File Write Script

This example writes to a file using the FileIO classes into the Yún device's filesystem. A shell script file is created in /tmp, and is executed afterwards.

Hardware Required

Yún board or shield

Circuit

There is no circuit for this example.

Yun Fritzing

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

Code

Include the FileIO header, for communicating with the filesystem. #include <FileIO.h>

In setup(), initialize Bridge, Serial communication, and FileSystem. Wait for an active serial connection, and call a custom function uploadScript() which will upload your file, before starting loop().

void setup() {

  Bridge.begin();

  Serial.begin(9600);

  while(!Serial);  // wait for Serial port to connect.

  Serial.println("File Write Script example\n\n");

  FileSystem.begin();

  uploadScript();
}

loop() will just execute your script every 5 seconds by calling another custom function, runScript().

void loop() {

  runScript();

  delay(5000);
}

Your uploadScript() function will create a shell script in the Linux file system that will check the network traffic of the WiFi interface. Create the file and open it by creating an instance of the File@ class, and callingFileSystem.open()@@ indicating where you would like to create the script. You'll store the script in "/tmp", which resides in RAM, to preserve the limited number of FLASH memory read/write cycles.

void uploadScript() {

  File script = FileSystem.open("/tmp/wlan-stats.sh", FILE_WRITE);

Write the contents of the script to the file with File.print(). begin by printing the header, "#!/bin/s", then the utility ifconfig. @ifconfig@ is a command line utility for controlling network interfaces. you'll be looking at the WiFi interface, which is referred to as "wlan0". The utility grep will search the output of ifconfig. You're looking for the number of bytes received , so search for the keywords "RX bytes" and close the file.

script.print("#!/bin/sh\n");

  script.print("ifconfig wlan0 | grep 'RX bytes'\n");

  script.close();  // close the file

Instantiate a Process to make the script executable. chmod@ is a command that will change the modes of files. By sending thechmod@@ command and filepath, you can make your shell script run like an application.

Process chmod;

  chmod.begin("chmod");      // chmod: change mode

  chmod.addParameter("+x");  // x stays for executable

  chmod.addParameter("/tmp/wlan-stats.sh");

  chmod.run();
}

The runScript() function will create a Process that runs the script and prints the results to the Serial Monitor. Create a named Process, and start your script by calling Process.begin(filepath) and Process.run().

void runScript() {

  Process myscript;

  myscript.begin("/tmp/wlan-stats.sh");

  myscript.run();

Create a string to hold the output, and read the output into it

String output = "";

  while (myscript.available()) {

    output += (char)myscript.read();

  }

Remove the blank spaces at the beginning and end of the string and print it to the serial monitor :

output.trim();

  Serial.println(output);

  Serial.flush();
}

The complete sketch is below :


/*

  Write to file using FileIO classes.

 This sketch demonstrate how to write file into the YunShield/Yún filesystem.

 A shell script file is created in /tmp, and it is executed afterwards.

 created 7 June 2010

 by Cristian Maglie

 This example code is in the public domain.

 http://www.arduino.cc/en/Tutorial/FileWriteScript

 */

#include <FileIO.h>

void setup() {

  // Setup Bridge (needed every time we communicate with the Arduino Yún)

  Bridge.begin();

  // Initialize the Serial

  SerialUSB.begin(9600);

  while (!SerialUSB); // wait for Serial port to connect.

  SerialUSB.println("File Write Script example\n\n");

  // Setup File IO

  FileSystem.begin();

  // Upload script used to gain network statistics

  uploadScript();
}

void loop() {

  // Run stats script every 5 secs.

  runScript();

  delay(5000);
}

// this function creates a file into the linux processor that contains a shell script
// to check the network traffic of the WiFi interface
void uploadScript() {

  // Write our shell script in /tmp

  // Using /tmp stores the script in RAM this way we can preserve

  // the limited amount of FLASH erase/write cycles

  File script = FileSystem.open("/tmp/wlan-stats.sh", FILE_WRITE);

  // Shell script header

  script.print("#!/bin/sh\n");

  // shell commands:

  // ifconfig: is a command line utility for controlling the network interfaces.

  //           wlan0 is the interface we want to query

  // grep: search inside the output of the ifconfig command the "RX bytes" keyword

  //       and extract the line that contains it

  script.print("ifconfig wlan0 | grep 'RX bytes'\n");

  script.close();  // close the file

  // Make the script executable

  Process chmod;

  chmod.begin("chmod");      // chmod: change mode

  chmod.addParameter("+x");  // x stays for executable

  chmod.addParameter("/tmp/wlan-stats.sh");  // path to the file to make it executable

  chmod.run();
}

// this function run the script and read the output data
void runScript() {

  // Run the script and show results on the Serial

  Process myscript;

  myscript.begin("/tmp/wlan-stats.sh");

  myscript.run();

  String output = "";

  // read the output of the script

  while (myscript.available()) {

    output += (char)myscript.read();

  }

  // remove the blank spaces at the beginning and the ending of the string

  output.trim();

  SerialUSB.println(output);

  SerialUSB.flush();
}

Table of Contents

File Write Script

Hardware Required

Circuit

Code

See Also