Thanks for the quick reply.
I want to record for a long period of time (hours). If I had a tool that I could record for a fixed duration and output to a file, that's all I need. After that I could write a simple script to call that utility as needed, and write snippets (like 15 minutes worth) at a time to different files.
My guess is if I leave Audacity or something else running in recording mode for very long periods of time, it will run out of memory.