shell script to change MAC address

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:

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.