Install software:

opkg update
opkg install php5  php5-cli
opkg install php5-mod-sockets
opkg install php5-mod-json

Php code:

nano /mnt/sda1/bridge.php
#!/usr/bin/php-cli
<?php
require ("/usr/lib/php/bridge/bridgeclient.class.php");
$firstValue = $argv[1];
$secondValue = $argv[2];
$thirdValue = $argv[3];
$client = new bridgeclient();
$inputfile="/mnt/sda1/input.csv";
$inputstr=file_get_contents($inputfile);
$inputstr="1,2,3";
$client->put("D12",$inputstr);
$outputstr=$firstValue.','.$secondValue.','.$thirdValue;
$outputfile="/mnt/sda1/output.csv";
file_put_contents($outputfile, $outputstr);
?>
chmod 755 /mnt/sda1/bridge.php

ATmega32u4 code:

#include <Process.h>
void setup()
{
  Bridge.begin();
  while (!Serial);     // do nothing until the serial monitor is opened
  Serial.println("Start");
}
void loop()
{
  Process p;
  p.begin("/mnt/sda1/bridge.php");
  p.addParameter("4");
  p.addParameter("5");
  p.addParameter("6");
  p.run();
  char lbuffer[256];
  Bridge.get("D12", lbuffer, 256);
  //Serial.println(lbuffer);
  String str = String(lbuffer);
  int commaIndex = str.indexOf(',');
  int secondCommaIndex = str.indexOf(',', commaIndex + 1); //  Search for the next comma just after the first
  String firstValue = str.substring(0, commaIndex);
  String secondValue = str.substring(commaIndex + 1, secondCommaIndex);
  String thirdValue = str.substring(secondCommaIndex + 1); // To the end of the string
  Serial.println(firstValue);
  Serial.println(secondValue);
  Serial.println(thirdValue);
  delay(1000);
}