Beginning with Ash (Busybox). This is a "Quick & Dirty" (yep, I'm "learning") script for blinking QSS LED when it reaches every "min" value on "/etc/config/system" file. Firmware: OpenWRT | Gargoyle. Hardware: TP-LINK WR1043ND (with little changes it can be ported to another routers).

blink_options.sh

#!/bin/sh

led_off() {
    echo 0 > /sys/class/leds/tp-link:green:qss/brightness
    return $?
}

led_on() {
    echo 1 > /sys/class/leds/tp-link:green:qss/brightness
    return $?
}

remove_pid_file() {
    rm -f $PID_FILE
    return $?
}

# Interceptar las señales
trap 'led_off; remove_pid_file; exit $?' SIGHUP SIGINT SIGQUIT SIGTERM

# Guardar PID del proceso en un archivo temporal
PID_FILE="/tmp/run/blinkoption.pid"
echo $$ > $PID_FILE

MINS=''

# Obtener el nombre de los botones asignados al botón QSS (WPS) del router
BUTTONS=$(uci -q show system | grep -ioE '\w+.button=wps' | cut -d. -f1)

for button in $BUTTONS
    do
        MIN=$(uci -q get system.$button.min)
        MINS="$MINS $MIN"                       # Guardar mínimo en lista de mínimos
    done

# Apagar LED QSS antes de comenzar a destellar
led_off

COUNT=0
FLAG=0

while [[ $COUNT -le 90 ]];
    do
        for min in $MINS
            do
                if [[ "$COUNT" == "$min" ]]; then
                    led_on
                    break
                fi
            done
        sleep 1
        led_off

        COUNT=`expr $COUNT + 1`
    done

# Apagar LED QSS al finalizar
led_off

# Eliminar archivo temporal de PID
remove_pid_file

exit $?

etc_config_system

config button 'blink_option'
    option button 'wps'
	option action 'pressed'
	option handler '/sbin/blink_options.sh &'
	option min '0'
	option max '90'

config button 'stop_blinking'
	option button 'wps'
	option action 'released'
	option handler '/sbin/stop_blinking.sh &'
	option min '0'
	option max '90'

stop_blinking.sh

#!/bin/sh

PID_FILE="/tmp/run/blinkoption.pid"

if [ -f $PID_FILE ]; then
    PID=$(cat $PID_FILE)
    echo $PID
    kill $PID
    rm -f $PID_FILE
fi

exit $?