The distance monitor

Now it's time to see how our park assistant can work in practice. A possible implementation of the code is reported in the chapter_02/distance_mon.sh script in the book's example code repository. The following code snippet shows the main code:

# Ok, do the job
while sleep .1 ; do
   # Read the current distance from the sensor
   d=$($d_fun)
   dbg "d=$d"

   # Manage the LEDs
   leds_man $d
done

The functioning is simple—the code periodically reads the distance from the sensor by using the function pointed by the d_fun variable, and then turns the LEDs on and off, according to the value of the distance d (in cm) by using the leds_man function.

The d_fun variable holds the name of the function that should read the distance by using the ADC, that is, read_adc, or the name of the function that uses the serial port, that is, read_tty. The following are the two functions:

function read_adc () {
   n=$(cat $ADC_DEV)

   d=$(bc -l <<< &quot...