Send commands to already running process

[The Linux Kid]

Hi everyone,

I'm working on a project that requires my web based programs (written in PHP, however I could write the interface in Perl if needeed) to be able to send commands and get responses from a process thats running.

The program takes input from STDIN and then outputs to STDOUT - basically, how do I get my PHP/Perl program to write to the programs STDIN and then read from its STDOUT?

I've googled, I'm sure its possible, but I couldn't find the right search terms.

Thanks in advance!