The thing I am look for is exactly in server nature. It's just I am trying to get avoid from going through the TCP layer.
For example, I have a daemon keep monitoring different folders. And while certain condition happen to the files, it raise another perl script to ask for what to do about them. I will input some command via STDIN, and then send back to the daemon server.
For another example, I have a shortcut on desktop, and I can drop files to it, and it calls a script with a file list as ARGV. the scrip then ask the server if they are identical to some existed files. ( The server has carried all the MD5 code of the monitoring (sub)folders ).