Repeat command automatically in Linux

while true; do
    sleep 5
    ls -l
done

Watch every 5 seconds ...

watch -n 5 ls -l

If you wish to have visual confirmation of changes, append --differences prior to the ls command.

According to the OSX man page, there's also

The --cumulative option makes highlighting "sticky", presenting a running display of all positions that have ever changed. The -t or --no-title option turns off the header showing the interval, command, and current time at the top of the display, as well as the following blank line.

Linux/Unix man page can be found here