%post question adding real user name

["Alexander Rau \(private\)" <alexander_rau@xxxxxxxxx>]

I would like to add a real user name by running the following script in
the %post section but I can's get it to work. Any ideas why?

dialog --title "Enter Name" --inputbox "Please enter your name" 8 60
2>/tmp/name.$$

SEL=$?

NA2=`cat /tmp/name.$$`
case $SEL in
  0)  chfn -f $NA2 username ;;
  1) echo "Cancel is Pressed" ;;
  255) echo "[ESCAPE] key pressed" ;;
esac

rm -f /tmp/name.$$

Thanks