Using the controls in a program

Now that we know how to disconnect the LEDs from the system control and turn them on, let's put it together in a program.

Type the following program and name it ledon.sh:

ledon.sh
1: #!/bin/sh
2: # Replace the names with what is used on your system
3: # Disconnect all 4 LEDs on the BeagleBone so we can use it.
4: echo none > /sys/class/leds/beaglebone:green:usr0/trigger
5: echo none > /sys/class/leds/beaglebone:green:usr1/trigger
6: echo none > /sys/class/leds/beaglebone:green:usr2/trigger
7: echo none > /sys/class/leds/beaglebone:green:usr3/trigger
8: # Turn on all 4 LEDs
9: echo 255 > /sys/class/leds/beaglebone:green:usr0/brightness
10: echo 255 > /sys/class/leds/beaglebone:green:usr1/brightness
11: echo 255 > /sys/class/leds/beaglebone:green:usr2/brightness
12: echo 255 > /sys/class/leds/beaglebone:green:usr3/brightness

Let's analyze the preceding program:

• The first line tells the Linux kernel that this is a shell script...