watch. From the manpage:
watch - execute a program periodically, showing output fullscreen
watch [-dhvt] [-n <seconds>] [--differences[=cumulative]] [--help] [--interval=<seconds>] [--no-title] [--version] <command>
watch runs command repeatedly, displaying its output (the first screenfull). This allows you to watch the program output change over time. By default, the program is run every 2 seconds; use
--interval to specify a different interval.
--differences flag will highlight the differences between successive updates. The
--cumulative option makes highlighting "sticky", presenting a running display of all positions that have ever changed. [...]
watch will run until interrupted.
Note that "realtime" would have to be approximated by "once a second" (for example) here...