Arduino Yún Shell Commands

Use Process to run shell commands.

This sketch demonstrates running Linux shell commands on a Yún device.

It runs the wifiCheck script (located at /usr/bin/pretty-wifi-info.lua) on the Linux processor, then uses grep to get the signal strength.

On the board, parseInt() is called to read the WiFi signal strength as an integer, and uses that number to fade an LED with

analogWrite()
.

Hardware Required

  • Yún board or shield

  • Yún device connected to a wireless network

  • 220 ohm resistor

  • LED

  • hook-up wires

  • breadboard

Circuit

A red LED connected to digital pin 9 through a 220 ohm resistor on the breadboard.

The circuit for this tutorial.
The circuit for this tutorial.

image developed using Fritzing. For more circuit examples, see the Fritzing project page

Schematic

The schematic for this tutorial.
The schematic for this tutorial.

image developed using Fritzing. For more circuit examples, see the Fritzing project page

Code

Include the Process class in your sketch.

#include <Process.h>

In

setup()
, you'll want to initialize Bridge and start a serial connection. Before running the rest of the sketch, wait for a serial connection to become active.

1void setup() {
2
3 Bridge.begin();
4
5 Serial.begin(9600);
6
7 while (!Serial);
8}

Create a named Process with which you'll use to run the WiFi status script and grep.

1void loop() {
2
3 Process p;

Pass

runShellCommand()
the path of the script you wish to run, along with any additional commands. In this case, you'll call "grep Signal" to pull out just the signal strength of the WiFi connection.

p.runShellCommand("/usr/bin/pretty-wifi-info.lua | grep Signal");

Wait until the process finishes so you get the entire output

while(p.running());

Once the process has finished running, use

parseInt()
to look for an integer that represents the signal strength. It should be in the range of 0 - 100. Map the result to a value between 0 and 255 with
map()
and use that value to adjust the brightness of the LED on pin 9 with
analogWrite()
. Print the signal strength to the serial monitor and wait for a few seconds before starting again.

1while (p.available()) {
2
3 int result = p.parseInt();
4
5 int signal = map(result, 0, 100, 0, 255);
6
7 analogWrite(9, signal);
8
9 Serial.println(result);
10
11 }
12
13 delay(5000);
14}

The LED should change its brightness as the WiFi signal strength fluctuates.

Complete Sketch

The complete sketch is below:

1/*
2
3 Running shell commands using Process class.
4
5 This sketch demonstrate how to run linux shell commands
6
7 using a YunShield/Yún. It runs the wifiCheck script on the Linux side
8
9 of the Yún, then uses grep to get just the signal strength line.
10
11 Then it uses parseInt() to read the wifi signal strength as an integer,
12
13 and finally uses that number to fade an LED using analogWrite().
14
15 The circuit:
16
17 * YunShield/Yún with LED connected to pin 9
18
19 created 12 Jun 2013
20
21 by Cristian Maglie
22
23 modified 25 June 2013
24
25 by Tom Igoe
26
27 This example code is in the public domain.
28
29 http://www.arduino.cc/en/Tutorial/ShellCommands
30
31 */
32
33#include <Process.h>
34
35void setup() {
36
37 Bridge.begin(); // Initialize the Bridge
38
39 SerialUSB.begin(9600); // Initialize the Serial
40
41 // Wait until a Serial Monitor is connected.
42
43 while (!SerialUSB);
44}
45
46void loop() {
47
48 Process p;
49
50 // This command line runs the WifiStatus script, (/usr/bin/pretty-wifi-info.lua), then
51
52 // sends the result to the grep command to look for a line containing the word
53
54 // "Signal:" the result is passed to this sketch:
55
56 p.runShellCommand("/usr/bin/pretty-wifi-info.lua | grep Signal");
57
58 // do nothing until the process finishes, so you get the whole output:
59
60 while (p.running());
61
62 // Read command output. runShellCommand() should have passed "Signal: xx&":
63
64 while (p.available()) {
65
66 int result = p.parseInt(); // look for an integer
67
68 int signal = map(result, 0, 100, 0, 255); // map result from 0-100 range to 0-255
69
70 analogWrite(9, signal); // set the brightness of LED on pin 9
71
72 SerialUSB.println(result); // print the number as well
73
74 }
75
76 delay(5000); // wait 5 seconds before you do it again
77}

Last revision 2016/05/25 by SM

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