The following is a demonstration of the rwbypid.d script,
Here we run it for a few seconds then hit Ctrl-C,
Tracing... Hit Ctrl-C to end.
^C
PID CMD DIR COUNT
11131 dtrace W 2
20334 sshd W 17
20334 sshd R 24
1532 Xorg W 69
1659 mozilla-bin R 852
1659 mozilla-bin W 1128
1532 Xorg R 1702
In the above output, we can see that Xorg with PID 1532 has made 1702 reads.