exec command?

Hey all, Simple Question here for you, i can't find out how to do it at php.net.... I want to call an .exe file from a script it's a keygenerator accepting a MAC address as input and puts out a serial number as out put. in DOS you would run it like this: c:\paul\source>keygen 00-00-00-00-00 it would output a serial number. what i want to do is call the keygen.exe file from a php script and print the out put to the screen. any ideas? - paul -