Program a bot

Something I was interested in as well, but I want to learn how to program a bot for web forums, etc. Like something for my personal use for testing and making demo content on web forums. All of the forums I work with use PHP scripting. Are there bots already made that can be modified for this type of thing, or does one have to specifically program a bot per their forum software? for example, myBB and Xenforo are the forums I install most.

Would it be a bot in some PHP form?