shell script to change MAC address

[thims]

While I am at it figured I would post this little snippet aswell.
I do realize there are other utilities to spoof the MAC address of devices, but I would rather us my own solution. (plus I was bored).

General Usage:
-h print help
-s generate random mac address and assign it
-u set mac address to what it was from the beginning

ToDo:
- add CLI flag to define interface
- add CLI flag to manually define mac address
- resolve issue with assigning the MAC, ifconfig has issues with certain mac address's not sure why yet.

Download: mediafire.com/download.php?hean10e25zi
Code:

#!/bin/bash
#
# Synopsis: MAC address spoofing utility
# Author:		thims (thims DOT local AT gmail DOT com)
# Version:  0.1
# Date:			20091104
# Comments: 
# ToDo:
#				- figure out why certain MAC addresss cause ifconfig to exit with error (Error: could not set spoofed MAC address, possibly try running againg)


# Editable variables
iface=wlan0															#desired interface
origMAC=ff:ff:ff:ff:ff:ff								#original MAC address


### Code Begins ###
spfMAC=
alph=(0 1 2 3 4 5 6 7 8 9 A B C D E F)
alph_len=${#alph[*]}


function help() {
cat << EOF
Usage: $0 [args]
    -h, --help     -  Print this help and exit
    -s, --spoof    -  Spoof MAC address to a randomly generated address
    -u, --unspoof  -  Return spoofed MAC address to original MAC address
EOF
}

function die() {
	if [ -n "$1" ] ;then
		echo "$1"
	fi
	exit 1
}

function genMAC() {
	for i in $(seq 6) 
	do
		for x in $(seq 2) 
		do
			spfMAC=${spfMAC}${alph[$((RANDOM % alph_len))]}
		done
		spfMAC=${spfMAC}:
	done
	spfMAC=${spfMAC:0:17}
}

function changeIface() {
	MAC="$1"
	
	ifconfig $iface &> /dev/null
	if [ $? -gt 0 ] ;then
		die "Error: IFACE $iface does not exist(possibly down?)"
	fi


	ifconfig $iface down
	ifconfig $iface inet hw ether $MAC up &> /dev/null
	# the following if is in place because ifconfig was being picky about certain MAC addresss
	if [ $? -gt 0 ] ;then
		die "Error: could not set spoofed MAC address, possibly try running againg"
	fi
}


if [ $UID -gt 0 ] ;then
	die "Error: Sorry dude, gotta be root!"
fi

while [ $# -gt 0 ] 
do
	case "$1" in
		"-h"|"--help")
			help
			die
		;;
		"-s"|"--spoof")
			genMAC
			changeIface $spfMAC
		;;
		"-u"|"--unspoof")
			changeIface $origMAC
		;;
		*)
			help
			die
		;;
	esac
	shift
done

All feeback welcome, I would love to hear your thoughts.