exec.js

var watch = require('fs').watch
var exec = require('child_process').exec

var echoFile = (fileName) => {
  console.log('execute command...')
  exec('less ' + fileName, (error, stdout, stderr) => {
    console.log(stdout)
  })
}
watch('index.js', (event, fileName) => {
  console.log(event + ' to ' + fileName)
  echoFile(fileName)
})