child_process.exec()

child_process.exec(command[, options][, callback])

Spawns a shell then executes the command within that shell, buffering any generated output.

const exec = require('child_process').exec;
const child = exec('cat *.js bad_file | wc -l',
  (error, stdout, stderr) => {
    console.log(`stdout: ${stdout}`);
    console.log(`stderr: ${stderr}`);
    if (error !== null) {
      console.log(`exec error: ${error}`);
    }
});

If a callback function is provided, it is called with the arguments (error, stdout, stderr). On success, error will be null. On error, error will be an instance of Error. The error.code property will be the exit code of the child process while error.signal will be set to the signal that terminated the process. Any exit code other than 0 is considered to be an error.

The stdout and stderr arguments passed to the callback will contain the stdout and stderr output of the child process. By default, Node.js will decode the output as UTF-8 and pass strings to the callback. The encoding option can be used to specify the character encoding used to decode the stdout and stderr output. If encoding is 'buffer', Buffer objects will be passed to the callback instead.

The options argument may be passed as the second argument to customize how the process is spawned. The default options are:

{
  encoding: 'utf8',
  timeout: 0,
  maxBuffer: 200*1024,
  killSignal: 'SIGTERM',
  cwd: null,
  env: null
}

If timeout is greater than 0, the parent will send the the signal identified by the killSignal property (the default is 'SIGTERM') if the child runs longer than timeout milliseconds.

The maxBuffer option specifies the largest amount of data (in bytes) allowed on stdout or stderr - if this value is exceeded then the child process is terminated.

Note: Unlike the exec() POSIX system call, child_process.exec() does not replace the existing process and uses a shell to execute the command.