General :: Output Pid's From Ps To A Comma Delimited File?

need to monitor pecific processes over a time frame in terms of the amount of memory and cpu usage it utilizes. I can do this using the top -p <pid> option and using ps to retrieve the pid's. However, seeing that the pid's might differ and it needs to be run on about 13 different machines, I would like to write a script for this that can be run at set intervals. My problem that I have is this:

- When running top -p <pid> I can specify a comma seperated list of the processes required to monitor at that specific time.

- I can use ps -ef | grep <process> | grep -v grep| awk '{ print $2 }' to retrive the list of pid's and output this to a file.

However, how can I output these to the file as a comma seperated list without having to manually do this every time? The reason for this is (an example), lets say I want to monitor the cpu and memory usage of postgresql as well as all its child processes, then I would ps grep for postgres and get the list of pid's for instance.This list then needs to be passed to top -p as a comma seperated list of pid's I suspect that awk or sed might have some options available for this but I do not know this well enough.