what language i need to know for writing bots

C# gets my vote, back in my days when i first started coding i found it very easy to pick up - great for a beginner.

Id say no to PHP, for the reasons mentioned above. It is a great language, but not ideal for bot building in my humble opinion.

Looking at it from another angle .net is very widely used commercially (This is not exclusive to .net but it is certainly one of the big languages out there today). If you got your coding skills up to scratch you will find a multitude of commercial contracts you could apply for in the future.

+1 for Java. I haven't used it much, but it's pretty powerful and can efficiently handle multi-threading. Not to mention it's cross platform.

If you alredy work with PHP, then you should be aware, that every reqest (also, from CRON) goes with single apache process. So you need several megabytes of RAM to handle request. Remebmer that process is not thread - process is a lot heaviest thing.

For PHP to improve multithreading we can study Apache documentation for chaginc process-per-request logic to thread-per-request logic, if I remebrer it calls "workers" in apache or something like that. But it can bring some concurrent programming issues.

You can do a lot with all these languages that you have mentioned above.. They can help a lot.

A recommended book-> Webbots, Spiders, and screenscrapers - Michael Schrenk

You should now Computer Languages