build.js

var fs = require('fs')
var pegjs = require('pegjs')
var overrideAction = require('pegjs-override-action')

var input     = __dirname + '/grammar.pegjs'
var output    = __dirname + '/parser.js'
var overrides = __dirname + '/overrides.js'

if (require.main === module) {
  if (process.argv[2] == '-w') {
    watch()
  } else {
    console.log(getSource())
  }
}

function getSource () {
  delete require.cache[require.resolve('./overrides')]
  var grammar = fs.readFileSync(input, 'utf8')
  var parserSource = pegjs.buildParser(grammar, {
    output: "source",
    allowedStartRules: [
      'script',
      'command',
      'argument',
      'continuationStart'
    ],
    plugins: [overrideAction],
    overrideActionPlugin: require('./overrides')
  })
  return 'module.exports = parse\n\n' +
         parse + '\n' +
         'var parser=' + parserSource + '\n' +
         'module.exports.SyntaxError = parser.SyntaxError\n';

}

function watch () {
  fs.watchFile(input, onChange)
  fs.watchFile(overrides, onChange)

  function onChange (curr, prev) {
    if (curr.mtime > prev.mtime) {
      try {
        var source = getSource()
        fs.writeFileSync(output, source + '\n')
        console.error("Wrote " + output)
      } catch (err) {
        console.error(err.message)
      }
    }
  }
}

/**
 * This isn't called directly, but stringified into the resulting source
 */
function parse (input, opts) {
  // Wrap parser.parse to allow specifying the start rule
  // as a shorthand option
  if (!opts) {
    opts = {}
  }
  else if (typeof opts == 'string') {
    opts = { startRule: opts }
  }
  return parser.parse(input, opts)
}