For example, the pv utility shows me the current rate of data transfer and updates every second. I'd like to save that output to a file, so that I can see at what rate data was being transferred second by second. I can't use a simple redirect like (pv /dev/zero > /dev/null) 2> out.txt.
Use screen, which provides a kind of virtual text terminal. When you run a program like pv from within screen (by typing
screen pv), you can save a snapshot of the screen with Control-a, h.