Extract_compressed_fs is SUPERFAST this way ?!?!

I was trying to edit a script I'm working on, when I made a mistake that may be very fortunate... :)
I used the following code :

Code:

---

SOURCE="/home/user/KNOPPIX/KNOPPIX"
DESTINATION="/home/user/testdir/temp.iso"
TEMP="/home/user/testdir/temp.log"

(extract_compressed_fs $SOURCE > $DESTINATION) 2>&1 | \
(head -n1 | cut -f1 -d ' ' > $TEMP) | cut -f2 -d ' '

---

It was meant for a progress window I was trying to make, but when I executed it, it was finished immediately, so I figured the code was wrong.
(in fact, it probably is wrong...)
When I mounted the created temp.iso however, it looked like (and still does) a complete filesystem !
Have I found an ultrafast way to convert to a temp.iso ?
Maybe somebody here has an idea about this... :?: