[dev] wmii status bar config

HI everybody!
I'm happy to use wmii after tweaking some things, making autorun scripts and
binding hotkeys, all is done. But I have another question.
I want to config my status bar, I want it to show some terminal output of
my sensors or any bash script. Now it displays 'average load, date and
time'. And I don't have a clue from which file does this info come from for
wmii. I don't need average load info, what I need is to display terminal
output of a custom script in my status bar. How do I do it?
There was something about "wmiir read /bar" in docs, but I haven't found
this line in my /usr/local/bin/wmii.rc file. So now I'm puzzled a bit.

-- 
Tian