gistfile1.js

var spawn = require('child_process').spawn,
    grep    = spawn('grep', ['-v Foo', 'file.txt']);

grep.stdout.on('data', function (data) {
  console.log('stdout: ' + data);
});

grep.stderr.on('data', function (data) {
  console.log('stderr: ' + data);
});

grep.on('exit', function (code) {
  console.log('child process exited with code ' + code);
});