Upgrade WiFi AP (e.g on OpenWRT) when there is a stronger BSSID in vicinity (based on signal strength). Useful when you are a member of a SSID which has multiple APs under the same SSID but you don't want to commit to only one BSSID.

check_connection.sh

#!/bin/sh

COUNT=0
LIMIT=5
INTERFACE=wlan1

NAME=$(basename $0)
CLEAN_NAME=${NAME%.sh}
PID="/var/run/$CLEAN_NAME.pid"
LOGGER="logger -t $CLEAN_NAME -s"

check_status() {
    if [ ! -f "$PID" ]; then
        echo 0 > $PID
    fi
    pid=$(cat "$PID")
    ps|egrep "^[ ]*$pid .*$NAME" 2>&1 >/dev/null

    if [ $? -eq 0 ]; then
        $LOGGER "Already running, exiting..."
        exit
    fi

    echo $$ > "$PID"
}

check_status

while true; do
    ping -4 -w1 -c1 8.8.8.8 2>&1 >/dev/null

    if [ ! $? -eq 0 ]; then
        if [ $COUNT -lt $LIMIT ]; then
            if [ $COUNT -eq 0 ]; then
                # Run a scan on the wifi interface, incase that would recover the connection
                iw $INTERFACE scan 2>&1 >/dev/null
            fi
            COUNT=$(( $COUNT + 1 ))
            $LOGGER "Connection test failed! ($COUNT/$LIMIT)"

            continue
        fi
        $LOGGER "Limit reached, upgrading AP..."
        /root/scripts/upgrade_ap.sh force
    fi
    COUNT=0
    sleep 2
done

crontab

0 * * * * /root/scripts/check_connection.sh
*/2 * * * * /root/scripts/upgrade_ap.sh

upgrade_ap.sh

#!/bin/sh

# SSID you are a member of
SSID=
# Which interface to do a iw scan on
WIFI_IF=wlan1
# Limit for how many times to search for AP
LIMIT=2
# Delay in seconds between iw scans
DELAY=2
# Wait for N seconds to give connection time to establish
WAIT=10

# GENERAL VARIABLES
# if script is called with "force", switch to first best AP available
NAME=$(basename $0)
CLEAN_NAME=${NAME%.sh}
PID="/var/run/$CLEAN_NAME.pid"
FORCE=$1
LOGGER="logger -t $CLEAN_NAME -s"
# Target is used to find correct line in /etc/config/wireless
# e.g:
#   option bssid '00:00:00:00:00:00' #target
TARGET=" #target"
PREV=$(sed -nre "s/.*(')([[:alnum:]:]+)('$TARGET)/\2/p" /etc/config/wireless)
NEW=$PREV
COUNT=0

check_status() {
    if [ ! -f "$PID" ]; then
        echo 0 > $PID
    fi
    pid=$(cat "$PID")
    ps|egrep "^[ ]*$pid .*$NAME" 2>&1 >/dev/null

    if [ $? -eq 0 ]; then
        $LOGGER "Already running, exiting..."
        exit
    fi

    echo $$ > "$PID"
}

reload_wifi() {
    wifi
    sleep $WAIT
}

check_status

while true; do
    LINE=$(iw $WIFI_IF scan \
        | grep -i "SSID: $SSID" -B 8 \
        | sed -e "s/(on $WIFI_IF)//" \
        | egrep "(BSS|signal)" \
        | awk '{printf $2 "|"}' \
        | sed -re 's/([^|]+)\|([^|]+)\|?/\2 \1\n/g' \
        | sort \
        | head -n 1)

    BEST=${LINE#* }
    SIGNAL=${LINE% *}

    if [ "$BEST" == "" ]; then
        echo "Nothing found..."
        continue
    fi

    if [ "$BEST" == "$PREV" ]; then
        if [ "$PREV" != "$NEW" ]; then
            $LOGGER "Found previous station: $PREV ($SIGNAL), canceling..."
        fi
        NEW=$BEST
        break
    fi

    NEW=$BEST

    $LOGGER "Found better station: $BEST ($SIGNAL)"

    if [ "$FORCE" == "force" ]; then
        $LOGGER "Force mode activated! No time to loop!"
        break
    fi

    COUNT=$(( $COUNT + 1 ))

    if [ $COUNT -gt $LIMIT ]; then
        break
    fi

    sleep $DELAY
done

if [ "$PREV" != "$NEW" ]; then
    $LOGGER "Found better AP: $NEW, was: $PREV"
    sed -i -re "s/(')([[:alnum:]:]+)('$TARGET)/\1$NEW\3/" /etc/config/wireless
    reload_wifi
elif [ "$FORCE" == "force" ]; then
    $LOGGER "AP didn't change but force mode was activated! Reloading wifi..."
    reload_wifi
fi