Bash script to connect to strongest unencrypted wifi AP

Question

Here's a little bash script that looks at the available wifi APs that your card can see, and automatically connects you to the AP with the highest quality and that is also unencrypted. I'm just posting it in case anyone wants to improve upon it or use it. And yes, my bash knowledge kinda sucks.
Just call it like "wifi.sh wlan0" as root.
#!/bin/bash
# Finds the strongest unencrypted AP and tries to connect to it via dhcp
# Call this script like "wifi.sh wlan0"
interface=$1
iwlist $interface scan > blah
NumAPs=`cat blah | grep ESSID | wc -l`
BestAP=0
BestQuality=-1
for i in `seq 1 $NumAPs`;
do
# Check if AP is encrypted
Encryption=`cat blah | grep Encryption | head -n$i | tail -n1 | cut -d":" -f2`
if [ $Encryption = "off" ]; then
# Find AP with the highest quality
QUALITY=`cat blah | grep Quality | head -n$i | tail -n1 | cut -d":" -f2 | cut -d"/" -f1 | sed 's/ //g'`
if [ $QUALITY -gt $BestQuality ]; then
BestQuality=$QUALITY
BestAP=$i
fi
fi
done
if [ $BestAP -gt 0 ]; then
# Yay, we found an unencrypted AP:
echo Connecting to...
ESSID=`cat blah | grep ESSID | head -n$BestAP | tail -n1 | cut -d""" -f2`
echo ESSID=$ESSID
MODE=`cat blah | grep Mode | head -n$BestAP | tail -n1 | cut -d":" -f2`
echo Mode=$MODE
CHANNEL=`cat blah | grep Channel | head -n$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
rm blah
fi

Answer 1

For whatever reason, your quality line uses an equal sign whereas every other line of your scan has a colon (and most people have a colon for every line). Too weird..
Anyway, give this a shot:
#!/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