Richard said:
"I usually just do:

iw-scan > scanfile.wi &
tail -f scanfile.wi"

to use tee, do this:
iw-scan > tee scanfile.wi

tee takes the input and sends one copy to the named file and one to stdout. So, yes, you can further redirect this:

iw-scan > tee scanfile.wi >> tee masterfile.wi

This will put this scan in scanfile.wi, and *append* to masterfile.wi, and also to STDOUT (your screen).

GNUbie