diff --git a/bin/generate-identifier-regex.js b/bin/generate-identifier-regex.js
index f02a5b126..07e4540a0 100644
--- a/bin/generate-identifier-regex.js
+++ b/bin/generate-identifier-regex.js
@@ -1,57 +1,60 @@
 'use strict';
 
 // Which Unicode version should be used?
-var pkg = require('../package.json');
-var dependencies = Object.keys(pkg.devDependencies);
-var unicodeVersion = dependencies.find((name) => /^unicode-\d/.test(name));
+let pkg = require('../package.json')
+let dependencies = Object.keys(pkg.devDependencies)
+let unicodeVersion = dependencies.find((name) => /^unicode-\d/.test(name))
 
-var start = require(unicodeVersion + '/Binary_Property/ID_Start/code-points.js')
-    .filter(function(ch) { return ch > 0x7f; });
-var last = -1;
-var cont = [0x200c, 0x200d].concat(require(unicodeVersion + '/Binary_Property/ID_Continue/code-points.js')
-    .filter(function(ch) { return ch > 0x7f && search(start, ch, last + 1) === -1; }));
+let start = require(unicodeVersion + '/Binary_Property/ID_Start/code-points.js').filter(ch => ch > 0x7f)
+let last = -1
+let cont = [0x200c, 0x200d].concat(require(unicodeVersion + '/Binary_Property/ID_Continue/code-points.js')
+    .filter(ch => ch > 0x7f && search(start, ch, last + 1) === -1))
 
 function search(arr, ch, starting) {
-  for (var i = starting; arr[i] <= ch && i < arr.length; last = i++)
-    if (arr[i] === ch)
-      return i;
-  return -1;
-}
-
-function pad(str, width) {
-  while (str.length < width) str = "0" + str;
-  return str;
+  for (let i = starting; arr[i] <= ch && i < arr.length; last = i++)
+    if (arr[i] === ch) return i
+  return -1
 }
 
 function esc(code) {
-  var hex = code.toString(16);
-  if (hex.length <= 2) return "\\x" + pad(hex, 2);
-  else return "\\u" + pad(hex, 4);
+  let hex = code.toString(16)
+  return hex.length <= 2 ? hex.padStart(2, "0") : "\\u" + hex.padStart(4, "0")
 }
 
 function generate(chars) {
-  var astral = [], re = "";
-  for (var i = 0, at = 0x10000; i < chars.length; i++) {
-    var from = chars[i], to = from;
-    while (i < chars.length - 1 && chars[i + 1] === to + 1) {
-      i++;
-      to++;
-    }
+  let astral = [], re = ""
+  for (let i = 0, at = 0x10000; i < chars.length; i++) {
+    let from = chars[i], to = from
+    while (i < chars.length - 1 && chars[i + 1] === to + 1) {i++; to++}
     if (to <= 0xffff) {
-      if (from === to) re += esc(from);
-      else if (from + 1 === to) re += esc(from) + esc(to);
-      else re += esc(from) + "-" + esc(to);
+      if (from === to) re += esc(from)
+      else if (from + 1 === to) re += esc(from) + esc(to)
+      else re += esc(from) + "-" + esc(to)
     } else {
-      astral.push(from - at, to - from);
-      at = to;
+      astral.push(from - at, to - from)
+      at = to
     }
   }
-  return {nonASCII: re, astral: astral};
+  return {nonASCII: re, astral: astral}
 }
 
-var startData = generate(start), contData = generate(cont);
-
-console.log("let nonASCIIidentifierStartChars = \"" + startData.nonASCII + "\"");
-console.log("let nonASCIIidentifierChars = \"" + contData.nonASCII + "\"");
-console.log("const astralIdentifierStartCodes = " + JSON.stringify(startData.astral));
-console.log("const astralIdentifierCodes = " + JSON.stringify(contData.astral));
+let startData = generate(start), contData = generate(cont)
+
+let code = [
+  `    let nonASCIIidentifierStartChars = "${startData.nonASCII}"`,
+  `    let nonASCIIidentifierChars = "${contData.nonASCII}"`,
+  `    const astralIdentifierStartCodes = ${JSON.stringify(startData.astral)}`,
+  `    const astralIdentifierCodes = ${JSON.stringify(contData.astral)}`
+]
+
+if (process.argv.length != 3) {
+  console.log(code.join("\n"))
+} else {
+  let {readFile} = require('fs')
+  readFile(process.argv[2], "utf8", function(err, data) {
+    if (err) throw err
+    for (let line of code)
+      data = data.replace(new RegExp(/.* = /.exec(line)[0] + ".*"), line)
+    process.stdout.write(data)
+  })
+}