Retrieve process network usage (since restart, if neccessary) via Bash script

I've been hunting for a while on how to get the network usage of a process in Linux using a Bash script, but I've only found the same answers repeated over and over again.

It'd be nice if there was a way to programamatically retrieve t开发者_如何学编程he network usage of a process, instead of having some poor tech stare at a terminal 24/7 running an instance of ntop.

Does anyone know of a way to do this?

Thanks.

The only thing I've come across is:

cat /proc/PID/net/dev

However, it's not accurate and reports statistics from the whole system. (virtually identical to /proc/net/dev