Creating and controlling external processes

1433440766.js

/**
 * Executing external commands
 * 
 * when you need to lauch an external shell command or an executable file, you may do so by using the child_process module. 
 * You can import module like this
*/

var child_process = require('child_process');

// you can the use the exec function that is defined in the module like thí

var exec = child_process.exec;
exec(command, callback);

/**
 * the first argument to the exec function is a string with the command as you would lauch it from the shell.
 * the second argument is a function callback.
 * you should expect three arguments in this callback: error, stdout, stderr
*/

exec('ls', function(err, stdout, stderr){
  //...
});

// a more complete example of executing an external command
var exec = require('child_process').exec;
exec('cat *.js | wc -l', function(err, stdout, stderr){
  if(err){
    console.log('child process exited with error code ' + err.code);
    return;
  }
  console.log(stdout);
});

// you can also pass an optional argument containing some configuration options before the callback  function

var exec = require('child_process').exec;
var options = {
  timeout:1000,
  killSignal: 'SIGKILL'
};
exec('cat *.js | wc -l', options, function(err, stdout, stderr){
  // ...
});

/**
 * The available options are:
 * cwd - current working directory. Use this if you want to force the current working directory
 * encoding - the expected encoding for the child output, default utf8
 * * node supports these encodings: ascii, utf8, ucs2, base64
 * timeout - the timeout in milliseconds for execution of the command, default 0
 * maxBuffer - specifies the maximum size in bytes of the output allowed on the stdout or the stderr stream, default to 200 * 1024
 * killSignal - the signal to be sent to the child if it times out or exceeds the output buffers, default SIGTERM
 * env - environment variables to be passed into the child process, default to null
 *