Interacting with GPIOs from a shell (command line):
Change directory to the base of the gpio class filesystem
$ cd /sys/class/gpio
Display currently exported gpios
$ ls -l
At this point, you will see two "files": "export", and "unexport", both with root writable access. User write access should be added to make the following commands a little easier.. (Eliminate sudo requirement)
Configure "export" and "unexport" for full access:
$ chmod 222 export unexport
If we wish to work with GPIO 4, the following command will allow us to interract with this GPIO:
Export gpio4
$ echo 4 > export
Once this command has been executed, a new directory, "gpio4" should now be visable
Change into this directory and list the contents:
$ cd gpio4
$ ls -l
At this point, you should see something like the following "files":
active_low
direction
edge
power
subsystem -> ../../../../class/gpio
uevent
value
Display the current value for "direction":
$ cat direction
in
Set the gpio for output:
$ echo out > direction (options: "in", "out", "low", "high")
Set the gpio value - set high:
$ echo 1 > value
Set the gpio value - set low:
$ echo 0 > value
Assuming an LED is attached to this gpio, toggle the line low and high 10 times:
for i in {1..10}
do
echo 1 > value
sleep 1
echo 0 > value
sleep 1
done
After typing the above set of commands and then hitting enter, the LED should blink 10 times. Pressing the up arrow to access the previous command should display something like the following:
for i in {1..10}; do echo 1 > value; sleep 1; echo 0 > value; sleep 1; done