I plan on developing on a Single Board Computer that runs linux.
This board will run a daemon I create that does some controlling of the ADC functions on board and such.

This board will also host a web server for all the interfacing.
What do I need to do to make a PHP/CGI/etc... script be able to "talk" to this daemon? I also need for it to return data as well.

Sorry its so broad, but I just need a few pointers to get started.