I figured this out the other day from idle curiosity. There is occassionally the need to have a never ending loop to be executed directly from the bash commandline instead of writing a script.

I used this to run sl (yes sl, not ls - try it - I love it) repeatedly.

    $ while true; do ; done

for example

    $ while true; do sl; done

Bear in mind that this loop is infinite and there is no way to cancel out of it except to kill of the terminal.