Filling up Custom fields with automation

Hi,

I have 4 custom fields:

Field1: XXXXX
Field12: XXXXX is good
Field13: XXXXX is available for discount
Field14: Grab XXXXX here

As you can see that Field12, Field13 and Field14 totally depends on Field11.

Currently I am manually filling up all these in Custom Fields box of Post page.

Please guide me how I can automate this by just filling up Field1 so that other fields gets filled up. Any kid of help is appreciated.

Thanks,
Rajesh