Bash script to connect to strongest unencrypted wifi AP

#!/bin/bash
# Finds the strongest unencrypted AP and tries to connect to it via dhcp
# Call this script like "wifi.sh wlan0"
TEMP=/tmp/bestap.tmp
LOCK=/var/lock/bestap.lock
if [ `whoami` != "root" ];then
       echo "Sorry, you need to be root to run this program"
       exit 1
fi

if [[ -z $1 ]];then
       echo "USAGE: $0 device"
       exit 1
else
       interface=$1
fi

# Checking for lock
if [[ -e $LOCK ]];then
       exit 1; # Too simply nothing to do here :)
else
       touch $TEMP $LOCK
fi

isNotInteger()
{
   x=$1
   case $x in
       *[!0-9])
           return 0 ;;
       *)
           return 1 ;;
   esac
}

# Proggy
iwlist $interface scan > $TEMP
NumAPs=`cat $TEMP | grep ESSID | wc -l`
BestAP=0
BestQuality=-1
for i in `seq 1 $NumAPs`;
do
  # Check if AP is encrypted
  Encryption=`cat $TEMP | grep Encryption | head -n$i | tail -n1 | cut -d":" -f2`
  if [ $Encryption = "off" ]; then
     # Find AP with the highest quality
     QUALITY=`cat $TEMP | grep Quality | head -n$i | tail -n1 | cut -d":" -f2 | cut -d"/" -f1 | sed 's/ //g'`
     if isNotInteger "$QUALITY"; then
       # If we didn't find an integer, try this instead:
       QUALITY=`cat $TEMP | grep Quality | head -n$i | tail -n1 | cut -d"=" -f2 | cut -d"/" -f1 | sed 's/ //g'`
     fi
     if [ "$QUALITY" -gt "$BestQuality" ]; then
        BestQuality=$QUALITY
        BestAP=$i
     fi
  fi
done
if [ $BestAP -gt 0 ]; then
  # Yay, we found an unencrypted AP:
  echo Connecting to...
  ESSID=`cat $TEMP | grep ESSID | head -n$BestAP | tail -n1 | cut -d""" -f2`
  echo ESSID=$ESSID
  MODE=`cat $TEMP | grep Mode | head -n$BestAP | tail -n1 | cut -d":" -f2`
  echo Mode=$MODE
  CHANNEL=`cat $TEMP | grep Channel | head -n$BestAP | tail -n1 | cut -d"(" -f2 | sed 's/Channel //g' | sed 's/)//g'`
  echo Channel=$CHANNEL
  # Connect
  iwconfig $interface essid $ESSID mode $MODE channel $CHANNEL
  if [ -e /etc/dhcpc/dhcpcd-${interface}.pid ]; then
     rm /etc/dhcpc/dhcpcd-${interface}.pid
  fi
  dhcpcd $interface
  # Cleanup
fi
rm -f $TEMP $LOCK