Hi Juanito
Yes, I realize that. The command is not compiled into busybox but is included in /usr/bin/:
tc@box:~$ which length
/usr/bin/length
tc@box:~$ ls -l /usr/bin/length
lrwxrwxrwx 1 root root 17 Nov 16 2011 /usr/bin/length -> ../../bin/busybox
tc@box:~$ length
length: applet not found
tc@box:~$