fseventer does not support Yosemite until further notice and the suggestions here don't work for me so how can I monitor an installer as it writes files to the file system? I also tried Sloth but it only shows currently open files at a specific point in time.
This not application specific (it will show all) but you can find the one you are looking for.
This “traces” disk I/O execution live. Each time a disk I/O completes, a line of output is printed to summarize it, including process name and filename details:
sudo iosnoop UID PID D BLOCK SIZE COMM PATHNAME 503 54079 R 286522800 4096 Google Chrome ??/Cache/data_2
Derman Enterprises File Control
… makes it easy to determine what's been changed anywhere on your system. …
On OS X 10.11.1, attempts to analyse
– during an installation by MacPorts – result in a 'No Items Were Processed' dialogue in File Control. So I assume that El Capitan is incompatible with such applications …
… but File Control might work with Yosemite. If not, please vote down this answer.
(I have El Capitan for test purposes, and I can run Mavericks later, but no Yosemite test environment.)