP, so I can't help there, but why not keep the data and code separate? The generic pathing at the beginning is just data. Throw it in a file or DB or something; you seem to use a config file.
Also why not keep IRC and other stuff separated. A bot on IRC is there to relay messages, not scan for SQLI.
Again, I'm not a php person, but even the logging could do with an array a for loop and then eval or something kinda similar.
I do condone you on regex however. I always hated regex and probably always will lol. I know php is a web server and web-of-things kinda deal, but this seems more application specific and a bit less server service driven. Keep the IRC even, but I would see something like this with pretty buttons instead of IRC commands to a bot directly. Anyway, API or something why not a framework?
Good job though. Keep on, and on will be keeping.