the first I suspect you need to give full path
/home/knoppix/my-html-script > my-file.html

on the second, su=root=GOD!
root can do ANYTHING, even destroy the computer hardware that is, if you know how, perhaps in some extreme case, by sheer bad luck.

by destroy I mean something like, hmm, hard to choose one from list of bad things.
i think this will ilustrate,
it is quite possible to wipe proms and thus permanently trash DVD, CD, BIOS, HDD...
by permanently I mean it requires sending back to manufacturer to repair hardware (or having preprogrammed replacement parts and a good electronic background), and likley professional help on recovering the data in the HDD.