I needed to find out which files a process was using. I used the following commands to do this.
The ps command to get the process id (PID) of the process.
$ ps -aef | grep
Then the lsof command to list the files being used by the process.
$ lsof -p
If you want to count the files being used, use the following command.
$ lsof -p | wc -l
Have fun.