Hello there,
What are looking for is an auto responder to facebook page.
But, first of all, i need to knonw that the page you want to be auto commented is yours, you own it. Because Facebook API dont allow us to generate auto comment on the page you dont owned.
Yes what i did last time is the script can manage multiple group/fanpage. You can also custom the autopost based on the keywords input by user.
IF the page you want to auto commented is not yours, then is not possible at the current time. Because Facebook limits it in their API.
Thank you